Editing Adrenal gland (section)

==Structure==
[[File:Adrenal glands.jpg|thumb|Adrenal glands, anterior (left) and posterior (right) surface]]
The adrenal glands are located on both sides of the body in the [[retroperitoneum]], above and slightly [[Anatomical terms of location#Medial and lateral|medial]] to the [[kidney]]s. In humans, the right adrenal gland is pyramidal in shape, whereas the left is semilunar or crescent shaped and somewhat larger.<ref name=Thomas2013 /> The adrenal glands measure approximately 5&nbsp;cm in length, 3&nbsp;cm in width, and up to 1&nbsp;cm in thickness.<ref>{{cite journal|url=http://www.medscape.com/viewarticle/543510_2|title=CT and MRI of Adrenal Masses|author=Antonio Carlos A. Westphalen and Bonnie N. Joe|journal=Appl Radiol|year=2006|volume=35|issue=8|pages=10–26}}</ref> Their combined  weight in an adult human ranges from 7 to 10 grams.<ref>{{cite book|last1=O'Hare|first1=A. Munro Neville, Michael J.|title=The Human Adrenal Cortex Pathology and Biology – An Integrated Approach|date=1982|publisher=Springer London|isbn=9781447113171|pages=Chapter 4: Structure of the adult cortex}}</ref> The glands are yellowish in colour.<ref name=Thomas2013>{{cite book|editor=Thomas, Paul|title=Endocrine Gland Development and Disease|date=2013|publisher=Elsevier Science|location=Burlington|isbn=9780123914545|pages=241}}</ref>

The adrenal glands are surrounded by a [[adipose capsule of kidney|fatty capsule]] and lie within the [[renal fascia]], which also surrounds the kidneys. A weak [[septum]] (wall) of [[connective tissue]] separates the glands from the kidneys.<ref name=Moore>{{cite book |vauthors=Moore KL, Dalley AF, Agur AM |date=2013 |title=Clinically Oriented Anatomy, 7th ed. |publisher=Lippincott Williams & Wilkins |pages=294, 298|isbn=978-1-4511-8447-1 }}</ref> The adrenal glands are directly below the [[thoracic diaphragm|diaphragm]], and are attached to the [[crura of the diaphragm]] by the renal fascia.<ref name=Moore />

Each adrenal gland has two distinct parts, each with a unique function, the outer [[adrenal cortex]] and the inner [[adrenal medulla|medulla]], both of which produce hormones.<ref name=Kay2015>{{cite web|last1=Kay|first1=Saundra|title=Adrenal Glands|url=http://emedicine.medscape.com/article/940347-overview|website=Medscape|access-date=1 August 2015}}</ref>

===Adrenal cortex===
{{Main|Adrenal cortex}}
[[File:Adrenal cortex labelled.jpg|thumb|right|Section of human adrenal gland [[histology|under the microscope]], showing its different layers. From the surface to the center: zona glomerulosa, zona fasciculata, zona reticularis, medulla. In the medulla, the central adrenomedullary vein is visible.]]
The adrenal cortex is the outer region and also the largest part of an adrenal gland. It is divided into three separate zones: zona glomerulosa, zona fasciculata and zona reticularis. Each zone is responsible for producing specific hormones.
The adrenal cortex is the outermost layer of the adrenal gland. Within the cortex are three layers, called "zones". When [[Histology|viewed under a microscope]] each layer has a distinct appearance, and each has a different function.<ref name="whitehead">{{cite book |author1=Whitehead, Saffron A. |author2=Nussey, Stephen |title=Endocrinology: an integrated approach |publisher=BIOS |location=Oxford |year=2001 |pages=122 |isbn=978-1-85996-252-7 }}</ref> The [[adrenal cortex]] is devoted to production of [[hormone]]s, namely [[aldosterone]], [[cortisol]], and [[androgen]]s.<ref name="safeuses">{{cite book |author=Jefferies, William McK |title=Safe uses of cortisol |publisher=Charles C. Thomas |location=Springfield, Ill |year=2004 |isbn=978-0-398-07500-2 }}</ref>

