pituitary gland

The pituitary gland secretes hormones regulating a wide variety of bodily activities, including trophic hormones that stimulate other endocrine glands. For a while, this led scientists to call it the master gland, but now we know that it is in fact regulated by hormones released from the hypothalamus.

The pituitary gland is physically attached to the brain by the pituitary, or hypophyseal stalk connected with the median eminence.

Sections

It is divided into two sections: the anterior lobe (adenohypophysis) and the posterior lobe (neurohypophysis).

Posterior pituitary (neurohypophysis)

The posterior lobe is connected to a part of the brain called the hypothalamus via the infundibulum (or stalk), giving rise to the hypothalamohypophyseal tract. Hormones are made in nerve cell bodies positioned in the hypothalamus, and these hormones are then transported down the nerve cell's axons to the posterior pituitary. Hypothalamic neurons fire such hormones, releasing them into the capillaries of the pituitary gland.

The hormones secreted by the posterior pituitary are

• Oxytocin comes from the paraventricular nucleus in the Hypothalamus
• Antidiuretic hormone (ADH - also known as vasopressin), comes from the supraoptic nucleus in the Hypothalamus

Anterior pituitary (Adenohypophysis)

The anterior lobe is derived from oral ectoderm, composed of glandular epithelium it communicates with the hypothalamus via a network of capillaries.

The anterior pituitary produces and secretes:

• growth hormone
• prolactin
• follicle-stimulating hormone
• luteinizing hormone
• thyroid-stimulating hormone
• adrenocorticotropic hormone
• endorphins
• and other hormones

It does this in response to releasing hormones produced by the hypothalamus. These travel to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophyseal portal system. These hypothalamic signalling hormones include:

• TRH (thyrotropin-releasing hormone)
• CRH (corticotropin-releasing hormone)
• DA (dopamine, "prolactin inhibiting factor"/PIF)
• GnRH (gonadotropin-releasing hormone)
• GHRH (growth hormone releasing hormone)

These hormones from the hypothalamus cause release of the respective hormone from the pituitary, i.e. TRH releases TSH, CRH releases ACTH, GnRH releases FSH and LH and GHRH causes the release of GH except for DA, which constantly inhibits the release of prolactin normally. There is also an interaction between the hormones from the hypothalamus, i.e. TRH induces the release of prolactin.

The control of release of hormones from the pituitary is in a negative feedback loop. Their release is inhibited by increasing levels of hormones from the target gland on which they act.

Intermediate lobe

There is also an intermediate lobe in many animals. For instance in fish it is believed to control physiological colour change. In adult humans it is just a thin layer of cells between the anterior and posterior pituitary, nearly indistinguishable from the anterior lobe. The intermediate lobe produces melanocyte-stimulating hormone (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.

Functions

The pituitary gland helps control the following body processes:

• Growth
• Blood pressure
• Some aspects of pregnancy and childbirth
• Breast milk production
• Sex organ functions in both women and men
• Thyroid gland function
• The conversion of food into energy (metabolism)
• Water and osmolarity regulation in the body

See also

• Growth hormone deficiency
• Hypopituitarism
• Acromegaly
• Pickardt syndrome
• Pituitary adenoma
• Sheehan syndrome
• Syndrome of inappropriate antidiuretic hormone
• Diabetes insipidus
• Head and neck anatomy

External links

• The Pituitary Gland, from the UMM Endocrinology Health Guide
• NeuroNames hier-382
• Oklamoma State, Endocrine System
• Histology at BU 14201loa