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Oldest of the non-nutritive sweeteners.
Currently produced from purified, manufactured methyl anthranilate, a substance occurring naturally in grapes. It is 300 times sweeter than sucrose, heat stable and does not promote dental caries. Saccharin has a long shelf life, but a slightly bitter aftertaste. It is not metabolized in the human digestive system, is excreted rapidly in the urine and does not accumulate in body.

Saccular aneurysm

A balloon-like outpouching of a vessel (the more common type of aneurysm).


A fluid in the mouth containing water (99.5 percent), digestive enzymes, lysozyme (an enzyme that kills bacteria), proteins, antibodies (IgA), and various ions. Saliva lubricates the mouth, moistens food during chewing, protects the mouth against pathogens, and begins the chemical digestion of food.
Saliva is produced by the following glands:

  • Three pairs of salivary glands, the parotid, submandibular, and sublingual, lie outside the mouth. They deliver their secretions to the mouth via ducts.
  • Buccal glands are located in the mucosa that lines the mouth.

Chemical digestion is carried out by the digestive enzyme salivary amylase, which breaks down polysaccharides (starch and glycogen) into short chains of glucose, especially the disaccharide maltose (which consists of two glucose molecules).

saline water

water that contains significant amounts of dissolved solids.

Here are our parameters for saline water:
Fresh water - Less than 1,000 parts per million (ppm)
Slightly saline water - From 1,000 ppm to 3,000 ppm
Moderatly saline water - From 3,000 ppm to 10,000 ppm
Highly saline water - From 10,000 ppm to 35,000 ppm


Gram-negative bacterium, occurring in many animals, especially poultry and swine. In the environment,salmonella can be found in water, soil, insects, factory and kitchen surfaces, animal fecal matter, and raw meats, poultry (including eggs) and seafood.

Saltatory conduction

A mechanism of transmission of information (Action Potentials, APs) along a type of neuron.
Saltatory transmission occurs in myelianted neurons, i.e., neurons which have a myelin sheath along the length of the neuron’s axon. This myelin sheath is discontinuous with the gaps between successive segments of the sheath, called the nodes of Ranvier, being free from the insulating sheath and containing high concentrations of voltage-gated Na+ channels. Here the AP is regenerated freshly and then it’s current flows through the myelinatd region to the next node where another AP is generated. Thus it almost appears as if the AP “jumps” from one node to the next – hence salutatory conduction (from the Latin “saltare” – to jump).


One or more individual events or measurements selected from the output of a process for purposes of identifying characteristics and performance of the whole.
In assyas, a sample, or replicate, is an aliquot of a baseline standard specimen, standard specimen, control specimen, or unknown specimen, and all of the reagents which comprise an individual immunoassay incubation medium.

Sample blank

An unknown sample blank is an aliquot from a specimen which is used to measure the amount of nonspecific activity or the amount of endogenous analyte present in the specimen. The response from the activity blank is subtracted from the response of the sample before computing the specimen concentration. The concentration of the concentration blank is subtracted from the concentration of the sample to generate the specimen concentration.


By saponification of high methoxyl pectins, low methoxyl pectins are produced.


Functional component of soybeans, soy foods and soy protein containing food which may lower LDL cholesterol and may contain anti-cancer enzymes.


An organism that acts as a decomposer by absorbing nutrients from dead organic matter.


Structure-activity relationship. The way in which altering the molecular structure of drugs alters their interaction with a receptor, enzyme, etc.


Rare inflammation of the lymph nodes and other tissues throughout the body.


A cancer of the bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.


The specialized plasma membrane surrounding a muscle cell (muscle fiber); capable of propagating Action Potentials.


The fundamental, repeating unit of striated muscle, delimited by the Z lines.

Sarcoplasmic reticulum

A modified form of endoplasmic reticulum in striated muscle cells that stores calcium used to trigger contraction during stimulation.
An inter-connected sequence of internal membrane-bound compartments inside the muscle fibres of skeletal muscles
The SR is equivalent structurally to the endoplasmic reticulum in other cells, but where the ER is part of the cellular machinery for the final preparation of proteins and other molecules for transport and export, the SR is predominantly a store for Ca++ in skeletal muscle. This allows regulation of skeletal muscle contraction by controlling the release of the Ca++ from the SR since Ca++ is required to bind to regulatory proteins before interactions between myosin and actin, the contractile proteins in skeletal muscle, can occur to cause muscle contraction.

Saturated fat (saturated fatty acid)

A fatty acid in which all carbons in the hydrocarbon tail are connected by single bonds, thus maximizing the number of hydrogen atoms that can attach to the carbon skeleton; all carbons contain a hydrogen, and therefore, no double bonds exist.
In general, fats that contain a majority of saturated fatty acids are solid at room temperature, although some solid vegetable shortenings are up to 75 percent unsaturated. Some common fatty acids in foods include palmitic, stearic and myristic acids. Saturated fatty acids are more stable than unsaturated fatty acids because of their chemical structure. Stability is important to prevent rancidity and off flavours and odours.

Saturation threshold

Stimulus intensity which results in the maximum sensitivity extent that can be described qualitatively.
Further increases in stimulus intensity do not affect the sensitivity extent, but can lead to discomfort.


A quantity that is defined by its magnitude only (e.g., energy, temperature); A quantity that has size but no direction.

Scalene triangle

A triangle with three unequal sides.

Scanning Electron Microscopy

A type of electron microscope that images the sample surface by scanning it with a high-energy beam of electrons in a raster (see Raster plot) scan pattern.
The electrons interact with the atoms that make up the sample producing signals that contain information about the sample's surface topography, composition and other properties such as electrical conductivity.

Scatchard Analysis

A Scatchard analysis is a computation of the number of binding sites and the affinity constants for each subclass of binder present plus a measurement of the amount of nonspecific binding.
When the proper Scatchard model is chosen, the coefficients from a Scatchard analysis of a single assay provide direct measurements of the number of binding sites and the affinity constant of each binder subclass, which are then statistically compared to those from the reference assay set.

Schild analysis

Calculation of the potency of competitive antagonists according to the method of Arunlakshana and Schild (1959) This is a null method, i.e. it makes no assumptions about the nature of the coupling between receptor binding and the response, but simply assumes that any particular level of response is associated with a unique degree of occupation and activation of the receptors by the agonist. There are a number of other assumptions and criteria, the most important of which are that (a) the agonist acts only at a single receptor type; (b) the binding of both agonist and antagonist is competitive and reversible; (c) responses are measured when both agonist and antagonist are at equilibrium with the receptors; and (d) the antagonist causes parallel rightward shifts of the log agonist concentration-response curve with no depression of the maximum response. See Schild plot and Schild slope.

Schild equation

The equation:
(conc. ratio - 1) = (antagonist conc.)/KB
where conc. ratio = concentration ratio for the agonist (see above) and KB = dissociation equilibrium constant for the antagonist. The Gaddum equation (see pKB) is the logarithmic transformation of this equation.

Schild plot

A graph of log (concentration ratio - 1) against log (antagonist concentration). An example is shown in Fig. C. The intercept on the log concentration axis is equal to the pA2 value, while the slope gives information about the nature of the antagonism.

Schild slope

The slope of a Schild plot should equal 1 if all of the assumptions underlying the method of analysis are fulfilled. A slope which is significantly greater than 1 may indicate positive cooperativity in the binding of the antagonist, depletion of a potent antagonist from the medium by receptor binding or non-specific binding (e.g. to glassware or partitioning into lipid), or lack of antagonist equilibrium. A slope which is significantly less than 1 may indicate negative cooperativity in the binding, or removal of agonist by a saturable uptake process, or it may arise because the agonist is acting at a second receptor type (this can also cause curved Schild plots). There are many other reasons why slopse differ from the theoretical value, but most of them are difficult to prove. See Kenakin (1987) for a thorough discussion. If the slope of a Schild plot is greater than 1, the calculated pA2 value will be an underestimate of the pKB value (i.e. the antagonist is less potent than expected). Conversely, if the slope is less than 1, the calculated pA2 value will overestimate the pKB value.

Schizoaffective disorder

A depressive or manic syndrome that precedes or develops concurrently with psychotic symptoms incompatible with an affective disorder.
Includes some symptoms characteristic of schizophrenia and other symptoms seen in major affective disorders.

Schizoid personality disorder

Manifested by shyness, oversensitivity, social withdrawal, frequent daydreaming, advoidance of close competitive relationships and eccentricity.
Persons with this disorder often react to disturbing experiences with apparent detachment and are unable to express hostility and ordinary aggressive feelings.


A serious mental disorder characterized by verbal incoherence, severely impaired interpersonal relations, disturbance in thought processes, cognitive deficits, and inappropriate or blunted affect. The person may also exhibit hallucinations or delusions.

Schizophreniform disorder

Clinical features are the same as seen in schizophrenia, but lasting less than six months and longer than one week.
This disorder is believed to have different correlates than schizophrenia, including a better prognosis.

Schizotypal personality disorder

The essential features are various oddities of thinking, perception communication, and behavior not severe enough to meet the criteria for schizophrenia.
No single feature is invariably present. The disturbance in thinking may be expressed in magical thinking, ideas of reference or paranoid ideation. Perceptual disturbances may include recurrent illusions, depersonalization or derealization. Often there are marked peculiarities in communication; concepts may be expressed unclearly or oddly, using words deviatnly, but never to the point of behavioral manifestation include social isolation and constricted or inappropriate affect that interferes with rapport in face-to-face interaction.

Schwann cells

A type of glial cell found in the peripheral nervous system that forms an nsulating layer called the myelin sheath around the axon of some neurons.


tough, opaque membrane of the eyebulb which maintains the size and form of the bulb and attaches to muscles that move the bulb; the whites of the eyes.


An abnormal lateral curvature of the spine


An area of decreased or absent vision surrounded by an area of less depressed or normal vision.

Screening (a library, in molecular genetics)

To screen a library is to select and isolate individual clones out of the mixture of clones.
For example, if you needed a cDNA clone of the pituitary glycoprotein hormone alpha subunit, you would need to make (or buy) a pituitary cDNA library, then screen that library in order to detect and isolate those few bacteria carrying alpha subunit cDNA.
There are two methods of screening which are particularly worth describing: screening by hybridization, and screening by antibody.
Screening by hybridization: involves spreading the mixture of bacteria out on a dozen or so agar plates to grow several ten thousand isolated colonies. Membranes are laid onto each plate, and some of the bacteria from each colony stick, producing replicas of each colony in their original growth position. The membranes are lifted and the adherent bacteria are lysed, then hybridized to a radioactive piece of alpha DNA (the source of which is a story in itself - see "Probe"). When X-ray film is laid on the filter, only colonies carrying alpha sequences will "light up". Their position on the membranes show where they grew on the original plates, so you now can go back to the original plate (where the remnants of the colonies are still alive), pick the colony off the plate and grow it up. You now have an unlimited source of alpha cDNA.
Screening by antibody: is an option if the bacteria and plasmid are designed to express proteins from the cDNA inserts (see "Expression clones"). The principle is similar to hybridization, in that you lift replica filters from bacterial plates, but then you use the antibody (perhaps generated after olde tyme protein purification rituals) to show which colony expresses the desired protein.


One of the most commonly used orthopedic fixation devices. Screws are designed for different uses and for placement in different types of bone. Screws can be used as single standalone devices, as components of hardware constructs (e.g. plates with screws), or as separate devices complementing other hardware (e.g. interfragmentary screws and plates with screws for fracture fixation).

