Pulmonary Circulation

Deoxygenated blood returning from all parts of the body except the lungs enters the right atrium, where it is then pumped into the right ventricle. When the right ventricle contracts, the deoxy-genated blood is sent through the pulmonary artery to the lungs. The pulmonary artery is the only artery that carries deoxygenated blood. The pulmonary artery branches into two smaller arteries, with one artery going to each lung. These arteries branch into arte-rioles and then into capillaries in the lungs.

Endothelium •

Smooth -muscle

Connective' tissue

Vein

(returns blood to the heart) figure 46-6

Like an artery, a vein has three layers: the outer layer of connective tissue, the middle layer of smooth muscle, and the inner layer of endothelial tissue.

figure 46-7

The cardiovascular system transports materials throughout the body and distributes heat.

figure 46-7

The cardiovascular system transports materials throughout the body and distributes heat.

figure 46-8

The pulmonary circulation between the heart and the lungs involves the pulmonary arteries and the pulmonary veins. Deoxygenated blood flows from the right side of the heart to the lungs. Oxygenated blood is returned to the left side of the heart from the lungs. This is the opposite of systemic and coronary blood flow, in which oxygen-rich blood flows from the heart and oxygen-poor blood is returned to the heart.

Superior vena cava Pulmonary arteries

From head

To head To body rv

ventricle

Right \ ventricle \

Inferior vena cava figure 46-9

Notice three subsystems of systemic circulation. Other subsystems transport blood between the heart and the head, arms, and other organs.

figure 46-9

Notice three subsystems of systemic circulation. Other subsystems transport blood between the heart and the head, arms, and other organs.

From body

In the lungs, carbon dioxide diffuses out of the capillaries and oxygen diffuses into the capillaries. The oxygenated blood then flows into venules, which merge into the pulmonary veins that lead to the left atrium of the heart. From the left atrium, blood is pumped into the left ventricle and then to the body through the aorta. In Figure 46-8, trace the path blood takes as it passes through pulmonary circulation.

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