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Pituitary gland

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The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the brain, protruding off the bottom of the hypothalamus. The human pituitary gland is oval shaped, about 1 cm in diameter, 0.5–1 gram (0.018–0.035 oz) in weight on average, and about the size of a kidney bean.[2][3]

Pituitary gland
Lateral view
Lateral view of hypothalamus–pituitary complex
Details
PrecursorNeural and oral ectoderm, including Rathke's pouch
SystemEndocrine system
ArterySuperior hypophyseal artery, infundibular artery, prechiasmal artery, inferior hypophyseal artery, capsular artery, artery of the inferior cavernous sinus[1]
Identifiers
Latinhypophysis cerebri, glandula pituitaria
MeSHD010902
NeuroLex IDbirnlex_1353
TA98A11.1.00.001
TA23853
FMA13889
Anatomical terms of neuroanatomy

There are two main lobes of the pituitary, an anterior lobe, and a posterior lobe joined and separated by a small intermediate lobe. The anterior lobe (adenohypophysis) is the glandular part that produces and secretes several hormones. The posterior lobe (neurohypophysis) secretes neurohypophysial hormones produced in the hypothalamus. Both lobes have different origins and they are both controlled by the hypothalamus.

Hormones secreted from the pituitary gland help to control growth, blood pressure, energy management, all functions of the sex organs, thyroid gland, metabolism, as well as some aspects of pregnancy, childbirth, breastfeeding, water/salt concentration at the kidneys, temperature regulation, and pain relief.

Structure

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In humans, the pituitary gland rests upon the hypophyseal fossa of the sphenoid bone, in the center of the middle cranial fossa. It sits in a protective bony enclosure called the sella turcica, covered by the dural fold diaphragma sellae.[4]

The pituitary gland is composed of the anterior pituitary, the posterior pituitary, and an intermediate lobe that joins them.[5] The intermediate lobe is avascular and almost absent in humans. In many animals, these three lobes are distinct. The intermediate lobe is present in many animal species, particularly in rodents, mice, and rats, which have been used extensively to study pituitary development and function.[6] In all animals, the fleshy, glandular anterior pituitary is distinct from the neural composition of the posterior pituitary, which is an extension of the hypothalamus.[6]

The height of the pituitary gland ranges from 5.3 to 7.0 mm. The volume of the pituitary gland ranges from 200 to 440 mm3.[7] Its most common shape, found in 46% of people is flat, it is convex in 31.2% and concave in 22.8%.[7]

Anterior

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Main article: Anterior pituitary

The anterior pituitary lobe (adenohypophysis) arises from an evagination of the oral ectoderm (Rathke's pouch). This contrasts with the posterior pituitary, which originates from neuroectoderm.

Endocrine cells of the anterior pituitary are controlled by regulatory hormones released by parvocellular neurosecretory cells in the hypothalamic capillaries leading to infundibular blood vessels, which in turn lead to a second capillary bed in the anterior pituitary. This vascular relationship constitutes the hypophyseal portal system. Diffusing out of the second capillary bed, the hypothalamic releasing hormones then bind to anterior pituitary endocrine cells, upregulating or downregulating their release of hormones.[8]

The anterior lobe of the pituitary can be divided into the pars tuberalis (pars infundibularis) and pars distalis (pars glandularis) that constitutes ~80% of the gland. The pars intermedia (the intermediate lobe) lies between the pars distalis and the pars tuberalis, and is rudimentary in the human, although in other species it is more developed.[6] It develops from a depression in the dorsal wall of the pharynx (stomal part) known as Rathke's pouch.

The anterior pituitary contains several different types of cells[9] that synthesize and secrete hormones. Usually there is one type of cell for each major hormone formed in anterior pituitary. With special stains attached to high-affinity antibodies that bind with distinctive hormone, at least 5 types of cells can be differentiated.

