Anterior pituitary

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Anterior pituitary
Pituitary gland.png
Pituitary gland. (Most of the orange region is "pars distalis", but the part at the top is "pars tuberalis".)
Gray1181.png
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)
MeSH Anterior+Pituitary+Gland
Dorlands/Elsevier a_14/12111161

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Phone:617-632-7753



The anterior pituitary (also called the adenohypophysis, from Greek adeno, "gland"; hypo, "under"; physis, "growth"; hence, glandular undergrowth) comprises the anterior lobe of the pituitary gland and is part of the endocrine system. Unlike the posterior lobe, the anterior lobe is genuinely glandular, hence the root adeno in its name.

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.

Regions

The term "pars distalis" is sometimes used as a synonym for the the anterior pituitary, but this is not quite correct. The anterior pituitary is usually divided into three regions:

  • pars distalis ("distal part") - the majority of the anterior pituitary
  • pars tuberalis ("tubular part") - a sheath extending up from the pars distalis and wrapping around the pituitary stalk
  • pars intermedia ("intermediate part") - sits between the bulk of the anterior pituitary and the posterior pituitary and is often very small in humans

The function of the tuberalis is not well characterized, and most of the rest of this article refers primarily to the distalis.

Embryology

Unlike the posterior pituitary (pars nervosa), which originates from neural ectoderm, the anterior pituitary arises from an invagination of the oral mucosa called Rathke's pouch (which is itself ectoderm derived).

This differentiation is exhibited by the fact that while the posterior pituitary merely secretes those hormones produced in the hypothalamus (ADH and oxytocin), the anterior pituitary actually produces its hormones, while being under control of the hypothalamus as to when they should be secreted.

Major hormones secreted

Hormone Other names Symbol(s) Secretory cells (staining type) Target Effect
Adrenocorticotropic hormone Corticotropin ACTH Corticotrophs (basophil) Adrenal gland Secretion of glucocorticoids
Endorphins - - - - Inhibit perception of pain
Follicle-stimulating hormone - FSH Gonadotrophs (basophil) Ovaries, Testes Growth of reproductive system
Growth hormone Somatotropin GH, STH Somatotrophs (acidophil) Liver, adipose tissue Promotes growth; lipid & carbohydrate metabolism
Luteinizing hormone (females), Interstitial Cell Stimulating Hormone (males) Lutropin LH, ICSH Gonadotrophs (basophil) Ovaries, Testes Sex hormone production
Prolactin - PRL Lactotrophs, also known as Mammotrophs (acidophil) Ovaries, mammary glands Secretion of estrogens/progesterone; milk production
Thyroid-stimulating hormone Thyrotropin TSH Thyrotrophs (basophil) Thyroid gland Secretion of thyroid hormones

A useful acronym for the hormones secreted by the anterior pituitary is 'FLAT PEG' (FSH, LH, ACTH, TSH, Prolactin, Endorphins, GH).

Hypothalamic releasing and release-inhibiting factors

Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the hypothalamus. Neuroendocrine neurons in the hypothalamus project axons to the median eminence, at the base of the brain. At this site, these neurons can release substances into small blood vessels that travel directly to the anterior pituitary gland (the hypothalamo-hypophysial portal vessels).

Name Other Names Abbreviations Location Function
Corticotropin-releasing hormone Corticotropin-releasing factor, Corticoliberin CRH, CRF parvocellular neuroendocrine neurons in the paraventricular nucleus with vasopressin, stimulates secretion of ACTH
Dopamine Prolactin-inhibiting hormone DA, PIH neuroendocrine neurons of the arcuate nucleus inhibits secretion of prolactin
Gonadotropin-releasing hormone Luteinising-hormone releasing hormone GnRH, LHRH neuroendocrine neurons in the medial preoptic and arcuate nuclei stimulates secretion of LH and FSH
Growth hormone-releasing hormone Growth-hormone-releasing factor, somatocrinin GHRH, GHRF, GRF arcuate nucleus neuroendocrine neurons stimulates secretion of growth hormone
Somatostatin Growth hormone-inhibiting hormone, Somatotropin release-inhibiting factor SS, GHIH, SRIF neuroendocrine neurons of the periventricular nucleus inhibits secretion of growth hormone
Thyrotropin-releasing hormone Thyrotropin-releasing factor, Thyroliberin, Protirelin TRH, TRF parvocellular neuroendocrine neurons in the paraventricular and anterior hypothalamic nuclei stimulates secretion of TSH
Vasopressin Arginine vasopressin, Antidiuretic hormone, Argipressin AVP, ADH parvocellular neuroendocrine neurons in the paraventricular nucleus with Corticotropin-releasing hormone, stimulates secretion of ACTH

Additional images

See also

External links

fi:Adenohypofyysi



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