Theaorta(/eɪˈɔːrtə/ay-OR-tə;pl.:aortasoraortae) is the main and largestarteryin the human body, originating from theleft ventricleof theheart,branching upwards immediately after, and extending down to theabdomen,where it splits at theaortic bifurcationinto two smaller arteries (thecommon iliac arteries). The aorta distributesoxygenatedblood to all parts of the body through thesystemic circulation.[1]
Structure
editSections
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In anatomical sources, the aorta is usually divided into sections.[2][3][4][5]
One way of classifying a part of the aorta is by anatomical compartment, where thethoracic aorta(or thoracic portion of the aorta) runs from theheartto thediaphragm.The aorta then continues downward as theabdominal aorta(or abdominal portion of the aorta) from the diaphragm to theaortic bifurcation.
Another system divides the aorta with respect to its course and the direction of blood flow. In this system, the aorta starts as theascending aorta,travelssuperiorlyfrom the heart, and then makes ahairpin turnknown as theaortic arch.Following the aortic arch, the aorta then travelsinferiorlyas thedescending aorta.The descending aorta has two parts. The aorta begins to descend in the thoracic cavity and is consequently known as thethoracic aorta.After the aorta passes through thediaphragm,it is known as theabdominal aorta.The aorta ends by dividing into two major blood vessels, thecommon iliac arteriesand a smaller midline vessel, themedian sacral artery.[6]: 18
Ascending aorta
editTheascending aortabegins at the opening of theaortic valvein the left ventricle of the heart. It runs through a commonpericardial sheathwith thepulmonary trunk.These two blood vessels twist around each other, causing the aorta to start outposteriorto the pulmonary trunk, but end by twisting to its right andanteriorside.[7]: 191, 204 The transition from ascending aorta to aortic arch is at the pericardial reflection on the aorta.[8]: Plate 211
At the root of the ascending aorta, thelumenhas small pockets between thecuspsof theaortic valveand the wall of the aorta, which are called theaortic sinusesor the sinuses of Valsalva. The left aortic sinus contains the origin of theleft coronary arteryand the right aortic sinus likewise gives rise to theright coronary artery.Together, these two arteries supply the heart. Theposterioraortic 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.[7]: 191
Aortic arch
editTheaortic archloops over the leftpulmonary arteryand the bifurcation of thepulmonary trunk,to which it remains connected by theligamentum arteriosum,a remnant of thefetal circulationthat is obliterated a few days after birth. In addition to these blood vessels, the aortic arch crosses theleft main bronchus.Between the aortic arch and the pulmonary trunk is a network of autonomic nerve fibers, thecardiac plexusoraortic plexus.The leftvagus nerve,which passesanteriorto the aortic arch, gives off a major branch, therecurrent 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: fromproximaltodistal,they are thebrachiocephalic trunk,theleft common carotid artery,and the leftsubclavian artery.The brachiocephalic trunk supplies the right side of the head and neck as well as the right arm andchest 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 theintervertebral discbetween the fourth and fifththoracic vertebrae.[7]: 209
Thoracic aorta
editThethoracic aortagives rise to theintercostalandsubcostalarteries, as well as to the superior and inferiorleft bronchial arteriesand variable branches to theesophagus,mediastinum,andpericardium.Its lowest pair of branches are the superior phrenic arteries, which supply the diaphragm, and the subcostal arteries for the twelfth rib.[9]: 195
Abdominal aorta
editTheabdominal aortabegins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebra.[10]It gives rise tolumbarand musculophrenic arteries,renalandmiddle suprarenal arteries,and visceral arteries (theceliac trunk,thesuperior mesenteric arteryand theinferior mesenteric artery). It ends in a bifurcation into theleft and right common iliac arteries.At the point of the bifurcation, there also springs a smaller branch, themedian sacral artery.[9]: 331
Development
editThe ascending aorta develops from the outflow tract, which initially starts as a single tube connecting the heart with theaortic arches(which will form the great arteries) in early development but is then separated into the aorta and the pulmonary trunk.
