Left atrium

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Left atrium
Anterior (frontal) view of the opened heart. White arrows indicate normal blood flow.
Computer rendering of a human left atrium.
Latin	atrium sinistrum
Artery	circumflex branch of left coronary artery
Vein	oblique vein of the left atrium
Dorlands/Elsevier	a_71/12167887

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.

Contents 1 Structure 2 Foramen ovale 3 Blood supply 4 Animals 5 Additional images 6 See also

[edit] 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.

[edit] Foramen ovale

Main article: Foramen ovale (heart)

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.

[edit] 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.

[edit] 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.

[edit] Additional images

Heart seen from above.

Base and diaphragmatic surface of heart.

[edit] See also

• Right atrium

v • d • e Anatomy of torso, cardiovascular system: heart Structures atria (interatrial septum, musculi pectinati) • ventricles (interventricular septum, trabeculae carneae, chordae tendinae, papillary muscle) • valves • cusps Regions base • apex • grooves (coronary/atrioventricular, interatrial, anterior interventricula, posterior interventricular) • surfaces (sternocostal, diaphragmatic) • borders (right, left) Right heart (vena cavae, coronary sinus) → right atrium (atrial appendage, fossa ovalis, limbus of fossa ovalis, crista terminalis, valve of the inferior vena cava, valve of the coronary sinus) → tricuspid valve → right ventricle (conus arteriosus, moderator band/septomarginal trabecula)  → pulmonary valve → (pulmonary artery and pulmonary circulation) Left heart (pulmonary veins) → left atrium (atrial appendage) → mitral valve → left ventricle → aortic valve (aortic sinus) → (aorta and systemic circulation) Layers pericardium: fibrous pericardium • serous pericardium (pericardial cavity, epicardium/visceral layer) • pericardial sinus myocardium • endocardium • cardiac skeleton (fibrous trigone, fibrous rings) Conduction system Cardiac pacemaker • SA node • AV node• bundle of His • Purkinje fibers