D
Deoxyribonucleic acid (DNA): A double stranded, helical nucleic acid molecule capable of replicating and determining the inherited structure of acells proteins
Deoxyribose: The sugar component of DNA, having one less hydroxyl group than ribose, the sugar component of RNA.
Depolarisation: An electrical state in an excitable cell whereby the inside of the cell is made less negative relative to the outside than at the resting membrane potential. A neuron membrane is depolarised if a stimulus decreases its voltage from the resting potential of -70mV in the direction of zero voltage.
Diabetes Insipidous: Disease due to lack of antidiuretic hormone.
Diabetes Mellitus: Disease that enhances blood glucose levels due to lack of insulin.
Diffusion: The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.
Dose-Response Relationship: The relationship between (1) the dose, actually based on "administration dose" (i.e. exposure) rather than actual absorbed dose, and (2) the extent of therapeutic or toxic effect produced by the xenobiotic.
E
EC50: The molar concentration of an agonist, which produces 50% of the maximum possible response for that agonist.
ED50: The dose of a drug that is pharmacologically effective for 50% of the population exposed to the drug or a 50% response in a biological system that is exposed to the drug.
Effector cell: A muscle cell or gland cell that performs the bodyís responses to stimuli; responds to signals from the brain or other processing center of the nervous system.
Efficacy: A term introduced by Stephenson (1956) to describe the way in which agonists vary in the response they produce even when they occupy the same number of receptors.
Electrochemical gradient: The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential.
Endocytosis: The cellular uptake of macromolecules and particulate substances by localised regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle.
Endogenous: Part of the internal environment of a living organism.
Endoplasmic reticulum (ER): An extensive membranous network in eukaryotic cells, continous with the outer nuclear membrane and composed of ribosome studded (rough) and ribosome free (smooth) regions.
Endothelium: The innermost, simple squamous layer of cells lining the blood vessels: the only constituent structure of capillaries.
Excitatory postsynaptic potential (EPSP): An electrical change (depolarisation) in the membrane of a postsynaptic neurone caused by the binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic receptor; makes it more likely for a postsynaptic neurone to generate an action potential.
Exocytosis: The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.
F
Fibrillation: Cardiac, heart flutter and irregular beats.