Anterior pituitary

Anterior pituitary
Anterior pituitary
	Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic.
Details
Precursor	oral mucosa (Rathke's pouch)
Artery	superior hypophyseal
Vein	hypophyseal
Identifiers
Latin	lobus anterior hypophyseos
MeSH	D010903
NeuroNames	407
NeuroLex ID	birnlex_1581
TA98	A11.1.00.002
TA2	3855
FMA	74627
	Anatomical terminology [edit on Wikidata]

A major organ of the endocrine system, the anterior pituitary, also called the adenohypophysis, is the glandular, anterior lobe of the pituitary gland. The anterior pituitary regulates several physiological processes including stress, growth, and reproduction.

Its regulatory functions are achieved through the secretion of various peptide hormones that act on target organs including the adrenal gland, liver, bone, thyroid gland, and gonads. The anterior pituitary itself is regulated by the hypothalamus and by negative feedback from these target organs.

Disorders of the anterior pituitary are generally classified by the presence of over- or underproduction of pituitary hormones. For example, a prolactinoma is a pituitary adenoma that overproduces prolactin. In Sheehan's syndrome of postpartum hypopituitarism, the anterior pituitary uniformly malfunctions and underproduces all hormones. Proper function of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone levels.

Anatomy

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 multiple parts:

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.^{[citation needed]}
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.

Embryology

The anterior pituitary arises from an invagination of the oral ectoderm and forms Rathke's pouch. This contrasts with the posterior pituitary, which originates from neuroectoderm.

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 glucocorticoids
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.

Regulation

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).

Etymology

The anterior pituitary is also known as the adenohypophysis, meaning "glandular undergrowth", from the Greek adeno ("gland"), hypo ("under"), and physis ("growth").

Additional images

The anterior pituitary is the anterior, glandular lobe of the pituitary gland.

External links

Histology image: 14002loa – Histology Learning System at Boston University
Embryology at unc.edu