Editing Aorta (section)

==Structure==

===Sections===
[[File:Relations of the aorta, trachea, esophagus and other heart structures.svg|thumb|250x250px|Course of the aorta in the thorax (anterior view), starting posterior to the [[main pulmonary artery]], then anterior to the right [[Pulmonary artery|pulmonary arteries]], the [[human trachea|trachea]] and the [[esophagus]], then turning posteriorly to course dorsally to these structures.]]
In anatomical sources, the aorta is usually divided into sections.<ref>{{cite book |last=Tortora |first=Gerard J. |title=Principles of Human Anatomy |edition=Seventh |pages=341, 367, 369 |publisher=Harper Collins |year=1995 |isbn=978-0-673-99075-4}}</ref><ref>{{cite book |last1=Tortora |first1=Gerard J. |first2=Sandra Reynolds |last2=Grabowski |title=Principles of Anatomy and Physiology |edition=Eighth |page=634 |publisher=Harper Collins |year=1996 |isbn=978-0-673-99355-7}}</ref><ref>{{cite book |last1=Hole |first1=John W. Jr. |first2=Karen A. |last2=Koos |title=Human Anatomy |edition=Second |page=479 |publisher=Wm. C. Brown |year=1994 |isbn=978-0-697-12252-0}}</ref><ref>{{cite book |last=De Graaff |first=Van |title=Human Anatomy |edition=Fifth |pages=548–549 |publisher=WCB McGraw-Hill |year=1998 |isbn=978-0-697-28413-6}}</ref>

One way of classifying a part of the aorta is by anatomical compartment, where the [[thoracic aorta]] (or thoracic portion of the aorta) runs from the [[heart]] to the [[thoracic diaphragm|diaphragm]]. The aorta then continues downward as the [[abdominal aorta]] (or abdominal portion of the aorta) from the diaphragm to the [[aortic bifurcation]].

Another system divides the aorta with respect to its course and the direction of blood flow. In this system, the aorta starts as the [[ascending aorta]], travels [[Anatomical terms of location#Superior and inferior|superiorly]] from the heart, and then makes a [[hairpin turn]] known as the [[aortic arch]]. Following the aortic arch, the aorta then travels [[Anatomical terms of location#Superior and inferior|inferiorly]] as the [[descending aorta]]. The descending aorta has two parts. The aorta begins to descend in the thoracic cavity and is consequently known as the [[thoracic aorta]]. After the aorta passes through the [[Thoracic diaphragm|diaphragm]], it is known as the [[abdominal aorta]]. The aorta ends by dividing into two major blood vessels, the [[common iliac artery|common iliac arteries]] and a smaller midline vessel, the [[median sacral artery]].<ref name="Sobotta">{{cite book|editor1-last=Putz|editor1-first=R.|editor2-last=Pabst|editor2-first=R.|title=Atlas van de menselijke anatomie
|language=nl
|type=Translated from German (Atlas der Anatomie des Menschen)|edition=3rd|year=2006|publisher=Bohn Stafleu van Loghum|isbn=978-90-313-4712-4}}</ref>{{rp|18}}

====Ascending aorta====
{{Main|Ascending aorta}}
The [[ascending aorta]] begins at the opening of the [[aortic valve]] in the left ventricle of the heart. It runs through a common [[pericardium|pericardial sheath]] with the [[pulmonary trunk]]. These two blood vessels twist around each other, causing the aorta to start out [[posterior (anatomy)|posterior]] to the pulmonary trunk, but end by twisting to its right and [[anterior]] side.<ref name="Gray's Anatomy for Students">{{cite book|last1=Drake|first1=Richard L.|last2=Vogl|first2=Wayn A.|last3=Mitchell|first3=Adam W. M.|title=Gray's Anatomy for Students|edition=2nd|year=2010|publisher=Churchill Livingstone (Elsevier)|isbn=978-0-443-06952-9}}</ref>{{rp|191,204}}
The transition from ascending aorta to aortic arch is at the pericardial reflection on the aorta.<ref name="Netter">{{cite book|last=Netter|first=Frank H.|title=Atlas of Human Anatomy|url=https://archive.org/details/atlasofhumananat00nett_0|url-access=registration|edition=3rd|year=2003|publisher=ICON Learning Systems|isbn=978-1-929007-21-9}}</ref>{{rp|Plate 211}}

At the root of the ascending aorta, the [[lumen (anatomy)|lumen]] has  small pockets between the [[cusps of heart valves|cusps]] of the [[aortic valve]] and the wall of the aorta, which are called the [[aortic sinus]]es or the sinuses of Valsalva. The left aortic sinus contains the origin of the [[left coronary artery]] and the right aortic sinus likewise gives rise to the [[right coronary artery]]. Together, these two arteries supply the heart. The [[posterior (anatomy)|posterior]] aortic sinus does not give rise to a coronary artery. For this reason the left, right and posterior aortic sinuses are also called left-coronary, right-coronary and non-coronary sinuses.<ref name="Gray's Anatomy for Students"/>{{rp|191}}

