Blood Circulation

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Chapter: Anatomy and Physiology for Health Professionals: The Heart

The heart consists of two pumps located side by side, which supply blood to the pulmonary circuit and systemic circuit .


Blood Circulation

The heart consists of two pumps located side by side, which supply blood to the pulmonary circuit and systemic circuit . Blood enters the pulmonary circuit from the right ventricle through the pulmonary trunk, which extends upward posteriorly from  the heart. It divides into right and left pulmonary arteries, which enter the right and left lungs, respectively. Repeated divisions connect to arterioles and capillary networks associated with the walls of the alveoli, where gas is exchanged between blood and air. The pulmonary capillaries lead to venules and then veins. Four pulmonary veins, two from each lung, return blood to the left atrium, completing the  vascular¬≠ loop of the pulmonary circuit. Capillaries are also called exchange vessels because their thin walls allow the exchange of dissolved gases, nutri-ents, and waste products between surrounding tis-sues and the blood.

The systemic circuit involves the movement of freshly oxygenated blood from the left atrium to the left ventricle and then into the aorta and its branches, leading to all body tissues. Eventually, it makes its way to the companion vein system that returns blood to the right atrium. FIGURE 18-1 shows the two circuits of blood circulation.



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