Aorta

Aorta

Discussion
Ask a question about 'Aorta'
Start a new discussion about 'Aorta'
Answer questions from other users
Full Discussion Forum
 
Encyclopedia
The aorta is the largest artery
Artery
Arteries are blood vessels that carry blood away from the heart. This blood is normally oxygenated, exceptions made for the pulmonary and umbilical arteries....

 in the body
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...

, originating from the left ventricle
Left ventricle
The left ventricle is one of four chambers in the human heart. It receives oxygenated blood from the left atrium via the mitral valve, and pumps it into the aorta via the aortic valve.-Shape:...

 of the heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...

 and extending down to the abdomen, where it branches off into two smaller arteries (the common iliacs). The aorta distributes oxygenated blood to all parts of the body through the systemic circulation
Systemic circulation
Systemic circulation is the part of the cardiovascular system which carries oxygenated blood away from the heart to the body, and returns deoxygenated blood back to the heart. This physiologic theory of circulation was first described by William Harvey...

.

The course of the aorta



The aorta is usually divided into five segments/sections:
  • Ascending aorta
    Ascending aorta
    The ascending aorta is a portion of the aorta commencing at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart’s...

    —the section between the heart and the arch of aorta
  • Arch of aorta—the peak part that looks somewhat like an inverted "U"
  • Descending aorta
    Descending aorta
    The descending aorta is part of the aorta, the largest artery in the body. The descending aorta is the part of the aorta beginning at the aortic arch that runs down through the chest and abdomen. The descending aorta is divided into two portions, the thoracic and abdominal, in correspondence with...

    —the section from the arch of aorta to the point where it divides into the common iliac arteries
    • Thoracic aorta
      Thoracic aorta
      The thoracic aorta is contained in the posterior mediastinal cavity.It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth thoracic vertebra, at the aortic hiatus in the diaphragm where it...

      —the half of the descending aorta above the diaphragm
      Thoracic diaphragm
      In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...

    • Abdominal aorta
      Abdominal aorta
      The abdominal aorta is the largest artery in the abdominal cavity. As part of the aorta, it is a direct continuation of the descending aorta .-Path:...

      —the half of the descending aorta below the diaphragm
      Thoracic diaphragm
      In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...


In other animals


All amniote
Amniote
The amniotes are a group of tetrapods that have a terrestrially adapted egg. They include synapsids and sauropsids , as well as their fossil ancestors. Amniote embryos, whether laid as eggs or carried by the female, are protected and aided by several extensive membranes...

s have a broadly similar arrangement to that of humans, albeit with a number of individual variations. In fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

, however, there are two separate vessels referred to as aortas. The ventral aorta carries de-oxygenated blood from the heart to the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s; part of this vessel forms the ascending aorta in tetrapods (the remainder forms the pulmonary artery
Pulmonary artery
The pulmonary arteries carry deoxygenated blood from the heart to the lungs. They are the only arteries that carry deoxygenated blood....

). A second, dorsal aorta carries oxygenated blood from the gills to the rest of the body, and is homologous
Homology (biology)
Homology forms the basis of organization for comparative biology. In 1843, Richard Owen defined homology as "the same organ in different animals under every variety of form and function". Organs as different as a bat's wing, a seal's flipper, a cat's paw and a human hand have a common underlying...

 with the descending aorta of tetrapods. The two aortas are connected by a number of vessels, one passing through each of the gills.
Amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s also retain the fifth connecting vessel, so that the aorta has two parallel arches.

Embryological development


In mammalian and avian embryological development, the pharyngeal arch (aortic arches
Aortic arches
The aortic arches or pharyngeal arch arteries are a series of six paired embryological vascular structures which give rise to several major arteries...

) arteries contribute to the normal pattern of the great arteries. The fourth aortic arch vessel survives in these vertebrates as the arch of the aorta, the third aortic arch vessel persists as the brachiocephalic artery or the root of the internal carotid, and the six arch contributes to the pulmonary arteries. The smooth muscle of the great arteries and the population of cells that form the aorticopulmonary septum
Aorticopulmonary septum
The aorticopulmonary septum is developmentally formed from neural crest, specifically the cardiac...

 that separates the aorta and pulmonary artery is derived from cardiac neural crest
Cardiac neural crest
The cardiac neural crest complex is a form of neural crest.The cardiac neural crest develops from the dorsal neural tube. It overlaps the vagal neural crest and migrates to populate the pharyngeal arches 3, 4 and 6 and to the heart, forming connective tissue that separates the great vessels of the...

. 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 semilunar valves
Heart valve
A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...