SDS-PAGE electrophoresis (sodium dodecyl sulfate polyacrylamide gel electrophoresis)

A technique to separate proteins (and even DNA and RNA molecules) according only to their size.
SDS is an anionic detergent which denatures secondary and non–disulfide–linked tertiary structures, and applies a negative charge to each protein in proportion to its mass. Proteins are mixed with SDS. Without SDS, different proteins with similar molecular weights would migrate differently due to differences in mass charge ratio, as each protein has an isoelectric point and molecular weight particular to its primary structure. This is known as Native PAGE. SDS binds to and unfolds the protein, giving a near uniform negative charge along the length of the polypeptide, i.e., complexes with fairly constant charge to mass ratios.
The mixture is separated electrophoretically in a polyacrylamide gel (see Polyacrylamide gel) The electrophoretic migration rate through the gel is determined only by the size of the complexes. Molecular weights are determined by simultaneously running marker proteins of known molecular weight. Usually, smaller proteins migrate through the gel faster than larger proteins. (see Electrophoresis)


1. A line that intersects a circle or a curve in two places.
2. The reciprocal of the cosine.


The unit of measure of an angle that is 1/60 of a minute.

Second messenger

Intracellular substance (e.g. cyclic AMP or inositol phosphates), the concentration of which may be controlled by activation of membrane receptors and which can control further intracellular events (e.g. protein phosphorylation, neurotransmitter release or membrane polarisation).

Secondary active transport

Many amino acids and sugars are accumulated by cells in transport processes driven by ion gradients. This process, Secondary or Indirect active transport, uses downhill flow of an ion to pump some other molecule or ion against its gradient.
The ion is moved down its concentration gradient using some transporter (a protein molecule). In the process the transporter moves the other molecule. This can be in the same direction as the ion or in opposite direction. The driving ion is usually sodium (Na+) with its gradient established by the Na+/K+ ATPase (hence the energy use).
e.g., Na+/Glucose transport in the small intestine.

Secondary battery

battery that can be recharged

Secondary hyperalgesia

Increased responsiveness to mechanical stimuli only in a region of the body surrounding a region that has been recently subjected to painful stimuli.
see Hyperalgesia for details

Secondary immunity

Resistance to an antigen the second time it appears.
Because of the presence of B and T memory cells produced during the Þrst exposure to the antigen, the second response is faster and more massive and lasts longer than the primary immune response.

Second law of thermodynamics

The principle whereby every energy transfer or transformation increases the entropy of the universe.
Ordered forms of energy are at least partly converted to heat, and in spontaneous reactions, the free energy of the system also decreases.

Second messenger

A small, nonprotein, water-soluble molecule or ion, such as calcium ion or cyclic AMP, that relays a signal to a cell's interior in response to a signal received by a signal receptor protein.

Secondary compound

A chemical compound synthesized through the diversion of products of major metabolic pathways for use in defense by prey species

Secondary consumer

A member of the trophic level of an ecosystem consisting of carnivores that eat herbivores.

Secondary immune response

The immune response elicited when an animal encounters the same antigen at some later time. The secondary immune response is more rapid, of greater magnitude, and of longer duration than the primary immune response.

Secondary productivity

The rate at which all the heterotrophs in an ecosystem incorporate organic material into new biomass, which can be equated to chemical energy.

Secondary sex characteristics

Characteristics of animals that distinguish between the two sexes but that do not produce or convey gametes. Includes facial hair of the human male and enlarged hips and breasts of the female.

Secondary structure

The localized, repetitive coiling or folding of the polypeptide backbone of a protein due to hydrogen bond formation between peptide linkages.
Short repetitive stuctural elements in protein chains (polypeptides) that form helices (alpha helix), extended sheets (beta sheets) or random coils.

Secondary waste water treatment

treatment (following primary wastewater treatment) involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems and which generally removes 80 to 95 percent of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or chemical-physical methods. Activated sludge and trickling filters are two of the most common means of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen in trickling filters or in the activated sludge process. This treatment removes floating and settleable solids and about 90 percent of the oxygen-demanding substances and suspended solids. Disinfection is the final stage of secondary treatment.


1. The discharge of molecules synthesized by the cell.
2. In the vertebrate kidney, the discharge of wastes from the blood into the filtrate from the nephron tubules.


A region bounded by two radii of a circle and the arc whose endpoints lie on those radii.


Living in a fixed location, as with most plants, tunicates, sponges, etc.
Contrast with motile.


Usually applied to material in suspension in water or recently deposited from suspension.
Suspended sediment: very fine particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.
Suspended-sediment concentration: the ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.
Suspended-sediment discharge: -the quantity of suspended sediment passing a point in a stream over a specified period of time. When expressed in tons per day, it is computed by multiplying water discharge (in cubic feet per second) by the suspended-sediment concentration (in milligrams per liter) and by the factor 0.0027

Sedimentary rock

rock formed of sediment, and specifically: (1) sandstone and shale, formed of fragments of other rock transported from their sources and deposited in water; and (2) rocks formed by or from secretions of organisms, such as most limestone. Many sedimentary rocks show distinct layering, which is the result of different types of sediment being deposited in succession.

Sedimentation tank

wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal.


--(1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, or other body of water, or from a field.


The union of a point, A, and a point, B, and all the points between them.


A churning of food in the small intestine through muscular constriction of the intestinal wall.
This process is similar to peristalsis, except that the rhythmic timing of the muscle constrictions forces the food backward and forward rather than forward only.


A seizure is characterized by involuntary movement or a change in consciousness or behavior.
It usually lasts only a few minutes. It may be associated with loss of consciousness, loss of bowel and bladder control and tremors. May also cause aggression or other behavioral change. Seizures may be classified by cause, by area of the brain involved, or by clinical symptoms.

Seizure disorders

Seizures are symptoms of underlying disorders of the brain.
A seizure occurs when bursts of unorganized electrical impulses interfere with normal brain function.
An uncontrolled discharge of nerve cells which may spread to other cells nearby or throughout the entire brain. Seizures may be classified by cause, by area of the brain involved, or by clinical symptoms.


The process by which the forms of organisms in a population that are better adapted to the environmental conditions increase in frequency relative to less well-adapted forms over a number of generations.
Process which favors one feature of organisms in a population over another feature found in the population. This occurs through differential reproduction—those with the favored feature produce more offspring than those with the other feature, such that they become a greater percentage of the population in the next generation.

Selection coefficient

The difference between two fitness values, representing a relative measure of selection against an inferior genotype.

Selective permeability

A property of biological membranes that allows some substances to cross more easily than others.

Selective pressure

An environmental factor that favors the survival and reproduction of those genetic variants within a population that are better adapted to the environment.


Relative potency of a drug between two receptor subtypes for the same endogenous ligand. This is a relative rather than absolute term that should always be qualified (e.g. prazosin is 30-fold selective for <28>1-adrenoceptors relative to <28>2-adrenoceptors). Compare specificity.


The union of egg and sperm produced by a single hermaphroditic organism.

self-tapping screw

A screw that cuts its own thread holes in bone as it is screwed into place. Prior to inserting a screw in cortical bone, a guide hole is first drilled that has the same diameter as the core diameter of the screw to be inserted. For a  nonself-tapping, a tap is then inserted which cuts the thread holes for the screw. The screw is then inserted. A self-tapping screw has one or more cutting edges at the screw tip that cut the threads holes in the side of the guide hole in which the screw is inserted. Thus, a separate tapping step is eliminated shortening operative time. See nonself-tapping screw.

Self supplied water

water withdrawn from a surface- or ground-water source by a user rather than being obtained from a public supply. An example would be homeowners getting their water from their own well.


The component of language most concerned with the meaning and understanding of language.


The fluid that is ejaculated by the male during orgasm; contains sperm and secretions from several glands of the male reproductive tract.

Semicircular canals

A three-part chamber of the inner ear that functions in maintaining equilibrium.

Semiconservative replication of DNA

A proposed model of DNA replication.
In this model the DNA helix is unwound and each strand serves as a template for the synthesis of a new complementary strand, which is linked to the old strand, i.e., each new DNA molecule consists of one-half of the parental DNA along with an entirely new complementary strand. Thus the new DNA would consist of one new and one old strand of DNA. (see Conservative replication and Dispersive replication)

Semilunar valve

A valve located at the two exits of the heart, where the aorta leaves the left ventricle and the pulmonary artery leaves the right ventricle.

Seminal vesicle

A gland in males that secretes a fluid (a component of semen) that lubricates and nourishes sperm.

Seminiferous tubules

Highly coiled tubes in the testes in which sperm are produced.

Senile dementia

A chronic, progressive dementia associated with generalized atrophy of the brain with the death of neurons due to unknown causes, although there are several promising theories under study (e.g., autoimmunity, slow virus, cholinergic deficiency).
It is not due to aging per se, but may be a late form of Alzheimer's disease.
Deterioration may range from minimum to severe. It must be carefully separated from reversible brain syndrome, resulting from many causes.


Feeling stimuli which activate sensory organs of the body, such as touch, temperature, pressure and pain. Also seeing, hearing, smelling and tasting.
Results from impulses sent to the brain from activated receptors and sensory neurons.

Sense RNA

Refers to the mRNA sequence that is translated into protein.

Sense strand

A gene has two strands: the sense strand and the anti-sense strand. The Sense strand is, by definition, the same 'sense' as the mRNA; that is it can be translated exactly as the mRNA sequence can.
Given a sense strand with the following sequence:

          5' - ATG GGG CCA CGG CTG TGA - 3'
               Met Gly Pro Arg Leu stop

The anti-sense strand will read as follows (note that the strand has been reversed and complemented):

          5' - TCA CAG CCG TGG CCC CAT - 3'

The duplex DNA will pair as follows:

          5' - ATGGGGCCACGGCTGTGA - 3'
          3' - TACCCCGGAGCCGACACT - 5'

Note however that when the RNA is transcribed from this sequence, the ANTI-SENSE strand is used as the template for RNA polymerization. After all, the RNA must base-pair with its template strand, so the process of transcription produces the complement of the anti-sense strand.


The sensitivity of an test method is the lowest concentration that can be reliably measured using that test method.
1. In psychology, the quality of being sensitive. As, for example, sensitivity training, training in small groups to develop a sensitive awareness and understanding of oneself and of ones relationships with others. 2. In disease epidemiology, the ability of a system to detect epidemics and other changes in disease occurrence. 3. In screening for a disease, the proportion of persons with the disease who are correctly identified by a screening test. 4. In the definition of a disease, the proportion of persons with the disease who are correctly identified by defined criteria.


Refers to all aspects of movement and sensation and the interaction of the two.

Sensory aphasia (Also referred to as "receptive aphasia")

Inability to understand the meaning of written, spoken, or tactile speech symbols because of disease or injury to the auditory and visual brain centers.

Sensory integration

Interaction of two or more sensory processes in a manner that enhances the adaptiveness of the brain.

Sensory modality

Refers to any one of the five sensory avenues for receiving information: seeing, hearing, touching, tasting, and smelling.

Sensory neuron

neuron (nerve cell) that transmits information from external and internal sensory organs to the central nervous system.

Sensory receptor

A specialized structure that responds to specific stimuli from an animal's external or internal environment, converting the physical or chemical energy of the stimulus into a biological response that can be signalled by neurons to the central nervous system.