====Zona glomerulosa====
The outermost zone of the adrenal cortex is the [[zona glomerulosa]]. It lies immediately under the fibrous capsule of the gland. Cells in this layer form oval groups, separated by [[trabeculae|thin strands]] of connective tissue from the fibrous capsule of the gland and carry wide [[capillary|capillaries]].<ref name="wheater">{{cite book | title=Wheater's Functional Histology: A Text and Colour Atlas | publisher=Elsevier |vauthors=Young B, Woodford P, O'Dowd G | year=2013 | isbn=978-0702047473 | page=329 | edition=6th}}</ref>

This layer is the main site for production of [[aldosterone]], a [[mineralocorticoid]], by the action of the enzyme [[aldosterone synthase]].<ref name="pmid1775135">{{cite journal |vauthors=Curnow KM, Tusie-Luna MT, Pascoe L, Natarajan R, Gu JL, Nadler JL, White PC |title=The product of the CYP11B2 gene is required for aldosterone biosynthesis in the human adrenal cortex. |journal=Mol. Endocrinol. |volume=5 |issue=10 |pages=1513–1522 |date=October 1991 |pmid=1775135 |doi= 10.1210/mend-5-10-1513 |url=https://academic.oup.com/mend/article-pdf/5/10/1513/10490358/mend1513.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://academic.oup.com/mend/article-pdf/5/10/1513/10490358/mend1513.pdf |archive-date=2022-10-09 |url-status=live |doi-access=free }}</ref><ref name="pmid8333830">{{cite journal |vauthors=Zhou M, Gomez-Sanchez CE |title=Cloning and expression of a rat cytochrome P-450 11 beta-hydroxylase/aldosterone synthase (CYP11B2) cDNA variant. |journal=Biochem Biophys Res Commun |volume=194 |issue=1 |pages=112–117 |date=July 1993 |pmid=8333830 |doi= 10.1006/bbrc.1993.1792 }}</ref> Aldosterone plays an important role in the long-term [[regulation of blood pressure]].<ref name=marieb>{{cite book|last1=Marieb|first1=EN|last2=Hoehn|first2=K|title=Human anatomy & physiology|date=2012|publisher=Pearson|isbn=978-0321743268|pages=629|edition=9th}}</ref>

====Zona fasciculata====
The [[zona fasciculata]] is situated between the zona glomerulosa and zona reticularis. Cells in this layer are responsible for producing [[glucocorticoid]]s such as [[cortisol]].<ref name=Kaplan.Physio>{{cite book|title=Kaplan USMLE Step 1 Physiology Lecture Notes|year=2011|author=Dunn R. B.|author2=Kudrath W.|author3=Passo S.S.|author4=Wilson L.B.|pages=263–289|chapter=10}}</ref> It is the largest of the three layers, accounting for nearly 80% of the volume of the cortex.<ref name="ross">{{cite book | title=Histology: A Text and Atlas | url=https://archive.org/details/histologytextatl00ross | url-access=limited | publisher=Lippincott Williams & Wilkins |vauthors=Ross M, Pawlina W | year=2011 | isbn=978-0-7817-7200-6 | pages=[https://archive.org/details/histologytextatl00ross/page/n727 708], 780| edition=6th}}</ref> In the zona fasciculata, cells are arranged in columns radially oriented towards the medulla. Cells contain numerous lipid droplets, abundant [[Mitochondrion|mitochondria]] and a complex [[endoplasmic reticulum#smooth endoplasmic reticulum|smooth endoplasmic reticulum]].<ref name="wheater" />