====Aortic arch====
{{main|Aortic arch}}
The [[aortic arch]] loops over the left [[pulmonary artery]] and the bifurcation of the [[pulmonary trunk]], to which it remains connected by the [[ligamentum arteriosum]], a remnant of the [[fetal circulation]] that is obliterated a few days after birth. In addition to these blood vessels, the aortic arch crosses the [[left main bronchus]]. Between the aortic arch and the pulmonary trunk is a network of autonomic nerve fibers, the [[cardiac plexus]] or ''aortic plexus''. The left [[vagus nerve]], which passes [[anterior]] to the aortic arch, gives off a major branch, the [[recurrent laryngeal nerve]], which loops under the aortic arch just lateral to the ligamentum arteriosum. It then runs back to the neck.

The aortic arch has three major branches: from [[Anatomical terms of location#Proximal and distal|proximal]] to [[Anatomical terms of location#Proximal and distal|distal]], they are the [[brachiocephalic trunk]], the [[common carotid artery|left common carotid artery]], and the left [[subclavian artery]]. The brachiocephalic trunk supplies the right side of the head and neck as well as the right arm and [[chest wall]], while the latter two together supply the left side of the same regions.

The aortic arch ends, and the descending aorta begins at the level of the [[intervertebral disc]] between the fourth and fifth [[thoracic vertebrae]].<ref name="Gray's Anatomy for Students"/>{{rp|209}}

====Thoracic aorta====
{{Main|Thoracic aorta}}
The [[thoracic aorta]] gives rise to the [[intercostal artery|intercostal]] and [[subcostal artery|subcostal]] arteries, as well as to the superior and inferior [[bronchial artery|left bronchial arteries]] and variable branches to the [[esophagus]], [[mediastinum]], and [[pericardium]]. Its lowest pair of branches are the superior phrenic arteries, which supply the diaphragm, and the subcostal arteries for the twelfth rib.<ref name=GRAYS2005>{{cite book |last=Drake |first=Richard L. |title=Gray's anatomy for students |year=2005 |publisher=Elsevier/Churchill Livingstone |location=Philadelphia |isbn=978-0-8089-2306-0 |author2=Vogl, Wayne |author3=Tibbitts, Adam W.M. Mitchell |author4=illustrations by Richard |author5=Richardson, Paul}}</ref>{{rp|195}}

====Abdominal aorta====
{{Main|Abdominal aorta}}
The [[abdominal aorta]] begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebra.<ref name="Lech2017">{{cite journal|last1=Lech|first1=C|last2=Swaminathan|first2=A|title=Abdominal Aortic Emergencies|journal=Emergency Medicine Clinics of North America|date=November 2017|volume=35|issue=4|pages=847–67|doi=10.1016/j.emc.2017.07.003|pmid=28987432}}</ref> It gives rise to [[lumbar arteries|lumbar]] and musculophrenic arteries, [[renal artery|renal]] and [[middle suprarenal artery|middle suprarenal arteries]], and visceral arteries (the [[celiac trunk]], the [[superior mesenteric artery]] and the [[inferior mesenteric artery]]). It ends in a bifurcation into the [[Common iliac artery|left and right common iliac arteries]]. At the point of the bifurcation, there also springs a smaller branch, the [[median sacral artery]].<ref name=GRAYS2005 />{{rp|331}}

===Development===
The ascending aorta develops from the outflow tract, which initially starts as a single tube connecting the heart with the [[aortic arches]] (which will form the great arteries) in early development but is then separated into the aorta and the pulmonary trunk.

The [[aortic arches]] start as five pairs of symmetrical arteries connecting the heart with the [[dorsal aorta]], and then undergo a significant remodelling<ref>{{Cite journal|last1=Bamforth|first1=Simon D.|last2=Chaudhry|first2=Bill|last3=Bennett|first3=Michael|last4=Wilson|first4=Robert|last5=Mohun|first5=Timothy J.|last6=Van Mierop|first6=Lodewyk H.S.|last7=Henderson|first7=Deborah J.|last8=Anderson|first8=Robert H.|date=2013-03-01|title=Clarification of the identity of the mammalian fifth pharyngeal arch artery|journal=Clinical Anatomy|language=en|volume=26|issue=2|pages=173–182|doi=10.1002/ca.22101|issn=1098-2353|pmid=22623372|s2cid=7927804|url=https://eprint.ncl.ac.uk/fulltext.aspx?url=184287/7AD54A38-B35D-477A-9763-226F0551002C.pdf&pub_id=184287}}</ref> to form the final asymmetrical structure of the [[great arteries]], with the 3rd pair of arteries contributing to the [[Common carotid artery|common carotids]], the right 4th forming the base and middle part of the right [[subclavian artery]] and the left 4th being the central part of the [[aortic arch]]. The smooth muscle of the great arteries and the population of cells that form the [[aorticopulmonary septum]] that separates the aorta and pulmonary artery is derived from [[cardiac neural crest]]. This contribution of the neural crest to the great artery smooth muscle is unusual as most smooth muscle is derived from [[mesoderm]]. In fact the smooth muscle within the abdominal aorta is derived from mesoderm, and the coronary arteries, which arise just above the [[Heart valve|semilunar valves]], possess smooth muscle of mesodermal origin. A failure of the aorticopulmonary septum to divide the great vessels results in [[persistent truncus arteriosus]].