Sensory seizure

A seizure that is characterized primarily by visual, auditory, gustatory, olfactory, or emotional sensations.

Separation (in assays)

Separation is the process of physically separating the bound ligand from the free ligand before either fraction can be measured.

Septic tank

a tank used to detain domestic wastes to allow the settling of solids prior to distribution to a leach field for soil absorption. Septic tanks are used when a sewer line is not available to carry them to a treatment plant. A settling tank in which settled sludge is in immediate contact with sewage flowing through the tank, and wherein solids are decomposed by anaerobic bacterial action.


A systemic inflammatory response to infection that results in large-scale tissue destruction at sites far away from the original injury site.
Bacterial infection spread throughout the bloodstream; also called blood poisoning.

Septo-optic dysplasia

A rare condition in which there is abnormal development in part of brain that can cause changes in a child’s eyes and also problems in the pituitary gland.


A partition or thin wall dividing two cavities or masses of softer tissue into compartments.

Settling tank

an open lagoon into which wastewater contaminated with solid pollutants is placed and allowed to stand. The solid pollutants suspended in the water sink to the bottom of the lagoon and the liquid is allowed to overflow out of the enclosure.


The linear arrangement of building blocks in biological macromolecules like DNA, RNA, protein and polysaccharides.
DNA and RNA macromolecules are linear polymers of nucleotides. Proteins are linear polymers of amino acids. Polysaccharides are linear and branched polymers of monosaccharides (sugars). While the sequence of RNA and proteins are encoded for by the nucleotide sequence in DNA (the genes and genomes), polysaccharides which play important roles in physiology are not encoded for by genetic information, but rather by the spatial and temporal activity of enzymes that synthesize these polysaccharides.

Sequenced Inventory of Communication Development (SICD)

A testing instrument which assesses receptive language skills or what the child understands. A receptive communication age is provided by the results of the test. It also assesses his/her expressive language skills or how a child expresses/communicates his/her thoughts. An expressive communication age is also provided by the results of the test.

Sequence alignment

Procedure for the linear comparison of two or more molecular sequences in order to identify those positions that are likely to have a common evolutionary origin.
Series of characters that are in the same order in the sequences are used as reference points, and hypothetical gaps may be inserted in order to make similar regions line up with one another.

Sequencing (of actions)

Reading, listening, expressing thoughts, describing events or contracting muscles in an orderly and meaningful manner.

Sequencing (of nucleotides)

Determination of the order of nucleotides (base sequences) in a DNA or RNA molecule or the order of amino acids in a protein.
Note Sequence = Succession of bases in the DNA molecule.

Sequencing (of memory)

Storage and retrieval of information requiring
a specified order of input and recall; i.e., counting, days of the week, months of the year, words in a sentence.

Sequence Number

The sequence number of an unknown record is the order each unknown is placed in an unknown file.

Sequence tagged site (STS)

Short (200 to 500 base pairs) DNA sequence that has a single occurrence in the human genome and whose location and base sequence are known.
Detectable by polymerase chain reaction, STSs are useful for localizing and orienting the mapping and sequence data reported from many different laboratories and serve as landmarks on the developing physical map of the human genome. Expressed sequence tags (ESTs) are STSs derived from cDNAs.


Used to combine with trace metals in the environment to render them inactive.

Serial processing (of sensory information)

The relaying and analysis of sensory information along a single pathway, with each higher stage of the pathway performing some relatively more complex processing.
In all sensory systems nerve fibres from the receptor surface at the periphery (i.e., the skin, the ear, the eye, etc) do not carry information directly to the cortex that is responsible for perception. Instead information is relayed via a succession of sensory nuclei in the Central Nervous System to arrive at the cortex, and even then be relayed to multiple cortical areas. This serves to reduce the energetic demands on neurons which may otherwise have to be able to provide nutrients and other substances and remove waste products from very long axons. (Imagine a single neuron being responsible for relaying pain information from your toe all the way up to your cortex for perception.) In serial processing, neurons in each successive sensory relay nucleus are believed to process the information in some slightly more sophisticated way from the incoming input, thereby sending a more refined output to the next level of processing. (see Parallel processing)


The sum of a sequence.

Serious Emotional Disturbance/Disorder (SED)

When a child or adolescent exhibits behavioral, emotional and/or social impairment that consequently disrupts their academic and/or developmental progress, family and/or interpersonal relationships, and has impaired functioning that has continued for at least one year, or has an impairment of short duration and high severity.


Group of related microorganisms distinguished by its composition of antigens.


Attached; not free to move about.


A well defined group of objects.

sewage treatment plant

--a facility designed to receive the wastewater from domestic sources and to remove materials that damage water quality and threaten public health and safety when discharged into receiving streams or bodies of water. The substances removed are classified into four basic areas:
[1] greases and fats;
[2] solids from human waste and other sources;
[3] dissolved pollutants from human waste and decomposition products; and
[4] dangerous microorganisms.
Most facilities employ a combination of mechanical removal steps and bacterial decomposition to achieve the desired results. Chlorine is often added to discharges from the plants to reduce the danger of spreading disease by the release of pathogenic bacteria.


a system of underground pipes that collect and deliver wastewater to treatment facilities or streams.

Sex chromosomes

The X and Y chromosomes in human beings that determine the sex of an individual.
Females have two X chromosomes in diploid cells; males have an X and a Y chromosome. The sex chromosomes comprise the 23rd chromosome pair in a karyotype.

Sex hormone binding globulin (SHBG)

A carrier protein that binds to the hormones testosterone and estradiol making them non-bioavailable.

Sex linked condition

A condition that is passed from parents to child through a sex chromosome. Mothers are carriers of the condition without having it themselves.
Examples include muscular dystrophy and hemophilia.

Sex linked genes

Genes located on one sex chromosome but not the other.

Sex linked trait

An inherited trait, such as color discrimination, determined by a gene located on a sex chromosome and that therefore shows a different pattern of inheritance in males and females.

Sexual dimorphism

A special case of polymorphism based on the distinction between the secondary sex characteristics of males and females.

Sexual reproduction

A type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents.
Sexual reproduction involves meiosis and syngamy.

Sexual selection

Selection based on variation in secondary sex characteristics, leading to the enhancement of sexual dimorphism.

Sheltered Workshop

A work setting that provides transitional and/or long-term employment in a controlled and protected working environment for those who are unable either to compete or to function in the open job market due to their disabilities.
May provide vocational evaluation and work adjustment services.

Short bowel syndrome

Lack of major portions of the small bowel.


Fats used in the baking or frying of foods. Shortenings impart tender qualities to baked goods. Additives such as emulsifiers, antioxidants, anti-foaming agents, flavouring, etc may be present, depending on the intended use of the product.

Short Interfering RNA (siRNA)

Specific short sequences of double-stranded RNA (dsRNA) of 19-21 base pairs (bp) in length, which trigger degradation of messenger RNA (mRNA) possessing the same sequence (as those siRNAs) within a cell; as part of the cellular process known as RNA interference (RNAi).
Because that degradation of mRNA thereby shuts-down (quells) production of the corresponding protein, siRNA (via RNAi) constitutes a pathway that cells utilize to regulate/silence gene expression. Relevant promoters within the DNA are silenced via DNA methylation and/or chromatin remodeling. The siRNA can be utilized by man to cause gene silencing/knockout.
In plants and nematodes, such RNA interference-induced gene silencing spreads (e.g., from the site of dsRNA entry-into-organism) throughout the organism; apparently via mediation/transport by the transmembrane (i.e., through the plasma membrane) protein known as SID-1.
In animals, such RNA interference tends to be localized at/near site of dsRNA entry-into-organism. For example, relevant siRNA has been utilized to quell the (over)production of vascular endothelial growth factor (VEGF) in laboratory animals; thereby helping prevent some age-related macular degeneration (AMD) damage. Relevant siRNA has been utilized to quell (over) production of apolipoprotein B in laboratory animals; thereby lowering serum cholesterol and bloodstream levels of low-density lipoproteins (LDLP).

Shotgun cloning

Cloning of DNA fragments randomly generated from a genome; The practice of randomly clipping a larger DNA fragment into various smaller pieces, cloning everything, and then studying the resulting individual clones to figure out what happened.The technique for obtaining the desired gene involves "chopping up" the entire genetic complement of a cell using restriction enzymes, then attaching each (resultant) DNA fragment to a vector and transferring it into a bacterium, and finally screening those (engineered) bacteria to locate the bacteria that are producing the desired product (e.g., a protein)
For example, if one was studying a 50 kb gene, it "may" be a bit difficult to figure out the restriction map. By randomly breaking it into smaller fragments and mapping those, a master restriction map could be deduced.

Shotgun sequencing

A way of determining the sequence of a large DNA fragment.
The large fragment is shotgun cloned (see above), and then each of the resulting smaller clones ("subclones") is sequenced. By finding out where the subclones overlap, the sequence of the larger piece becomes apparent. Note that some of the regions will get sequenced several times just by chance.


A structure made up of two main bones: the scapula ( shoulder blade ) and the humerus (the long bone of the upper arm). The end of the scapula, called the glenoid, is a socket into which the head of the humerus fits, forming a flexible ball-and-socket joint . The scapula is an unusually shaped bone. It extends up and around the shoulder joint at the rear to create a roof called the acromion and around the shoulder joint at the front to constitute the coracoid process. The shoulder joint is cushioned by cartilage that covers the face of the glenoid socket and the head of the humerus. The joint is stabilized by a ring of fibrous cartilage around the glenoid socket that is called the labrum . Ligaments connect the bones of the shoulder and tendons join these bones to surrounding muscles. The biceps tendon attaches the biceps muscle to the shoulder and helps stabilize the joint. Four short muscles that originate on the scapula pass around the shoulder where their tendons fuse together to form the rotator cuff .

Shuttle Vector

A vector capable of replicating in two unrelated species.


A procedure to draw off excessive fluid in the brain. A tube that is surgically inserted between two blood vessels, two spaces, or two organs. Its purpose is to drain excess fluid and relieve pressure.
Shunts are most commonly placed between the ventricles (cavities) of the brain and other organs such as the abdomen, e.g., a surgically-placed tube running from the ventricles which deposits fluid into either the abdominal cavity, heart or large veins of the neck.. An example is the ventriculo-peritoneal shunt used to drain cerebrospinal fluid in hydrocephalus.

Sickle-cell anemia (SCA)

An inherited disease that has a profound effect on the function and structure of red blood cells.

Sickle-cell trait (SCT)

Refers to a person who is a carrier of the sickle-cell anemia, but does not actually suffer the disease effects.

Side Scatter (SSC) (in flow cytometry)

Light scattered at a 90 degree angle as a cell passes through the laser beam. This measurement is related to the internal granularity or complexity of a particle
Also called 90o scatter or right angle scatter.

Signal peptide

A stretch of amino acids on polypeptides that targets proteins to specific destinations in eukaryotic cells.

Signal to Noise Ratio (SNR)

The difference between the level of a stimulus or signal and the level of the background noise against which it is presented.
Although called a Ratio, it is generally calculated as a straight difference between the levels of the signal and the noise. This is when the two levels are expressed in decibel or some other logarithmic form, since the division of two logs is the difference between them.

