Physiology and pathophysiology of coronary circulation

The heart supplies blood to itself through two coronary arteries that support the coronary circulation. Both arteries lie outside of the heart muscle running along the atrioventricular groove and branch off into a system of smaller vessels that supply the muscle cells. Because of the high oxygen requirements of the myocardium, capillary density is very high, (accounting for ∼15 percent of the total cardiac mass). After giving off its oxygen and nutrients in the capillaries, the venous blood flows through coronary veins draining directly into the right atrium. Other drainage is by means of thebesian veins, which drain directly into the right heart, and anterior cardiac veins that empty into the right atrium. Small intramural collateral vessels represent functionally important elements that connect the coronaries and can enlarge after coronary obstruction, providing near-normal flow at rest to the distal segment of the diseased artery. When the heart needs to work harder than during basal conditions, the coronary arteries dilate, thus varying the resistance to the blood flow and increasing the oxygen supply to the heart.