Coronary circulation is the circulation of blood in the blood vessels that supply the heart muscle (myocardium). Coronary arteries supply oxygenated blood to the heart muscle, and cardiac veins drain away the blood once it has been deoxygenated. Because the rest of the body, and most especially the brain, needs a steady supply of oxygenated blood that is free of all but the slightest interruptions, the heart is required to function continuously.
Therefore its circulation is of major importance not only to its own tissues but to the entire body and even the level of consciousness of the brain from moment to moment. Interruptions of coronary circulation quickly cause heart attacks (myocardial infarctions), in which the heart muscle is damaged by oxygen starvation. Such interruptions are usually caused by ischemic heart disease (coronary artery disease) and sometimes by embolism from other causes like obstruction in blood flow through vessels.
It starts as coronary orifices in the aorta and supplies the blood to the heart muscles through right and left coronary arteries. These orifices are in free communication with aorta both during systole and diastole.
The main coronary artery branches into right and left coronary arteries. The left coronary artery is more important in dog, cat and ruminants, whereas in man, swine, horse and some primates the right coronary artery is more prominent.
The left coronary artery gives of the left circumflex branch which runs along the auriculo-ventricular groove and distributes about 80% of the total blood flow to the heart.
It supplies mainly the atria and left ventricle, A.V. node, inter ventricular septum. The right coronary artery nourishes the right ventricular muscles.
The venous system of the heart comprises the great cardiac veins, which empties through the coronary sinus drains the blood supplied by the left coronary artery into the right atrium of the heart, whereas the anterior cardiac veins collect the blood supplied by the right coronary artery and discharge their blood into the right atrium. Small amount of blood is drained through the besian veins directly into the right ventricle and other chambers of the heart.
About 4% of the cardiac output flows through the coronary arteries to meet the very high oxygen demand by the cardiac muscles under normal condition (10-15 ml of O2 is taken by cardiac muscle from each 100 ml of blood as against 5 ml/100 ml in skeletal muscles). This blood supply may be increased to 40% during heavy muscular exercise.
In the left coronary artery the blood flow is decreased during systole because of the high coronary resistance developed by the contraction of ventricular muscles. However, this gets reversed during ventricular diastole which shows increased coronary blood flow. On the other hand the right coronary artery shows increased blood flow during systole and lower during diastole.
If a coronary artery is gradually blocked by stenosis, there may be a progressive development of new blood vessels from the pre-existing capillaries, known as the collateral vessels.
The pulmonary circulation is the portion of the circulatory system which carries deoxygenated blood away from the right ventricle, to the lungs, and returns oxygenated blood to the left atrium and ventricle of the heart. The term pulmonary circulation is readily paired and contrasted with the systemic circulation. The vessels of the pulmonary circulation are the pulmonary arteries and the pulmonary veins.
A separate system known as the bronchial circulation supplies oxygenated blood to the tissue of the larger airways of the lungs.