Pituitary. Pituitary structure

The pituitary gland , the hypophysis (glandula pituitaria), is often called the lower appendage of the brain. This unpaired formation is elongate-rounded, somewhat flattened in anteroposterior direction.

The pituitary body, enclosed in a dense (fibrous) membrane, is located in the Turkish saddle. Outside the pituitary gland is covered with a hard shell of the brain, dura mater encephali, which stretches between the anterior and posterior oblique processes of the sphenoid bone and the back of the saddle and which fuses with the pituitary gland. The plate of a hard shell so tightened, the diaphragm of the saddle, diaphragma sellae, forms a roof over the pituitary fossa, fossa hypophysialis. In the diaphragm of the saddle there is a small hole through which the funnel passes, infundibulum. By means of its pituitary gland is connected with the gray hillock located on the bottom wall of the third ventricle. From the side, the pituitary is surrounded by cavernous sinuses.

The size of the pituitary gland is very individual: the anterolateral one varies from 5 to 11 mm, the uppermost - from 6 to 7 mm, the transverse - from 12 to 14 mm; Weight 0,3-0,7 g.

Pituitary lobe

The pituitary gland consists of anterior lobe (adenohypophysis) and posterior lobe (neurohypophysis).

1) Lobus anterior (adenohypophisis). 2) Lobus posterior (neurohypophisis). 3) Infundibulum. 4) pars tuberalis. 5) pars intermedia. 6) pars distalis.

Both shares of development, structural and functional characteristics are not the same.

Adenohypophysis (anterior lobe), adenohypophysis (lobus anterior), larger than the posterior lobe, on a section of brownish-red color, depending on the number of blood vessels. In the adenohypophysis, the anterior major part, located in the hypophyseal fossa of the Turkish saddle, is distinguished; A distinctly prominent narrow section directly adjoining the neurohypophysis, an intermediate part, pars intermedia, and a small part lying outside the fossa of the Turkish saddle (above the diaphragm of the saddle), - the tuberous part, the pars tuberalis.

In the anterior lobe there are different sizes, shapes and structures of epithelial cells.

Neurohypophysis (posterior lobe), neurohypophysis (lobus posterior), on the cut has a grayish-yellowish color, which is due to the presence of a brownish-yellowish pigment. In the posterior lobe, the posterior major part and the medial prominence are distinguished.

The neurohypophysis includes a funnel, an infundibulum connecting the pituitary gland with a gray tuber, tuber cinereum, the hypothalamus.

The posterior lobe consists of a large number of neuroglial tissue and a small number of ependymic cells. Between the fibers of glia is located the specified pigment, its amount increases with age.

Pituitary Hormones

The anterior pituitary gland produces a group of tropic hormones. One of the most important is the growth hormone (STH), which regulates the growth and development of the body and affects the function of pancreatic islets. A number of hormones stimulate mainly the function of other endocrine glands. So, the function of the adrenal cortex stimulates adrenocorticotropic hormone (ACTH), thyroid - thyroid-stimulating hormone (TSH), sex glands - gonadotropic hormone (GTG), etc.

Hormones of the posterior lobe of the pituitary gland (vasopressin and oxytocin) are in fact a product of neurosecretion of the nerve cells of the nuclei (supraoptic and paraventricular, nucleus supraopticus and nucleus paraventricularis) of the hypothalamus, the intermediate brain. The neurosecret of these cells along the nerve fibers that form the tractus supraopticohypophysialis and tractus paraventriculohypophysialis, enters the neurohypophysis. There it is deposited and then goes to the flow of blood. Hormones of the posterior lobe of the pituitary gland enhance the contraction of the smooth muscles of the vessels and uterus, regulate the secretion of mammary glands (prolactin), and vasopressin has an effect on the reverse absorption of water (reabsorption) in the renal tubules.

Innervation: the nerve fibers from the inner carotid plexus (from the upper cervical node of the sympathetic trunk) are directed to the distal part of the pituitary gland along the walls of the vessels suitable for it, the nerve fibers from the nuclei of the hypothalamus and the nuclei located in the region above the optic crosphere follow the posterior lobe of the sympathetic trunk.

Blood supply: each part of the pituitary has a separate blood supply, and anastomosing between the upper and lower pituitary arteries takes part in it. The first move away from the internal carotid artery (after its exit from the cavernous sinus) and from the posterior connective arteries. The lower pituitary arteries also move away from the internal carotid artery, but at the site of its passage through the cavernous sinus. Not branched in the distal part of the pituitary gland, these vessels follow the neurohypophysis, where they already branch up to the capillaries.

The venous capillaries of the neurohypophysis merge into venules, and the latter pass to the portal (portal) veins of the pituitary gland.

These veins enter the distal part (adenohypophysis). Here they break up into thin branches that continue into the network of sinusoidal capillaries. Thus, the bringing in vessels of the main anterior lobe of the adenohypophysis are not arteries, but portal veins of the pituitary gland. The outflow of venous blood from the latter occurs in the cavernous and interstitial sinuses of the hard shell of the brain. Features of the anatomy of the intragonal vessels of the pituitary gland are of functional significance.