Anterior pituitary

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The anterior pituitary (also called the adenohypophysis) comprises the anterior lobe of the pituitary gland and is part of the endocrine system. Under the influence of the hypothalamus, the anterior pituitary produces and secretes several peptide hormones that regulate many physiological processes including stress, growth, and reproduction.

Anatomy and development

The adenohypophysis is a pea-size gland anterior to the neurohypophysis, caudal to the hypothalamus, and sits in the medial aspect of the brain. Its blood is supplied by the superior and inferior hypophyseal arteries, and it secretes hormones into the hypophyseal vein.

The anterior pituitary is derived from the ectoderm of the roof of the embryonic mouth. An outpocketing of this ectoderm forms Rathke's pouch, which pinches off from the oral ectoderm and fuses with the developing posterior pituitary. The anterior wall of Rathke's pouch becomes the pars distalis and pars tuberalis, while the posterior wall gives rise to the pars intermedia. Together, the pars distalis, tuberalis, and intermedia comprise the anterior pituitary.

Histology

When stained by Periodic acid-Schiff, three main types of secretory cell can be seen: chromophobes (which don't take on any stain), basophils (which stain purple, and are not related to the blood cell), and acidophils (stain orange). About half of the cells are chromophobes, 40% are acidophils, and 10% are basophils.

Basophilic staining cells produce the hormones that specifically act on other endocrine organs, such as TSH, ACTH, FSH and LH. Acidophils produce growth hormone and prolactin. Chromophobes are presumed to be "empty" cells, having already released their granules of hormone.

Physiology

Five different cell types are recognised by the hormone they produce:

• Basophils:
  • thyrotropes secrete thyroid-stimulating hormone (TSH)
  • gonadotropes secrete luteinizing hormone (LH) and follicle-stimulating hormone (FSH)
  • corticotropes secrete adrenocorticotropic hormone (ACTH)
• Acidophils:
  • lactotropes secrete prolactin
  • somatotropes secrete growth hormone.

Electron microscopy and immunohistochemistry allow further identification of the hormone produced by the cells.

Major hormones secreted

Hormone	Target	Effect
Adrenocorticotropic hormone (ACTH)	Adrenal gland	Secretion of glucocorticoids
Follicle-stimulating hormone (FSH)	Ovaries, Testes	Growth of reproductive system
Growth hormone (GH)	Liver, Adipose Tissue	Promotes growth; lipid & carbohydrate metabolism
Luteinizing hormone (LH)	Ovaries, Testes	Sex hormone production
Prolactin	Ovaries, mammary glands	Secretion of estrogens/progesterone; milk production
Thyroid-stimulating hormone (TSH)	Thyroid gland	Secretion of thyroid hormones

Role in disease

Hyposecretion of anterior pituitary hormones (hypopituitarism) can occur due to hypothalamic lesions, pituitary tumors, granulomas, infections, ischemia, hemorrhage and trauma. There can be a selective, partial or complete loss of pituitary hormone activity. Initial symptoms are due to insufficient levels of the target hormones. Testing must be conducted to confirm that decreased levels of pituitary hormones exist.

Hypersecretion mostly results from pituitary adenomas and hyperplasia. Prolactin secreting adenomas and growth hormone or ACTH secreting tumors are common examples. Damage to the hypothalamus or the tract (such as decreased inhibiting factors) can occur.

fr:Anté-hypophyse