In the living condition, the blood keeps on circulating in the body all the time. Circulating blood in the body in this way is called blood circulation. The blood enters into the body through the heart and ducts. The blood starts its journey from a place and returns back on the same place after completing its journey all over the body. The blood keeps on moving in the closed circuit throughout life which is in this way-
The blood reaches in aorta from the left ventricle – in artery- in arterioles- in capillaries- in venules – in veins – in venae cavae – in Right atrium- in Right t ventricle- in pulmonary artery- in pulmonary veins-in left atrium and by reaching again in left ventricle keeps on moving in the whole body on the base of this circuit.
The blood starts its journey from the left ventricle and from this place it reaches into different body portions by the aorta. The aorta emerges from the heart and raises a little high and after turning a little further it bends downwardly by making arch. In this way, its raised portion is called ascending aorta, the portion of arch turning forwardly is called aortic arch and the coming down portion is called descending arota. Left and right coronary arteries emerge from the ascending aorta just above the aortic valve and supply blood to the heart. Three big arteries emerge from the aortic arch which completes the blood supply of upper organs. The descending aorta supplies blood by coming down and dividing into branches and sub branches of abdominal and lower organs through the diaphragm. Blood ducts get changed into fine capillaries for reaching each cell. Capillaries get filled with carbon dioxide and other waste products after distributing nutritive elements and oxygen.
Small ducts filled with waste products are called venules. Such several venules make veins by collecting venous blood. Several veins gather impure blood of vertical and lower organs and supply it into the right atrium of the heart.
After providing blood to the heart, the coronary artery reaches into the left atrium by returning from there in the form of coronary vein. In this way, the right atrium stores impure blood of all over the body and supply it into the right ventricle. The impure blood reaches into the lungs through the pulmonary artery for purifying. The blood absorbs oxygen from the breathing air and returns carbon dioxide and other gases into the exhaling air and in this way the blood gets oxygenated. The blood returns back into the left atrium by four pulmonary veins. The atrium supplies pure blood into the left ventricle and thus the circulation of the blood gets completed and this circulation remains continue throughout the life.
Blood circulatory system is that transit system of the body through which sustenance, oxygen, water and all other necessary substances reach in the cells of tissues and waste products of such places are brought. Blood, heart and blood vessels are included in it.