What Is Coronary Circulation?

Coronary circulation refers to the blood circulation that supplies the heart itself. The arteries of the coronary system are the left and right coronary arteries and their branches, which carry blood to nourish myocardial cells. Blood flows through the capillaries and veins and returns to the right atrium. The coronary arteries are the first pair of branches of the aorta. They have high blood pressure, fast blood flow, and short circulation paths, so the blood supply to the coronary arteries is quite sufficient. The normal operation of the coronary circulation ensures that the heart can continuously pump blood. The main anatomical characteristics are: the coronary branches that vertically penetrate the myocardium are easily squeezed when the myocardium contracts, the capillaries of the myocardial tissue are very rich, and the anastomosis between the coronary arteries is small.

Coronary circulation refers to the blood circulation that supplies the heart itself. The arteries of the coronary system are the left and right coronary arteries and their branches, which carry blood to nourish myocardial cells. Blood flows through the capillaries and veins and returns to the right atrium. The coronary arteries are the first pair of branches of the aorta. They have high blood pressure, fast blood flow, and short circulation paths, so the blood supply to the coronary arteries is quite sufficient. The normal operation of the coronary circulation ensures that the heart can continuously pump blood. The main anatomical characteristics are: the coronary branches that vertically penetrate the myocardium are easily squeezed when the myocardium contracts, the capillaries of the myocardial tissue are very rich, and the anastomosis between the coronary arteries is small.

Chinese name

Coronary circulation

Foreign name

coronary circulation

Meaning

Supply blood circulation to the heart itself

Anatomical characteristics of coronary circulation

The myocardial blood supply comes from the left and right coronary arteries at the root of the aorta, enters the right atrium via arterioles, capillaries, and small veins through the coronary sinus or anterior cardiac vein. The branches of the coronary arteries in the epicardium often penetrate vertically into the myocardium. Branching in the inner and middle, or branching vertically through the myocardium in the endocardium, this structural feature makes these blood vessels vulnerable to compression during myocardial contraction, which reduces blood flow and even interrupts blood flow. The capillary network of the coronary circulation is extremely rich. The ratio of the number of capillaries to the number of myocardial fibers is 1: 1. When compensatory hypertrophy occurs, the diameter of myocardial fibers increases, but the number of capillaries does not increase accordingly. Myocardium is more prone to hypoxia. Coronary arteries have collateral anastomosis near, distal, or between different branches. These anastomotic branches are more subendocardial and less epicardial. The diameter of the anastomotic branch is small and the blood flow is very small. Therefore, when coronary arteries are obstructed, it is impossible to establish collateral circulation immediately, which often leads to myocardial infarction. If the blood flow of a certain coronary artery gradually decreases, the anastomotic branch may gradually expand within a few weeks, increasing the blood flow, thereby establishing a new effective collateral circulation. This is an important compensatory process for coronary heart disease. However, the establishment of collateral circulation takes a certain amount of time. Sudden blockage of large coronary branches can often cause myocardial ischemia and even endanger life.

Coronary circulation blood flow characteristics

Coronary blood flow:

The average coronary blood flow in normal humans was 79ml / min · 100g of left ventricular muscle. Since most of the coronary arteries are deeply buried in the myocardium, the rhythmic contraction of the myocardium has a great effect on coronary blood flow.

The supply of myocardial blood is mainly during diastole. Blood flow is unevenly distributed in different myocardial regions. Using the method of radioactive isotope uptake of the myocardium, all left ventricular regions, including the base, apex, septum, and free wall, were measured to be 50 to 100% higher than the right ventricle and atrium. Except for the left ventricle, the blood flow of other parts of the heart is in the order of right ventricle, left atrium, right atrium, interventricular tract, sinoatrial node, and atrioventricular node. The blood flow distribution in the endocardial region was higher than that in the epicardial region, about 4: 3. The ratio of membrane blood flow to adventitia blood flow in the ischemic area is reduced, which means that the endocardium is more severely affected than the epicardium during myocardial ischemia.

The amount of coronary blood flow depends on the difference between the blood pressure at the beginning of the coronary arteries (the same as the aortic pressure) and the blood pressure of the right atrium, and the resistance of the blood flow through the coronary arteries. Increasing arterial blood pressure can increase myocardial blood flow, and low arterial blood pressure (such as late hemorrhagic shock) can cause myocardial ischemia and damage, tachycardia, too short diastole, and also reduce coronary blood flow.

