Editing Anterior pituitary (section)

==Structure==
[[File:1808 The Anterior Pituitary Complex.jpg|thumb|right|200px|The anterior pituitary complex]]
The [[pituitary gland]] sits in a protective bony enclosure called the [[sella turcica]] (''Turkish chair/saddle''). It is composed of three lobes: the anterior, intermediate, and posterior lobes. In many animals, these 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 [[pars nervosa]] of the [[posterior pituitary]].{{cn|date=May 2022}}

The anterior pituitary is composed of three regions, the pars distalis, pars tuberalis, and pars intermedia.
===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 [[chromophobe cell]]s and [[chromophil|chromophil cells]].<ref name=":0">{{Cite book|title = DiFiore's Atlas of Histology with Functional Correlations|url = https://books.google.com/books?id=sH87M12QswcC|publisher = Lippincott Williams & Wilkins|date = 2013-01-01|isbn = 9781451113419|language = en|first1 = Victor P.|last1 = Eroschenko|first2 = Mariano S. H. di|last2 = Fiore}}</ref> The chromophils can be further divided into [[acidophils]] (alpha cells) and [[basophil cell|basophils]] (beta cells).<ref name=":0" /> These cells all together produce hormones of the anterior pituitary and release them into the blood stream.{{cn|date=May 2022}}

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.
<gallery mode=packed heights=180>
File:Histology of pars distalis of the anterior pituitary with chromophobes, basophils, and acidophils, annotated.jpg|Microanatomy of the pars distalis showing chromophobes, basophils, and acidophils
File:Histology of anterior pituitary eosinophilic follicles.jpg|Eosinophilic follicles are a common normal finding in the anterior pituitary.
</gallery>

===Pars tuberalis===
The pars tuberalis (tubular part) forms a part of a highly vascularised sheath extending up from the pars distalis, which joins with the [[pituitary stalk]] (also known as the infundibular stalk or '''infundibulum'''), arising from the posterior lobe. (The pituitary stalk connects the hypothalamus to the posterior pituitary.) The function of the pars tuberalis is poorly understood. However, it has been seen to be important in receiving the endocrine signal in the form of [[TSHB]] (a  β subunit of TSH), informing the pars tuberalis of 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]].<ref>{{cite journal | last1 = Ikegami | first1 = K | last2 = Iigo | first2 = M | last3 = Yoshimura | first3 = T | year = 2013 | title = Circadian clock gene Per2 is not necessary for the photoperiodic response in mice | journal = PLOS ONE | volume =  8| issue = 3| page =  e58482| pmid = 23505514 | doi = 10.1371/journal.pone.0058482 | pmc = 3591342 | bibcode = 2013PLoSO...858482I | doi-access = free }}</ref><ref>{{cite journal | last1 = Dardente | first1 = H | year = 2012 | title = Melatonin-dependent timing of seasonal reproduction by the pars tuberalis: pivotal roles for long daylengths and thyroid hormones | journal = Journal of Neuroendocrinology | volume = 24 | issue = 2 | pages = 249–66 | doi = 10.1111/j.1365-2826.2011.02250.x | pmid = 22070540 | s2cid = 12723490 }}</ref> Earlier studies have shown localization of melatonin receptors in this region.<ref>{{cite journal | last1 = Morgan | first1 = PJ | last2 = Williams | first2 = LM | year = 1996 | title = The pars tuberalis of the pituitary: a gateway for neuroendocrine output | journal = Reviews of Reproduction | volume =  1| issue = 3| pages =  153–61| pmid = 9414453 | doi = 10.1530/ror.0.0010153 }}</ref>

Principal cells of the pars tuberalis are low columnar in form, with the cytoplasm containing numerous lipid droplets, glycogen granules, and occasional colloid droplets. A sparse population of functional gonadotrophs are present (indicated by immunoreactivity for [[ACTH]], [[Follicle-stimulating hormone|FSH]], and [[Lutenizing Hormone|LH]]).<ref>Ross, Michael. Histology: A Text and Atlas. 5th ed., 2006. pp 695</ref>

===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 [[ectoderm]], more specifically from that of [[Rathke's pouch]], part of the developing [[hard palate]] in the embryo. Rathke's pouch is also [[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]].<ref name="Nelson, R. J. 2011">Nelson, R. J. (2011) An Introduction to Behavioral Endocrinology, 4th Edition. Sunderland, MA: Sinauer Associates, Inc.{{ISBN|978-0878936205}}</ref>