Everything about The Left Atrium totally explained
The
left atrium is one of the four
chambers in the
human heart. It receives
oxygenated
blood from the
pulmonary veins, and pumps it into the
left ventricle, via the bicuspid valve.
Structure
Blood is pumped through the left atrioventricular orifice, which contains the
mitral valve. A normal left atrium may be up to 5.5cm in maximum diameter; any larger than this is a sign of
cardiac failure. This may occur in cases of
mitral regurgitation.
The left atrium of a human faces more or less posteriorly. It is named 'left' based on the chamber's embryological and (putative) evolutionary origin. The term 'base' of the heart sometimes refers to the left atrium, though 'base' is an ambiguous term.
Attached to the left atrium is the
left auricular appendix (auricle). This auricle is a common site for formation of
thrombi, which may embolise causing stroke or ischemic gut.
Atrial fibrillation makes this more likely.
Foramen ovale
There is a foramen ovale (oval hole) between the right and left atrium in the fetus. After birth, this should close over and become the fossa ovale. If it does not, this is an
atrial septal defect (hole in the heart). In the fetus, the right atrium pumps blood into the left atrium, bypassing the pulmonary circulation (which is useless in a fetus). In an adult, a septal defect would result in flow in the reverse direction - from the left atrium to the right - which will reduce cardiac output, potentially cause
cardiac failure and in severe or untreated cases, death.
Blood supply
The left atrium is supplied mainly by the
left circumflex coronary artery, though the branches are too small to be identified in a cadaveric human heart and are not named.
The
oblique vein of the left atrium is partly responsible for venous drainage; it derives from the embryonic left
superior vena cava.
Animals
Many other animals, including mammals, also have four-chambered hearts, and have a left atrium. The function in these animals is similar. Some animals (amphibians, reptiles) have a three-chambered heart, in which the blood from each atrium is mixed in the single ventricle before being pumped to the aorta. In these animals, the left atrium still serves the purpose of collecting blood from pulmonary veins.
Additional images
Image:Gray494.png|Heart seen from above.
Image:Gray556.png|Base and diaphragmatic surface of heart.
Further Information
Get more info on 'Left Atrium'.
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