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The basic unit for the imaginary number = -1.

Iatrogenic disorders or diseases

Those caused inadvertently as a consequence of medical treatment.


Where an agonist causes an inhibitory response, the IC50 is the molar concentration which produces 50% of its maximum possible inhibition. The concentration of competing ligand which displaces 50% of the specific binding of the radioligand. The IC50 value is converted to an absolute inhibition constant Ki) using the Cheng-Prusoff equation (see Ki).


A dose which causes 50% of the maximum possible inhibition of a response for a given drug.

Ideal gas

One which obeys the ideal gas law.  At low pressures, real gases behave like ideas gases.

Identification Fields

Three identification fields are used to identify the unknown specimens and are common to all test methods. The first field is the sequence number of each unknown record. In unknown files, the sequence number is preceded by Uk- for all unknown specimen concentrations which are included in subpopulation distributional tests. Unknown specimen concentrations which are not included in subpopulation distributional tests are designated as excluded samples and are identified by an Ex- before the specimen's sequence number. The second field contains the concentration results for each unknown specimen. The third field contains the identification of the unknown specimen. The identification field is used to merge to LIM files when dual labeled assays are measured.


An equation that is true for all values of the variable.

Identitiy disorder

Severe subjective distress caused by an adolescent's inability to achieve an integrated sense of self.

Identitiy element

If * is an operator, then the identity element, I, for * is the number such that
I * a = a. The identity for addition is zero, and the identity for multiplication is 1.

Identitiy matrix

A square matrix with ones along the diagonal and zeros everywhere else. If I is an identity matrix, then IA = A.


A parasitoid that paralyses and arrests the development of its host.
Compare to koinobiont.


A structure produced by the organism, as opposed to a xenosome or foreign body. Used to refer to the elements which make up or adhere to the test of some amoebae.

Imaginary number

A number of the form ni, where n is a real number, and i2 = -1.


Incapable of mixing or attaining homogeneity.

Immittance audiometry

Tests of the function of the ear drum position and of muscle eflexes in the middle ear reflexes, Tympanometry and acoustic reflex measurement which allow determination of the functionality of the middle ear and its reflex pathways.


Not moving, sometimes used to refer to cells which are fixed to the substrate.

Immovable joint

A joint in which the bones interlock and are held together by fibers or bony processes that prevent the joint from moving; e.g., the bones of the cranium.

Immune system

A highly specific defensive reaction of the body to invasion by a foreign substance or organism. Consists of a primary response in which the invader is recognized as foreign, or "not-self," and eliminated and a secondary response to subsequent attacks by the same invader. Mediated by two types of lymphocytes B cells, which mature in the bone marrow and are responsible for antibody production, and T cells, which mature in the thymus and are responsible for cell-mediated immunity.


A technique that detects and measures a specific antigen or biological substance by employing antibodies (e.g., dot blot, western blot, and ELISA). An immunoassay is a ligand binding assay which uses an antibody and the antibody's corresponding antigen as the binder and ligand. The term immunoassay is often expanded to include any procedure in which the quantitation of an analyte depends on the progressive saturation of a specific binder or ligand, either of which may be the analyte, and the subsequent determination of the analyte's distribution between the bound and free fractions. This includes competitive protein binding assays, where the binder is a naturally occurring binding protein, and receptor assays, where the binder is a naturally occurring cell receptor.

Immunofluorometric Assay

Immunofluorometric assays (IFMA) are sandwich assays in which one binder (or ligand) is used to capture the analyte and then a second binder or ligand conjugate, tagged with a fluorescent compound or fluorescent-converting enzyme, binds to the analyte. This reaction forms a sandwich complex of binder-analyte-conjugate or ligand-analyte-conjugate which is then measured. The standard curve of an IFMA assay has a positive slope and is often asymmetrical

Immunoglobulin (Ig)

One of the class of proteins comprising the antibodies.


A method that analyses the proteins in cells or tissues using antibodies against the factor of interest.

Immunometric Assay

Immunometric assays are immunoassays in which the tracer is a labeled binder.
Most immunometric assays involve two binders, both present in excess. The first binder is usually absorbed onto a solid phase and is used to capture the ligand (analyte). The second binder, the tracer, binds to another epitope on the ligand analyte. Both binders are present in large excess. These assays are sometimes called sandwich binding assays. Presumably, all of the analyte is bound in these binder-ligand-binder complexes. As the concentration of analyte is increased, the measured response is increased. The standard curve of an immunometric assay has a positive slope and is often asymmetrical.

Immunoradiometric Assay

Immunoradiometric assays (IRMA) are immunometric assays in which one binder (or ligand) is used to capture the analyte and a second binder, tagged with a radioisotope, then binds to the analyte. This forms a sandwich complex of binder-analyte-conjugate or ligand-analyte-conjugate which is then measured. The standard curve of an IRMA assay has a positive slope and is often asymmetrical.

Immunosuppressive drugs

Medication to prevent the body from rejecting implanted organs or tissues through immune reactions against those organs.


The coupling of an antibody and a molecule that is toxic to the cell.

Impact interactions

The reactions between impacts (between the impacts of just one action and/or between the impacts of multiple actions).

Impact reference zone

Areas which are representative of the environmental characteristics of a particular region to be used for assessing the effect of activities in that region on the marine environment.

