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internal secretion[in′tərn·əl si′krē·shən]
the formation and release by the endocrine glands (glands of internal secretion) of specific physiologically very active products—hormones—directly into the blood or other tissue fluids. The hormones elaborated by the glands are released in definite proportions to coordinate biochemical reactions—that is, to regulate metabolism, growth, and development and thereby ensure the normal functioning of the body and its adaptation to constantly changing environmental conditions. Change in the body’s “demands” may intensify or inhibit the formation of a secretion (incretion) and its release (mobilization) into the blood. The functioning of the endocrine glands is influenced by many factors (trauma, pain, high and low temperatures, infection, poisoning, radiant energy, oxygen insufficiency, and others), which may under certain conditions either increase their functioning (hyperfunction) or decrease it (hypofunction). Disruption of homeostasis (relative constancy of the body’s internal environment) changes internal secretion directly or reflexly. Most often it is the pituitary gland, the adrenal cortex and medulla, and the thyroid gland that react. The increased secretion of hormones by these glands produces various physiological effects (intensification of metabolism, change in body temperature and blood pressure, and others), aimed at adapting the body to changing environmental conditions.
Disturbances of internal secretion may be caused chiefly by dysfunction of the endocrine glands. Dysfunction may consist in excessive or insufficient formation or release of hormones (hyper- or hyposecretion and, accordingly, hyper-and hypofunction), or it may be related to qualitative changes in the hormones. The enzymes that take part in the synthesis and destruction of individual hormones play a special role in glandular dysfunction. Disturbances of internal secretion may also arise even with normal functioning of the glands when the action of the hormones is altered by changes in the physicochemical conditions of the environment (increase or decrease in concentration of H+ ions, K+ and Ca++ salts, amino acids, and other metabolic products, as well as the binding of hormones to proteins), in tissues and organs, and in sites of action of the hormones. Enzymes, as well as inhibitors and activators of individual glands, play an important part in these phenomena.
Functional disturbances of the glands of internal secretion are important in the origin of many diseases, particularly endocrinopathy. Injury to a particular gland gives rise to characteristic symptoms that can be regarded as independent diseases, such as diffuse goiter, hypothyroidism, hyper- and hypoparathyroidism, and diabetes mellitus. However, in case of functional disturbance of any one gland, other endocrine glands usually become involved to some degree because their activities are closely related and they function as a single physiological system. This process produces complex disorders known as pluriglandular syndromes—that is, the functional impairment of several glands at the same time. Functional impairment of different glands gives rise to similar clinical syndromes. These diseases are diagnosed by determining the content of hormones and their metabolic products (metabolites) in the blood and urine and by running tests involving the administration of hormone activators and inhibitors and then determining the hormones in biological fluids. The diseases may also be diagnosed by using radioactive indication of hormones to study hormone metabolism, by determining blood sugar and free and bound insulin (in diabetes mellitus), by studying the uptake of radioactive iodine (131I and 132I) by the thyroid gland, and by studying protein-bound iodine and iodine extracted with butanol (in diseases of the thyroid).
Substitution or stimulation hormone therapy is prescribed for functional deficiencies of particular glands of internal secretion. To induce a more sustained effect, certain hormonal preparations are used in the form of microcrystalline suspensions (hypodermically or intramuscularly), as well as in the form of hypodermic or intramuscular implantation of fused crystals. To inhibit the breakdown of hormones in the body preparations are injected that inactivate the enzymes that split the hormones, thereby preserving the amount of hormones formed in the body. If the endocrine glands are over-active, treatment consists of chemical blocking (drugs) or physical blocking (exposure to X-rays) of the functioning of the glands. Or the glands, especially if they are affected with tumors, may be removed by surgery. The method of treatment is chosen in accordance with the course of the disease and reactivity of the body.
REFERENCESBolezni endokrinnoi sistemy. Moscow, 1966. (Mnogotomnoe rukovodstvo po vnutrennim bolezniam, Vol. 7.)
Shereshevskii, N. A. Klinicheskaia endokrinologiia. Moscow, 1957.
Modern Trends in Endocrinology, series [1-2]. Edited by H. Gardiner-Hill. London, 1958-1961.
L. M. GOL’BER