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|Anterior pituitary gland|
|Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic.|
|Latin||lobus anterior hypophyseos|
|Gray's||subject #275 1275|
|Precursor||oral mucosa (Rathke's pouch)|
A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe that together with the posterior lobe, the (posterior pituitary) makes up the pituitary gland (hypophysis). The anterior pituitary regulates several physiological processes including stress, growth, reproduction and lactation.
Its regulatory functions are achieved through the secretion of various peptide hormones that act on target glands and organs including the adrenal glands, liver, bone, thyroid, and gonads. The anterior pituitary itself is regulated by the hypothalamus and by negative feedback from these targets.
Disorders of the anterior pituitary are generally classified by the of overproduction or underproduction of pituitary hormones. For example, an overproduction of prolactin can give rise to a pituitary adenoma (a benign tumour) called a prolactinoma. In hypopituitarism, the anterior pituitary underproduces one or more of the hormones; panhypopituitarism is the condition where the gland uniformly malfunctions and underproduces all of the hormones. Proper function of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels.
The pituitary gland is a pea-sized gland that sits in a protective bony enclosure called the sella turcica. It is composed of three lobes: anterior, intermediate, and posterior. In many animals, these three lobes are distinct. However, in humans, the intermediate lobe is but a few cell layers thick and indistinct; as a result, it is often considered part of the anterior pituitary. In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary.
The anterior pituitary is composed of three regions:
- Pars distalis
- The pars distalis, or "distal part", comprises the majority of the anterior pituitary and is where the bulk of pituitary hormone production occurs. Occasionally, "pars distalis" is incorrectly used as a synonym for the anterior pituitary.
- Pars tuberalis
- The pars tuberalis, or "tubular part", forms a sheath extending up from the pars distalis and wrapping around the pituitary stalk. Its function is poorly understood.
- Pars intermedia
- The pars intermedia, or "intermediate part", sits between the pars distalis and the posterior pituitary and is often very small in humans.
The anterior pituitary has three types of epithelial cell: basophil cells and acidophil cells, which are chromophils meaning that they stain easily; and amphophils, or chromophobes, cells which do not readily stain. Together these cells are responsible for the production of the anterior pituitary hormones.
Major hormones secreted
|Hormone||Other names||Symbol(s)||Structure||Secretory cells||Staining||Target||Effect|
|Adrenocorticotropic hormone||Corticotropin||ACTH||Polypeptide||Corticotrophs||Basophil||Adrenal gland||Secretion of glucocorticoid, mineralocorticoid and androgens|
|Beta-endorphin||Polypeptide||Corticotrophs||Basophil||Opioid receptor||Inhibit perception of pain|
|Thyroid-stimulating hormone||Thyrotropin||TSH||Glycoprotein||Thyrotrophs||Basophil||Thyroid gland||Secretion of thyroid hormones|
|Follicle-stimulating hormone||-||FSH||Glycoprotein||Gonadotrophs||Basophil||Gonads||Growth of reproductive system|
|Luteinizing hormone||Lutropin||LH, ICSH||Glycoprotein||Gonadotrophs||Basophil||Gonads||Sex hormone production|
|Growth hormone||Somatotropin||GH, STH||Polypeptide||Somatotrophs||Acidophil||Liver, adipose tissue||Promotes growth; lipid and carbohydrate metabolism|
|Prolactin||Lactogenic hormone||PRL||Polypeptide||Lactotrophs and Mammotrophs||Acidophil||Ovaries, mammary glands||Secretion of estrogens/progesterone; milk production|
The acidophilic cells (GH and PRL) have extensive rough endoplasmic reticulum and produce single chain polypeptides without any glycosylation or phosphorylation. Basophilic staining results from lysosome action modifying the hormones (or prohormones in the case of corticotrophs) by glycosylation.
An easy mnemonic to remember the hormones produced and secreted by the anterior pituitary is "FLATPEG".
Hormone secretion from the anterior pituitary gland is regulated by releasing hormones secreted by the hypothalamus. Neuroendocrine cells in the hypothalamus project axons to the median eminence, at the base of the brain. At this site, these cells can release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophysial portal vessels).
The anterior pituitary is also known as the adenohypophysis, meaning "glandular undergrowth", from the Greek adeno ("gland"), hypo ("under"), and physis ("growth").
Marieb, E. 2004. Human Anatomy and Physiology. Benjamin Cummings: New York.
Wheater, P., Burkitt, H., Daniels, V. 1987. Functional Histology. Churchill Livingstone: New York.