Signal transduction cascade (or pathway)

The sequence of processes or reactions between the application or arrival of a signal or stimulus and the production of a response to that stimulus or signal.
In cell signalling it refers to a series of sequential events, such as protein phosphorylations, consequent upon binding of ligand by a transmembrane receptor, that transfers a signal through a series of intermediate molecules until final regulatory molecules, such as transcription factors, is modified in response to the signal.
In sensory physiology it refers to the sequence of events between the arrival of a stimulus such as light or sound at the receptor organ and the production of a receptor potential in the appropriate receptor cell.

Signal Variation

Signal variation is the variation in the measurement of the tracer label from assay run to assay run.
Signal variation is due to many factors including detector instrument drift, isotopic decay, enzyme denaturation, and substrate degradation. Signal variation will distort the binding variation from assay run to assay run if it is not factored out.

Sign stimulus

An external sensory stimulus that triggers a fixed action pattern.


Incoporating silica.


Two polygons are similar if their corresponding sides are proportional.


Similarity in biology refers to the relatedness of nucleic acid and amino acid sequences and protein structures.
Similarity can be expressed in percent identity referring to the percentage of building blocks in any two or more sequences found in the same string or pattern. Similarity is used to infer homology, a term in evolutionary biology that indicates a common ancestry between sequences or structures, i.e., to modern genes or proteins, albeit not identical but highly similar (~72%) are evolutionarily related and have diverged and accumulated changes independently from each other after a speciation event. Similarities around 25% identity or lower can no longer indicate an evolutionary relationship.

Simple harmonic motion

A repeating motion about a central equilibrium point (pendulum, weighted spring).


The practice of mimicking some or all of the behavior of one system with a different, dissimilar system.
Also known as Modelling (as in modelling the behaviour of a real system in an mock-up/aritifical system).

Simultaneous equations

A group of equations that are all true at the same time.


In a right triangle, the length of a side opposite an angle divided by the length of the hypotenuse of the triangle.

Single-gene disorder

Hereditary disorder caused by a mutant allele of a single gene (e.g., Duchenne muscular dystrophy, retinoblastoma, sickle cell disease).

Single photon emission computed tomography (SPECT) imaging.

A technique used to image the distribution of radiopharmaceuticals in the human body.The most common tracer is 99mTc labeled hexamethylpropylene amineoxime (HMPAO) which can cross the blood-brain barrier. Uptake in the brain is proportional to cerebral blood flow at the time of IV administration. Gamma cameras detect the radiation (gamma rays) released in 360 degrees and create multiplanar images

Single Nucleotide Polymorphism (SNP)

Variations in the sequence of DNA among individuals that are present in humans with a frequency of about once in every 1000 bases, and useful in assessing the patterns of inheritance in genetic linkage studies.

Sinoatrial (SA) node

The pacemaker of the heart, located in the wall of the right atrium.
It is the area of the vertebrate heart that initiates the heartbeat; located where the superior vena cava enters the right atrium. At the base of the wall separating the two atria is another patch of nodal tissue called the atrioventricular node (AV).

Sinusoidal gratings

A family of gray-scale visual patterns that's widely used as a stimulus in visual neuroscience. A stimulus design based on the Fourier theory of signal analysis. Since any visual image can be mathematically decomposed as the sum of many sinusoidal gratings, sinusoidal gratings are, in a way, the basic "vocabulary" of images. It is therefore important to understand how the brain’s neurons respond to them.

Sink hole

a depression in the Earth's surface caused by dissolving of underlying limestone, salt, or gypsum. Drainage is provided through underground channels that may be enlarged by the collapse of a cavern roof.


Small interefering RNA.

Sister chromatids

Replicated forms of a chromosome joined together by the centromere and eventually separated during mitosis or meiosis II.

Sister group

The two clades (groups) resulting from the splitting of a single lineage.

Skeletal muscle

Striated muscle, attached to the skeleton and limbs and generally responsible for the voluntary movements of the body.


Two lines that are not in the same plane.


Skewness is an asymmetrical frequency distribution in which the values are concentrated on one side of the central tendency and trail out on the other side.
If the trail is to the right or positive end of the scale, the distribution is said to be positively skewed. If the distribution trails off to the left or negative side of the scale, it is said to be negatively skewed.

Skip pattern

In survey research, the sequence of questions asked and skipped.
For instance, persons who answer one question that indicates they did not vote in the last election would trigger a "skip" so that the interviewer would not ask those respondents questions about how they voted in the last election.

Sleep apnea

The temporary stoppage of breathing during sleep, often resulting in daytime sleepiness. The most common form of sleep apnea is obstructive sleep apnea. In obstructive sleep apnea, the muscles of the soft palate around the base of the tongue and the uvula relax, obstructing the airway. The airway obstruction causes the level of oxygen in the blood to fall (hypoxia), increases the stress on the heart, elevates blood pressure, and prevents the patient from entering REM sleep, the restful and restorative stage of sleep. In other words, sleep apnea causes deprivation of quality sleep.
The symptoms of obstructive sleep apnea include loud snoring and/or abnormal pattern of snoring with pauses and gasps. Other symptoms include excessive daytime sleepiness, memory changes, depression, and irritability. In some patients sleep apnea can contribute to high blood pressure, heart failure, stroke, and heart attack.
Obstructive sleep apnea typically affects middle-age, overweight men, and may affect women in later years. It can be aggravated by alcohol, sleeping pills and tranquilizers taken at bedtime.
Sleep laboratories monitor different stages of sleep, diagnose sleep apnea, determine the type (obstructive or central) and severity of sleep apnea, and design treatment. General measures in treating obstructive sleep apnea include losing excessive weight, avoiding alcohol and sedatives, sleeping on one side, and medications to relieve nasal congestion. CPAP (continuous positive airway pressure) is an effective treatment for sleep apnea. A mask is worn over the nose during sleep while compressed air is gently forced through the nose to keep the airway open. Different patients need different mask sizes and different pressure levels for optimal treatment results. Another type of treatment for obstructive sleep apnea is ENT surgery. In an operation called UPPP, the surgeon removes excessive soft tissue from the back of the throat to relieve obstruction.
(see Apnea)

Sliding filament model

The theory explaining how muscle contracts.It is based on changes within a sarcomere, the basic unit of muscle organization, stating that thin (actin) filaments slide across thick (myosin) filaments, shortening the sarcomere; the shortening of all sarcomeres in a myofibril shortens the entire myofibril.


The slope of a line is the tangent of that line; The slope of a line is the change in the vertical coordinates/the change in the horizontal coordinates of any two points on the line. The tangent is the vertical distance of any two points on a line divided by the horizontal distance of the same two points. The slope in a linear regression is expressed as coefficient b.

Slot blot

Similar to a dot blot, but the analyte is put onto the membrane using a slot-shaped template.The template produces a consistently shaped spot, thus decreasing errors and improving the accuracy of the analysis.

Small for gestational age (SGA)

Low birth weight for a gestational age
calculated from the last normal menstrual period and corroborated by clinical assessment of the age of the infant at birth; sometimes described as growth retarded.
Weight is less than 10th percentile acceptable norms for the particular gestational age.

Small intestine

The region of the digestive system immediately after the stomach.
It consists of three sections:

  • The duodenum, about 25 cm (10 in) long, receives chyme from the stomach through the pyloric sphincter. Ducts that empty into the duodenum deliver pancreatic juice and bile from the pancreas and liver, respectively.
  • The jejunum, about 2.5 m (8 ft) long, is the middle section of the small intestine.
  • The ileum, about 3.6 m (12 ft) long, is the last section of the small intestine. It ends with the ileocecal valve (sphincter), which regulates the movement of chyme into the large intestine and prevents backward movement of material from the large intestine.

The functions of the small intestine include

  • Mechanical digestion. Segmentation mixes the chyme with enzymes from the small intestine and pancreas. Bile from the liver separates fat into smaller fat globules. Peristalsis moves the chyme through the small intestine.
  • Chemical digestion. Enzymes from the small intestine and pancreas break down all four groups of molecules found in food (polysaccharides, proteins, fats, and nucleic acids) into their component molecules.
  • Absorption. It is the primary location in the GI tract for absorption of nutrients:
  • Carbohydrates, proteins, nucleic acids, and water-soluble vitamins. The components of these molecules are absorbed by facilitated diffusion or active transport. They are then passed to blood capillaries.
  • Vitamin B12. Vitamin B12 combines with intrinsic factor (produced in the stomach) and is absorbed by receptor-mediated endocytosis. It is then passed to the blood capillaries.
  • Lipids and fat-soluble vitamins. Because fat-soluble vitamins and the components of lipids are insoluble in water, they are packaged and delivered to cells within water-soluble clusters of bile salts called micelles. They are then absorbed by simple diffusion and, once inside the cells, mix with cholesterol and protein to form chylomicrons. The chylomicrons are then passed to the lymphatic capillaries. When the lymph eventually empties into the blood, the chylomicrons are broken down by lipoprotein lipase, and the breakdown products, fatty acids and glycerol, pass through blood capillary walls to be absorbed by various cells.
  • Water and electrolytes. About 90 percent of the water in chyme is absorbed, as well as various electrolytes (ions), including Na-, K-, Cl−, nitrates, calcium, and iron.

(see Large Intestine)

Small nuclear ribonucleoprotein (snRNP)

One of a variety of small particles in the cell nucleus, composed of RNA and protein molecules. Its functions are not fully understood, but some form parts of spliceosomes, active in RNA splicing.

Small Ubiquitin-related Modifier (SUMO)

A "partner protein" which readily fuses with certain other protein molecules and causes: (a) enhanced expression of those other protein molecules, (b) enhanced solubility of those other protein molecules, (c) correct folding of those other protein molecules.In some cases, the SUMO protein binds to histones (i.e., certain proteins complexed-with DNA in chromsomes) of chromosomes/genes across an organism's genome; thereby repressing the transcription of many of the genes across that genome in order to protect it (e.g., from cancer). Such a SUMO-binding process is called sumoylation.When sumoylation occurs in applicable plant tissues (i.e., those containing receptors for abscisic acid), it negatively regulates (or even halts) the seed germination and/or root growth which normally results from abscisic acid signaling

Smooth endoplasmic reticulum (ER)

That portion of the endoplasmic reticulum that is free of ribosomes.

Smooth muscle

A type of muscle lacking the striations of skeletal and cardiac muscle because of the uniform distribution of myosin filaments in the cell.


Small nuclear RNA.Forms complexes with proteins to form snRNPs; involved in RNA splicing, polyadenylation reactions, other unknown functions (probably)


Small Nuclear RiboNucleoProtein particles (“snerps”).Complexes between small nuclear RNAs and proteins, and which are involved in RNA splicing and polyadenylation reactions

SNP, Single Nucleotide Polymorphism

A position in a genomic DNA sequence that varies from one individual to another.
It is thought that the primary source of genetic difference between any two humans is due to the presence of single nucleotide polymorphisms in their DNA. Furthermore, these SNPs can be extremely useful in genetic mapping (see 'Genetic Mapping') to follow inheritance of specific segments of DNA in a lineage. SNP-typing is the process of determining the exact nucleotide at positions known to be polymorphic.

Social dominance

A hierarchical pattern of social organization involving domination of some members of a group by other members in a relatively orderly and long-lasting pattern.


The study of social behavior based on evolutionary theory.


A term sometimes used to describe persons with extreme disregard for and hostility toward society. A person who is sociopathic is aggressively antisocial and shows no remorse.

Sodium benzoate

Chemical preservative that is particularly effective against yeasts.