Impact zone

Zone where impacts (direct, indirect, cumulative, and/or interactive) result from an activity.

Impermeable layer

a layer of solid material, such as rock or clay, which does not allow water to pass through.


Any surgically placed, nonbiological material whose purpose is to promote healing of tissues or serve as a replacement of structures such as joints.


A conditional statement.


A type of learned behavior with a significant innate component, acquired during a limited critical period.

Improper fraction

A fraction with a numerator that is greater than the denominator.

Impulse Control

Refers to the individual's ability to withhold inappropriate verbal or motor responses while completing a task.  Persons who act or speak without first considering the consequences are viewed as having poor impulse control.

Inactive Sulphides

Polymetallic sulphides through which warm water is no longer flowing into the overlying seawater (i.e., they are “cold”).  Disturbance of these sulphides may result in renewal of hydrothermal fluxes into the water column, turning inactive sulphides into active sulphides (hence the concept of “dormant” sulphides). Synonomous with dormant sulphides.


The mating of individuals that are closely related genetically.

Inbreeding depression

A reduction in fitness and vigour of individuals as a result of increased homozygosity through inbreeding in a normally outbreeding population.


The center of a circle that is inscribed in a triangle.   The intersection of the angle bisectors of the triangle.

Incentive spirometer

A biofeedback device that records respiratory volume or flow to provide encouragement and feedback for the patient to take a deeper breath


The circle that can be inscribed in a triangle.

Inclusive fitness

The relative number of an individual's alleles that are passed on from generation to generation, either as a result of his or her own reproductive success, or that of related individuals.

Incomplete dominance

A type of inheritance in which F1 hybrids have an appearance that is intermediate between the phenotypes of the parental varieties.

Incomplete metamorphosis

A type of development in certain insects, such as grasshoppers, in which the larvae resemble adults but are smaller and have different body proportions. The animal goes through a series of molts, each time looking more like an adult, until it reaches full size.


Inability to control excretions; Inability to control bowel and bladder functions. Urinary incontinence is inability to keep urine in the bladder. Fecal incontinence is inability to retain feces in the rectum. Many people who are incontinent can become continent with training.


The term applied to two substances to indicate that one material cannot be mixed with the other without the possibility of a dangerous such as fire, explosion or release of toxic vapors.

Increasing function

A function is increasing if f(a) > f(b) when ab.


A small change, usually indicated by the greek letter delta.


The incubation of an immunoassay is the time during which the ligand binding occurs.

Indefinite integral

The sum of the antiderivative of a function and an arbitrary constant.

Independent variable

In an experiment, when one factor is manipulated, a second factor responds; The factor that is manipulated; The input number to a function..

Indeterminate cleavage

A type of embryonic development in deuterostomes, in which each cell produced by early cleavage divisions retains the capacity to develop into a complete embryo.

Indeterminate growth

A type of growth characteristic of plants, in which the organism continues to grow as long as it lives.

Index Standard

The index standard is a baseline standard which is used to calculate the sample's response ratio in one standard tests. The index standard's adjusted response can either be the numerator or the denominator to the sample's adjusted response. This ratio is then multiplied by the concentration of the index standard for the sample concentration.

Indirect Impacts (in environmental science)

Impacts on the environment that are not a direct result of an activity, often produced away from the activity or as a result of a complex pathway (physical, chemical, biological).  Synonymous with second-level impacts, third-level impacts, and secondary impacts.

Induced fit

The change in shape of the active site of an enzyme so that it binds more snugly to the substrate, induced by entry of the substrate.

Induced pluripotent stem cells (iPSCs)

Somatic (adult) cells reprogrammed to enter an embryonic stem cell–like state by being forced to express factors important for maintaining the "stemness" of embryonic stem cells (ESCs).  Mouse iPSCs demonstrate important characteristics of pluripotent stem cells, including the expression of stem cell markers, the formation of tumors containing cells from all three germ layers, and the ability to contribute to many different tissues when injected into mouse embryos at a very early stage in development. Human iPSCs also express stem cell markers and are capable of generating cells characteristic of all three germ layers.

Inducible genes

Genes that are expressed to form their products (inducible gene products) according to an external stimulus. See Housekeeping genes


(1) The ability of one group of embryonic cells to influence the development of another.
(2) In genetics, the phenomenon in which the presence of a substrate (the inducer) initiates transcription and translation of the genes coding for the enzymes required for its metabolism.
(3) The process by which an object having electrical or magnetic properties produces similar properties in a nearby object, usually without direct contact

Inductively Coupled Plasma Mass Spectrometry

A type of mass spectrometry that is highly sensitive and capable of the determination of a range of metals and several non-metals at concentrations below one part in 1012.
Based on coupling together an inductively coupled plasma as a method of producing ions (ionization) with a mass spectrometer as a method of separating and detecting the ions. ICP-MS is also capable of monitoring isotopic speciation for the ions of choice. Similar to Atomic Absroption Spectrophotometry, it usually requires a sample to be removed from an object, and it has similar analytical capabilities. It differs, however, in that the excitation source is an argon plasma, heated to around 10,000 degrees Celsius, rather than a flame, and it is the light emitted by a sample that is measured, rather than light which is absorbed. The main advantage of ICP-AES is its speed of operation - it can accurately measure 30 or 40 elements in a matter of minutes. (Latter section source: British Museum)

Industrial water use

water used for industrial purposes in such industries as steel, chemical, paper, and petroleum refining. Nationally, water for industrial uses comes mainly (80%) from self-supplied sources, such as a local wells or withdrawal points in a river, but some water comes from public-supplied sources, such as the county/city water department.


