Pituitary Gland Structure and Function

The pituitary gland, also known as the hypophysis, is a small endocrine gland located in the sella turcica of the sphenoid bone at the base of the skull.

The pituitary gland is connected to the hypothalamus via the pituitary stalk, also known as the hypophyseal stalk.

The pituitary gland is divided into two main parts: the anterior pituitary (adenohypophysis) and the posterior pituitary (neurohypophysis).

The anterior pituitary is derived from the ectoderm and originates from an upward growth called Rathke's pouch, which originates from the pharyngeal epithelium.

The posterior pituitary originates from the neuroectoderm and forms as a downward diverticulum from the hypothalamus.

The relationship between the hypothalamus and the pituitary gland is called the hypothalamo-hypophyseal relationship. This relationship is crucial for regulating hormone production and secretion.

Hypothalamic hormones are transported to the anterior pituitary and the posterior pituitary, but the mechanism of transport differs between the two divisions.

Pars intermedia is a small, relatively avascular structure located between the anterior and posterior pituitary. It plays a role in regulating certain hormonal functions.

The anterior pituitary gland is known as the master gland because it controls the activity of other endocrine glands by releasing hormones.

The anterior pituitary gland is divided into three main parts: pars distalis, pars tuberalis, and pars intermedia.

Chromophobe cells are non-secretory cells in the anterior pituitary that form 50% of the total cells. They are considered precursors to chromophil cells.

Chromophil cells are secretory cells in the anterior pituitary, classified by staining properties as acidophilic or basophilic.

Acidophilic cells, also known as alpha cells, form 35% of the chromophil cells in the anterior pituitary and are stained by acidic dyes.

Basophilic cells, also known as beta cells, form 15% of the chromophil cells in the anterior pituitary and are stained by basic dyes.

Somatotropes are acidophilic cells in the anterior pituitary that produce growth hormone (GH).

Corticotropes are basophilic cells in the anterior pituitary that secrete adrenocorticotropic hormone (ACTH).

ACTH has 39 amino acids, but only the first 24 are essential for its activity. The last 13 amino acids resemble those found in beta melanocyte stimulating hormone. Increased ACTH levels lead to increased skin pigmentation.

Beta-endorphin, a fragment of beta-lipotrophin, is found in the brain and gastrointestinal tract. It acts as a neurotransmitter and has analgesic properties, reducing pain.

The hypothalamus, located in the brain, controls the anterior pituitary by secreting releasing and inhibiting hormones (factors), also known as neurohormones.

Hypothalamic hormones travel to the anterior pituitary through special blood vessels called the hypothalamo-hypophyseal portal vessels.

GHRH stimulates the release of growth hormone, while GHRP stimulates both GHRH and growth hormone release. Somatostatin (GHIH) inhibits growth hormone release.

TRH stimulates the release of thyroid stimulating hormone (TSH), which controls thyroid hormone production.

CRH stimulates the release of ACTH from the anterior pituitary, which then acts on the adrenal glands to produce cortisol.

GnRH stimulates the release of FSH and LH from the anterior pituitary. FSH and LH are important for the production of sex hormones (estrogen, progesterone, testosterone).