Anterior pituitary

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 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 ectoderm and forms the Rathke's pouch.

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

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
Beta-endorphin			Corticotrophs (basophil)	Opioid receptor	Inhibit perception of pain
Human growth hormone	Somatotropin	hGH, STH	Somatotrophs (acidophil)	Liver, adipose tissue	Promotes growth; lipid & carbohydrate metabolism
Thyroid-stimulating hormone	Thyrotropin	TSH	Thyrotrophs (basophil)	Thyroid gland	Secretion of thyroid hormones
Follicle-stimulating hormone	-	FSH	Gonadotrophs (basophil)	Gonads	Growth of reproductive system
Luteinizing hormone	Lutropin	LH, ICSH	Gonadotrophs (basophil)	Gonads	Sex hormone production
Prolactin	Lactogenic hormone	PRL	Lactotrophs, also known as Mammotrophs (acidophil)	Ovaries, mammary glands	Secretion of estrogens/progesterone; milk production

One mnemonic used to remember the hormones produced by the anterior pituitary is: FLAT PEG (FSH, LH, ACTH, TSH, Prolactin, Endorphins and 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