The tendency of a body to remain at rest or stay in motion in  straight line unless acted upon by an external force.

Infantile perseveration

The articulation part of delayed speech where a youngster relies on speech as his or her main means of communication and attempts words, phrases, and sentences, but does so immaturely because of sound omissions and substitutions.

Infantile psychosis

A disorder of early childhood manifested by impaired contact with reality, absence of meaningful verbal communication, withdrawal from social interactions, and unevenness between mental and emotional functioning, as well as a disparity among motor, visual, social and adaptive behavior.

Infantile spasms

Seizures experienced by infants (three months to two years of age), characterized by flexor spasms of the arms, legs, and head.  Also known as jackknife seizures.


Organisms that live within the sediment. Synonymous with endofauna.
Hence: Infauna = pertaining to the infauna.


The growth of a parasitic organism within the body. (A parasitic organism is one that lives on or in another organism and draws its nourishment therefrom.) A person with an infection has another organism (a "germ") growing within him, drawing its nourishment from the person.


A limitless quantity.


flow of water from the land surface into the subsurface.


A basic way in which the body reacts to infection , irritation or other injury, the key feature being redness, warmth, swelling and pain . Inflammation is now recognized as a type of nonspecific immune response .

Inflammatory bowel disease (IBD)

A group of chronic intestinal diseases characterized by inflammation of the bowel -- the large or small intestine. The most common types of inflammatory bowel disease (IBD) are ulcerative colitis and Crohn disease

Inflammatory response

The body's reaction to invading infectious micro-organisms. A line of defense triggered by penetration of the skin or mucous membranes, in which small blood vessels in the vicinity of an injury dilate and become leakier, enhancing the infiltration of leukocytes; may also be widespread in the body. The response includes an increase in blood flow to the affected area, the release of chemicals that draw white blood cells, an increased flow of plasma, and the arrival of monocytes to clean up the debris.

Inflection point

A point on a curve such that the curve is concave up on one side of the point, and concave down on the other side of the point.


The application of computers and statistics to the management of information. For example, in the Human Genome Project, informatics has permitted the development and use of methods to search databases quickly, analyze DNA sequence information, and predict protein sequence and structure from DNA sequence data.

Information Theory

A branch of mathematics developed by Claude Shannon that is now widely applied to understanding how a train of action potentials in a neuron signals information.
Information Theory provides a theoretical framework for expressing how much information is transmitted and how efficient information is encoded in communication. Since the most important function of neurons is communicating with each other, Information Theory found many applications in neurophysiology. Physiologists sometimes use quantities as entropy, information rate, or mutual information to compare the efficiency of neural systems to theoretical models.


Constant administration of a solution, usually via a catheter


A heterotrophic mode of nutrition in which other organisms or detritus are eaten whole or in pieces.


In a cladistic (phylogenetic) analysis, the set of taxa which are hypothesized to be more closely related to each other than any are to the outgroup. The subgroups of the group whose phylogeny is reconstructed.


The process of genetic transmission of characteristics from parents to offspring; The features of an organism are determined by a set of chromosomes. These originate in the parents and are passed on to an offspring during fertilisation. It follows then that since chromosomes are inherited, all the features of an organism must be inherited.

Inhibitory postsynaptic potential (IPSP)

An electrical change (specifically a hyperpolarisation) in the membrane of a postsynaptic neurone caused by the binding of an inhibitory neurotransmitter from a presynaptic cell to a postsynaptic receptor. The IPSP moves the membrane potential of the post-synaptic cell further away from the threshold for an Action Potential, thereby making it less likely that the post-synaptic cell will produce a response that can be propagated along it’s length and then to the next cell in the series.  Thus the IPSP makes it less likely that the post-synaptic neuron will be exicted by another excitatory input.

Initiation codon

Three-base sequence (AUG) on the messenger RNA that codes for the amino acid methionine. Methionine represents the start command for protein synthesis.


Refers to a person’s ability to begin a series of behaviors directed toward a goal.

In-line field

Ohmic heating system where the electric field is aligned along the product flow path.

Injection well

refers to a well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don't deliver drinking water, unused aquifers, or below freshwater levels.


Harm or hurt. The term "injury" may be applied in medicine to damage inflicted upon oneself as in a hamstring injury or by an external agent on as in a cold injury . The injury may be accidental or deliberate, as with a needlestick injury . The term "injury" may be synonymous (depending on the context) with a wound or with trauma .

Innate Immune Response

Refers collectively to the inherent "first lines of immune defense" in the organism.
The "first lines of immune defense" (e.g., complement cascade, etc.), which are initiated, e.g.: in humans and some animals by TLR (i.e., toll-like receptors), a category of cellular transmembrane proteins which "recognize" certain features (e.g., antigens) present on the exterior of invading pathogens; in plants by PAMPs (Pathogen-Associated Molecular Patterns) which "recognize" certain features (e.g., a 22-amino acid peptide on the exterior of flagella of certain invading pathogenic bcteria. For example, the TLR 11 class of TLRs specifically sense the presence of pathogenic bacteria which infect the urinary tract. The TLR 7 and TLR 8 collectively specifically sense the single-stranded RNAs (ssRNA) which are present within some pathogenic viruses.

