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Answer:
two capillary beds
Explanation:
Capillary beds are networks of capillaries that supply blood to the organs and/or areas of the body, in which nutrients and gas exchange (i.e., O2 and CO2) between red blood cells and tissues take place. Smaller arteries (i.e., arterioles) diverge into capillary beds composed of 10 to 100 capillaries, the smallest blood vessels in the body that connect the arterioles and the venules. Red blood cells usually flow into a capillary bed from a metarteriole (i.e., a microvessel that connects arterioles and capillaries). Red blood cells sometimes pass through two capillary beds before reaching the heart. The left heart ventricle is a muscle required for pumping red O2-rich blood out through the aortic valve into the aorta, whereas arteries are large blood vessels that branch into arterioles in order to carry blood to the capillary beds.