S.No. Type of cell Hormone secreted Percentage
of type of cell
1. Somatotropes human Growth Hormone (hGH) 30–50%
2. Corticotropes AdrenoCorticoTropic Hormone (ACTH) 20%
3. Thyrotropes Thyroid-Stimulating Hormone (TSH) 3–5%
4. Gonadotropes Gonadotropic hormones = both Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) 3–5%
5. Lactotropes Prolactin (PRL) 3–5%

Posterior

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Main article: Posterior pituitary

The posterior pituitary consists of the posterior lobe and the pituitary stalk (infundibulum) that connects it to the hypothalamus. It develops as an extension of the hypothalamus, from the floor of the third ventricle. The posterior pituitary hormones are synthesized by cell bodies in the hypothalamus. The magnocellular neurosecretory cells, of the supraoptic and paraventricular nuclei located in the hypothalamus, project axons down the infundibulum to terminals in the posterior pituitary. This simple arrangement differs sharply from that of the adjacent anterior pituitary, which does not develop from the hypothalamus.

The release of pituitary hormones by both the anterior and posterior lobes is under the control of the hypothalamus, albeit in different ways.[8]

Function

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Pituitary hormones

The anterior pituitary regulates several physiological processes by secreting hormones. This includes stress (by secreting ACTH), growth (by secreting GH), reproduction (by secreting FSH and LH), metabolism rate (by secreting TSH) and lactation (by secreting prolactin). The intermediate lobe synthesizes and secretes melanocyte-stimulating hormone. The posterior pituitary (or neurohypophysis) is a lobe of the gland that is functionally connected to the hypothalamus by the median eminence via a small tube called the pituitary stalk (also called the infundibular stalk or the infundibulum). It regulates hydroelectrolytic stability (by secreting ADH), uterine contraction during labor and human attachment (by secreting oxytocin).

Anterior

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The anterior pituitary synthesizes and secretes hormones. All releasing hormones (-RH) referred to can also be referred to as releasing factors (-RF).

Somatotropes:

Corticotropes:

Thyrotropes:

Gonadotropes:

Lactotropes:

  • Prolactin (PRL), whose release is inconsistently stimulated by hypothalamic TRH, oxytocin, vasopressin, vasoactive intestinal peptide, angiotensin II, neuropeptide Y, galanin, substance P, bombesin-like peptides (gastrin-releasing peptide, neuromedin B and C), and neurotensin, and inhibited by hypothalamic dopamine.[11]

These hormones are released from the anterior pituitary under the influence of the hypothalamus. Hypothalamic hormones are secreted to the anterior lobe by way of a special capillary system, called the hypothalamic-hypophysial portal system.

There is also a non-endocrine cell population called folliculostellate cells.

Posterior

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The posterior pituitary stores and secretes (but does not synthesize) the following important endocrine hormones:

Magnocellular neurons:

Hormones

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Hormones secreted from the pituitary gland help control the following body processes:

Development

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The development of the pituitary gland, or hypophysis, is a complex process that occurs early in embryonic life and involves contributions from two distinct embryonic tissues. Here’s a detailed explanation:

1.Embryological Origin The pituitary gland develops from two embryonic tissues: Rathke's pouch: An ectodermal outpocketing from the roof of the primitive oral cavity, or stomodeum, which gives rise to the anterior pituitary (adenohypophysis). Infundibulum: A downward extension from the neuroectoderm of the diencephalon in the brain, which forms the posterior pituitary (neurohypophysis).

2. Developmental Stages Formation of Rathke's pouch (4th week of gestation): During the 4th week, an invagination of the oral ectoderm occurs, creating Rathke's pouch.

Differentiation and Migration (5th to 6th week): Rathke's pouch grows towards the developing brain. The upper part of the pouch eventually constricts and detaches from the oral cavity. Cells in Rathke's pouch differentiate to form three parts of the adenohypophysis: the pars distalis, pars intermedia, and pars tuberalis.

Formation of the Posterior Pituitary (4th to 8th week): The infundibulum from the diencephalon elongates downward, forming a stalk that connects with Rathke’s pouch. This stalk will develop into the pars nervosa, or posterior pituitary. Specialized cells from the hypothalamus, known as pituicytes, migrate to the posterior pituitary, where they help store and release hormones such as oxytocin and vasopressin.