Innate preferences

Preferences existing from birth and not acquired through learning or conditioning processes.

Innate releasing mechanism

In ethology, a circuit within an animal's brain that is hypothesized to respond to a specific stimulus, setting in motion, or "releasing," the sequence of movements that constitute a fixed action pattern.

Inner cell mass (ICM)

The cluster of cells inside the blastocyst that protrudes into one end of the cavity. These cells give rise to the embryo and some of the extraembryonic membranes, and ultimately the foetus. The ICM cells are used to generate embryonic stem cells.


Pertaining to, or derived from, non-biological material.

Inositol triphosphate (IP3)

The second messenger, which functions as an intermediate between certain nonsteroid hormones and the third messenger, a rise in cytoplasmic Ca2+ concentration.

Inscribed polygon

A polygon placed inside a circle so that each vertex of the polygon touches the circle.


In a complete plasmid clone, there are two types of DNA - the "vector" sequences and the "insert". The vector sequences are those regions necessary for propagation, antibiotic resistance, and all those mundane functions necessary for useful cloning. In contrast, however, the insert is the piece of DNA in which you are really interested.

Insertion (DNA)

A type of mutation in which a new DNA base is inserted into an existing sequence of DNA bases. This shifts the reference frame in protein synthesis, resulting (sometimes) in altered amino acid sequences.

Insertion (muscle)

The position at which the other end of the muscle (i.e. from its origin) is attached, by means of a tendon, to the moveable bone. The end of the muscle that usually moves when the muscle contracts. (See Origin).  The term has been replaced by the newer term Attachment.

Insertion sequence (DNA)

The simplest kind of a transposon, consisting of inserted repeats of DNA flanking a gene for transposase, the enzyme that catalyzes transposition.

Insight learning

The ability of an animal to perform a correct or appropriate behavior on the first attempt in a situation with which it has had no prior experience.

In situ conditions

Conditions where genetic resources exist within ecosystems and natural habitats, and, in the case of domesticated or cultivated species, in the surroundings where they have developed their distinctive properties

In situ gene banks

All measures to maintain live animal breeding populations, including those involved in active breeding programmes in the agro-ecosystem where they either developed or are now normally found, together with husbandry activities that are undertaken to ensure the continued contribution of these resources to sustainable food and agricultural production, now and in the future.

In situ hybridisation

A technique that measures the presence of messenger RNA (i.e., a gene product) in histological sections. A nucleic acid (DNA or RNA) probe is used to detect and identify specific complementary sequences of DNA in chromosomes or RNA in bacteria, eukaryotic cells, and tissue.

Insoluble fibre

Type of dietary fiber found in wheat bran, cauliflower, cabbage and other vegetables and fruits which helps move foods through the digestive system and thereby may decrease the risks of cancers of the colon and rectum. Insoluble fiber may also help reduce the risk of breast cancer.


The perception or complaint of inadequate or poor-quality sleep because of one or more of the following: difficulty falling asleep; waking up frequently during the night with difficulty returning to sleep; waking up too early in the morning; or unrefreshing sleep. Insomnia is not defined by the number of hours of sleep a person gets or how long it takes to fall asleep. Individuals vary normally in their need for, and their satisfaction with, sleep. Insomnia may cause problems during the day, such as tiredness, a lack of energy, difficulty concentrating, and irritability. Initial insomnia is difficulty in falling asleep. Middle insomnia involves an awakening, followed by difficulty returning to sleep, but eventually doing so. Terminal insomnia is awakening at least two hours before one's usual waking time and being unable to return to sleep.

Inspiratory capacity

The volume of air that can be inhaled after a normal exhalation


A vertebrate hormone that lowers blood glucose levels by promoting the uptake of glucose by most body cells and the synthesis and storage of glycogen in the liver; also stimulates protein and fat synthesis; secreted by endocrine cells of the pancreas called islets of Langerhans.

Insulin-dependent diabetes (Type 1 diabetes)

A condition in which the body's immune system destroys the cells in the pancreas that produce insulin. Insulin allows glucose to enter the cells of the body to provide energy. Persons with type 1diabetes must take daily insulin injections.
(see Non-insulin-dependent diabetes)

Insulin infusion pump

Battery-operated devices that dispense insulin to diabetic patients on a continuous basis.

Insulin-like growth factor 1 (IGF-1)

A polypeptide protein hormone similar in molecular structure to insulin. IGF-1 plays an important role in childhood growth and continues to have anabolic effects in adults.

Insulin resistance

A condition in which the body needs more insulin than normal to control the blood sugar that increases a person’s risk of diabetes and heart disease.Usually associated with obesity.

Insulin sensitizers

Agents which make cells more responsive to insulin. They are commonly used in patients with type 2 diabetes.

Insulin shock

A situation in which a diabetic receives too much insulin and then uses up all available carbohydrates. Insulin shock may be associated with seizures.

Insurmountable antagonist

Alternative name for unsurmountable antagonist (see antagonist).


