active transport - the movement of substances across a biological membrane against its concentration gradient, with the help of energy input and specific transport proteins.
alimentary canal - a hollow, tubular cavity extending through animals open at both ends; for ingestion, digestion, and secretion of food materials.
apical - opposite to the base; apex.
basolateral membrane- the cell membrane along the base and sides of the cell.
countercurrent system - a pair of opposed channels containing fluid flowing in opposite directions and having an energetic gradient directed across one channel to the other.
countercurrent multiplier - a countercurrent system where the exchange between the two channels is a function of the distance along the gradient.
elasmobranch - the cartilaginous fishes (the sharks, skates, and rays).
epithelium - a tissue consisting of tightly adjoining cells that cover a surface or line a canal or cavity, and that serves to enclose and protect.
euryhaline - able to tolerate wide variations in salinity.
fenestrated - many- pored.
hemolymph - the blood of invertebrates with open circulatory systems.
homeostasis - relative internal stability maintained by physiological control systems.
hyperosmotic - containing a higher solute concentration than the surrounding environment.
hypertonic - see "hyperosmotic."
hypoosomotic - containing a lower solute concentration than the surrounding environment.
hypotonic - see "hypoosmotic."
integument - a covering or envelope. In animals, the skin, exoskeleton, tunic, cuticle, or other covering.
interstitial fluid - fluid between cells or tissues.
lumen - the interior of a cavity or duct.
metazoan - all animals other than sponges.
osmoconformer - an organism that exhibits little or no osmoregulation; body fluids follow changes in osmolarity of environment.
osmolarity - the effective osmotic pressure; solute concentration expressed as molarity.
osmolyte - a substance that serves the special purpose of raising osmotic pressure, or lowers the freezing point of body fluid.
osmoregulator - an organism that controls internal osmolarity with changes in environmental osmolarity.
osmosis - the movement of pure solvent form a solution of an area of low solute concentration to an area of high solute concentration through a semipermeable membrane separating the two solutions.
oxidative metabolism - metabolic water is produced by cellular respiration when electrons and hydrogen are added to oxygen.
renal clearance - that volume of plasma containing the quantity of a freely filtered substance that appears in the glomerular filtrate per unit time.
stenohaline - able to tolerate only a narrow range of salinities.
teleost - one of the bony fishes.