Sodium metabisulphite

Chemical preservative that is effective against moulds and yeasts.

Sodium nitrite

Salt used in smoked or cured fish and in meat-curing preparation. It acts as a preservative and colour fixative. Can combine with chemicals in the stomach to form nitrosamine, a carcinogenic substance.

Sodium-potassium pump

A special transport protein in the plasma membrane of animal cells that transports sodium out of and potassium into the cell against their concentration gradients.
It plays a critical role in many cells in creating and maintaining the resting membrane potential, the difference in charge across the membrane at rest. The presence of the resting membrane potential allows that cell to signal a change (an input) by changing that resting membrane potential. Thus if the sodium-potassium pump ceased to function the cell would not be able to carry out its function. Since cells using this mechanism include nerve and muscle cells, death can ensue.


A three dimensional object that completely encloses a volume of space.

Solid Phase (in assays)

Binder or ligand can be absorbed onto solid phase surfaces, such as microtiter wells, magnetic particles, or plastic beads. This immobilized reactant can then capture ligand or binder from the liquid phase. The soluble free fraction can then be washed away.

Soluble fibre

Type of dietary fiber found in psyllium, cereals, oatmeal, apples, citrus fruits, beans and other foods which increases the viscosity in the gut and acts to reduce high blood cholesterol levels which decreases the risk of cardiovascular disease.

Solute, solvent and salvation

Solute: The substance dissolved in a solution.
Solution: A mixture of a solvent and a solute. In some solutions, such as sugar water, the substances mix so thoroughly that the solute cannot be seen. But in other solutions, such as water mixed with dye, the solution is visibly changed..
Solvation: The process by which solvent molecules surround and interact with (dissolve) solute molecules.
Solvent: A gas or liquid that dissolves or disperses something else, thus forming a solution. Water dissolves more substances than any other, and is known as the "universal solvent"..

Solution hybridization

A method closely related to RNase protection, designed to measure the levels of a specific mRNA species in a complex population of RNA. An excess of radioactive probe is allowed to hybridize to the RNA, then single-strand specific nuclease is used to destroy the remaining unhybridized probe and RNA. The "protected" probe is separated from the degraded fragments, and the amount of radioactivity in it is proportional to the amount of mRNA in the sample which was capable of hybridization. This can be a very sensitive detection method.

Somatic cells

Any cell in the body except gametes (sperm and eggs) and their precursors.

Somatic cell mutation

Mutation in a cell that is acquired during the lifetime of an organism and which cannot be genetically inherited by offspring.

Somatic cell nuclear transfer (SCNT)

A technique that combines an enucleated egg and the nucleus of a somatic cell to make an embryo. SCNT can be used for therapeutic or reproductive purposes, but the initial stage that combines an enucleated egg and a somatic cell nucleus is the same.

Somatic nervous system

The branch of the motor division of the vertebrate peripheral nervous system composed of motor neurons that carry signals to skeletal muscles in response to external stimuli.

Somatic (adult) stem cells

A relatively rare undifferentiated cell found in many organs and differentiated tissues with a limited capacity for both self renewal (in the laboratory) and differentiation.
Such cells vary in their differentiation capacity, but it is usually limited to cell types in the organ of origin. This is an active area of investigation.


Sensory activity having its origin elsewhere (e.g., the skin, muscles, internal organs) than in the special sense organs (i.e., structures such as the eyes and ears) and conveying information to the brain about the state of the body proper and its immediate environment.
Conveys information from superficial and deep structures about touch, pressure, vibration, pain, temperature, cold, warmth, etc.


hormone, produced by the pituitary gland, that stimulates protein synthesis and promotes the growth of bone; also known as growth hormone.

S1 end mapping

A technique to determine where the end of an RNA transcript lies with respect to its template DNA (the gene).

S1 nuclease

An enzyme which digests only single-stranded nucleic acids.


A computer picture of areas inside the body created by bouncing high-energy sound waves (ultrasound) off internal tissues or organs.
Also called ultrasonogram.


Sugar alcohol, suitable for diabetics.

Southern blots

A technique which allows the detection of a specific DNA sequence present in a large, complex sample of DNA; involves transfer by absorption of DNA fragments separated in electrophoretic gels to membrane filters for detection of specific base sequences by radiolabeled complementary probes.
Named after ts inventor and developer, the British biologist Edwin M. Southern.
High molecular weight DNA is digested, by restriction endonucleases into smaller fragments which are then separated into bands by electrophoresis on an agarose gel. A sheet of nylon or nitrocellulose membrane is applied against the agarose gel to transfer the DNA bands to the membrane. Depending on the type of membrane used, it is then baked at high temperatures (60-100 oC) or exposed to UV radiation to permanently covalently cross-link the DNA bands to the membrane. The membrane is then exposed to and incubated with a radiolabelled probe, a single-stranded DNA with the sequence of interest, so that the DNA on the membrane can hybridize with the probe. Excess (unbound) probe is washed away and the pattern of hybridization is visualized on X-ray film by autoradioghraphy.
A Southern blot is routinely used to check for the presence of a DNA sequence in a DNA sample. It is particularly useful in detecting large gene rearrangements/deletions and large trinucleotide repeat expansions. It is also used to determine the molecular weight of a restriction fragment and to measure relative amounts in different samples.


A wave of pressure travelling through an elastic medium (e.g., air, water) by mechanical disturbance (vibration) of molecules of medium

Sous vide

Process in which food is prepared, vacuum packed, cooked to pasteurise (sterilise) the food and chilled.
These foods can be refrigerated for up to 60 days.

Southern blot

Procedure which transfers elecrophoretically separated DNA fragments on an agarose gel to nitrocellulose filters for detection by hybridization with a labeled probe complementary to the sequence of interest; the position on the filter of the probe, when exposed to x-ray film, appears as a band on an autoradiogram


A chamber that is attached to a metered dose inhaler (MDI) to help reduce the velocity of the aerosol and stabilize the particle size by removing larger particles from suspension

Spacer DNA

Lengths of DNA between genes (especially rRNA genes) which are not transcribed into mRNA

Spastic hemiplegra

Damage to the telencephalon resulting in stiffness of two extremities on the same side. There may be involvement of all four extremities with one side more involved than the other. This is referred to as bilateral hemiplegra or, occasionally, as spastic quadriplegia.

Spastic quadriplegia

Involvement of all four extremities. Damage to telencephalon resulting in a poverty of movement due to increased stiffness equal in all four extremities equally.


An involuntary increase in muscle tone (tension) that occurs following injury to the brain or spinal cord, causing the muscles to resist being moved. Resistance of a limb to passive stretch due to increased tone in either flexors or extensors (usually extensors) but not both. Characteristics may include increase in deep tendon reflexes, resistance to passive stretch, clasp knife phenomenon, and clonus. Increased muscle tone (hypertonic), involuntary resistance of weak muscle caused by passive range of motion followed by sudden relaxation of muscle, associated with exaggeration of reflexes. Causes stiffness, awkward movements, and loss of voluntary muscle control.
(See Rigidity)


Rinsing grains to extract residual sugar that clings to the grains after they have been mashed. Warm water is poured over the grains and hops above a strainer.

Spatial ability

Ability to perceive the construction of an object in both two and three dimensions.
Spatial ability has four components: the ability to perceive a static figure in different positions, the ability to interpret and duplicate the movements between various parts of a figure, the ability to perceive the relationship between an object and a person's own body sphere, and the ability to interpret the person's body as an object in space.

Spatial frequency

A measure of how rapidly a stimulus changes across space.
In practice neuronal sensitivity to spatial frequency is measured by presenting alternating light and dark strips with the variable parameter being the number of light/dark changes or cycles per degree visual angle.
High SFs effectively mean fine detailed stimuli (i.e., changes in the object’s details are closely spaced, or at high frequency) whereas Low SFs mean that there is little variation in the details of the object (e.g., larger forms/shapes).


(1) Of cells, having particular functions in a multicellular organism.
(2) Of organisms, having special adaptations to a particular habitat or mode of life.

Special relativity

The observable effects on a body in motion. 
As velocity increases, time slows down, mass increases and lengths contract.


The origin of new species in evolution; The splitting of an evolutionary lineage producing (usually) two new, separate species, which thus begin their own, unique evolutionary historiesA group of organisms that are able to interbreed all belong to the same species.  It follows then that organisms that are unable to interbreed belong to separate species. Speciation is the central process of macroevolution, the evolution of novel forms.


A group of organisms (individuals) that can interbreed and reproduce with each other; A group of organisms belong to the same biological species, if they are capable of interbreeding to produce fertile offspring; A group of organisms that share a common gene pool as well as a unique evolutionary history distinct from other groups of organisms.
Used to distinguish sexually reproducing organisms into groups. Individuals from two different species cannot have offspring. They are said to be reproductively isolated. The biologist Ernst Mayr formulated this definition of a species advancing our understanding of the mechanism of evolution of higher organisms. For microbes, the species definition does not properly apply, because they do not reproduce sexually, but have an efficient mechanism to exchange genetic material even between evolutionarily distant forms. This exchange of genes is known as horizontal gene transfer. Unlike sexual reproduction, it usually involves only a fraction of an organisms genome that is being transferred and is a mechanisms of increasing genetic variability among microorganisms that does not depend on cellular reproduction (cell division).
However, the definition of a species is more difficult than one might think. Over the years, a variety of different species concepts have been proposed, and the debate about the most appropriate definition is ongoing. The biological test of a species is not always available, and so there is also a morphological species concept based on anatomical similarities, i.e., members possess similar anatomical characteristics.

Species diversity

The number and relative abundance of species in a biological community.

Species richness

The number of species in a biological community.


A theory maintaining that species living the longest and generating the greatest number of species determine the direction of major evolutionary trends

Species homologue (or species variant)

Relative potency of a drug between two receptor subtypes for the same endogenous ligand. This is a relative rather than absolute term that should always be qualified (e.g. prazosin is 30-fold selective for <28>1-adrenoceptors relative to <28>2-adrenoceptors). Compare specificity.

Species specific

Characteristic of (and limited to) a particular species.


Unique; for example, the proteins in a given organism, the enzyme catalyzing a given reaction, or the antibody to a given antigen.

Specific activity

The specific activity of a tracer is the activity of the label per unit mass of the labeled material.

Specific conductance

A measure of the ability of water to conduct an electrical current as measured using a 1-cm cell and expressed in units of electrical conductance, i.e., Siemens per centimeter at 25 degrees Celsius.
Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality, specific conductance is used in ground water monitoring as an indication of the presence of ions of chemical substances that may have been released by a leaking landfill or other waste storage or disposal facility. A higher specific conductance in water drawn from downgradient wells when compared to upgradient wells indicates possible contamination from the facility.

Specific gravity

Measure of the density of a liquid. The ratio of the density of a body to the density of water, the latter being taken as unity.

Specific heat

Ability of a material to store heat; The amount of heat that must be absorbed or lost for 1 g of a substance to change its temperature 1°C..
Described technically as the amount of energy required to raise the temperature of unit mass of an object by a unit increment in temperature.


The specificity of a binder is the ability of its binding site to distinguish between the ligand to which the binder is specific and other compounds. Relative potency of a drug between the receptors for two different endogenous ligands (e.g. sulpiride is specific for dopamine receptors when compared with 5HT receptors). Compare selectivity.