The set of numbers containing zero, the natural numbers, and all the negatives of the natural numbers.


If  dF(x)/dx = f(x), then F(x) is an integral of f(x).   The area under the curve of a function above the x - axis.

Integral membrane proteins

Proteins found within the cell membrane (i.e., they are integral to the membrane and not easily extracted from it).There are two categories of integral membrane proteins:
Carrier proteins, which are found on the inner or outer surface of the cell membrane (hence called Inner/Outer membrane proteins ).  They bind a substrate and undergo a conformational change that results in transport of the substrate across membrane.
Channel proteins span the membrane (henceTransmembrane proteins) forming aqueous pores that allowing a substrate through provided it fulfils the criteria of size and charge to enter and pass through the middle water-filled pore.


A function that is to be integrated.


The process of finding an integral.

Integumentary system  

The skin and its derivatives (hair, nails, feathers, horns, antlers, and glands. The system which, in multi-cellular animals, protects against invading foreign micro-organisms and prevent the loss or exchange of internal fluids.

Intelligence quotient, or IQ

A score derived from one of several different standardized tests attempting to measure intelligence. Although the term "IQ" is still in common use, the modern IQ score is a mathematical transformation of a raw score on an IQ test, based on the rank of that score in a normalization sample. Thus the scoring of modern IQ tests is now based on a projection of the subject's measured rank on the Gaussian bell curve with a center value (average IQ) of 100, and a standard deviation of 15, although different tests may have different standard deviations.


Device for delivering high pressure process liquid generally by using a large diameter low pressure piston to drive a small diameter high pressure piston. The ratio of intensification is directly proportional to the ratio of the area of the large diameter piston divided by the area of the small diameter piston. A 20:1 intensification ratio is common. The pressure in the low pressure cylinder may be used to estimate the pressure of the high pressure process liquid. Intensifiers may be operated as single or multiple stroke devices.

Intention tremor

An involuntary trembling which is heightened when a movement is attempted.
Coarse, rhythmical movements of a body part that become intensified the harder one tries to control them.


The x-intercept of a curve is the point where the curve crosses the x - axis, and the y - intercept of a curve is the point where the curve crosses the y - axis.


Sensations rising from within the body (e.g., the feeling of fullness after a meal).

Interdisciplinary approach (in medicine)

A method of diagnosis, evaluation, and individual program planning in which two or more specialists, such as medical doctors, psychologists, recreational therapists, social workers, etc., participate as a team, contributing their skills, competencies, insights, and perspectives to focus on identifying the developmental needs of the person with a disability and on devising ways to meet those needs.


Process permitting the random rearrangement of the fatty acids in the triglyceride molecules and is widely used in the manufacture of lauric specialty fats for the purpose of changing the chemical properties of the fat.


An interferant is a substance which alters the ligand-binder reaction or the label signal.


Device based on principle that two waves with the same phase that coincide will amplify each other while two waves of opposite phase will cancel each other out.
Can be based on different waves, including radio waves, laser light, or matter waves.


Measurement device in which a beam of electromagnetic radiation is split and subsequently recombined after travelling different pathlengths so that the beams interfere and produce an interference pattern. This pattern can be used to measure a wide variety of physical parameters.


A chemical messenger of the immune system, produced by virus-infected cells and capable of helping other cells resist the virus. A family of small (cytokines) proteins (produced by vertebrate cells following a virus infection) that interfere with (i.e., block) translation of viral DNA.Via that blocking, interferons prevent synthesis of proteins needed for viral reproduction, so interferons possess potent antiviral effects. Secreted interferons bind to the plasma membrane of other cells in the organism and induce an antiviral state in them (conferring resistance to a broad spectrum of viruses). Three classes of interferons have been isolated and purified, so far: a-interferon (originally called leukocyte interferon), β-interferon (beta interferon or fibroblast interferon), and γ-interferon (gamma interferon or immune interferon, a lymphokine). These proteins have been cloned and expressed in Escherichia coli (E. coli), which has enabled large quantities to be produced for evaluation of the interferons as possible antiviral and anticancer agents. To date, interferons have been used to treat Kaposi's sarcoma, hairy cell leukemia, venereal warts, multiple sclerosis, and hepatitis.
Alpha Interferon: Also written as a- interferon. One of the interferons, it has been shown to prolong life and reduce tumor size in patients suffering from Kaposi's sarcoma (a cancer that affects approximately 10 percent of people with acquired immune deficiency syndrome). It is also effective against hairy-cell leukemia and may work against other cancers. It has been approved by the U.S. FDA for use against certain types of sarcoma. Recent research indicates that injections of alpha interferon can limit the liver damage typically caused by hepatitis C, a viral disease.
Beta Interferon: A protein that binds to a receptor located on the surface of T cells, slowing down the body's immune response (e.g., normally after the immune response has defeated an infection). Manmade beta interferon was approved by the US FDA (Food & Drug Administration) for use to treat multiple sclerosis (MS), a disease that is caused by an immune response that fails to ever shut down.
Gamma Interferon: Produced by T lymphocytes.


Between two genes; e.g. intergenic DNA is the DNA found between two genes.
The term is often used to mean non-functional DNA (or at least DNA with no known importance to the two genes flanking it). Alternatively, one might speak of the "intergenic distance" between two genes as the number of base pairs from the polyA site of the first gene to the cap site of the second. This usage might therefore include the promoter region of the second gene.


