HYPOTHALAMIC POLYPEPTIDE HORMONE

hypothalamus region of the brain lying below the thalamus and making up the floor of the third cerebral ventricle. The hypothalamus contains a control centre for many functions of the autonomic nervous system, and it has important links with the endocrine system because of its complex interaction with the pituitary gland that lies beneath it. The hypothalamus and pituitary gland are connected by both nervous and chemical pathways. Nerve tracts from the hypothalamus stimulate the posterior pituitary's release of oxytocin and vasopressin; these are hormones that cause smooth-muscle contractions in the circulatory and reproductive systems. Hormones secreted from the hypothalamus into a portal vein leading to the anterior pituitary trigger that gland's release of growth hormone, adrenocorticotropic hormone, luteinizing hormone, and other major pituitary products. In addition to its effects on the endocrine system, the hypothalamus also influences the body's caloric intake and weight regulation, establishing a stable set point for individual weight gain. The hypothalamus also regulates body heat in response to variations in external temperature, contains a centre that determines wakefulness and sleep, and regulates fluid intake and feelings of thirst. Injuries or diseases affecting the hypothalamus usually produce symptoms of pituitary dysfunction or of diabetes insipidus; in the latter disorder, the absence of antidiuretic hormone (a hormone that promotes the reabsorption of water in the kidneys) produced by the hypothalamus induces the rapid loss of water from the body through frequent urination. Hypothalamic disease can also cause insomnia and unusual fluctuations in body temperature.