3. Hormone Production and Functional Maturity By around the 12th to 16th week of gestation, the anterior pituitary begins producing hormones like growth hormone (GH), adrenocorticotropic hormone (ACTH), and others essential for fetal development. The posterior pituitary functions primarily in storage, as it stores hormones produced by the hypothalamus and releases them into the bloodstream.

4. Final Structural Differentiation The pituitary gland achieves its final form, including the complete separation of anterior and posterior lobes, by the end of the first trimester The gland remains connected to the hypothalamus by the pituitary stalk, allowing it to integrate signals from the brain and regulate various endocrine functions in the body. This dual-origin structure and function are what make the pituitary gland a unique and critical component of the endocrine system, acting as a bridge between the nervous and endocrine systems.

Clinical significance

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Main article: Pituitary disease
 
Normal-sized hand (left) and enlarged hand caused by acromegaly (right)

Some of the diseases involving the pituitary gland are:

All of the functions of the pituitary gland can be adversely affected by an over- or under-production of associated hormones.

The pituitary gland is important for mediating the stress response, via the hypothalamic–pituitary–adrenal axis (HPA axis). Critically, pituitary gland growth during adolescence can be altered by early life stress such as childhood maltreatment or maternal dysphoric behavior.[12]

It has been demonstrated that, after controlling for age, sex, and BMI, larger quantities of DHEA and DHEA-S tended to be linked to larger pituitary volume.[13] Additionally, a correlation between pituitary gland volume and Social Anxiety subscale scores was identified which provided a basis for exploring mediation. Again controlling for age, sex, and BMI, DHEA and DHEA-S have been found to be predictive of larger pituitary gland volume, which was also associated with increased ratings of social anxiety.[13] This research provides evidence that pituitary gland volume mediates the link between higher DHEA(S) levels (associated with relatively early adrenarche) and traits associated with social anxiety.[13] Children who experience early adrenarcheal development tend to have larger pituitary gland volume compared to children with later adrenarcheal development.[13]

History

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Etymology

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Look up pituitary gland or hypophysis in Wiktionary, the free dictionary.

Pituitary gland

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The Greek physician Galen referred to the pituitary gland by only using the (Ancient Greek) name ἀδήν,[14] gland.[15] He described the pituitary gland as part of a series of secretory organs for the excretion of nasal mucus.[14] Anatomist Andreas Vesalius translated ἀδήν with glans, in quam pituita destillat, "gland in which slime (pituita[16]) drips".[14][17] Besides this 'descriptive' name, Vesalius used glandula pituitaria, from which the English name pituitary gland[18] is ultimately derived.

The expression glandula pituitaria is still used as official synonym beside hypophysis in the official Latin nomenclature Terminologia Anatomica.[19] In the seventeenth century the supposed function of the pituitary gland to produce nasal mucus was debunked.[14] The expression glandula pituitaria and its English equivalent pituitary gland can only be justified from a historical point of view.[20] The inclusion of this synonym is merely justified by noting that the main term hypophysis is a much less popular term.[21]

Hypophysis

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Note: hypophysial (or hypophyseal) means "related to the hypophysis (pituitary gland)".

The anatomist Samuel Thomas von Sömmerring coined the name hypophysis.[14] This name consists[14][20] of ὑπό ('under')[15] and φύειν ('to grow').[15] In later Greek ὑπόφυσις is used differently by Greek physicians as outgrowth.[14] Sömmering also used the equivalent expression appendix cerebri,[14][17] with appendix as appendage.[16] In various languages, Hirnanhang[17] in German and hersenaanhangsel[22] in Dutch, the terms are derived from appendix cerebri.

Other animals

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The pituitary gland is found in all vertebrates, but its structure varies among different groups.

