Pulmonary loop

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The pulmonary loop of the circulatory system delivers deoxygenated blood to the respiratory membranes of the lungs. Blood is delivered through a closed loop system. The pulmonary loop is fed by the right ventricle, through the pulmonary semilunar valve, into the pulmonary trunk, into right and left pulmonary arteries. The pulmonary loop delivers blood to the lungs only, for the purpose of gas exchange in the respiratory membranes of the lungs. The progression in vessels is: arteries, arterioles, capillaries, venules, and veins. The capillary beds are the functional part of the blood delivery system. They deliver carbon dioxide to the respiratory membranes. Once the delivery is made, the capillaries permit oxygen to diffuse across the simple squamous epithelium of the lungs and capillaries. The four pulmonary veins, two on each side, direct blood back to the left atrium. Blood contines to circulate through the body via the systemic loop.