A protein produced naturally by our bodies to stimulate our immune systems.
A class of 24 different cytokines, that "carry a signal" between different leukocyte populations within the immune system of an organism. Interleukin-1, a chemical regulator (cytokin) secreted by macrophages that have ingested a pathogen or foreign molecule and have bound with a helper T cell; stimulates T cells to grow and divide and elevates body temperature. Interleukin-2, secreted by activated T cells, stimulates helper T cells to proliferate more rapidly.

Interleukin-1 (IL-1)

A cytokine (glycoprotein) released by activated macrophages.It is released during the inflammatory stage of immune system response to an infection, which promotes the growth of epithelial (skin) cells and white blood cells. Research has indicated that too much IL-1 is linked to the development of rheumatoid arthritis, diabetes, inflammatory bowel disease, and other autoimmune diseases.

Intermediate filament

A component of the cytoskeleton that includes all filaments intermediate in size between microtubules and microfilaments.

Internal energy generation

Heat generation within a material and throughout its volume due to the presence of an energy source that is dissipated throughout the volume

Internal medicine

A medical specialty dedicated to the diagnosis and medical treatment of adults. A physician who specializes in internal medicine is referred to as an internist. A minimum of seven years of medical school and postgraduate training are focused on learning the prevention, diagnosis, and treatment of diseases of adults. Subspecialties of internal medicine include allergy and immunology, cardiology (heart), endocrinology (hormone disorders), hematology (blood disorders), infectious diseases, gastroenterology (diseases of the gut), nephrology (kidney diseases), oncology (cancer), pulmonology (lung disorders), and rheumatology ( arthritis and musculoskeletal disorders).

International Units (IU)

Measure of biological activity of a chemical agent such as vitamins, drugs,


An association neuron; a nerve cell within the central nervous system that forms synapses with sensory and motor neurons and integrates sensory input and motor output.


The myelinated region of a myelinated neuron that lies between two successive nodes of Ranvier, the gaps between the myelinated sections.


The period between cell divisions when growth and replacement occur in preparation for the next division. During interphase, cellular metabolic activity is high, chromosomes and organelles are duplicated, and cell size may increase. Interphase accounts for 90% of the time of each cell cycle. It is divided into three phases known as gap 1 (G1), synthesis (S), and gap 2 (G2). It is followed by mitosis, the M phase.


Arising or occurring between species.


Pertaining to, or occurring within, the spaces between sediment particles or cells.

Interstitial cells

Cells scattered among the seminiferous tubules of the vertebrate testis that secrete testosterone and other androgens, the male sex hormones.

Interstitial fluid

The internal environment of vertebrates, consisting of the fluid filling the spaces between cells and surrounding the cells in body tissues.

Interstitial fluid motion

Motion of fluid in the spaces between solid particles.

Intervertebral disk

A pad of cartilage between two vertebrae that acts as a shock absorber.

In-the-ear hearing aid

A hearing aid that fits entirely in the concha of the ear.


Within the brain.


Within the skull.

Intracranial pressure (ICP)

Cerebrospinal fluid (CSF) pressure measured from a needle or bolt introduced into the CSF space surrounding the brain. It reflects the pressure inside of the skull.


Arising or occurring within  species; involving the members of one species.

Intralocular pressure

pressure of the eye, regulated by resistance to the flow of aqueous humor
through a fine sieve-like trabecular meshwork (eye’s drainage system); the
older the person, the more likely it is that the trabecular meshwork becomes
hardened and obstructed, preventing the normal flow of aqueous humor from
passing out at the proper rate and causing an increase in the intraocular pressure

Intra-uterine growth retardation  (IUGR)

Failure of the fetus to grow sufficiently within known parameters and expectations.
Fetal head size, as measured by ultrasound, is one method used to monitor fetal growth rate and differentially detect patterns of growth retardation. Fetal growth patterns are influenced by the inherent growth potential of the fetus and the growth support received by way of the placenta from the mother.

Intraventricular hemorrhage

Blood hemorrhage within the brain. The advent of the CT scan has allowed for a grading system to determine the severity (Grades 0 - IV). It is the most frequent cause of neurologic damage to a premature infant. There is an approximate 40 to 50 percent incidence rate among babies born before 35 weeks gestation.

Intrinsic activity

A term devised by Ariens in 1954 which attempted to describe the mathematical relationship between receptor occupancy and tissue response. It has now largely been replaced by efficacy, because the definition of intrinsic activity means that it varies for a particular agonist between different tissues, but efficacy, in theory, does not. However, intrinsic activity is now widely used as an empirical measure of the maximal response to a test agonist as a fraction of that to a full agonist of the same pharmacological class.

Intrinsic rate of increase

The difference between the number of births and the number of deaths, symbolized as rmax; the maximum population growth rate.


The transplantation of genes between species resulting from fertile hybrids mating successfully with one of the parent species.


A noncoding nucleotide sequence intervening between exons (coding regions), within a eukaryotic gene, that is excised from a gene transcript during RNA processing. A sequence of nucleotides in a gene which after transcription into mRNA is excised (spliced) and is consequently no longer present when the mRNA is translated into polypeptide (contrast to Exon). Note that although the 3' flanking region is often transcribed, it is removed by endonucleolytic cleavage and not by splicing. It is not an intron.