The division of the pituitary described above is typical of mammals, and is also true, to varying degrees, of all tetrapods. However, only in mammals does the posterior pituitary have a compact shape. In lungfish, it is a relatively flat sheet of tissue lying above the anterior pituitary, but in amphibians, reptiles, and birds, it becomes increasingly well developed. The intermediate lobe is, in general, not well developed in any species and is entirely absent in birds.[23]

The structure of the pituitary in fish, apart from the lungfish, is generally different from that in other animals. In general, the intermediate lobe tends to be well developed, and may equal the remainder of the anterior pituitary in size. The posterior lobe typically forms a sheet of tissue at the base of the pituitary stalk, and in most cases sends irregular finger-like projection into the tissue of the anterior pituitary, which lies directly beneath it. The anterior pituitary is typically divided into two regions, a more anterior rostral portion and a posterior proximal portion, but the boundary between the two is often not clearly marked. In elasmobranchs, there is an additional, ventral lobe beneath the anterior pituitary proper.[23]

The arrangement in lampreys, which are among the most primitive of all fish, may indicate how the pituitary originally evolved in ancestral vertebrates. Here, the posterior pituitary is a simple flat sheet of tissue at the base of the brain, and there is no pituitary stalk. Rathke's pouch remains open to the outside, close to the nasal openings. Closely associated with the pouch are three distinct clusters of glandular tissue, corresponding to the intermediate lobe, and the rostral and proximal portions of the anterior pituitary. These various parts are separated by meningial membranes, suggesting that the pituitary of other vertebrates may have formed from the fusion of a pair of separate, but associated, glands.[23]

Most armadillos also possess a neural secretory gland very similar in form to the posterior pituitary, but located in the tail and associated with the spinal cord. This may have a function in osmoregulation.[23]

There is a structure analogous to the pituitary in the octopus brain.[24]

Intermediate lobe

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Although rudimentary in humans (and often considered part of the anterior pituitary), the intermediate lobe located between the anterior and posterior pituitary is important to many animals. For instance, in fish, it is believed to control physiological color change. In adult humans, it is just a thin layer of cells between the anterior and posterior pituitary. The intermediate lobe produces melanocyte-stimulating hormone (MSH), although this function is often (imprecisely) attributed to the anterior pituitary.[citation needed]

The intermediate lobe is, in general, not well developed in tetrapods, and is entirely absent in birds.[23]

Additional images

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  •  
    Frontal view
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    Showing position of pituitary gland
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    Pituitary and pineal glands
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    Depiction of pituitary gland
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    Mesal aspect of a brain sectioned in the median sagittal plane

