What is the hypothalamus?

The hypothalamus is an almond sized gland located deep in the skull, directly above the sinus cavities, and brain stem, and below the thalamus. It serves as the only connection between the nervous system and the endocrine system. Many consider the most important function of the hypothalamus. For the most part it does not produce hormones that are sent into the bloodstream but indirectly affects the endocrine system via producing and secreting hypothalamic-releasing hormones which instruct the pituitary gland to release hormones. It is also responsible for helping maintain homeostasis (maintaining system balance and stability) including body temperature, blood pressure, fatigue, hunger, thirst, and circadian cycles.

Hormones of the Hypothalamus

Thyrotropin-releasing hormone (Prolactin-releasing hormone): Produced in the parvocellualar neurosecretory neurons this hormone primarily stimulates the anterior pituitary release of thyroid-stimulating hormone , as well prolactin.

Dopamine (prolatctin-inhibiting hormone): Produced in the dopamine neurons of the arcuate nucleus this hormone will inhibit the release a prolactin from the anterior pituitary.

Growth hormone releasing hormone: Produced in the neuroendocrine cells of the Arcuate nucleus this hormone will stimulate the anterior pituitary’s release of the Growth hormone.

Somatostatin (growth hormone inhibiting hormone): Produced in the neuroendocrine neurons of the periventricular nucleus this hormone inhibits the release of Growth hormone by the anterior pituitary.

Gonadotropin-releasing hormone: Produced in the neuroendocrine cells of the preoptic area this hormone stimulates the release of follicle-stimulating hormone, and the luteinizing hormone from the anterior pituitary.

Corticotropin-releasing hormone: Produced in the parvocellular neurosecretory neurons this hormone stimulates the release of Adrenocorticotropic hormone by the anterior pituitary.

Oxytocin: Produced in the magnocellular neurosecretory this hormone cells causes Uterine contraction and lactation.

Vasopressin (antidiuretic hormone): Produced in the Parvocellular neurosecretory neurons this hormone promotes water reabsorption increasing blood volume.

As you can see the hypothalamus and the pituitary glands are a pair, though both do perform functions unrelated to each other. They both have been referred to as the master gland, because in many ways they instruct the entire system of endocrine glands. The hypothalamus communicates with the pituitary through the pituitary stalk via a several capillaries and veins. Hormones will be deposited into the hypophyseal artery capillary bed below the hypothalamus in the stalk, and then transported to the anterior region of the pituitary via the hypothalmic-hypophyseal portal veins.