Glossary of Terms & Definitions
Listed Alphabetically - "I"

Idiopathic: of unknown cause. 

Immunity: The state of being resistant to injury, particularly by poisons, foreign proteins and invading pathogens.

Immunology: The branch of science that deals with the responses of the body when challenged by antigens.

Impaired glucose tolerance: a metabolic state between normal glucose regulation and overt diabetes. Generally, blood glucose levels are higher than normal, but lower than those accepted as diagnostic for diabetes.

Infection: Invasion and multiplication of microorganisms in body tissues, which may be in apparent or characterized by cellular injury.

Insoluble: not dissolvable. With respect to bioavailability, certain substances form insoluble complexes that cannot be dissolved in digestive secretions, and therefore cannot be absorbed by the digestive tract.

Insulin: a peptide hormone secreted by the b-cells of the pancreas required for normal glucose metabolism.

Insulin resistance: diminished responsiveness to insulin.

Intracellular fluid (ICF): the volume of fluid inside cells.

Intron: A region of DNA that does not code for the synthesis of a protein.

In vitro: literally "in glass" referring to a test or research done in the test tube, outside a living organism.

In vivo: "inside a living organism". An in vivo assay evaluates a biological process occurring inside the body.

Ion: an atom or group of atoms that carries a positive or negative electric charge as a result of having lost or gained one or more electrons.

Ion channel: a protein, embedded in a cell membrane that serves as a crossing point for the regulated transfer of an ion or a group of ions across the membrane.

Isomers: compounds that have the same numbers and kinds of atoms but that differ in the way the atoms are arranged.