Specific learning disability

A disorder in understanding or using spoken or written language, characterized by imperfect ability to listen, think, speak, read, write, spell, or do mathematical calculations. The term includes students with conditions such as perceptual handicaps, brain injury, minimal brain dysfunction, dyslexia and developmental aphasia. The term does not include students who have learning problems which are primarily the result of visual, hearing, or motor handicaps; mental retardation; or environmental, cultural or economic disadvantage.


A specimen is standard calibrator material, known control material, or material from an unknown subject which is collected for subsequent measurement.


A spectrophotometer is a detector instrument that measures the amount of monchromatic light passing through a solution by means of an adjustable monochromator such as a prism or diffraction grating.


The study of spectra, that is, the dependence of physical quantities on frequency.
Examples: UV spectroscopy, Near IR, etc.

Speech audiometry

Measurement of the ability to hear speech under various conditions of intensity and noise interference using sound-field as well as earphones and bone oscillators.

Speech-language Pathology Services

A continuum of services including prevention, identification, diagnosis, consultation, and treatment of patients regarding speech, language, oral and pharyngeal sensorimotor function.

Speech Reception Threshold (SRT) Test

A test to determine the lowest sound intensity level at which fifty percent or more of the spondaic test words (words of two syllables having equal stress) are repeated correctly

S phase

Synthesis phase of the cell cycle, during interphase, in which the cell duplicates its DNA.


The set of all points in space that are a fixed distance from a given point.


Delicate pointed structures lying external to the body and usually pointed away from it.Like spines, but invariably excreted and more delicate.

Spider-web diagram

Diagram representing a product's sensory profile. Measured intensities are plotted on radial lines, emanating from a central point.

Spike sorting

A technique to distinguish the action potentials (the “spikes”) produced nearly-simultaneously by a number of neurons close to a recording electrode
Depending on its characteristics, a recording microelectrode placed in a brain structure in which there is a number of neurons close together, may record action potentials from a number of these neurons if they are active. Thus the electrode "hears" spikes generated by many nearby neurons. Because the distance of each active neuron from the electrode is different and because the characteristics of each neuronal cell body may be slightly different, each action potential has its own “signature” in terms of its shape, size and timing. It is therefore often possible to use computer programs to "sort" the different spikes on the basis of a combination of these characteristics (e.g., the width of the action potential + the size + the rate of rise of the upstroke of the AP etc) so that action potentials from different neurons are separated from each other. This allows data to be collected from a number of different active neurons in the one structure but at the same time.

Spina bifida (Also known as myelomeningocele)

It is a birth defect of the backbone, often called "open spine". It results from a more common and usually less severe form of failure of proper fusion of the neural tube due where there is failure of the neural arches of the vertebrae to meet, fuse, and enclose the spinal cord.
In children with this defect, the backbone never closes completely. It can cause many other conditions such as mental retardation, lack of control of the leg muscles, lack of bowel and bladder control and/or curvature of the spine.
The three types of spina bifida (from mild to more severe) are Spina Bifida Occulta, Meningocele, and Myelomeningocele.
spina bifida cystica: A malformation of the spinal column in which a tumorlike sack is produced on the infant's back.
spina bifida meningocele: A cystic swelling or tumor like sack that contains spinal fluid, but no nerve tissue.
spina bifida myclomeningocele: A cystic swelling or tumorlike sack that contains both spinal fluid and nerve tissue.
spina bifida occulta: A mild type of spina bifida in which there is an opening in one or more of the vertebrae (bones) of the spinal column without apparent damage to the spinal cord. Many people with spina bifida occulta ever know they have it because they experience little or no symptoms.

Spinal cord

The major column of nerve tissue that is connected to the brain and lies within the vertebral canal and from which the spinal nerves emerge. Thirty-one pairs of spinal nerves originate in the spinal cord: 8 cervical , 12 thoracic , 5 lumbar, 5 sacral, and 1 coccygeal. The spinal cord and the brain constitute the central nervous system ( CNS ). The spinal cord consists of nerve fibers that transmit impulses to and from the brain. Like the brain, the spinal cord is covered by three connective-tissue envelopes called the meninges . The space between the outer and middle envelopes is filled with cerebrospinal fluid ( CSF ), a clear colorless fluid that cushions the spinal cord against jarring shock. Also known simply as the cord.

Spinal fusion

Operative method of strengthening and limiting motion of the spinal column.
Can be performed with a variety of metal instruments and bone grafts, or bone grafts alone.

Spinal meningitis

An inflammation of the membranes of the spinal cord.

Spinal nerves

Nerves of the peripheral nervous system (and therefore nerves connecting to the body) that originate from or terminate in the spinal cord.
There are 31 pairs (i.e.,62 nerves in total) of spinal nerves. Spinal nerves are mixed nerves containing sensory nerves (nerve fibres carrying information from the body to the central nervous system) and motor nerve fibers (carrying controller information from the central nervous system to muscles of the body).
(see Cranial Nerves)

Spinal stenosis

Narrowing of the spaces in the spine, resulting in compression of the nerve roots or spinal cord by bony spurs or soft tissues, such as disks, in the spinal canal. This occurs most often in the lumbar spine (in the low back) but also occurs in the cervical spine (in the neck) and less often in the thoracic spine (in the upper back).


1) The column of bone known as the vertebral column, which surrounds and protects the spinal cord. The spine can be categorized according to level of the body: i.e., cervical spine (neck), thoracic spine (upper and middle back), and lumbar spine (lower back). See also vertebral column. 2) Any short prominence of bone. The spines of the vertebrae protrude at the base of the back of the neck and in the middle of the back. These spines protect the spinal cord from injury from behind.


Measurement of ventilatory ability (respiration) by assessing lung capacity and flow, including the time necessary for exhaling the total volume of inhaled air.
To obtain an accurate reading, the subject has to stand or sit up straight, inhale maximally, get a good selof their mouth around the mouthpiece of the spirometer, blow out as hard and fast as possible, and continue to exhale until they can no longer do so for at least 6 seconds and up to 15 seconds if necessary. This should be repeated until at least 3 technically reliable values are obtained.
Spirometry provides 3 basic values: (1) the Forced Vital Capacity (FVC), the maximum air that can be exhaled, (2) the Forced Expiratory Volume in 1 second, FEV1, and (3) the Forced Expiratory Ratio (FER or also called FEV 1%), which is calculated as FEV1 / FVC.

Splice variants

Variants in the mature mRNA spliced from a single gene, resulting in different proteins with different size and functionality, from the one gene.
During transcription of a DNA template the mRNA cuts out (splices out) the intron sequences of a gene and strings together the exon sequences (the RNA and protein coding sequences). Usually, eukaryotic genes consist of several exons/introns and sometimes not all exons are used in the final mature RNA. Ultimately, a single gene can be spliced into more than one mature mRNA producing splice variants.


A process during protein synthesis where the mRNA cuts out the intron sequences and strings together the exon (coding) sequences derived from a DNA template during transcription. Usually, eukaryotic genes consist of several exons/introns and sometimes not all exons are used in the final mature RNA. Ultimately, a single gene can be spliced into more than one mature mRNA producing splice variants. Splice variants give rise to proteins with different size and functionality.


Pertaining to the vertebrae
Spondylalgia - Pain in vertebra(e).
Spondylarthritis - Arthritis of the spine.
Spondylarthrocace - Tuberculosis of the spine; spondylocace.
Spondylexarthrosis - Dislocation of a vertebra.
Spondylitis - Inflammation of vertebrae, including types such as ankylosing, rheumatoid, traumatic, spondylitis deformans, Kümmel, and Marie-Strümpell d.
Spondylizema - Depression or downward displacement of a vertebra, with destruction or softening of one below it.
Spondylodynia - Pain in vertebra(e).
Spondyloepiphyseal dysplasia - Disorder of growth affecting both the spine and the ends of long bones.
SpondylolisthesiS - A defect in the construct of bone between the superior and inferior facets with varying degrees of displacement so the vertebra with the defect and the spine above that vertebra are displaced forward in relationship to the vertebrae below. It is usually due to a developmental defect or the result of a fracture.
SpondylolysiS - Displacement of one vertebrae over another with fracture of a posterior portion of the vertebra. A defect in the neural arch between the superior and inferior facets of vertebrae without separation at the defect and therefore no displacement of the vertebrae. It may be unilateral or bilateral and is usually due to a developmental defect but may be secondary to a fracture.
Spondylomalacia - Softening of vertebrae; Kümmell disease.
Spondylopathy - Any vertebral disorder.
Spondylopyosis - Infection in vertebra(e).
Spondyloschisis - Congenital fissure (splitting) of vertebral arch.
Spondylosis - Ankylosis of the vertebra; often applied nonspecifically to any lesion of the spine of a degenerative nature. Bony replacement of ligaments around the disc spaces of the spine, associated with decreased mobility and eventual fusion; marginal osteophyte.
Spondylosyndesis - Surgical immobilization or ankylosis by fusion of the vertebral bodies with a short bone graft in cases of tuberculosis of the spine; spondylodesis, Albee procedure.
Spondylotomy - Incision into a vertebra or vertebral column; rachiotomy.

Spontaneous Recovery

The recovery which occurs as damage to body tissues heals.
This type of recovery occurs with or without rehabilitation and it is very difficult to know how much improvement is spontaneous and how much is due to rehabilitative interventions. However, when the recovery is guided by an experienced rehabilitation team, complications can be anticipated and minimized; the return of function can be channeled in useful directions and in progressive steps so that the eventual outcome is the best that is possible.


Unicellular body produced by plants, fungi, and some microorganisms; A single cell that is dispersed as a reproductive unit, or that encapsulates a cell during unfavorable environmental conditions; in organisms with an alternation of generations; the products of meiosis are spores. Often a resting stage, encased in a protective coat, adapted to resist heat, desiccation, or other unfavorable environmental conditions, e.g., inactive or dormant state of some rod-shaped bacteria. It is the part of mould that reproduces and causes the mould to spread. It is the mould's version of a seed.
Spores can give rise to a new individual either directly or after fusion with another spore.


The phase of the life cycle of sexually reproducing plants and algae in which the spores are produced. The diploid stage in the life cycle of an organism undergoing an alternation of generations. The sporophyte is multicellular and develops from the diploid zygote. The mature sporophyte meiotically produces haploid spores that later generate the gametophyte generation.


The process of spore development.

Square root

of a number, x, is the number that, when multiplied by itself gives the number, x.


Simple Sequence Repeat. See 'Microsatellite'.


Substances which allow food compounds which do not mix well to be mixed and stay in a homogeneous state.

Stable transfection

A form of transfection experiment designed to produce permanent lines of cultured cells with a new gene inserted into their genome.Usually this is done by linking the desired gene with a "selectable" gene, i.e. a gene which confers resistance to a toxin (like G418, aka Geneticin). Upon putting the toxin into the culture medium, only those cells which incorporate the resistance gene will survive, and essentially all of those will also have incorporated the experimenter's gene.

Stabilizing selection

Selection favouring individuals in the middle of the distribution of phenotypes in a population and disfavouring the extremes. Also called normalizing selection.


Performing exams and tests to learn the extent of the cancer within the body, especially whether the disease has spread from the original site to other parts of the body. It is important to know the stage of the disease in order to plan the best treatment.

Standard (in assays)

Standard samples are aliquots of calibration specimens containing predetermined quantities of the analyte. The response of each standard, along with the standard's predetermined concentration, is used to construct a standard curve. From this standard curve, sample concentrations can be computed using the response from the sample.

