Anterior pituitary

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Anterior pituitary gland
Median sagittal through the hypophysis of an adult monkey. Semidiagrammatic.
Details
PrecursorOral mucosa (Rathke's pouch)
Arterysuperior hypophyseal
Veinhypophyseal
Identifiers
Latinlobus anterior hypophysis
MeSHD010903
NeuroNames407
NeuroLex IDbirnlex_1581
TA98A11.1.00.002
TA23855
FMA74627
Anatomical terminology

A major

glandular, anterior lobe that together with the posterior lobe (posterior pituitary, or the neurohypophysis) makes up the pituitary gland (hypophysis) which, in humans, is located at the base of the brain, protruding off the bottom of the hypothalamus
.

The anterior pituitary regulates several

growth, reproduction, and lactation. Proper functioning of the anterior pituitary and of the organs it regulates can often be ascertained via blood tests that measure hormone
levels.

Structure

The anterior pituitary complex

The

neural composition of the posterior pituitary.[citation needed
]

The anterior pituitary is composed of three regions:

Pars distalis

The pars distalis (distal part) comprises the majority of the anterior pituitary and is where the bulk of pituitary hormone production occurs. The pars distalis contains two types of cells, including

acidophils (alpha cells) and basophils (beta cells).[1] These cells all together produce hormones of the anterior pituitary and release them into the blood stream.[citation needed
]

Nota bene: The terms "basophil" and "acidophil" are used by some books, whereas others prefer not to use these terms. This is due to the possible confusion with white blood cells, where one may also find basophils and acidophils.

  • Microanatomy of the pars distalis showing chromophobes, basophils, and acidophils
    Microanatomy of the pars distalis showing chromophobes, basophils, and acidophils
  • Eosinophilic follicles are a common normal finding in the anterior pituitary.
    Eosinophilic follicles are a common normal finding in the anterior pituitary.
Pars tuberalis
The
photoperiod (length of day). The expression of this subunit is regulated by the secretion of melatonin in response to light information transmitted to the pineal gland.[2][3] Earlier studies have shown localization of melatonin receptors in this region.[4]
Pars intermedia
The pars intermedia (intermediate part) sits between the pars distalis and the posterior pituitary, forming the boundary between the anterior and posterior pituitaries. It is very small and indistinct in humans.

Development

The anterior pituitary is derived from the

ectodermal
in origin.

The pouch eventually loses its connection with the pharynx, giving rise to the anterior pituitary. The anterior wall of Rathke's pouch proliferates, filling most of the pouch to form the pars distalis and the pars tuberalis. The posterior wall of the anterior pituitary forms the pars intermedia. Its formation from the soft tissues of the upper palate contrasts with the posterior pituitary, which originates from neuroectoderm.[5]

Function

The anterior pituitary contains five types of endocrine cell, and they are defined by the hormones they secrete:

lactotropes (PRL); gonadotropes (LH and FSH); corticotropes (ACTH) and thyrotropes (TSH).[6] It also contains non-endocrine folliculostellate cells
which are thought to stimulate and support the endocrine cell populations.

Hormones secreted by the anterior pituitary are trophic hormones (Greek: trophe, "nourishment"). Trophic hormones directly affect growth either as hyperplasia or hypertrophy on the tissue it is stimulating. Tropic hormones are named for their ability to act directly on target tissues or other endocrine glands to release hormones, causing numerous cascading physiological responses.[5]

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
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 Lactotropin PRL Polypeptide
Lactotrophs
Acidophil
testes, prostate
Secretion of
prostatic hyperplasia
ACTH
secretion

[7][8]

Role in the endocrine system

Hypothalamic control

Hormone secretion from the anterior pituitary gland is regulated by hormones secreted by the

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-hypophyseal portal vessels
).

Other mechanisms

Aside from hypothalamic control of the anterior pituitary, other systems in the body have been shown to regulate the anterior pituitary's function.

GABA can either stimulate or inhibit the secretion of luteinizing hormone (LH) and growth hormone (GH) and can stimulate the secretion of thyroid-stimulating hormone (TSH). Prostaglandins are now known to inhibit adrenocorticotropic hormone (ACTH) and also to stimulate TSH, GH and LH release.[9] Clinical evidence supports the experimental findings of the excitatory and inhibitory effects GABA has on GH secretion, dependent on GABA's site of action within the hypothalamic-pituitary axis.[10]

Effects of the anterior pituitary

Thermal homeostasis

The homeostatic maintenance of the anterior pituitary is crucial to our physiological well being. Increased plasma levels of

ACTH increase metabolism and induce cutaneous vasoconstriction, increased plasma levels also result in hyperthermia and prolactin decreases with decreasing temperature values. follicle-stimulating hormone (FSH) also may cause hypothermia if increased beyond homeostatic levels through an increased metabolic mechanism only.[11]

Gonadal function

ovulation cycle in female mammals, whilst in the males, LH stimulates the synthesis of androgen which drives the ongoing will to mate together with a constant production of sperm.[5]

HPA axis

Main article

Hypothalamic-pituitary-adrenal axis

The anterior pituitary plays a role in stress response.

