HYPOPHYSIS (PITUITATY GLAND)

Hypophysis (pituitaty gland)

Anatomic features

Adenohypophysis (anterior pituitary), the glandular epithelial tissue, consists of three parts: pars distalis, pars intermedia, and pars tuberalis.

Most of the adenohypophysis has no direct arterial supply. The arteries give rise to fenestrated capillaries (the primary capillary plexus). These capillaries drain into portal vein, called the hypophyseal portal veins, that rive rise to a second fenestrated sinusoidal capillary network (the secondary capillary plexus).
Neurohypophysis (posterior pituitary), the neural secretory tissue, consists of pars nervosa and infundibulum.

Adenohypophysis (anterior pituitary)

Origin: evagination of the ectoderm of the oropharinx toward the brain (Rathke's pouch).

Function: play central roles in a number of regulatory feedback systems, "master organ" of the endocrine system.

Composition:

Cells of pars distalis: three histochemocal types of cells: basophils (10%), acidophils (40%), and chromophobes (50%).

Somatotropes, small round cells with dense 350 nm granules.

Function: Somatotropin (growth hormone, GH) stimulates kidney and liver to synthesize and secrete somatomedin, which stimulates the growth of long bones.

Mammotropes, cells of variable size with dense pleiomorphic 600 nm granules.

Function: Prolactin (PR) (lactogenic hormone, LTH) promotes mammary gland development, initiates and maintains milk secretion.

Adrenocorticotropes, round or oval cells with 100-300 nm granules and lipid droplets.

Function: Adrenocorticotropic hormone (ACTH) and lipotropins (LPH) maintain structure and stimulate secretion of glucocorticoids and gonadocorticoids of the adrenal cortex.

Conadotropes, large and small round cells with 200-250 nm granules.

Function: Follicle-stimulating hormone (FSH) stimulates follicular development in the ovary and spermatogenesis in the testis. Luteinizing hormone (LH) regulates ovulation, corpus luteum formation and its steroid secretion, androgen secretion by interstitial (Leydig) cells of the testis.

Thyrotropes, large polygonal cells with 150 nm granules.

Function: Thyrotropin (TSH) stimulates growth of thyroid epithelial cells and release of thyroid hormones to the blood.

Cells of pars intermedia:

Basophils

Function: Melanocyte-stimulating hormone (MSH) stimulates pigment production in melanocytes.

Chromophobes

Function: Adrenocorticotropic hormone (ACTH) and lipotropins (LPH) maintain structure and stimulate secretion of glucocorticoids and gonadocorticoids of the adrenal cortex.

Cells of pars tuberalis, cuboidal epithelial cells, are arranged in short clusters and cords.

Function is not clear.

Neurohypophysis (Posterior Pituitary)

Origin: derivation of the downgrowth of neuroectoderm of the floor of the third ventricle (diencephalon) of the developing brain.

Function: storage and releasing site for secretory product of the neurons of the supraoptic and paraventricular nuclei of hypothalamus.

Composition:

Nonmyelinated axons and nerve endings of neurosecretory neurons whose cell bodies lie in the hypothalamus.

Function: Vasopressin (antidiuretic hormone, ADH) controls blood pressure by altering the permeability of kidney collecting tubules. Oxytocin promotes contraction of smooth muscle of the uterus and myoepithelial cells of the breast.

Pituicytes

Function: association with the fenestrated capillaries similar to the astrocytes in the central nervous system.