Hypothalamus

: The area of the brain that controls body temperature, hunger, and thirst.

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The ventral and medial region of the diencephalon forming the walls of the ventral half of the third ventricle; it is delineated from the thalamus by the hypothalamic sulcus, lying medial to the internal capsule and subthalamus, continuous with the precommissural septum anteriorly and with the mesencephalic tegmentum and central gray substance posteriorly. Its ventral surface is marked by, from before backward, the optic chiasma, the unpaired infundibulum that extends by way of the infundibular stalk into the posterior lobe of the hypophysis, and the paired mamillary bodies. The h. consists of the anterior hypothalamic area [TA], dorsal hypothalamic area [TA], intermediate hypothalamic area [TA], lateral hypothalamic area [TA], and posterior hypothalamic area [TA], each of these containing specific nuclei. It has afferent fiber connections with the mesencephalon, limbic system, cerebellum, and efferent fiber connections with the same structures and with the posterior lobe of the hypophysis; its functional connection with the anterior lobe of the hypophysis is established by the hypothalamohypophysial portal system. The h. is prominently involved in the functions of the autonomic (visceral motor) nervous system and, through its vascular link with the anterior lobe of the hypophysis, in endocrine mechanisms; it also appears to play a role in neural mechanisms underlying moods and motivational states. SEE ALSO: pituitary gland. [hypo- + thalamus]

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hy·po·thal·a·mus -'thal-ə-məs n, pl -mi -.mī a basal part of the diencephalon that lies beneath the thalamus on each side, forms the floor of the third ventricle, and includes vital autonomic regulatory centers (as for the control of food intake)

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n.

the region of the forebrain in the floor of the third ventricle, linked with the thalamus above and the pituitary gland below (see brain). It contains several important centres controlling body temperature, thirst, hunger, and eating, water balance, and sexual function. It is also closely connected with emotional activity and sleep and functions as a centre for the integration of hormonal and autonomic nervous activity through its control of the pituitary secretions (see neuroendocrine system, pituitary gland).

• hypothalamic adj.

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hy·po·thal·a·mus (hi″po-thalґə-məs) [hypo- + thalamus] [TA] the ventral part of the diencephalon, forming the floor and part of the lateral wall of the third ventricle. Anatomically, it includes the preoptic area, optic tract, optic chiasm, mammillary bodies, tuber cinereum, infundibulum, and neurohypophysis, but for physiological purposes the neurohypophysis is considered a distinct structure. The hypothalamus may be divided into five regions or areas (area hypothalamica rostralis, area hypothalamica dorsalis, area hypothalamica intermedia, area hypothalamica lateralis, and area hypothalamica posterior) or into three longitudinal zones (periventricular zone, medial zone, and lateral zone). The hypothalamic nuclei constitute that part of the corticodiencephalic apparatus that activates, controls, and integrates the peripheral autonomic mechanisms, endocrine activity, and many somatic functions, such as general regulation of water balance, body temperature, sleep, and food intake, as well as development of secondary sex characters. The hypothalamus secretes vasopressin and oxytocin, which are stored in the pituitary, as well as many releasing factors (hypophysiotropic hormones), by means of which it exerts control over functions of the adenohypophysis. hypothalamic adj

Hypothalamus as seen on the medial surface of a hemisection of the diencephalon and part of the brainstem and cerebellum.