Theaortic archesstart as five pairs of symmetrical arteries connecting the heart with thedorsal aorta,and then undergo a significant remodelling[11]to form the final asymmetrical structure of thegreat arteries,with the 3rd pair of arteries contributing to thecommon carotids,the right 4th forming the base and middle part of the rightsubclavian arteryand the left 4th being the central part of theaortic arch.The smooth muscle of the great arteries and the population of cells that form theaorticopulmonary septumthat separates the aorta and pulmonary artery is derived fromcardiac neural crest.This contribution of the neural crest to the great artery smooth muscle is unusual as most smooth muscle is derived frommesoderm.In fact the smooth muscle within the abdominal aorta is derived from mesoderm, and the coronary arteries, which arise just above thesemilunar valves,possess smooth muscle of mesodermal origin. A failure of the aorticopulmonary septum to divide the great vessels results inpersistent truncus arteriosus.
Microanatomy
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The aorta is anelastic artery,and as such is quite distensible. The aorta consists of a heterogeneous mixture ofsmooth muscle,nerves, intimal cells, endothelial cells, immune cells, fibroblast-like cells, and a complex extracellular matrix.[12]The vascular wall is subdivided into three layers known as thetunica externa,tunica media,andtunica intima.The aorta is covered by an extensive network of tiny blood vessels calledvasa vasorum,which feed the tunica externa and tunica media, the outer layers of the aorta.[13]The aortic arch containsbaroreceptorsandchemoreceptorsthat relay information concerning blood pressure and blood pH and carbon dioxide levels to themedulla oblongataof the brain. This information along with information from baroreceptors and chemoreceptors located elsewhere is processed by the brain and theautonomic nervous systemmediates 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 ofelastic fibers,collagens(predominately type III),proteoglycans,andglycoaminoglycans.[14]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,[15]but rather serves to increase the stiffness and viscoelasticity of the aortic wall when activated.
Variation
editVariations 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 indextrocardia,in which the heart is found on the right, orsitus inversus,in which the location of all organs are flipped.[9]: 188
Variations in the branching of individual arteries may also occur. For example, the leftvertebral arterymay arise from the aorta, instead of the leftcommon carotid artery.[9]: 188
Inpatent ductus arteriosus,a congenital disorder, the fetalductus arteriosusfails to close, leaving an open vessel connecting thepulmonary arteryto the proximaldescending aorta.[16]
Function
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The aorta supplies all of the systemic circulation, which means that the entire body, except for therespiratory zone of the lung,receives its blood from the aorta. Broadly speaking, branches from the ascending aorta supply the heart; branches from the aortic arch supply the head, neck, and arms; branches from the thoracic descending aorta supply the chest (excluding the heart and the respiratory zone of the lung); and branches from the abdominal aorta supply theabdomen.The pelvis and legs get their blood from the common iliac arteries.
Blood flow and velocity
editThe contraction of the heart during systole is responsible for ejection and creates a (pulse) wave that is propagated down the aorta, into thearterial tree.The wave is reflected at sites of impedance mismatching, such asbifurcations,where reflected waves rebound to return to semilunar valves and the origin of the aorta. These return waves create thedicrotic notchdisplayed in the aortic pressure curve during thecardiac cycleas these reflected waves push on theaortic semilunar valve.[17]With age, the aorta stiffens such that the pulse wave is propagated faster and reflected waves return to the heart faster before the semilunar valve closes, which raises the blood pressure. The stiffness of the aorta is associated with a number of diseases and pathologies, and noninvasive measures of the pulse wavevelocityare an independent indicator ofhypertension.Measuring the pulse wave velocity (invasively and non-invasively) is a means of determiningarterial stiffness.Maximum aortic velocity may be noted asVmaxor less commonly asAoVmax.
