Course of the aorta in the thorax (anterior view), starting posterior to themain pulmonary artery, then anterior to the rightpulmonary arteries, thetrachea and theesophagus, then turning posteriorly to course dorsally to these structures.
In anatomical sources, the aorta is usually divided into sections for easier understanding.[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 theheart to 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, travelssuperiorly from the heart, and then makes ahairpin turn known as theaortic arch. Following the aortic arch, the aorta then travelsinferiorly as 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 arteries and a smaller midline vessel, themedian sacral artery.[6]: 18
Theascending aorta begins at the opening of theaortic valve in the left ventricle of the heart. It runs through a commonpericardial sheath with thepulmonary trunk. These two blood vessels twist around each other, causing the aorta to start outposterior to the pulmonary trunk, but end by twisting to its right andanterior side.[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, thelumen has small pockets between thecusps of theaortic valve and the wall of the aorta, which are called theaortic sinuses or the sinuses of Valsalva. The left aortic sinus contains the origin of theleft coronary artery and the right aortic sinus likewise gives rise to theright coronary artery. Together, these two arteries supply the heart. Theposterior 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.[7]: 191
Theaortic arch loops over the leftpulmonary artery and the bifurcation of thepulmonary trunk, to which it remains connected by theligamentum arteriosum, a remnant of thefetal circulation that 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 plexus oraortic plexus. The leftvagus nerve, which passesanterior to 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 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 arches start 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 artery and 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 septum that 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.
A pig's aorta cut open, also showing some branching arteries.
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 containsbaroreceptors andchemoreceptors that relay information concerning blood pressure and blood pH and carbon dioxide levels to themedulla oblongata of the brain. This information along with information from baroreceptors and chemoreceptors located elsewhere is processed by the brain and theautonomic 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 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.
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 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 artery may arise from the aorta, instead of the leftcommon carotid artery.[9]: 188
Major aorta anatomy displaying ascending aorta, brachiocephalic trunk, left common carotid artery, left subclavian artery, aortic isthmus, aortic arch, and descending thoracic aorta
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.
The 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 notch displayed in the aortic pressure curve during thecardiac cycle as 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 wavevelocity are 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 asVmax or 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 effect of 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.
Central aortic blood pressure has 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]
Allamniotes have 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 aorta carries 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 aorta carries oxygenated blood from the gills to the rest of the body and ishomologous with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills.Amphibians also retain the fifth connecting vessel, so that the aorta has two parallel arches.[24]
The wordaorta stems from theLate Latinaorta fromClassical Greekaortē (ἀορτή), fromaeirō, "I lift, raise" (ἀείρω)[25] This term was first applied byAristotle when 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]
^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.
^Hole, John W. Jr.; Koos, Karen A. (1994).Human Anatomy (Second ed.). Wm. C. Brown. p. 479.ISBN978-0-697-12252-0.
^De Graaff, Van (1998).Human Anatomy (Fifth ed.). WCB McGraw-Hill. pp. 548–549.ISBN978-0-697-28413-6.
^Putz, R.; Pabst, R., eds. (2006).Atlas van de menselijke anatomie (Translated from German (Atlas der Anatomie des Menschen)) (in Dutch) (3rd ed.). Bohn Stafleu van Loghum.ISBN978-90-313-4712-4.
^abcDrake, Richard L.; Vogl, Wayn A.; Mitchell, Adam W. M. (2010).Gray's Anatomy for Students (2nd ed.). Churchill Livingstone (Elsevier).ISBN978-0-443-06952-9.
^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.
^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
^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.
^Romer, Alfred Sherwood; Parsons, Thomas S. (1977).The Vertebrate Body. Philadelphia, PA: Holt-Saunders International. pp. 419–421.ISBN978-0-03-910284-5.
^Harper, Douglas."Aorta".Online Etymology Dictionary. Retrieved5 January 2014.
^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.ISBN978-0-88125-506-5.