The resistance of blood flow through the coronary arteries mainly comes from three factors: the diameter of the arterioles, the pressure of extravascular myocardial contraction, and blood viscosity. Coronary artery is squeezed when myocardial contraction, so coronary blood flow is less in systole. The effect of blood viscosity is normally not noticeable. However, patients with angina pectoris have insufficient blood supply to the coronary arteries. After eating, the blood contains more fat and increases blood viscosity. Some people think that this may be a factor that promotes the lack of coronary blood supply and increases the incidence of angina pectoris. Coronary Changes in the arterial diameter are the most important factors affecting coronary blood flow. It is estimated that doubling the aortic pressure doubles coronary blood flow; while doubling the average coronary diameter, coronary blood flow can increase. Sixteen times. The body changes the caliber of small arteries through nerve and humoral factors is the main way to regulate blood supply to the heart muscle. Regarding both, body fluid regulation is the main.

Regulation of coronary circulation blood flow in coronary circulation

Body fluid regulation of coronary circulation:

Hypoxia is a strong stimulus to relax the coronary arteries. When the myocardium is obviously hypoxic, coronary blood flow can increase 5 times than usual. The mechanism of coronary artery dilatation caused by hypoxia has not been elucidated. Nowadays, there is a tendency to think that when tissue is hypoxic, it will produce certain vasodilating metabolites, mainly adenosine, which will expand the coronary arteries. That is to say, myocardial hypoxia can decompose adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and adenosine monophosphate (AMP). Adenosine monophosphate is dephosphorylated by 5-nucleotide enzymes existing in muscle fiber membranes, transverse tubes, and the like to become adenosine. Adenosine diffuses into small arteries around muscle fibers and exerts a vasomotor effect.

Cardiac activity is enhanced, and coronary flow increases during hypermetabolism, which is a self-regulation of coronary blood flow. Injecting intermediate metabolites such as adenosine, AMP, and nucleic acid decomposition products into the coronary arteries can increase coronary flow. ATP and ADP also dilate the coronary arteries and are several times stronger than adenine. However, under normal circumstances, ATP and ADP cannot penetrate the cell membrane, so they have no effect on the regulation of local blood vessels. The self-regulation of metabolic coronary arterial flow can also be explained by the "adenosine theory": that is, when the myocardial metabolism is excessive, it causes the oxygen partial pressure in the myocardium to decrease. Diffusion into extracellular fluid causes coronary arteries to dilate. Bradykinin is another metabolite that can expand coronary arteries, and its effect is 50 to 100 times stronger than adenosine. Some people think that it is one of the important factors that expand coronary arteries during myocardial ischemia, and it is the chemical that causes angina pectoris. Irritant. Decreased pH (acidosis) and increased CO2 partial pressure in the blood can slightly increase coronary flow, and a slight increase in K + concentration in the blood increases coronary flow, but excessive K + concentration increases coronary resistance and decreases flow. In addition, thyroxine promotes myocardial metabolism and increases myocardial oxygen consumption and coronary flow, posterior pituitary hormones contract coronary arteries, small amounts of angiotensin contract coronary arteries, and large amounts of coronary arterial flow increase due to increased myocardial oxygen consumption.

Nervous regulation of coronary circulation, coronary arteries are subject to sympathy and vagus nerve innervation. Chronic experimental dogs that completely remove the innervation of the coronary arteries have increased myocardial blood flow, suggesting that the general effect of the autonomic nerve on the coronary arteries is to constrict the blood vessels. In recent years, it has been proven that the direct effect of vagal nerve excitement expands the coronary arteries, and the direct effect of sympathetic nerve excitement causes contraction of the coronary arteries, which usually stimulates the sympathetic nerves to increase coronary flow. Caused by secondary expansion. Intracoronary injection of acetylcholine also dilates blood vessels and increases blood flow. Intracoronary injection of norepinephrine causes an initial contraction of the coronary arteries. Later, the coronary arteries dilate due to enhanced myocardial metabolism and flow increases. The coronary arteries have two kinds of adrenergic receptors, and 2. The alpha receptor causes a vasoconstrictor response, and the beta 2 receptor causes a diastolic response. Sympathetic nerves are stimulated to contract coronary arteries via alpha receptors, but whether coronary arteries are dilated directly via beta2 receptors has not been determined. Norepinephrine mainly acts on alpha receptors, and epinephrine acts on both alpha and beta2 receptors. Intravenous injections of norepinephrine and epinephrine indirectly increase coronary flow due to their promotion of myocardial metabolism. When the coronary arteries have obvious pathological stenosis, the sympathetic nerve stimulation often only shows a decrease in coronary flow. This may be due to the expansion of the coronary arteries due to the presence of metabolites, making the alpha receptor effect more obvious or for other reasons.