Standard curve

An immunoassay standard curve is a curve (or straight line) produced by mathematically fitting an equation to the data from a series of dilutions of an analyte of known concentration. The data is a plot of the response versus the concentration of each dilution.

Standard deviation

A measure of the spread of a sampling statistic, denoted by the Greek letter (sigma) for the estimated standard deviation. The standard deviation is the square root of the variance.

Standard length

The length of a fish measured from the tip of the snout to the end of the fleshy part of the body. This measurement is preferred by many ichthyologists because it ignores the tail fin, which can often be damaged in specimens.

Stanol/sterol esters

Functional component found in wood oils, corn, soy and wheat which may reduce the risk of coronary heart disease by lowering blood cholesterol levels.


A surgical process that replaces defective stapes in the ear with a prosthetic device.


A term used loosely to refer to refractile masses of polysaccharides, consisting of long chains of glucose units, which are accumulated as storage products in the cell.
The major complex carbohydrate of caloric value from plant products. Found very widely in plants, commonly as a form of energy storage in roots, tubers, fruits and seeds. In this respect it performs essentially the same functions as sugar, but is not sweet and not very soluble in water.

Start codon

The sequence of nucleotides (codon) on a messenger RNA molecule where protein synthesis begins. The start codon nucleotide sequence is AUG.

Static electricity

Describes the situation where objects carry a charge.


A period of little or no discernible change in a lineage.

Static magnetic field

Magnetic fields that have constant intensity over time and whose field direction is constant. The intensity varies periodically according to the frequency and type of wave in the magnet.

Statins (HMG-CoA Reductase)

A class of drugs that lower the level of cholesterol by reducing the body's production of cholesterol.


The mathematical procedure to describe probabilities and the random or non-random distribution of matter or occurrence of events.

Status epilepticus

Seizures that occur in series without intervening recovery periods.

Steady-state (equilibrium)

A process in biochemistry that refers to situations of high activity even though the overall structure and composition of cells seems not to change.
Steady state processes are used to explain metabolic homeostasis. The flow of water molecules in a river or free flowing traffic are examples of steady state processes where the overall movement of water molecules (cars) does not appear to change, although the composition of particular molecules (cars) is constantly changing.


Saturated fatty acid containing 18 carbon atoms in its molecular backbone that is essentially neutral in effect on coronary heart disease in humans (i.e., doesn’t appreciably increase low-density lipoproteins in the bloodstream).
Because of the heart disease neutrality and resistance to oxidation/breakdown, stearate-containing oils are an excellent cooking oil choice.

Stem cells

Cells with the ability to divide for indefinite periods in culture and to give rise to specialized cells.
Certain cells - present in the bodies of mammals even prior to birth, although also present in adult mammals - that can grow/differentiate into different cells/tissues of the (adult organism) body. Stem cells can divide and create another cell like themselves and can also divide and create a cell more differentiated than itself.
For example, bone marrow (stem) cells; some of which eventually mature into red blood cells or white blood cells. The stem cells that remain in the bone marrow maintain their own numbers by self-renewal divisions, yielding more (adult stem cell) cells to start the maturation process. This maturation process is stimulated and controlled by stem cell growth factor (SCF), granulocyte colony stimulating factor (G-CSF), and by granulocyte-macrophage colony stimulating factor (GM-CSF).

Stem group

All the taxa in a clade preceding a major cladogenesis event.
They are often difficult to recognize because they may not possess synapomorpies found in the crown group.


A narrowing in the diameter of a body canal due to new bone formation
May result in pressure on the spinal cord or nerve roots.

Stereotyped movementdisorders

Conditions characterized by abnormal gross motor behaviors (tics)


Chemical that destroys micro-organisms but does not remove soils.


Incapable of reproduction.


The method used to render a material free from living organisms.
Usual methods include steam under pressure, gas, and ionizing radiation.

Sticky ends

After digestion of a DNA with certain restriction enzymes, the ends left have one strand overhanging the other to form a short (typically 4 nt) single-stranded segment. This overhang will easily re-attach to other ends like it, and are thus known as "sticky ends".
For example, the enzyme BamHI recognizes the sequence GGATCC, and clips after the first G in each strand:

The overhangs thus produced can still hybridize ("anneal") with each other, even if they came from different parent DNA molecules, and the enzyme ligase will then covalently link the strands. Sticky ends therefore facilitate the ligation of diverse segments of DNA, and allow the formation of novel DNA constructs.


Essentially meaning Random; Referring to patterns or processes resulting from random factors, a stochastic event is based on random behavior.
A stochastic event is based on random behaviour. The occurrence of individual events cannot be predicted, although measuring the distribution of all observations usually follows a predictable pattern. These patterns can be described by statistical means. An example is the decay of radio active material, where a clump of matter has a measurable and thus predictable half-life time. It is impossible, however, to mark an individual atom and predict when it will decay and emit radiation. The latter process is a stochastic event.

Stoke's equation

Velocity at which a sphere will rise or fall in a liquid varies as the square of its diameter. For example, a fat globule with a diameter of 2 microns will rise 4 times faster than a fat globule with a diameter of 1 micron.


A surgical opening in the abdomen that allows drainage of either urine or stool into disposable bags.


A type of cyst, with a siliceous wall and a single plugged opening, formed by some chrysomonads (stramenopiles).

Stop (or Termination) codon

The sequence of nucleotides (codon) on a messenger RNA molecule where protein synthesis stops.


Deviation of eye movement which prevents the two eyes from moving in a parallel fashion. Crossed eyes (internal) or eyes that look outward (external).


The deformation of a body under an applied load.


The measure of the force acting on a body.

Stress riser

Places where stress lines from applied forces concentrate within a structure. Breakage is most likely to occur at these places. In long bones or orthopedic plates, for example, stress lines from forces applied at the ends tend to produce uniform cross sectional stress lines. Discontinuities, such as screw holes, redistribute these forces concentrating them close to the holes where fracture is most likely to occur.

Stress shielding

The removal of forces or stresses that normally act on bone. Stress shielding eventually leads to osteopenia.  A common site for stress shielding is the proximal femoral diaphysis after placement of a femoral prosthesis. The more tightly the stem of the prosthesis fits into the distal medullary canal, the greater the shift of body weight to the prosthetic stem from the proximal femoral cortex. This causes loss of the normal remodeling forces above the level at which the stem is fixated against the endosteal surface of the medullary canal resulting in osteopenia of the proximal femoral diaphysis.


A term used to describe the conditions of hybridization.
By varying the conditions (especially salt concentration and temperature) a given probe sequence may be allowed to hybridize only with its exact complement (high stringency), or with any somewhat related sequences (relaxed or low stringency). Increasing the temperature or decreasing the salt concentration will tend to increase the selectivity of a hybridization reaction, and thus will raise the stringency.


A block in the brain’s blood supply due to cerebral ischemia (ischemic stroke) or hemorrhage (hemorrhagic stroke) causing the sudden onset of neurological symptoms. Stroke can be caused by the rupture of a blood vessel, a clot, or pressure on a blood vessel (as by a tumor). Without oxygen, neurons in the affected area die and the part of the body controlled by those cells cannot function. A stroke can result in loss of consciousness and death. The symptoms of stroke include sudden numbness or weakness (usually on one side of the body), visual impairment, loss of balance or coordination, and difficulty speaking or comprehending speech.

Stromal cells

Non-blood cells derived from blood organs, such as bone marrow or fetal liver, which are capable of supporting growth of blood cells in vitro.
Stromal cells that make the matrix within the bone marrow are also derived from mesenchymal stem cells.

Structure, high-resolution

The high resolution structure of a molecule refers to its atomic organization in three-dimensional space. It is either obtained from analysis of diffraction patterns of high energy radiation (X-rays, electron waves) or nuclear magnetic resonance spectra (NMR). Structural information has an important place in biological studies at the molecular level, because structures can be used to elucidate the detailed mechanism of a chemical reaction, a biological binding events such as hormone signaling or immunological defenses, or nutrient transport (absorption) across intestinal epithelial cell layers and cell membranes. The structural analysis of DNA in 1953 has helped understand the mechanism of replication of genetic information during reproduction as well as the mechanism of genetic encoding, reading (transcription), and synthesis (translation)of amino acid sequences in proteins and enzymes

Structure Activity Realtionship by NMR (SAR by NMR)

A means for researchers in pharmaceutical companies to utilize NMR (nuclear magnetic resonance) to build the structure-activity model (e.g., of a "candidate pharmaceutical" molecule) for interactions with its target molecule (e.g., cell receptors). In SAR by NMR, NMR is utilized to detect even weak binding of ligands (fragments of the pharmaceutical candidate molecule) to receptor, then the ligands which successfully bind-to-target are assembled-together into an optimized-to-target pharmaceutical molecule.
A technique created in the late 1990s by Stephen Fesik and Phil Hajduk.
See also Quantitative Structure-Activity Relationship (QSAR).


All the information collected at a single time or for a single purpose or by a single principal investigator. A study may consist of one or more datasets and one or more files .


An interruption in the rhythm of speech characterized by hesitations, repetitions or prolongations of sounds, syllables, words, or phrases, for example: cow...boy, tuh-tuh-tuh-table, or sssun. Stuttering is recognized as a language disorder.

Subarachnoid hemorrhage

Blood in, or bleeding into, the space under the arachnoid membrane, most commonly from trauma or from rupture of an aneurysm.


If you have a cloned piece of DNA (say, inserted into a plasmid) and you need unlimited copies of only a part of it, you might "sub-clone" it. This involves starting with several million copies of the original plasmid, cutting with restriction enzymes, and purifying the desired fragment out of the mixture. That fragment can then be inserted into a new plasmid for replication. It has now been subcloned.


Transferring cultured cells, with or without dilution, from one culture vessel to another.


Beneath the dura mater, the outermost membrane surrounding the brain and spinal cord.

Subdural hematoma

A blood clot trapped under the dura mater, the outermost membrane surrounding the brain and spinal cord.


Change, when heated, from a solid state to a vapour without going through the liquid state.

Subpopulation Distributions

A subpopulation distribution is a frequency distribution of the analyte concentrations of all of the members of a subset of unknowns grouped according to related characteristics (e.g., sex and age).


A set, B, is a subset of another set, A, if every element in B is also an element of  A.


Subtypes of receptor are those which, in a single species, are activated by the same family of endogenous ligands but exhibit sufficient differences in their pharmacological properties or molecular structure to justify being classified separately. Traditionally, subtypes have been identified using drugs which can selectively activate them or antagonise the effects of agonists with markedly different potencies (the usual rule of thumb is that there should be at least a 10-fold difference in antagonist affinity, i.e. one log unit difference in pKB value, when postulating the existence of a novel receptor subtype (Kenakin et al., 1992)). Consequently, subtypes can only be identified when pharmacological tools are available. Molecular biological techniques have now determined the amino-acid sequence of many receptor proteins, and hence the degree of homology between receptor types to be measured. However, there is no established rule which differentiates receptor subtypes simply on the basis of the number of amino-acids which differ between them. Compare species homologue.


The only low-calorie sweetener that is made from sugar.
It is approximately 600-times sweeter and does not contain calories. Sucralose is highly stable under a wide variety of processing conditions. Thus, it can be used virtually anywhere sugar can, including cooking and baking, without losing any of its sugar-like sweetness.

