periodic variations of certain bodily functions that reflect patterns of vital activity.
Physiological rhythms occur in microorganisms, plants, animals, and man, as well as in cell and tissue cultures. Rhythmic activity is characteristic of photosynthesis, respiration, flowering, spore formation, cell division, motor activity, body temperature, metabolic processes, and the production of formed blood elements. In man, physiological rhythms occur in cycles of sleep and wakefulness, physical and mental work capacity, the excretion of certain substances by the kidneys, and the secretion of hormones. It has been established that the concentration of those adrenocortical hormones which increase man’s resistance to injury is highest in the morning. The secretion of these hormones increases because at this time a larger amount of adrenocorticotropic hormone of the pituitary gland (ACTH) is released into the blood, with a resulting stimulation of the adrenocortical function. The secretion of ACTH is in turn controlled by the rhythmic activity of the neural centers of the hypothalamus of the brain.
Physiological rhythms are believed to be hereditary and genetically controlled. The parameters of the rhythms change both during the development of an organism and when the organism is affected by stimuli; this is an important factor in the adaptation of plants and animals to changing environmental conditions. The mutual coordination of physiological rhythms and their coordination with periodic environmental changes constitute a reliable system for the regulation of functions. Disturbances in this system lead to disruption of the body’s vital activity and may cause diseases in animals and man.
REFERENCESRomanov, Iu. A., and V. P. Rybakov. “Problema biologicheskikh ritmov v fiziologii i meditsine.” In the collection Biologicheskie ritmy v mekhanizmakh kompensatsii narushennykh funktsii. Moscow, 1973.
Bünning, E. The Physiological Clock [2nd ed.]. New York, 1964.
Rensing, L. Biologische Rhythmen und Regulation. Jena, 1973.
Scheving, L. E., F. Halberg, and J. E. Pauly. Chronobiology. Stuttgart-Tokyo, 1974.
IU. A. ROMANOV