a part of the brain under the thalamus opticus.
The hypothalamus is part of the diencephalon, forming the walls and floor of the third ventricle; the pituitary body, or hypophysis, is suspended from it on a thin stalk. The hypothalamus is an aggregate of higher adaptive centers that integrate and adjust functions to the body’s coordinated activity, playing a major role in maintaining the metabolic level and in regulating the activity of the digestive, cardiovascular, endocrine, and other physiological systems. Thus, the hypothalamus is one of the most important members of a functional system that coordinates autonomic with psychic and somatic functions. It contains more than 30 paired clusters of nerve cells, called nuclei, and it is connected by a large number of neural pathways to the upper and lower divisions of the central nervous system. Certain hormones (for example, vasopressin) and a variety of biologically active substances are formed in the nerve cells of the hypothalamic nuclei. These active substances (the so-called releasing factors) enter the hypophysis by way of the blood vessels and nerve fibers and promote the secretion of hormones.
The hypothalamus exerts neurohumoral and hormonal control over the functions and regulates the activity of the endocrine glands according to the needs of the cells, organs, physiological systems, and the body as a whole. The hypothalamus is furnished with a rich network of blood vessels and receptors that sense the slightest changes in temperature and sugar, salt, water, and hormone content in the internal environment. Fluctuations in the composition and properties of the internal environment trigger corresponding mechanisms that organize feeding and sexual behavior and create the conditions necessary for the maintenance of constant body temperature. Structures that form part of a complex system regulating the alternation and maintenance of sleep and wakefulness are also present in the hypothalamus. The posterior portions of the hypothalamus consist largely of structures that, mostly with the help of the peripheral sym-patheticoadrenal apparatus, provide autonomic and endocrine support for physical and mental activity and adaptation of the body to changes in the external and internal environments (the so-called ergotropic state). The anterior portions of the hypothalamus regulate chiefly the restorative and assimilative processes (the so-called trophotropic state) and maintain the relative constancy of the body’s internal environment (homeostasis). Injury to the hypothalamus results in endocrine, metabolic, trophic, or autonomic disorders, including changes in thermoregulation, sleep and wakefulness, and emotion.
A. M. VEIN