Anatomy & Physiology

Anatomy & Physiology Study Guide

The Left Ventricle The two ventricles hold equal amounts of blood; however, the left ventricle has thicker walls and is much larger than the right ventricle. Its thick, muscular walls enable the left ventricle to develop pressure sufficient to push blood through the large systemic circuit, whereas the right ventricle needs to pump blood, at lower pressure, only about 15 cm (6 in.) to and from the lungs. The internal organization of the left ventricle resembles that of the right ventricle, except for the absence of a moderator band. The aortic valve prevents the backflow of blood into the left ventricle once the blood has been out of the heart and into the systemic circuit. From the ascending aorta, blood flows through the aortic arch and into the descending aorta. The ligamentum arteriosum connects the aortic arch to the pulmonary trunk. It is a fibrous band that is a remnant of a fetal blood vessel that once linked the pulmonary and systemic circuits to bypass the lungs before birth. The Heart Valves The heart has two pairs of one-way valves that stop the backflow of blood as the chambers contract. The atrioventricular (AV) valves prevent the backflow of blood from the ventricles to the atria when the ventricles are contracting.

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