, possess smooth muscle of mesodermal origin. A failure of the aorticopulmonary septum to divide the great vessels results in persistent truncus arteriosus
Persistent truncus arteriosus
Persistent truncus arteriosus , also known as Common arterial trunk, is a rare form of congenital heart disease that presents at birth...

.

Features



The aorta is an elastic artery
Elastic artery
An elastic artery is an artery with a large number of collagen and elastin filaments in the tunica media, which gives it the ability to stretch in response to each pulse...

, and as such is quite distensible. The blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...

 is highest (normal blood pressure is a reflection of aortic blood pressure) and most pulsatile in the aorta, as blood pressure decreases and becomes more smooth (and less pulsatile) as the blood travels from aorta to arteries to arterioles to capillaries, where metabolic exchange occurs. The aorta consists of a heterogeneous mixture of smooth muscle
Smooth muscle
Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

, nerves, intimal cells, endothelial cells, fibroblast-like cells, and a complex extracellular matrix. The vascular wall consists of several layers known as the tunica adventitia, tunica media
Tunica media
The tunica media is the middle layer of an artery or vein.-Artery:It is made up of smooth muscle cells and elastic tissue...

, and tunica intima
Tunica intima
The tunica intima is the innermost layer of an artery or vein. It is made up of one layer of endothelial cells and is supported by an internal elastic lamina...

. The thickness of the aorta encourages an extensive network of tiny blood vessels called vaso vasorum, which feed the layers of the aorta. The aortic arch contains baroreceptors and chemoreceptors that relay information concerning blood pressure and blood pH and carbon dioxide levels to the medulla oblongata of the brain. This information is processed by the brain and the autonomic nervous system
Autonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...

 mediates the homeostatic responses.

Within the tunica media, smooth muscle and the extracellular matrix are quantitatively the largest components of the aortic vascular wall. The fundamental unit of the aorta is the elastic lamella, which consists of smooth muscle and elastic matrix. The medial layer of the aorta consist of concentric musculoelastic layers (the elastic lamella) in mammals. The smooth muscle component does not dramatically alter the diameter of the aorta but rather serves to increase the stiffness and viscoelasticity of the aortic wall when activated. The elastic matrix dominates the biomechanical properties of the aorta. The elastic matrix forms lamella, consisting of elastic fibers
Elastic fibers
Elastic fibres are bundles of proteins found in extracellular matrix of connective tissue and produced by fibroblasts and smooth muscle cells in arteries. These fibers can stretch up to 1.5 times their length, and snap back to their original length when relaxed...

, collagens(predominately type III), proteoglycans, and glycoaminoglycans. 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
Diastole
Diastole is the period of time when the heart fills with blood after systole . Ventricular diastole is the period during which the ventricles are relaxing, while atrial diastole is the period during which the atria are relaxing...

, as during this time the aorta contracts passively. This Windkessel effect
Windkessel effect
Windkessel effect is a term used in medicine to account for the shape of the arterial pressure waveform in terms of the interaction between the stroke volume and the compliance of the aorta and large elastic arteries . Windkessel in German literally means 'air chamber', but is generally taken to...

 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.

Blood flow and velocity


The pulsatile
Pulsatile flow
Pulsatile blood flow in the body is a response to periodic variations in velocity. These pulsating characteristics have been shown to be a result of two pumps. As the primary pump, the heart causes the blood flow and velocity to oscillate from zero to very high rates as the valves at the entrances...

 nature of blood flow creates a pulse wave that is propagated down the arterial tree
Arterial tree
In anatomy, arterial tree is used to refer to all arteries and/or the branching pattern of the arteries. This article regards the human arterial tree. Starting from the aorta:- Ascending aorta :In anatomy, arterial tree is used to refer to all arteries and/or the branching pattern of the arteries....

, and at bifurcations
Aortic bifurcation
The aortic bifurcation is the point at which the abdominal aorta bifurcates into the left and right common iliac arteries. The aortic bifurcation occurs at the level of the fourth lumbar vertebrae....

 reflected waves rebound to return to semilunar valves and the origin of the aorta
Aorta
The aorta is the largest artery in the body, originating from the left ventricle of the heart and extending down to the abdomen, where it branches off into two smaller arteries...

. These return waves create the dicrotic notch displayed in the aortic pressure curve during the cardiac cycle
Cardiac cycle
The cardiac cycle is a term referring to all or any of the events related to the flow or blood pressure that occurs from the beginning of one heartbeat to the beginning of the next. The frequency of the cardiac cycle is described by the heart rate. Each beat of the heart involves five major stages...

 as these reflected waves push on the aortic semilunar valve
Heart valve
A heart valve normally allows blood flow in only one direction through the heart. The four valves commonly represented in a mammalian heart determine the pathway of blood flow through the heart...