Introduction of a tube into a hollow organ to restore or maintain patency if obstructed.e.g., The insertion of a tube through the nose or mouth into the trachea to provide artificial ventilation.


The local infolding of a layer of tissue, especially in animal embryos, so as to form a depression or pocket opening to the outside.

Invasive species

1. Incorporation of genes of one species into a gene pool of another species.
2. An introduced species that out-competes native organisms for space and/or resources.

Inverse agonist

A drug which produces an effect opposite to that of an agonist, yet acts at the same receptor. The best established examples act at the benzodiazepine receptor (see Schofield, 1989). Such compounds have also been described as negative antagonists, or as having negative efficacy.

Inversely proportional

y is inversely proportional to x if y = k/x.

Inversion (in cooking)

Hydrolysis of saccharose while cooking, saccharose alters to inverted sugar (fructose and glucose) thus reducing crystallization. Hence invert sugar: Mixture of glucose and fructose, normally prepared by the hydrolysis of sucrose, or inversion. Invert sugars help baked goods retain moisture and prolong shelf-life. Candy manufacturers use invert sugar to control graining. Invert sugar is some 10% sweeter than the equivalent amount of sucrose.

Inversion (in genetics)

An aberration in chromosome structure resulting from an error in meiosis or from mutagens; reattachment in a reverse orientation of a chromosomal fragment to the chromosome from which the fragment originated. A chromosomal mutation involving the removal of a chromosome segment, its rotation through l80 degrees, and its reinsertion in the same location. The replacement of a section of a chromosome in the reverse orientation.


Organisms not possessing a backbone.  Make up approximately 95% of the animal kingdom.

In vitro

Performed in a test tube or other laboratory apparatus.
See in situ.

In vitro culture

Storage of living materials as tissue culture, and may include cryopreservation (storage at low temperature, usually in liquid nitrogen)

In vitro fertilisation

Fertilization of ova in laboratory containers followed by artificial implantation of the early embryo in the mother's uterus.

In vitro selection

Selection at the cellular or callus stage of individuals possessing certain traits, such as herbicide resistance

Iodine value (IV)

Degree of unsaturation of a fat. Usually the oxidative stability of an oil increases as the iodine value is lowered.


An atom that has lost or gained electrons from its outer shell and therefore has a positive or negative charge, respectively. If an atom gains an electron it takes on a negative charge.  If the atom loses an electron it takes on a positive charge. An ion is symbolized by the letter of the element with a superscript plus or minus sign and sometimes a number, e.g., H+ (hydrogen ion), Ca+2 (calcium ion), Cl- (chloride ion); SO4-2 (sulphate ion).

Ion channels

Transmembrane proteins that contain a central water-filled pore through which ions may move down their concentration gradient.  These channels allow ions to move readily from one side of the cell membrane to the other (which they would not otherwise do given that they are strongly hydrophilic and therefore not likely to dissolve in the lipid bilayer of the cell membrane). Ion channels can be selective based on the criteria of their hydrated size (ion + cloud of water molecules) being smaller than the pore size, and the criterion of any charge attraction or repulsion between the ion and the protein moieties lining the channel.
(see G-protein coupled receptors or Ohmic ion channels or Rectifier ion channels))

Ionic bond

A chemical bond in which atoms of opposite charge are held together by electrostatic attraction (electro-magnetic attraction between ions of opposite charge).

Ion-Exchange Chromatography

A quantitative method for separating charged molecules of various sizes, from large proteins to small nucleotides

Ion pumps (also known as ATPase Ion pumps)

A type of Active or Direct Transport system, requiring energy expenditure by the cell to move ions from one side of the cell membrane across to the other side against the thermodynamic potential (i.e, the thermodynamic potential created by the electro-chemical gradient).
There are 3 classes of Direct or Primary active transport mechanisms:
Ion pumps (also known ATPase Ion pumps) – transport of ions.
There are 3 classes called P-, V-, and F- ATPase ion pumps.
P class ion pumps have the simplest structure: 4 transmembrane subunits, two a and two b polypeptides. The larger a subunit is phosphorylated during transport, and the transported ions move through this subunit. Examples: Na+/K+-ATPase pump in the cell membrane; Ca++-ATPase in membrane of muscle sarcoplasmic reticulum.
V and F classes of ion pumps are similar in structure to each other but unrelated to P-class pumps.  They transport only protons.
F-class pumps contain at least three kinds of transmembrane proteins & V-class pumps contain at least two kinds of proteins. Both contain at least five kinds of extrinsic polypeptides that form the cytosolic domain.
V-class maintain the low pH of plant vacuoles and of lysosomes and other vesicles in animal cells by using the energy release by ATP hydrolysis to pump protons from cytosolic to exoplasm up the proton electrochemical gradient.
F-class proton pumps are found in bacterial plasma membranes and in mitochondria and chloroplasts. In contrast to the V Pumps, they generally function to power synthesis of ATP from ADP and Pi by movement of protons from exoplasm to the cytoplasm down the proton electrochemical gradient.