Mean arterial pressure(MAP) is highest in the aorta, and the MAP decreases across the circulation from aorta to arteries to arterioles to capillaries to veins back to atrium. The difference between aortic and right atrial pressure accounts for blood flow in the circulation.[18]When the left ventricle contracts to force blood into the aorta, the aorta expands. This stretching gives the potential energy that will help maintain blood pressure duringdiastole,as during this time the aorta contracts passively. ThisWindkessel effectof the great elastic arteries has important biomechanical implications. The elastic recoil helps conserve the energy from the pumping heart and smooth out the pulsatile nature created by the heart. Aortic pressure is highest at the aorta and becomes less pulsatile and lower pressure as blood vessels divide into arteries, arterioles, and capillaries such that flow is slow and smooth for gases and nutrient exchange.
Clinical significance
editCentral aortic blood pressurehas frequently been shown to have greater prognostic value and to show a more accurate response to antihypertensive drugs than has peripheral blood pressure.[19][20][21]
- Aortic aneurysm– mycotic, bacterial (e.g.syphilis), senile, genetic, associated withvalvular heart disease
- Aortic coarctation– pre-ductal,post-ductal
- Aortic dissection
- Aortic stenosis
- Abdominal aortic aneurysm
- Aortitis,inflammation of the aorta that can be seen in trauma, infections, and autoimmune disease
- Atherosclerosis
- Ehlers–Danlos syndrome
- Marfan syndrome
- Trauma,such astraumatic aortic rupture,most often thoracic and distal to the left subclavian artery[22]and often quickly fatal[23]
- Transposition of the great vessels,see alsodextro-Transposition of the great arteriesandlevo-Transposition of the great arteries
Other animals
editAllamnioteshave a broadly similar arrangement to that of humans, albeit with a number of individual variations. Infish,however, there are two separate vessels referred to as aortas. Theventral aortacarries de-oxygenated blood from the heart to thegills;part of this vessel forms the ascending aorta in tetrapods (the remainder forms thepulmonary artery). A second,dorsal aortacarries oxygenated blood from the gills to the rest of the body and ishomologouswith the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills. Amphibiansalso retain the fifth connecting vessel, so that the aorta has two parallel arches.[24]
History
editThe wordaortastems from theLate LatinaortafromClassical Greekaortē(ἀορτή), fromaeirō,"I lift, raise" (ἀείρω)[25]This term was first applied byAristotlewhen describing the aorta and describes accurately how it seems to be "suspended" above the heart.[26]
The function of the aorta is documented in theTalmud,where it is noted as one of three major vessels entering or leaving the heart, and where perforation is linked to death.[27]
References
edit- ^Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1995).Human Biology Health.Englewood Cliffs, New Jersey: Prentice Hall.ISBN978-0-13-981176-0.
- ^Tortora, Gerard J. (1995).Principles of Human Anatomy(Seventh ed.). Harper Collins. pp. 341, 367, 369.ISBN978-0-673-99075-4.
- ^Tortora, Gerard J.; Grabowski, Sandra Reynolds (1996).Principles of Anatomy and Physiology(Eighth ed.). Harper Collins. p. 634.ISBN978-0-673-99355-7.
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- ^abcdDrake, Richard L.; Vogl, Wayne; Tibbitts, Adam W.M. Mitchell; illustrations by Richard; Richardson, Paul (2005).Gray's anatomy for students.Philadelphia: Elsevier/Churchill Livingstone.ISBN978-0-8089-2306-0.
- ^Lech, C; Swaminathan, A (November 2017). "Abdominal Aortic Emergencies".Emergency Medicine Clinics of North America.35(4): 847–67.doi:10.1016/j.emc.2017.07.003.PMID28987432.
- ^Bamforth, Simon D.; Chaudhry, Bill; Bennett, Michael; Wilson, Robert; Mohun, Timothy J.; Van Mierop, Lodewyk H.S.; Henderson, Deborah J.; Anderson, Robert H. (2013-03-01)."Clarification of the identity of the mammalian fifth pharyngeal arch artery".Clinical Anatomy.26(2): 173–182.doi:10.1002/ca.22101.ISSN1098-2353.PMID22623372.S2CID7927804.