. 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
Hypertension
Hypertension or high blood pressure is a cardiac chronic medical condition in which the systemic arterial blood pressure is elevated. What that means is that the heart is having to work harder than it should to pump the blood around the body. Blood pressure involves two measurements, systolic and...

. Measuring the pulse wave velocity (invasively and non-invasively) is a means of determining arterial stiffness
Arterial stiffness
Arteries stiffen as a consequence of age and arteriosclerosis. Age related stiffness occurs when the elastic fibres within the arterial wall begin to fray due to mechanical stress. The two leading causes of death in the developed world, myocardial infarction and stroke, are both a direct...

. Maximum aortic velocity may be noted as Vmax or less commonly as AoVmax.

Diseases/pathology

  • Aneurysm of sinus of Valsalva
    Aneurysm of sinus of Valsalva
    Aneurysm of the aortic sinus, also known as the sinus of Valsalva, is comparatively rare. When present, it is usually in either the right or in the noncoronary sinus, rarely in the left Aneurysm of the aortic sinus, also known as the sinus of Valsalva, is comparatively rare. When present, it is...

  • Aortic aneurysm
    Aortic aneurysm
    An aortic aneurysm is a general term for any swelling of the aorta to greater than 1.5 times normal, usually representing an underlying weakness in the wall of the aorta at that location...

     – myotic, bacterial (e.g. syphilis
    Syphilis
    Syphilis is a sexually transmitted infection caused by the spirochete bacterium Treponema pallidum subspecies pallidum. The primary route of transmission is through sexual contact; however, it may also be transmitted from mother to fetus during pregnancy or at birth, resulting in congenital syphilis...

    ), senile, genetic, associated with valvular heart disease
    Valvular heart disease
    Valvular heart disease is any disease process involving one or more of the valves of the heart . Valve problems may be congenital or acquired...

    • Dissecting aortic aneurysm
      Aortic dissection
      Aortic dissection occurs when a tear in the inner wall of the aorta causes blood to flow between the layers of the wall of the aorta and force the layers apart. The dissection typically extends anterograde, but can extend retrograde from the site of the intimal tear. Aortic dissection is a medical...

  • Aortic coarctation
    Aortic coarctation
    Coarctation of the aorta, or aortic coarctation, is a congenital condition whereby the aorta narrows in the area where the ductus arteriosus inserts.-Types:There are three types:...

     – pre-ductal
    Ductus arteriosus
    In the developing fetus, the ductus arteriosus , also called the ductus Botalli, is a shunt connecting the pulmonary artery to the aortic arch. It allows most of the blood from the right ventricle to bypass the fetus's fluid-filled lungs. Upon closure at birth, it becomes the ligamentum arteriosum...

    , post-ductal
  • Transposition of the great vessels
    Transposition of the great vessels
    Transposition of the great vessels is a group of congenital heart defects involving an abnormal spatial arrangement of any of the primary blood vessels: superior and/or inferior vena cavae , pulmonary artery, pulmonary veins, and aorta...

    , see also dextro-Transposition of the great arteries
    Dextro-Transposition of the great arteries
    dextro-Transposition of the great arteries , sometimes also referred to as complete transposition of the great arteries, is a birth defect in the large arteries of the heart...

     and levo-Transposition of the great arteries
    Levo-Transposition of the great arteries
    levo-Transposition of the great arteries , also commonly referred to as congenitally corrected transposition of the great arteries , is an acyanotic congenital heart defect in which the primary arteries are transposed, with the aorta anterior and to...

  • Atherosclerosis
    Atherosclerosis
    Atherosclerosis is a condition in which an artery wall thickens as a result of the accumulation of fatty materials such as cholesterol...

  • Marfan syndrome
    Marfan syndrome
    Marfan syndrome is a genetic disorder of the connective tissue. People with Marfan's tend to be unusually tall, with long limbs and long, thin fingers....

  • Ehlers–Danlos syndrome
  • Aortic stenosis
  • Trauma
    Physical trauma
    Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...

    , such as traumatic aortic rupture
    Traumatic aortic rupture
    Traumatic aortic rupture, also called traumatic aortic disruption or transection, is a condition in which the aorta, the largest artery in the body, is torn or ruptured as the result of trauma. The condition is frequently fatal due to the profuse bleeding that results from the rupture...

    , most often thoracic and distal to the left subclavian artery and frequently quickly fatal

External links



- Descending aorta - Abdominal aorta