Capillaries attach the smallest branches of arteries and veins. The capillaries are where molecules are swapped between the blood and the body's cells. The walls of veins are just one cell thick.
Pulmonary circulation moves blood between the heart and the lungs. It transports deoxygenated blood to the lungs to absorb oxygen and release carbon dioxide.
The oxygenated blood then flows back to the heart. While Coronary circulation is the circulation of blood in the blood vessels that supply the heart muscle (myocardium).
Thus,Capillaries therefore allow molecules to diffuse across the capillary walls.
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