Pituitary gland

The pituitary gland, or hypophysis, is an endocrine gland about the size of a pea that sits in the small, bony cavity (sella turcica) at the base of the brain.

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

Its posterior lobe is connected to a part of the brain called the hypothalamus via the infundibulum (or stalk), giving rise to the tuberoinfundibular pathway. The posterior lobe is thus composed of neural tissue neural ectoderm and is derived from hypothalamus, its fuction is to store oxytocin and Antidieuretic hormone. When hypothalamic neurons fire: hormones release into the capillaries of the lobe.

The posterior pituitary is, in effect, a projection of the hypothalamus. It does not produce its own hormones, but only stores and releases the hormones oxytocin and antidiuretic hormone (ADH - also known as vasopressin).

Anterior pituitary

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 lobe receives releasing hormones from the hypothalamus via a portal vein system known as the hypothalamic-hypophyseal portal system.

The anterior pituitary secretes:

It does this in response to a variety of chemical signals from the hypothalamus, which travel to the anterior lobe by way of a special capillary system from the hypothalamus, down the median eminence, to the anterior lobe. These 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. 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

External links

Glands | Endocrine system | Head and neck | Neuroendocrinology