adenohypophysis

Anterior pituitary gland
Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic.
Latin	lobus anterior hypophyseos
Gray's	subject #275 1275
Artery	superior hypophyseal
Vein	hypophyseal
Precursor	oral mucosa (Rathke's pouch)
MeSH	Anterior+Pituitary+Gland

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.

Hormone secretion

The posterior pituitary as a down growth of the brain, is a neurosecretory organ (Wheater, Burkitt & Daniels, 1987). The secretion of hormones from the posterior pituitary is controlled directly by neurons in the hypothalamus (Marieb, 2004). The connecting stalk between the hypothalamus and the lobes of the pituitary gland, the infundibulum, carries the hormones of the posterior pituitary from nuclei in the hypothalamus. The hypothalmic supraoptic nuclei manufacture anti-diuretic hormone and the hypothalmic paraventricular nuclei manufacture oxytocin. These hormones are then stored in pituitary axons until their release is triggered (Marieb, 2004).

The anterior pituitary is a glandular secretory organ (Wheater, Burkitt & Daniels, 1987). The secretion of hormones from the anterior pituitary is controlled by inhibiting and releasing factors secreted by neurons in the hypothalamus. These inhibiting and releasing factors are released into a primary capillary plexus where they travel, via portal veins, to a secondary capillary plexus where they stimulate the glandular tissue of the anterior pituitary to release its hormones.

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

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".

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

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

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See also

• Tropic hormones
• Pituitary adenoma
• Triple bolus test
• Posterior pituitary

References

Marieb, E. 2004. Human Anatomy and Physiology. Benjamin Cummings: New York.

Wheater, P., Burkitt, H., Daniels, V. 1987. Functional Histology. Churchill Livingstone: New York.

External links

• Histology at BU 14002loa
• Embryology at unc.edu