Human Anatomy Part 1 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2002

Special Part
Endocrine glands (ductless glands), glandulae endocrinae (glandulae sine ductibus)
Central Regulatory Organs - Pituitary Gland

The hypophysis, or Pituitary Gland (gl. pituitaria), is one of the Central Regulatory Organs of the Endocrine System. Located in the hypophysial fossa (fossa hypophysialis) of the sella turcica, it has an oval or spherical shape. The weight of the hypophysis in newborns does not exceed 0.15 g, while in adults it ranges from 0.5 to 0.6 g in men and 0.6 to 0.7 g in women. Superiorly, the gland is covered by the diaphragma sellae and is connected to the Hypothalamus via the infundibulum.

Structure OF THE hypophysis. The hypophysis consists of an anterior lobe (lobus anterior s. adenohypophysis) and a posterior lobe (lobus posterior s. neurohypophysis) (see Fig. 343). The anterior lobe is further subdivided into the pars tuberalis, pars intermedia, and pars distalis, whereas the posterior lobe comprises the infundibulum and the neural lobe (lobus nervosus).

The parenchyma of the posterior lobe is composed of Nervous Tissue (a type of neuroglia), hence its designation as the neurohypophysis. The pars tuberalis lies adjacent to the pituitary stalk and contacts the Inferior surface of the median eminence of the hypothalamus. The external surface of the hypophysis is enclosed by a Connective Tissue capsule.

The anterior lobe is significantly larger than the posterior lobe, accounting for approximately 70% of the total gland weight. On a cross-section, the organ exhibits a pale yellow color with a reddish tint due to a rich vascular network.

The middle or intermediate part of the adenohypophysis, the pars intermedia, consists of a narrow epithelial strip containing small cavities filled with a colloid substance.

The posterior lobe (lobus posterior) is rounded in shape and has a greenish-yellow hue resulting from pigment presence.

Functions of the hypophysis. The secretory Cells of the anterior pituitary produce so-called tropic Hormones which, with the exception of Growth Hormone (somatotropin), stimulate or maintain the hormone production of other pituitary-dependent glands at a specific level.

Overproduction of somatotropin by the anterior lobe (hyperfunction) during childhood leads to gigantism, with individual heights reaching 250 cm or more. Somatotropin hyperfunction in adults causes acromegaly, a disorder characterized by the enlargement of the face, Tongue, Nose, Lips, external ears, hands, and feet.

Deficient production (hypoproduction) of somatotropin in childhood results in growth retardation, known as Pituitary dwarfism. The height of such individuals typically ranges between 120 and 130 cm.

Hyperfunction (excess) of adrenocorticotropic hormone leads to Cushing's Disease, clinically manifested by fat deposition in the face and trunk, thin and disproportionate extremities, Osteoporosis, and bone fractures.

Excessive production of thyroid-stimulating hormone (thyrotropin) causes hyperactivity of The Thyroid Gland, whereas its hypofunction results in deficiency of this organ, known as hypothyroidism.

Overproduction of luteinizing hormone leads to hypergonadism, while decreased production results in hypogonadism.

Complete absence of anterior pituitary hormone secretion (due to trauma, tumors, etc.) leads to Skeletal Muscle atrophy and wasting, a clinical condition known as pituitary cachexia.

Endocrinocytes of the pars intermedia produce melanocyte-stimulating hormone (melanotropin), which is involved in pigment METABOLISM, as well as lipotropin, which enhances Lipid Metabolism.

The posterior pituitary stores two hormones: antidiuretic hormone (vasopressin) and oxytocin. As noted above, these hormones are synthesized by large neurosecretory cells in the supraoptic and paraventricular nuclei of the hypothalamus.

Antidiuretic hormone (vasopressin) increases Blood pressure by contracting vascular smooth muscle and decreases diuresis (urine output). A deficiency of vasopressin causes a clinical condition known as diabetes insipidus.

Oxytocin stimulates the contraction of uterine smooth muscle, particularly during childbirth, and is widely used in clinical practice to induce labor.

The function of the pars tuberalis remains not fully understood.