All three classes have one or more binding sites for ATP on the cytosolic face of the membrane.
All use the same basic mechanism: namely, a conformational change in proteins as they are reversibly phosphorylated by ATP.
All are reversible, i.e. can be made to run backward. If pumped ions are allowed to diffuse back through the membrane complex, ATP can be synthesized from ADP and inorganic phosphate.

Ionizing radiation

Rays of energy that move in short, fast wave patterns and can penetrate cells.

Ionotropic receptors

A receptor that contains an ion channel. Binding of the transmitter to the binding site opens or closes an ion channel. This modulates the flow of current compared to the resting state and thus alters the resting membrane potential of the target cell containing the receptors, producing a generator potential that may be called variously excitatory post-synpatic potential (in nerve), inhibitory post-synpatic potential (in nerve), end-plate potential (in muscle).

IPPB (Intermittent positive pressure breathing) therapy

The application of positive pressure using an IPPB ventilator to increase the overall volume of air inspired


circular, opaque, contractile diaphragm controlling the diameter of the pupil;divides the space between the lens and the cornea into an anterior and a posteriorchamber; the colored part of the eye surface containing dark pigment cells variously arranged in different people to produce different colored irises; pigment
absent in albinos.


Inflammation of the iris. The iris is the circular, colored curtain in the front of the visible of the eye. (The opening of the iris forms the pupil.)

Irrational numbers

A number that cannot be expressed as the ratio of two integers.

Irreversible antagonist

See antagonist.


the controlled application of water for agricultural purposes through manmade systems to supply water requirements not satisfied by rainfall. Here's a quick look at some types of irrigation systems.

irrigation water use

water application on lands to assist in the growing of crops and pastures or to maintain vegetative growth in recreational lands, such as parks and golf courses

Irritable Bowel Syndrome (IBS)

Irritable Bowel Syndrome (IBS) is a major functional gastrointestinal (GI) disorder affecting up to 10% of the population1. Symptoms of IBS include recurrent abdominal pain and discomfort due to heightened perception of mechanical events in the lower bowel. Remodelling of sensory pathways supplying the bowel is a key contributor to IBS symptom development and maintenance. An important question is where does this remodelling occur? Increased sensitivity of colonic afferent peripheral endings to mechanical stimuli is well documented in models of IBS. However, it is unknown how this increase in peripheral activity effects transmission into the CNS, specifically on colonic afferent central terminal activation of spinal cord neurons. Clinical studies suggest that an increase in sensory input contributes to the maintenance of sensitization in the spinal nociceptive pathways in IBS patients. Such sensitization leads to amplification of responses to both noxious (hyperalgesia) and innocuous (allodynia) mechanical stimuli.

The receptors mediating synaptic release and activation of DH neurons by SP, CGRP and glutamate are neurokinin receptors (NKrs), CGRP receptors (CGRPr), ionotropic glutamate receptors (iGluR) and metabotropic glutamate receptors (mGluR) respectively.
NKrs: NKrs (1, 2 and 3) are G-protein coupled receptors and regulate tachykininergic slow excitatory synaptic currents. There is a large body of work describing the role of NK1rs on nociresponsive DH neurons in mediating nociceptive signaling from the colon in normal and inflamed states. NKrs are not expressed by colonic afferent neurons, thus SP release is regulated by other ligands.


A substance that produces irritating effect when it contacts skin, eyes, nose, or respiratory system.


International Organization for Standards. A Geneva-based organization that sets standards for industrial and many other processes and equipment.


Line of constant pressure.


Type of phytoestrogen found in soybeans and soy-based foods which may reduce menopause symptoms.


A condition in which male and female gametes are morphologically indistinguishable.

Isolating mechanism

Mechanisms that prevent genetic exchange between individuals of different populations or species; they prevent mating or successful reproduction even when mating occurs; may be behavioral, anatomical, or physiological.

Isometric and isotonic contractions (of muscle)

Isotonic contraction is a contraction when a muscle shortens while exerting a constant force to match the load that is being lifted.
Isometric contraction is a contraction when the muscle length does not change because the force it is generating is insufficient to move the load to which it is attached. Most contractions in the body are a mixture of isometric and isotonic contractions.  Initially the contraction is in an isometric phase as the muscle generates enough force to lift a load.  Then it enters the isotonic phase as the muscle shortens at a constant force as it lifts the load.


A transformation of a figure that does not change the distances of any two  points in the figure.


The shape of a molecule.  The isomeric structure is determined by the order in which the atoms are bonded together. An isomer is one of several organic compounds with the same molecular formula but different structures and therefore different properties. The three types are structural isomers, geometric isomers, and enantiomers.

Isomorphic generations

Alternating generations in which the sporophytes and gametophytes look alike, although they differ in chromosome number.

Isosceles triangle

A triangle with at least two equal sides.

Isostatic Principle

Transmission of pressure is uniform and instantaneous,  independent of the size and geo metry of thefood


Line of constant temperature.

Isotonic solution

Solutions of equal solute concentration.


One of several atomic forms of an element; atoms with the same atomic number but different numbers of neutrons.Indicated by adding the mass number to the element's name, e.g., carbon 12 or 12C. An isotope is a nuclide with the same atomic number but different atomic mass. Unstable radioactive isotopes are used for labeling in radioimmunoassays (RIA) and immunoradiometric assays (IRMA).