ACTH release in a cascading effect that ends with the production of glucocorticoids from the adrenal cortex.[5]

Behavioral effects

Development
The release of GH, LH, and FSH are required for correct human development, including gonadal development.[12]
Breast-feeding
Release of the hormone prolactin is essential for lactation.[12]
Stress
Operating through the
amino acids), bone re-absorption (calcium mobilization), activation of the sympathetic nervous system response (fight or flight), anti-inflammatory effects, and inhibition of reproduction/growth.[12] When the anterior pituitary gland is removed (hypophysectomy) in rats, their avoidance learning mechanisms were slowed, but injections of ACTH restored their performance.[12] In addition, stress may delay the release of reproductive hormones such as luteinizing hormone (LH) and follicle-stimulating hormone (FSH).[15] This shows that the anterior pituitary gland is involved in behavioral functions as well as being part of a larger pathway for stress responses. It is also known that (HPA) hormones are related to certain skin diseases and skin homeostasis. There is evidence linking hyperactivity of HPA hormones to stress-related skin diseases and skin tumors.[16]
Aging
Operating through the
impotence[12][15] and frailty[17] in elderly men because of the eventual decrease in production of testosterone. This lower level of testosterone can have other effects, such as reduced libido, well-being and mood, muscle and bone strength, and metabolism.[15]
Tactile responding
It has been shown that infant mice who were stroked with a paintbrush (simulating motherly care) had more release and binding of growth hormone (GH) from the anterior pituitary gland.[12]
Circadian rhythms
Light information received by the eyes is transmitted to the
hypothalamic-pituitary-gonadal axis.[12] Melatonin can lower levels of LH and FSH, which will decrease levels of estrogen and testosterone. In addition, melatonin may affect production of prolactin.[18]

Clinical significance

Increased activity

epiphyseal plates in bones close in puberty.[12] The most common type of pituitary tumour is a prolactinoma which hypersecretes prolactin.[20] A third type of pituitary adenoma secretes excess ACTH, which in turn, causes an excess of cortisol to be secreted and is the cause of Cushing's disease.[12]

Decreased activity

Sheehan syndrome.[21]
If the hypopituitarism is caused by the blood loss associated with childbirth, the disorder is referred to as Sheehan syndrome.

History

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

See also

  • Triple bolus test
  • Hypothalamic–pituitary–somatic axis

References

  1. ^ .
  2. .
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  4. .
  5. ^
  6. ^ Le Tissier, P.R; Hodson, D.J; Lafont C; Fontanaud P; Schaeffer, M; Mollard, P. (2012) Anterior pituitary cell networks. Front Neuroendocrinol. Aug; 33(3):252-66
  7. ^ Malendowicz, L.K; Rucinski, M; Belloni, A.S; Ziolkowska, A; and Nussdorfer, G.C. (2007) Leptin and the regulation of the hypothalamic-pituitary-adrenal axis. Int Rev Cytol. 263: 63-102.
  8. ^ Sone, M. and Osamura, R.Y. (2001) Leptin and the pituitary. Pituitary. Jan-Apr; 4(1-2): 15-23.
  9. ^ Hedge, G.A. (1977) Roles for the prostaglandins in the regulation of anterior pituitary secretion. Life Sci. Jan 1;20(1):17-33.
  10. ^ Racagni, G; Apud, J.A; Cocchi, D; Locatelli, V; Muller, E.E. (1982) GABAergic control of anterior pituitary hormone secretion. Life Sci. Aug 30;31(9):823-38.
  11. ^ Lin, M.T; Ho, L.T; and Uang, W.N. (1983) Effects of anterior pituitary hormones and their releasing hormones physiological and behavioral functions in rats. J. steroid Biochem. Vol. 19(1) 433-38.
  12. ^ .
  13. .
  14. .
  15. ^ .
  16. ^ Jung Eun Kim; Baik Kee Cho; Dae Ho Cho; Hyun Jeong Park (2013). "Expression of Hypothalamic-Pituitary-Adrenal Axis in Common Skin Diseases: Evidence of its Association with Stress-related Disease Activity". National Research Foundation of Korea. Retrieved 4 March 2014.
  17. S2CID 43285151
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  18. .
  19. .
  20. .
  21. .

Further reading

  • 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