- ^Scipione, Corey A.; Hyduk, Sharon J.; Polenz, Chanele K.; Cybulsky, Myron I. (December 2023)."Unveiling the Hidden Landscape of Arterial Diseases at Single-Cell Resolution".Canadian Journal of Cardiology.39(12): 1781–1794.doi:10.1016/j.cjca.2023.09.009.
- ^Ritman, E; Lerman, A (2007)."The dynamic vasa vasorum".Cardiovascular Research.75(4): 649–658.doi:10.1016/j.cardiores.2007.06.020.ISSN0008-6363.PMC2121590.PMID17631284.
- ^Tsamis, A.; Krawiec, J. T.; Vorp, D. A. (2013)."Elastin and collagen fibre microstructure of the human aorta in ageing and disease: a review".Journal of the Royal Society Interface.10(83): 20121004.doi:10.1098/rsif.2012.1004.ISSN1742-5689.PMC3645409.PMID23536538.
- ^Leloup, Arthur J. A.; Van Hove, Cor E.; De Moudt, Sofie; De Meyer, Guido R. Y.; De Keulenaer, Gilles W.; Fransen, Paul (February 2019)."Vascular smooth muscle cell contraction and relaxation in the isolated aorta: a critical regulator of large artery compliance".Physiological Reports.7(4): e13934.doi:10.14814/phy2.13934.ISSN2051-817X.PMC6391714.PMID30810292.
- ^MedlinePlus > Patent ductus arteriosusUpdate Date: 21 December 2009
- ^Seeley, Rod; Stephens, Trent; Philip Tate (1992)."20".In Allen, Deborah (ed.).Anatomy and physiology(2 ed.). Mosby-Year Book, Inc. p.631.ISBN978-0-8016-4832-8.
- ^Nichols WW, O'Rourke MF. McDonald's Blood Flow in Arteries: Theoretical, Experimental and Clinical Principles. 4th ed. London, UK: Edward Arnold; 1998
- ^McEniery, Carmel M.; Cockcroft, John R.; Roman, Mary J.; Franklin, Stanley S.; Wilkinson, Ian B. (23 Jan 2014)."Central blood pressure: current evidence and clinical importance".European Heart Journal.35(26). Oxford University Press (OUP): 1719–1725.doi:10.1093/eurheartj/eht565.ISSN1522-9645.PMC4155427.
- ^Kesten, Steven; Qasem, Ahmad; Avolio, Alberto (2022-10-20)."Viewpoint: The Case for Non-Invasive Central Aortic Pressure Monitoring in the Management of Hypertension".Artery Research.28(4): 128–139.doi:10.1007/s44200-022-00023-z.ISSN1876-4401.
- ^Middeke, Martin (2017). "Zentraler aortaler Blutdruck: Bedeutender Parameter für Diagnostik und Therapie".Deutsche Medizinische Wochenschrift(in German).142(19). Georg Thieme Verlag KG: 1430–1436.doi:10.1055/s-0043-113212.ISSN0012-0472.
- ^Samett EJ. http:// emedicine /radio/topic44.htm Aorta, Trauma.eMedicine. Accessed on: April 24, 2007.
- ^Tambyraja, A; Scollay, JM; Beard, D; Henry, JM; Murie, JA; Chalmers, RT (2006)."Aortic Trauma in Scotland - A Population Based Study".European Journal of Vascular and Endovascular Surgery.32(6): 686–689.doi:10.1016/j.ejvs.2006.04.006.PMID16750920.
- ^Romer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body.Philadelphia, PA: Holt-Saunders International. pp. 419–421.ISBN978-0-03-910284-5.
- ^Illustrated Steadman's Dictionary, 24th ed.
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- ^Rosner, Fred (1995).Medicine in the Bible and the Talmud: Selections from classical Jewish sources(Augm. ed.). Hoboken, NJ: KTAV Pub. House. pp. 87–96.ISBN9780881255065.
