The aorta ( ; : aortas or aortae) is the main and largest artery in the human body, originating from the left ventricle of the heart, branching upwards immediately after, and extending down to the abdomen, where it splits at the aortic bifurcation into two smaller arteries (the common iliac arteries). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation.
Structure
Sections
In anatomical sources, the aorta is usually divided into sections.
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 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 superiorly from the heart, and then makes a hairpin turn known as the aortic arch. Following the aortic arch, the aorta then travels 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 diaphragm, it is known as the abdominal aorta. The aorta ends by dividing into two major blood vessels, the common iliac arteries and a smaller midline vessel, the median sacral artery.
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 with the
pulmonary trunk. These two blood vessels twist around each other, causing the aorta to start out posterior to the pulmonary trunk, but end by twisting to its right and
anterior side.
The transition from ascending aorta to aortic arch is at the pericardial reflection on the aorta.
At the root of the ascending aorta, the lumen has small pockets between the cusps of the aortic valve and the wall of the aorta, which are called the 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 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.
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 proximal to distal, they are the brachiocephalic trunk, the 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.
Thoracic aorta
The
thoracic aorta gives rise to the intercostal and
subcostal artery arteries, as well as to the superior and inferior
bronchial artery 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.
Abdominal aorta
The
abdominal aorta begins at the aortic hiatus of the diaphragm at the level of the twelfth thoracic vertebra.
It gives rise to
lumbar arteries and musculophrenic arteries,
renal artery and 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 left and right common iliac arteries. At the point of the bifurcation, there also springs a smaller branch, the median sacral artery.
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
Microanatomy
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.
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.
The aortic arch contains
and
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 , (predominately type III), , and .
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.
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.
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.[ MedlinePlus > Patent ductus arteriosus Update Date: 21 December 2009]
Function
The aorta supplies all of the systemic circulation, which means that the entire body, except for the
human 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 the
abdomen. The pelvis and legs get their blood from the common iliac arteries.
Blood flow and velocity
The contraction of the heart during systole is responsible for ejection and creates a (pulse) wave that is propagated down the aorta, into the
arterial tree. The wave is reflected at sites of impedance mismatching, such as bifurcations, where reflected waves rebound to return to semilunar valves and the origin of the aorta. These return waves create the dicrotic notch displayed in the aortic pressure curve during the
cardiac cycle as these reflected waves push on the
heart valve.
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 wave velocity are an independent indicator of
hypertension. Measuring the pulse wave velocity (invasively and non-invasively) is a means of determining arterial stiffness. Maximum aortic velocity may be noted as
Vmax or less commonly as
AoVmax.
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.[Nichols WW, O'Rourke MF. McDonald's Blood Flow in Arteries: Theoretical, Experimental and Clinical Principles. 4th ed. London, UK: Edward Arnold; 1998] 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 during diastole, as during this time the aorta contracts passively. This Windkessel 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.
Clinical significance
Aortic 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.
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Aortic aneurysm – mycotic, bacterial (e.g. syphilis), senile, genetic, associated with valvular heart disease
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Aortic coarctation – pre-ductal, post-ductal
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Aortic dissection
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Aortic stenosis
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Abdominal aortic aneurysm
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Aortitis, inflammation of the aorta that can be seen in trauma, infections, and autoimmune disease
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Atherosclerosis
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Ehlers–Danlos syndrome
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Marfan syndrome
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Physical trauma, such as traumatic aortic rupture, most often thoracic and distal to the left subclavian artery
[Samett EJ.
]
http://www.emedicine.com/radio/topic44.htm Aorta, Trauma. eMedicine.com. Accessed on: April 24, 2007. and often quickly fatal
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Transposition of the great vessels, see also dextro-Transposition of the great arteries and levo-Transposition of the great arteries
Other animals
All
have a broadly similar arrangement to that of humans, albeit with a number of individual variations. In
fish, however, there are two separate vessels referred to as aortas. The
ventral aorta carries de-oxygenated blood from the heart to the
; part of this vessel forms the ascending aorta in tetrapods (the remainder forms the
pulmonary artery). A second,
dorsal aorta carries oxygenated blood from the gills to the rest of the body and is homologous with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills.
also retain the fifth connecting vessel, so that the aorta has two parallel arches.
History
The word
aorta stems from the
Late Latin aorta from
Classical Greek aortē (ἀορτή), from
aeirō, "I lift, raise" (ἀείρω)
[Illustrated Steadman's Dictionary, 24th ed.] This term was first applied by
Aristotle when describing the aorta and describes accurately how it seems to be "suspended" above the heart.
The function of the aorta is documented in the Talmud, where it is noted as one of three major vessels entering or leaving the heart, and where perforation is linked to death.
External links
