AnatomyThoraxHeart

Left atrium and ventricle

Learning objectives

After going through this study unit you will be able to:

Identify the chambers of the heart.
Understand the function of the left atrium and ventricle and how they communicate with one another.
Identify and describe the anatomical landmarks of the left heart.

Watch video

The left atrium occupies the base (posterior part) of the heart. It receives oxygenated blood from the lungs via four pulmonary veins and pumps it into the left ventricle via the left atrioventricular orifice. This orifice features the left atrioventricular (mitral/bicuspid) valve which functions to seal the atrioventricular opening during the ventricular contraction (systole). This prevents regurgitation of blood into the left atrium and redirects blood flow through the aortic orifice during ventricular systole.

The left ventricle is the largest of all heart chambers, mainly due to the thickness of its muscular walls. It occupies most of the left pulmonary and inferior surfaces of the heart, including its apex. Once filled with blood, the left ventricle contracts and strongly ejects most of its contents into the aorta. The left ventricle and aorta are separated by the aortic orifice, which features the aortic (left semilunar) valve. This valve is closed during ventricular diastole, preventing backflow of blood in the left ventricle, and open during systole to allow the blood to enter systemic circulation.

Watch the following video and learn everything about the anatomy of the left atrium and ventricle, their functions and anatomical relations.

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Browse atlas

Take a closer look at the left atrium and ventricle in the gallery below.

Summary

Key points about the left atrium
Features	Receives oxygenated blood from the lungs via the pulmonary veins (4 ostia) Characteristics: Cuboidal chamber, thicker walls (compared to right atrium); has a small muscular pouch → left auricle of heart (contains pectinate muscles) Landmarks: T5 - T8 (supine), T6 - T9 (erect) Function: Reservoir for blood and active pumps that help fill the ventricles
Sinus of pulmonary veins	Portion of posterior wall of left atrium that receives pulmonary veins
Vestibule of left atrioventricular valve	Contains fibrous ring that supports the leaflets of left AV valve

Key points about the left ventricle
Features	Receives oxygenated blood from left atrium Characteristics: Long conical shape, thicker walls (compared to right ventricle), smooth inflow/outflow tracts Function: Pumps blood into systemic circulation
Aortic vestibule	Area immediately below aortic orifice, has fibrous walls that support leaflets of aortic valve
Trabeculae carneae	Muscular elevations that course along mainly apical parts of ventricular wall
Papillary muscles (superior/anterior, inferior/posterior), chordae tendineae	Muscular projections attached to cusps of left atrioventricular valve via tendinous cords (chordae tendineae) preventing prolapse
Apex of heart	Rounded anteroinferior extremity of heart formed by left ventricle; Located at left 5th intercostal space approximately 9 cm from median plane where apex beat (sounds of left AV valve closure) is maximal

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