===Microanatomy===
[[File:An opened aorta.jpg|thumb|250px|{{center|A pig's aorta cut open, also showing some branching arteries.}}]]
The aorta is an [[elastic artery]], and as such is quite distensible. The aorta consists of a heterogeneous mixture of [[smooth muscle]], nerves, intimal cells, endothelial cells, immune cells, fibroblast-like cells, and a complex extracellular matrix.<ref>{{Cite journal |last=Scipione |first=Corey A. |last2=Hyduk |first2=Sharon J. |last3=Polenz |first3=Chanele K. |last4=Cybulsky |first4=Myron I. |date=December 2023 |title=Unveiling the Hidden Landscape of Arterial Diseases at Single-Cell Resolution |url=https://linkinghub.elsevier.com/retrieve/pii/S0828282X2301663X |journal=Canadian Journal of Cardiology |language=en |volume=39 |issue=12 |pages=1781–1794 |doi=10.1016/j.cjca.2023.09.009}}</ref> The vascular wall is subdivided into three layers known as the [[tunica externa]], [[tunica media]], and [[tunica intima]]. The aorta is covered by an extensive network of tiny blood vessels called [[vasa vasorum]], which feed the tunica externa and tunica media, the outer layers of the aorta.<ref name="RitmanLerman2007">{{cite journal|last1=Ritman|first1=E|last2=Lerman|first2=A|title=The dynamic vasa vasorum|journal=Cardiovascular Research|volume=75|issue=4|year=2007|pages=649–658|issn=0008-6363|doi=10.1016/j.cardiores.2007.06.020|pmc=2121590|pmid=17631284}}</ref> The aortic arch contains [[baroreceptor]]s and [[chemoreceptor]]s that relay information concerning blood pressure and blood pH and carbon dioxide levels to the [[medulla oblongata]] of the brain. This information along with information from baroreceptors and chemoreceptors located elsewhere is processed by the brain and the [[autonomic nervous system]] mediates appropriate homeostatic responses.

Within the tunica media, smooth muscle and the extracellular matrix are quantitatively the largest components, these are arranged concentrically as musculoelastic layers (the elastic lamella) in mammals. The elastic lamella, which comprise smooth muscle and elastic matrix, can be considered as the fundamental structural unit of the aorta and consist of [[elastic fiber]]s, [[collagen]]s (predominately type III), [[proteoglycan]]s, and [[glycoaminoglycan]]s.<ref name="TsamisKrawiec2013">{{cite journal|last1=Tsamis|first1=A.|last2=Krawiec|first2=J. T.|last3=Vorp|first3=D. A.|title=Elastin and collagen fibre microstructure of the human aorta in ageing and disease: a review|journal=Journal of the Royal Society Interface|volume=10|issue=83|year=2013|pages=20121004|issn=1742-5689|doi=10.1098/rsif.2012.1004|pmid=23536538|pmc=3645409}}</ref> The elastic matrix dominates the biomechanical properties of the aorta. The smooth muscle component, while contractile, does not substantially alter the diameter of the aorta,<ref>{{Cite journal |last1=Leloup |first1=Arthur J. A. |last2=Van Hove |first2=Cor E. |last3=De Moudt |first3=Sofie |last4=De Meyer |first4=Guido R. Y. |last5=De Keulenaer |first5=Gilles W. |last6=Fransen |first6=Paul |date=February 2019 |title=Vascular smooth muscle cell contraction and relaxation in the isolated aorta: a critical regulator of large artery compliance |journal=Physiological Reports |volume=7 |issue=4 |pages=e13934 |doi=10.14814/phy2.13934 |issn=2051-817X |pmc=6391714 |pmid=30810292}}</ref> but rather serves to increase the stiffness and viscoelasticity of the aortic wall when activated.

===Variation===
Variations may occur in the location of the aorta, and the way in which arteries branch off the aorta. The aorta, normally on the left side of the body, may be found on the right in [[dextrocardia]], in which the heart is found on the right, or [[situs inversus]], in which the location of all organs are flipped.<ref name=GRAYS2005 />{{rp|188}}

Variations in the branching of individual arteries may also occur. For example, the left [[vertebral artery]] may arise from the aorta, instead of the left [[common carotid artery]].<ref name=GRAYS2005 />{{rp|188}}

In [[patent ductus arteriosus]], a congenital disorder, the fetal [[ductus arteriosus]] fails to close, leaving an open vessel connecting the [[pulmonary artery]] to the proximal [[descending aorta]].<ref name=medlineplus>[https://www.nlm.nih.gov/medlineplus/ency/article/001560.htm MedlinePlus > Patent ductus arteriosus] Update Date: 21 December 2009</ref>