====Zona reticularis====
The innermost cortical layer, the [[zona reticularis]], lies directly adjacent to the medulla. It produces [[androgen]]s, mainly [[dehydroepiandrosterone]] (DHEA), [[DHEA sulfate]] (DHEA-S), and [[androstenedione]] (the precursor to [[testosterone]]) in humans.<ref name=Kaplan.Physio /> Its small cells form irregular cords and clusters, separated by capillaries and connective tissue. The cells contain relatively small quantities of cytoplasm and lipid droplets, and sometimes display brown [[lipofuscin]] pigment.<ref name="wheater" />

===Medulla===
{{Main|Adrenal medulla}}
The [[adrenal medulla]] is at the center of each adrenal gland, and is surrounded by the adrenal cortex. The [[chromaffin cell]]s of the medulla are the body's main source of the [[catecholamine]]s, such as adrenaline and noradrenaline, released by the medulla. Approximately 20% noradrenaline (norepinephrine) and 80% adrenaline (epinephrine) are secreted here.<ref name=Kaplan.Physio />

The adrenal medulla is driven by the [[sympathetic nervous system]] via [[preganglionic fiber]]s originating in the [[thoracic spinal cord]], from vertebrae T5–T11.<ref name="essentialneuroscience">{{cite book |author1=Sapru, Hreday N. |author2=Siegel, Allan |title=Essential Neuroscience |publisher=Lippincott Williams & Wilkins |location=Hagerstown, MD |year=2007 |isbn=978-0-7817-9121-2 |url-access=registration |url=https://archive.org/details/essentialneurosc0000sieg }}</ref> Because it is innervated by [[preganglionic nerve fibers]], the adrenal medulla can be considered as a specialized [[sympathetic ganglion]].<ref name="essentialneuroscience"/> Unlike other sympathetic ganglia, however, the adrenal medulla lacks distinct synapses and releases its secretions directly into the blood.

===Blood supply===
The adrenal glands have one of the greatest blood supply rates per gram of tissue of any organ: up to 60 [[arteriole|small arteries]] may enter each gland.<ref name="isbn960-399-074-4">{{cite book |vauthors=Mirilas P, Skandalakis JE, Colborn GL, Weidman TA, Foster RS, Kingsnorth A, Skandalakis LJ, Skandalakis PN |title=Surgical Anatomy: The Embryologic And Anatomic Basis Of Modern Surgery |publisher=McGraw-Hill Professional Publishing |year=2004 |isbn=978-960-399-074-1 }}</ref> Three arteries usually supply each adrenal gland:<ref name=Thomas2013 />
* The [[superior suprarenal artery]], a branch of the [[inferior phrenic arteries|inferior phrenic artery]]
* The [[middle suprarenal artery]], a direct branch of the [[abdominal aorta]]
* The [[inferior suprarenal artery]], a branch of the [[renal artery]]
These blood vessels supply a network of small arteries within the capsule of the adrenal glands. Thin strands of the capsule enter the glands, carrying blood to them.<ref name=Thomas2013 />

[[Vein|Venous blood]] is drained from the glands by the [[suprarenal veins]], usually one for each gland:<ref name=Thomas2013 />
* The [[right suprarenal vein]] drains into the [[inferior vena cava]].
* The [[left suprarenal vein]] drains into the left [[renal vein]] or the left [[inferior phrenic vein]].

The central adrenomedullary vein, in the adrenal medulla, is an unusual type of blood vessel. Its structure is different from the other veins in that the [[smooth muscle]] in its [[tunica media]] (the middle layer of the vessel) is arranged in conspicuous, longitudinally oriented bundles.<ref name=ross />

===Variability===
The adrenal glands may not develop at all, or may be fused in the midline behind the [[aorta]].<ref name=Kay2015 /> These are associated with other [[congenital abnormality|congenital abnormalities]], such as failure of the kidneys to develop, or fused kidneys.<ref name=Kay2015 /> The gland may develop with a partial or complete absence of the cortex, or may develop in an unusual location.<ref name=Kay2015 />