hypothalamus

Also an endocrine gland, releasing hormones that travel in the hypothalamic-hypophyseal portal veins to affect anterior pituitary hormone production and secretion.

The hormones secreted that affect pituitary function are:

• Thyrotropin-releasing hormone (TRH) -- causes TSH and prolactin release
• Gonadotropin-releasing hormone (GnRH) -- causes LH and FSH release
• Growth hormone-releasing hormone (GHRH) -- causes GH release
• Corticotropin-releasing hormone (CRH) -- causes ACTH release
• Somatostatin -- inhibits release of GH and TSH
• Dopamine -- inhibits release of prolactin

In addition, ADH (antidiuretic hormone) and oxytocin are formed in the hypothalamus and travel in neurons down to the neurohypophysis and released into the circulation there.

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reference: http://arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/hypopit/overview.html

The endocrine system

The hypothalamus is a brain structure located deep within the brain. It is considered to be a part of the limbic system and plays a large role in both eating behavior and sexual behavior. It is connected to the pituitary gland.

Hypothalamic control of eating

The traditional view is that the lateral hypothalamus (LH) controls the initiation of eating (hunger) and the ventromedial hypothalamus controls the inhibition of eating (satiety). Newer research, however, shows that this is an oversimplification, and that hunger and satiety are in fact controlled by two fiber tracts: the Nigrostriatal Feeding System and the Paraventricular Satiety System.

Nigrostriatal Feeding System

This is a dopaminergic pathway running from the Substantia nigra through the Lateral Hypothalamus and to the Basal Ganglia. It is now believed this pathway is an integral part of the hunger system.

Paraventricular Satiety System

This system is made up of nerve fibers that go from the paraventricular nucleus of the hypothalamus, around the ventromedial nucleus and to the nucleus of the solitary tract (NST) and the dorsal motor nucleus of the vagus (DMV).

Hypothalamic control of sexual behavior

The hypothalamus influences behavior in 2 ways.

1. Stimulates manufacture and release of testosterone or female sex hormones such as estrogen.
2. Elicits sexual behavior

In males, the tuberal region of the hypothalamus secretes gonadotrophic-releasing hormones into the anterior pituitary gland, which in turn releases luteinizing hormone and follicle-stimulating hormone. These hormones stimulate sperm production and testosterone release.

In females, the pituitary gland secretes gonadotropphic-stimulating hormones that cause the ovaries to release female sex hormones. The estrogen released acts on the ventromedial hypothalamus to produce a sexual response.

Sexual behavior is controlled by the medial preoptic area of the hypothalamus. This area is about 2.5 times larger in males than in females. This area is stimulated by testosterone to elicit sexual activity. Pheromones detected by the olfactory bulb also stimulate this part of the hypothalamus.

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Source:
Klein, Stephen B. Biological Psychology. Prentice Hall, New Jersey: 2000.