| isocyclic compound | Any compound in which the constituent atoms, or any part of them, form a ring. Used mainly in organic chemistry where: 1) numerous compound's contain rings of carbon atoms (carbocyclic compound's) or carbon atoms plus one or more atoms of other types (heterocyclic compound's), usually nitrogen, oxygen, or sulfur; 2) where the atoms in the ring are all of the same element (homocyclic or isocyclic compound); 3) where the ring is saturated or contains nonconjugated double bonds (alicyclic compound), the compound is similar in properties to the corresponding acyclic compound (e.g., cyclohexane resembles hexane); 4) where the ring contains conjugated double bonds in a closed loop in which there are 4n + 2 (where n is an integer) delocalised π electrons (Huckel's rule) (aromatic compound; e.g., benzene, pyridine), it is more stable than the corresponding saturated ring and exhibits unusual chemical properties characteristic of itself and not of other types of rings or of acyclic compound's. These aromatic compounds have the ability to sustain an induced ring current. Synonym: closed chain compound, ring compound. (05 Mar 2000) |
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| open chain compound | An organic compound in which the chain does not form a ring. Synonym: aliphatic compound, open chain compound. (05 Mar 2000) |
| organic compound | <chemistry> A compound containing carbon. (11 Jan 1998) |
| lens, compound | <microscopy> A lens composed of two or more separate pieces of glass or other optical maternal. These component pieces or elements may or may not be cemented together. A common form of compound lens is a two-element objective, one element being a converging lens of crown glass and the other a diverging lens of flint glass. The combination of suitable glasses or other optical materials (plastics, minerals) properly ground and polished reduces aberrations normally present in a single lens. (05 Aug 1998) |
| accessory gland | A small mass of glandular structure, detached from but lying near another and larger gland, to which it is similar in structure and probably in function. (05 Mar 2000) |
| accessory parotid gland | An occasional islet of parotid tissue separate from the mass of the gland, lying anteriorly just above the commencement of the parotid duct. Synonym: glandula parotidea accessoria, admaxillary gland, glandula parotis accessoria, socia parotidis. (05 Mar 2000) |
| accessory thyroid gland | An isolated mass, or one of several such masses, of thyroid tissue, sometimes present in the side of the neck, or just above the hyoid bone (suprahyoid accessory thyroid gland), or even as low as the arch of the aorta. Synonym: glandula thyroidea accessoria, accessory thyroid, prehyoid gland, suprahyoid gland, thyroidea accessoria, thyroidea ima, Wolfler's gland. (05 Mar 2000) |
| acid gland | One of the gastric gland's secreting the hydrochloric acid of the gastric juice. Synonym: oxyntic gland. (05 Mar 2000) |
| acinotubular gland | A gland whose secretory elements are elongated acini. Synonym: acinotubular gland. (05 Mar 2000) |
| acinous gland | A gland in which the secretory unit(s) has a grapelike shape and a very small lumen; e.g., the exocrine part of the pancreas. (05 Mar 2000) |
| adenoma, sweat gland | A benign neoplasm derived from epithelial cells of sweat glands. (12 Dec 1998) |
| admaxillary gland | An occasional islet of parotid tissue separate from the mass of the gland, lying anteriorly just above the commencement of the parotid duct. Synonym: glandula parotidea accessoria, admaxillary gland, glandula parotis accessoria, socia parotidis. (05 Mar 2000) |
| adrenal gland | <anatomy, endocrinology> This gland is found above each kidney and it made up of an outer wall (cortex) that secretes important steroid hormones and an inner portion (medulla) that produces adrenaline (adrenaline) and noradrenaline (noradrenaline). The hormones help control heart rate, blood pressure, the way the body uses food, and other vital functions. (25 Jun 1999) |
| adrenal gland hypofunction | Adrenocortical hypofunction includes all conditions in which adrenal steroid hormone secretion falls below the requirements of the body. Adrenal insufficiency may be divided into two general categories: (1) those associated with primary inability of the adrenal to elaborate sufficient quantities of hormone and (2) those associated with a secondary failure due to a primary failure in the elaboration of adrenocorticotropin. (12 Dec 1998) |
| adrenal gland insufficiency | <endocrinology> A condition that results from the inadequate production of adrenal hormones (see Addison's disease). (27 Sep 1997) |