Right-to-left shunt
Encyclopedia
A right-to-left shunt is a cardiac
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...

 shunt
Cardiac shunt
Cardiac shunts is when the blood flow follows a pattern in the heart that deviates from the normal circuit of the circulatory system. It may be described as right-left, left-to-right or bidirectional, or as systemic-to-pulmonary or pulmonary-to-systemic. The direction may be controlled by left...

 which allows blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 to flow
Circulatory system
The circulatory system is an organ system that passes nutrients , gases, hormones, blood cells, etc...

 from the right heart
Right heart
Right heart is a term used to refer collectively to the right atrium and right ventricle of the heart; occasionally, this term is intended to reference the right atrium, right ventricle, and the pulmonary trunk collectively....

 to the left heart
Left heart
Left heart is a term used to refer collectively to the left atrium and left ventricle of the heart; occasionally, this term is intended to reference the left atrium, left ventricle, and the aorta collectively....

. This terminology is used both for the abnormal state in humans and for normal physiological shunts in reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...

s. Commonly found in turtles.

Human medical

A right-to-left shunt occurs when:
  1. there is an opening or passage between the atria
    Atria
    Atria may refer to:*Atrium , an anatomical structure of the heart*Atrium , a large open space within a building*Atria or Alpha Trianguli Australis, a star in the constellation Triangulum Australe...

    , ventricle
    Ventricle (heart)
    In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

    s, and/or great vessels
    Great vessels
    Great vessels is a term used to refer collectively to the four large vessels that bring blood to and from the heart. These are:*Superior vena cava*Inferior vena cava*Pulmonary artery*AortaAll four pulmonary veins are considered apart of the great vessels...

    ; and,
  2. right heart 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 higher than left heart pressure and/or the shunt has a one-way valvular
    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...

     opening.


Small physiological, or "normal", shunts are seen due to the return of bronchial artery blood and coronary blood through the Thebesian veins, which is deoxygenated, to the left side of the heart.

The most common cause of right-to-left shunt is the Tetralogy of Fallot
Tetralogy of Fallot
Tetralogy of Fallot is a congenital heart defect which is classically understood to involve four anatomical abnormalities...

, a congenital cardiac anomaly characterized by four co-existing heart defects. The four defects include:
  1. Pulmonary stenosis (narrowing of the pulmonary valve and outflow tract, obstructing blood flow from the right ventricle to the pulmonary artery)
  2. Overriding aorta
    Overriding aorta
    An overriding aorta is a congenital heart defect where the aorta is positioned directly over a ventricular septal defect, instead of over the left ventricle....

     (aortic valve is enlarged and appears to arise from both the left and right ventricles instead of the left ventricle, as occurs in normal hearts)
  3. Ventricular septal defect
    Ventricular septal defect
    A ventricular septal defect is a defect in the ventricular septum, the wall dividing the left and right ventricles of the heart.The ventricular septum consists of an inferior muscular and superior membranous portion and is extensively innervated with conducting cardiomyocytes.The membranous...

     (an abnormal hole between the ventricles)
  4. Right ventricular hypertrophy
    Ventricular hypertrophy
    Ventricular hypertrophy is the enlargement of ventricles in the heart. Although left ventricular hypertrophy is more common, enlargement can also occur in the right ventricle, or both ventricles.- Physiology :...

     (thickening of the muscular walls of the right ventricle, this is a result of the increased amount of work the heart has to do)

A right to left shunt frequently causes hypoxemia
Hypoxemia
Hypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...

 and is characterised by frequent chest infection.

Differentiation between a right to left shunt and pulmonary disease is often aided clinically by the results of a hyperoxia test
Hyperoxia test
A hyperoxia test is a test that is performed--usually on an infant-- to determine whether the patient's cyanosis is due to lung disease or a problem with blood circulation.:141...

.

Reptiles

Because most reptiles have a single ventricle and all reptiles have both a right aortic arch and a left aortic arch, all reptiles have the capacity for right-to-left shunt.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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