See also

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References

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  1. ^ Gibo H, Hokama M, Kyoshima K, Kobayashi S (1993). "[Arteries to the pituitary]". Nippon Rinsho. 51 (10): 2550–4. PMID 8254920.
  2. ^ Hall, John E.; Guyton, Arthur C. (2011). Guyton and Hall textbook of medical physiology (12th ed.). Philadelphia, PA: Saunders/Elsevier. p. 895. ISBN 9781416045748.
  3. ^ Standring, Susan (2016). Gray's anatomy: the anatomical basis of clinical practice (41st ed.). Philadelphia, PA: Elsevier. p. 499. ISBN 9780702052309. Digital version.
  4. ^ Mancall, Elliott L.; Brock, David G., eds. (2011). "Cranial Fossae". Gray's Clinical Anatomy. Elsevier Health Sciences. p. 154. ISBN 978-1-4377-3580-2.
  5. ^ Ganapathy MK, Tadi P (Jan 2020). "Anatomy, Head and Neck, Pituitary Gland". StatPearls [Internet]. StatPearls Publishing. PMID 31855373. Retrieved 24 Sep 2020.
  6. ^ a b c Melmed, Shlomo (2011). The Pituitary - (Third ed.). San Diego, CA: Academic Press is an imprint of Elsevier. pp. 23–25. ISBN 978-0-12-380926-1.
  7. ^ a b Yadav, Pratiksha; Singhal, Shubham; Chauhan, Surbhi; Harit, Saumya (2017). "MRI Evaluation of Size and Shape of Normal Pituitary Gland: Age and Sex Related Changes". Journal of Clinical and Diagnostic Research. doi:10.7860/JCDR/2017/31034.10933.
  8. ^ a b Boron, Walter F.; Boulpaep, Emile L. (2009). Medical Physiology (2nd ed.). Philadelphia: Saunders Elsevier. pp. 1016–1017. ISBN 978-1-4160-3115-4.
  9. ^ Textbook of Medical Physiology. Elsevier Saunders.
  10. ^ Dall’Olmo, Luigi; Papa, Nicole; Surdo, Nicoletta Concetta; Marigo, Ilaria; Mocellin, Simone (2023-08-22). "Alpha-melanocyte stimulating hormone (α-MSH): biology, clinical relevance and implication in melanoma". Journal of Translational Medicine. 21 (1): 562. doi:10.1186/s12967-023-04405-y. ISSN 1479-5876. PMC 10463388. PMID 37608347.
  11. ^ Shlomo Melmed (3 December 2010). The pituitary. Academic Press. p. 40. ISBN 978-0-12-380926-1.
  12. ^ Ganella, Despina E.; Allen, Nicholas B.; Simmons, Julian G.; Schwartz, Orli; Kim, Jee Hyun; Sheeber, Lisa; Whittle, Sarah (2015). "Early life stress alters pituitary growth during adolescence—A longitudinal study". Psychoneuroendocrinology. 53: 185–194. doi:10.1016/j.psyneuen.2015.01.005. hdl:10536/DRO/DU:30144589. PMID 25622011. S2CID 5247274.
  13. ^ a b c d Murray, CR; Simmons, JG; Allen, NB; Byrne, ML; Mundy, LK; Seal, ML; Patton, GC; Olsson, CA; Whittle, S (February 2016). "Associations between dehydroepiandrosterone (DHEA) levels, pituitary volume, and social anxiety in children". Psychoneuroendocrinology. 64: 31–9. doi:10.1016/j.psyneuen.2015.11.004. PMID 26600008. S2CID 22520320.
  14. ^ a b c d e f g h Hyrtl, J. (1880). Onomatologia Anatomica. Geschichte und Kritik der anatomischen Sprache der Gegenwart. Wien: Wilhelm Braumüller. K.K. Hof- und Universitätsbuchhändler.
  15. ^ a b c Liddell, H.G. & Scott, R. (1940). A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with the assistance of. Roderick McKenzie. Oxford: Clarendon Press.
  16. ^ a b Lewis, C.T. & Short, C. (1879). A Latin dictionary founded on Andrews' edition of Freund's Latin dictionary. Oxford: Clarendon Press.
  17. ^ a b c Schreger, C.H.Th.(1805). Synonymia anatomica. Synonymik der anatomischen Nomenclatur. Fürth: im Bureau für Literatur.
  18. ^ Anderson, D.M. (2000). Dorland's illustrated medical dictionary (29th edition). Philadelphia/London/Toronto/Montreal/Sydney/Tokyo: W.B. Saunders Company.
  19. ^ Federative Committee on Anatomical Terminology (FCAT) (1998). Terminologia Anatomica. Stuttgart: Thieme
  20. ^ a b Triepel, H. (1927). Die anatomischen Namen. Ihre Ableitung und Aussprache. Anhang: Biographische Notizen.(Elfte Auflage). München: Verlag J.F. Bergmann.
  21. ^ International Anatomical Nomenclature Committee (1966). Nomina Anatomica. Amsterdam: Excerpta Medica Foundation, p. 62
  22. ^ Pinkhof, H. (1923). Vertalend en verklarend woordenboek van uitheemsche geneeskundige termen. Haarlem: De Erven F. Bohn.
  23. ^ a b c d e Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 549–550. ISBN 0-03-910284-X.
  24. ^ Wells, M. J.; Wells, J. (1969). "Pituitary Analogue in the Octopus". Nature. 222 (5190): 293–294. Bibcode:1969Natur.222..293W. doi:10.1038/222293a0. PMID 5778406. S2CID 4159935.
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