The pressure exerted by the blood as it flows through the blood vessels is called blood pressure. A sphygmomanometer is a device for measuring blood pressure. It is of two types.
1. Hypertension: Systolic pressure is the maximum pressure exerted by the flowing blood on the walls of the arteries when the ventricles of the heart are contracted. It is equal to 120 mm Hg pressure.
2. Hypotension: Diastolic pressure is the pressure exerted by the flowing blood on the walls of the arteries when the ventricles of the heart are dilated. It is equal to 80 mm Hg pressure.

Blood flow through the heart is controlled by the ventricles. The capillaries open only to the forward flow of blood. Never open to backflow of blood. If the blood pressure in the atrium is high and the blood pressure in the ventricle is low, the bicuspid and tricuspid valves open. As a result, blood enters the ventricles from the atrium. When the ventricles contract with blood, the semilunar valves open and the bicuspid and tricuspid valves close. As a result blood enters the pulmonary artery and aorta. But cannot return to the atrium. Then, when the ventricular pressure decreases, the blood wants to flow back into the ventricle, but because the semilunar valve is closed, backflow does not occur. Blood flow is unidirectional as all capillaries are always open in one direction.

The heart is made up of cardiac muscle. Cardiac muscle has the longest resting period. It never ceases. Normally, when metabolic waste (lactic acid) accumulates in a cell, it is depleted. But because the cardiac muscle has a long resting period, metabolic wastes are released more easily. In addition, the heart muscle directly uses lactic acid as a nutrient. Therefore, waste cannot accumulate in the heart muscle. So the heart is sometimes exhausted.

The circulation in which the blood passes through the heart twice to circulate once throughout the body is called double circuit circulation. Bi-circular circulation occurs in the human heart. Two-circuit circulation consists of pulmonary circulation and systemic circulation.
1. Pulmonary Circulation: In pulmonary circulation, blood containing CO2 from the right ventricle of the heart enters the pulmonary artery through the semilunar ventricles. Blood comes to the lungs from the pulmonary artery. Blood is purified in the lungs. The O2-rich blood from the lungs then enters the left atrium through the pulmonary veins.
2. Systemic Circulation: In systemic circulation, O2 enriched blood enters the aorta or aorta from the left ventricle of the heart. From the aorta, blood flows through arteries and capillaries to various organs, tissues and cells. O2, nutrients, hormones etc reach the cells through blood.

Capillaries arise from some organs. Capillary networks join together to form veins. Blood travels from one organ to another through veins. In vertebrates there are two types of portal circulation namely hepatic and renal.

Coronary arteries arise from the roots of systemic arteries. O2-rich blood passes through the coronary arteries to the heart wall. The CO2-rich blood then returns to the heart through the coronary veins from the heart wall.

In pulmonary circulation, blood containing CO2 from the right ventricle of the heart enters the pulmonary artery through the semilunar ventricles. Blood comes to the lungs from the pulmonary artery. Blood is purified in the lungs. The O2-rich blood from the lungs then enters the left atrium through the pulmonary veins.

In systemic circulation, O2 enriched blood enters the aorta or aorta from the left ventricle of the heart. From the aorta, blood flows through arteries and capillaries to various organs, tissues and cells. CO2, nutrients, hormones etc. reach the cells through the blood.
Then blood containing CO2 enters the capillary network from various organs, tissues and cells. Blood comes from the capillary network into the veins. Blood from the veins reaches the veins. Veins from the upper part of the body supply blood to the superior vena cava and veins from the lower part to the inferior vena cava. Finally the blood containing CO2 enters the right atrium of the heart through superior vena cava and inferior vena cava. In this way, it takes 25-30 seconds for the blood to flow from the heart and return to the heart.

The process by which blood containing O2 from the heart passes through the blood vessels to different parts of the body and blood containing CO2 from different parts of the body returns to the heart is called blood circulation. Liver has the highest blood flow (1350 ml/min). Blood flows in the second volume (1100 ml/min) to the kidney and in the third volume (700 ml/min) to the brain.
The process of blood circulation in the human body is completed in four stages. Systemic circulation, pulmonary circulation, coronary circulation and portal circulation.

The process by which blood containing O2 from the heart passes through the blood vessels to different parts of the body and blood containing CO2 from different parts of the body returns to the heart is called blood circulation. Liver has the highest blood flow (1350 ml/min). Blood flows in the second volume (1100 ml/min) to the kidney and in the third volume (700 ml/min) to the brain.
The process of blood circulation in the human body is completed in four stages. Systemic circulation, pulmonary circulation, coronary circulation and portal circulation.
1. Systemic Circulation: In systemic circulation, O2 enriched blood enters the aorta or aorta from the left ventricle of the heart. From the aorta, blood flows through arteries and capillaries to various organs, tissues and cells. CO2, nutrients, hormones etc. reach the cells through the blood.
Then blood containing CO2 enters the capillary network from various organs, tissues and cells. Blood comes from the capillary network into the veins. Blood from the veins reaches the veins. Veins from the upper part of the body supply blood to the superior vena cava and veins from the lower part to the inferior vena cava. Finally the blood containing CO2 enters the right atrium of the heart through superior vena cava and inferior vena cava. In this way, it takes 25-30 seconds for the blood to flow from the heart and return to the heart.
2. Pulmonary Circulation: In pulmonary circulation, blood containing CO2 from the right ventricle of the heart enters the pulmonary artery through the semilunar ventricles. Blood comes to the lungs from the pulmonary artery. Blood is purified in the lungs. The O2-rich blood from the lungs then enters the left atrium through the pulmonary veins.
3. Coronary circulation: Coronary arteries arise from the roots of systemic arteries. O2-rich blood passes through the coronary arteries to the heart wall. The CO2-rich blood then returns to the heart through the coronary veins from the heart wall.
4. Portal Circulation: Capillaries arise from some organs. Capillary networks join together to form veins. Blood travels from one organ to another through veins. In vertebrates there are two types of portal circulation namely hepatic and renal.