resin /rez′in/ [L, resina] , 1. a mixture of carboxylic acids, essential oils, and terpenes (hydrocarbons of the formula C10H16), occurring as exudations on various trees and shrubs or produced synthetically. Resins are highly combustible semisolids or amorphous solids that are insoluble in water, although some are soluble in ethanol and others in carbon tetrachloride, ether, and volatile oils. Most are soft and sticky but harden after exposure to cold. 2. any of a variety of solid or semisolid amorphous substances that are insoluble in organic solvents but not in water. Orally administered bile-acid binding resins such as cholestyramine and colestipol interrupt the normal enterohepatic circulation of bile acids and increase their excretion in the stool. Since bile acids are synthesized by the liver from cholesterol, the liver extracts more LDL cholesterol from the plasma to replace them, and, as a consequence, circulating levels of LDL cholesterol decrease.
