Hypothalamus

The hypothalamus is part of the central nervous system.

Function of the hypothalamus

The hypothalamus is a small region located in the centre of the brain, and acts as a bridge between the autonomic nervous system and the endocrine system. It is involved in the regulation of major functions such as hunger, thirst, sleep, and body temperature. It is also involved in sexual behaviour and emotions.

Its endocrine functions (secretion of neurohormones) are involved in regulating the endocrine function of the pituitary, the gland located below it.

All or almost all of the hormones secreted by the hypothalamus influence the production of pituitary hormones:

• dopamine inhibits the production of prolactin;
• thyrotropin (TRH) stimulates the production of thyroid stimulating hormone (TSH);
• Somatocrinin (Growth Hormone Releasing Hormone - GH-RH) stimulates the release of the growth hormone somatotropin (GH);
• Somatostatin (GH-RIH) inhibits the release of GH;
• Gonadoliberin (or gonadotropin releasing hormone - GnRH) is responsible for the synthesis and secretion of FSH and LH (hormones) .
• Corticotropin releasing hormone (CRH) promotes the production of the hormone adrenocorticotrophin (ACTH);
• Ocytocin (involved in uterine contractions, lactation and attachment) and vasopressin (an antidiuretic hormone) are synthesised by the hypothalamus but are released into the blood circulation by the pituitary.

Structure of the hypothalamus

The hypothalamus is small (a few cubic centimetres) and made up of many pairs of nuclei formed by nerve cells located beneath the thalamus and above the pituitary gland. The pituitary gland is attached to the hypothalamus by a small stem, the pituitary stalk.

Hypothalamic neurones synthesise the different hormones and release them into an initial network of capillaries which meet to form a vein, the hypothalamic-pituitary portal system. This carries the hypothalamic hormones to the pituitary where they are released by a second capillary network to activate the pituitary neurones.