Suction catheter

A small flexible catheter that is used to suction the airway.

Sugar alcohols

Ingredients used to add sweet flavours to food. Those often used instead of sugars include sorbitol, mamitol, and xylitol. Many fruits and vegetables contain sugar alcohols naturally. They are also found in some sugarless gum, hard candies, jams and jellies. Besides adding sweetness, sugar alcohols also add texture, help foods stay moist, prevent browning when food is heated and give a cooling effect to the taste of food. They supply four calories per gram, but are absorbed slowly and incompletely and thus require little or no insulin for metabolism. They are not cavity-producing because they are not metabolized by bacteria that produce cavities.

Sugar bloom

Dry and hard to the touch, sugar bloom is the result of surface moisture dissolving sugar in the chocolate and subsequent recrystallization of the sugar on the chocolate surface. Visible as a dull white film on the surface of the chocolate. Typically caused by cold chocolate being exposed to a warm humid environment with resultant condensation forming on the product. A visual and textural defect only. The product is fine to eat.


Used to preserve the colour of foods such as dried fruits and vegetable, and to inhibit the growth of microorganisms in fermented foods such as wine.
Sulfites are safe for most people. A small segment of the population, however, has been found to develop shortness of breath or fatal shock shortly after exposure to these preservatives. Sulfites can provoke severe asthma attacks in sulfite-sensitive asthmatics.


Functional component of cruciferous vegetables (e.g., broccoli, kale, horseradish) which provides the health benefits of neutralizing free radicals and possibly reducing the risk of cancer.


The result of adding.

Summation, Temporal or Spatial (of Post-synaptic potentials)

Different ways of summing the Post-synaptic potentials (PSPs) produced by a cell in response to input from a neuron to sum.
Temporal summation occurs when the PSPs that are summing are produced by repetitive closely-spaced (in time) input from a single pre-synaptic terminal.
Spatial summation occurs when the PSPs that are summing are produced by repetitive closely-spaced (in time) input from many different pre-synaptic terminals.
Summation of the PSPs produces a larger Grand Post-synpatic Potential that, in the case of Excitatory PSPs, can lead to an Action Potential being produced by the post-synaptic cell.

Summation (of muscle contractions)

The addition of individual muscle twitch contractions to produce a larger contraction and more force.
Temporal summation occurs when the individual muscle twitches activated by a single input are activated so closely in time that the twitch contraction to an input occurs before the twitch contraction to a previous input has ceased. This results in a larger twitch contraction (i.e., more force).
Multiple motor unit summation occurs when stronger stimuli (or more brain activation) results in the activation of more motor units, leading to the activation of more muscle fibres in a muscle and therefore a larger contraction of the overall muscle, and more force.


The process in which the binding of a ligand to its receptor leads to a greater than normal response.
It is also termed upregulation to reflect the fact that, over time, there may be an actual increase in receptor number. It typically occurs in situations where there has been reduced synaptic activity.


A free radical form of molecular oxygen (O2Ÿ-).


Lying on one's back.


Movement of the forearm so that the palm is turned forward or upward.
(see also Pronation and Rotation)


Two angles are supplementary if their sum is 180 degrees.


Medicine contained in a capsule which is inserted into the rectum so that the medicine can be absorbed into the blood stream.

Suppressive gene interactions

Suppressive drug interactions are when one antibiotic can actually help bacterial cells to grow faster in the presence of another.
They occur in bacteria between protein and DNA synthesis inhibitors. Ribosomal gene levels are maintained despite DNA stress triggered by DNA synthesis inhibitors, leading to an imbalance between cellular DNA and protein content and reduced growth rate. Reducing ribosome production by deleting ribosomal RNA operons corrects this imbalance and, importantly, removes the suppressive drug interaction.

Surface markers

Proteins on the outside surface of a cell that are unique to certain cell types and that can be visualized using antibodies or other detection methods.

Surface tension

The attraction of molecules to each other on a liquid's surface. Thus, a barrier is created between the air and the liquid.


Fluid secreted by cells of the alveoli that reduces the surface tension of pulmonary fluids.It contributes to the elastic properties of pulmonary tissue.


A physician who treats disease, injury, or deformity by operative or manual methods. A medical doctor specialized in the removal of organs, masses and tumors and in doing other procedures using a knife (scalpel). The definition of a "surgeon" has begun to blur in recent years as surgeons have begun to minimize the cutting, employ new technologies that are "minimally invasive," use scopes, etc.


The word "surgery" has multiple meanings. It is the branch of medicine concerned with diseases and conditions which require or are amenable to operative procedures. Surgery is the work done by a surgeon. By analogy, the work of an editor wielding his pen as a scalpel is s form of surgery. A surgery in England (and some other countries) is a physician's or dentist's office.

Surrogate microbe

Non-pathogenic species and strain responding to a particular treatment in a manner equivalent to a pathogenic species and strain. The surrogate allows biological verification of the treatment without introducing pathogens into a food processing area. For example, PA 3679 is used as a surrogate microbe for Clostridium botulinum in thermal process validation. Listeria innocua Is a possible surrogate for L. monocytogenes.


very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension.

suspended-sediment concentration

the ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water-sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture.

suspended-sediment discharge

the quantity of suspended sediment passing a point in a stream over a specified period of time. When expressed in tons per day, it is computed by multiplying water discharge (in cubic feet per second) by the suspended-sediment concentration (in milligrams per liter) and by the factor 0.0027.

Suspended solids

Solids that are not in true solution and that can be removed by filtration.
Such suspended solids usually contribute directly to turbidity. --solids that are not in true solution and that can be removed by filtration. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods.

Suspension feeding

Feeding on suspended particles.
The most usual ploy is filter-feeding, but not all suspension feeders feed in this way.

Svedberg units

The unit for quantifying the sedimentation coefficient of macromolecules.
In general the greater the particle mass the greater the sedimentation coefficient but the relationship is not linear

Symbolic scale

Scale that uses pictures / symbols instead of words.


Living in association with another organism, normally to the mutual advantage of both or to the advantage of one - the other being unaffected.
Where there is a notable discrepancy in size, the term 'symbiont' is used to refer to the smaller member of the association which may occur inside (endosymbiont) or on the outside surface (ectosymbiont) of the larger member 'host'.


Two points are symmetric with respect to a third point if the segments joining them to the third point are equal.   Two points are symmetric with respect to a line if the line is the perpendicular bisector of the segment joining the points.

Sympathetic nervous system

A branch of the Autonomic Nervous System (ANS).
Together with the Parasympathetic component of the ANS, the Sympathetic nervous system controls mainly (but not exclusively) internal organs of the body such as the gut, the heart, the liver, the bladder, etc. The Sympathetic Nervous System is commonly well known for being responsible for the ‘flight or fight’ response. It acts to increase blood pressure, rate of breathing, increases blood flow to the skeletal muscles etc. The Sympathetic Nervous System is often viewed as mobilizing the body for action whereas the Parasympathetic is viewed as preparing the body for producing and storing energy reserves.


A shared ancestral character state (plesiomorphy).
A trait that is shared by two or more groups due to inheritance from a distant common ancestor.Symplesiomorphies are common to all the descendants of a distant common ancestor, and they cannot be used to infer close evolutionary relationships between subsets of these descendants.

Symmetrical Standard Curve

A symmetrical standard curve is one which yields a sigmoidal curve with both asymptotes elongated equally when the response of each standard is plotted against the logarithm of its respective concentration.
The inflection point of a symmetrical standard curve, where the mirror image of one half of the curve is superimposable on the other half, is the midpoint of the curve.


Species or populations occupying the same geographic area.


A mechanism for moving (transporting) two small molecules and/or ions in the same direction across a cell membrane
(see Antiport)

Systematic Error

Systematic error is the component of total error which is due to changes in the test method.


A character which is derived, and because it is shared by the taxa under consideration, is used to infer common ancestry (apomorphy).
A novel evolutionary trait that is shared by two or more groups due to inheritance froman immediate common ancestor.
Synapomorphies are used by phylogenetic biologists to infer close evolutionary relationships between organisms.

Syncytium (Plural = Syncitia)

Multinucleated mass of cytoplasm.

Synergistic effect

Effect that is achieved by the combination of two or more substances or organisms which neither alone could accomplish.


Bleeding of gels due to mechanical damage or too firm gellification (shrinking).


The process of union of two gametes; sometimes called fertilization.
It encompasses both plasmogamy and karyogamy.


A fluid filled cavity in the spinal cord.
Usually involving upper segments initially and involving the shoulder muscles.


The study of the historical evolutionary and genetic relationships among organisms and of their phenotypic similarities and differences.
Field of biology that deals with the diversity of life. Systematics is usually divided into the two areas of phylogenetics and taxonomy.

System file

A generic term for the native or internal storage format used by statistical software.
When statistical software reads a "raw" character format data file consisting of ASCII or EBCDIC characters, it must read each byte in sequence. It can be more efficient in its storage, retrieval and calculations by storing a data file in a special binary format called a system file. Typically, a system file for one brand of software cannot be read by another brand of software or by the same brand on another hardware platform. Some software is capable of creating an "export" file which can then be read by other software or on other platforms. Also, some software can "import" files from other software.

Systemic Lupus Erythematosus

(SLE or Lupus) An autoimmune disease characterized by acute and chronic inflammation of various tissues of the body
Patients with lupus produce abnormal antibodies in their blood that target tissues within their own body rather than foreign infectious agents. Because the antibodies and accompanying cells of inflammation can affect tissues anywhere in the body, lupus has the potential to affect a variety of areas. Sometimes lupus can cause disease of the skin, heart, lungs, kidneys, joints, and/or nervous system. When only the skin is involved, the condition is called lupus dermatitis or cutaneous lupus erythematosus. A form of lupus dermatitis that can be isolated to the skin, without internal disease, is called discoid lupus. When internal organs are involved, the condition is referred to as systemic lupus erythematosus (SLE).
Both discoid and systemic lupus are about eight times more common in women than men. The disease can affect all ages but most commonly begins from 20 to 45 years of age and is somewhat more frequent in African Americans and people of Chinese and Japanese descent.


The synapse is a specialized portion of a neuron or nerve cell that is used for cell to cell communication with other neurons and muscle cells. The chemical synapse contains packaged neurotransmitters that can be released upon an electrical signal (action potential) reaching the synapse from the dendrites and cell body of the neuron, where action potentials originate (where synapses of other neurons interact with the signaling cell). A neuron can have multiple synapses, often with different signaling properties being excitatory or inhibitory synapses. Multiple synapses signaling to a receiving neuron or muscle can strengthen a stimulus or inhibition by activating some or all of the synapses through addition of signaling strength. In addition to chemical synapses, electrical synapses are propagating an action potential signal without a neurotransmitter, but directly by coupling membranes of adjacent cells using gap junctions. The feature of both chemical and electrical synapses allows the signal to propagate unidirectional. The signal cannot reverse. However, feedback signals between the signaling and receiving cell to strengthen or weaken the synaptic interaction, a process called synaptic plasticity.

SyndromeA set of signs and symptoms that tend to occur together and which reflect the presence of a particular disease or an increased chance of developing a particular disease.

Synovial joint

The most movable type of joint. The bones are covered by connective tissue, the interior of which is filled with synovial fluid, and the ends of the bones are covered with cartilage.


The order and way in which words and sequences of words are combined into phrases, clauses, and sentences (rules of grammar).