The human circulatory system consist of the heart and blood vessels. Heart is situated inside the thoracic cage and consists of four chambers. The four chambers are two atria and two ventricles. The right atrium receives impure blood through large veins from the upper and lower regions of the body. Through an opening namely atrioventricular opening the right atrial blood passes into the right ventricl From the right ventricle arises the pulmonary trunk. The pulmonary trunk divides and breaks up into capillaries in the lung. Due to contraction of the right ventricle, the blood is carried to the lungs. In the alveoli of the lungs the impure blood gives of carbon dioxide and takes up oxygen and thus the gas purification is done.
The pure blood coming from the lungs is carried through atrioventricular opening to the left ventricle. A large artery known as the aorta arises from the left ventricle. The left ventricle contracts and the pure blood is pumped out to the aorta. The aorta and its atrial branches which break up into capillaries carry the pure blood to the head and neck regions, superior and inferior extremities, thorax, abdomen and trunk. The veins carries the impure blood from different regions of the body provided valves into the right atrium. This course of human circulatory system is called major circulation. The right atrium sends blood to the right ventricle and the cycle is repeated. The amount of blood ejected per ventricle per minute is about 5 litres and which is known as cardiac output. Heart beats from 70 to 80 times per minute.
– It is well known to us that the blood is the most important fluid in our body. So in human circulatory system the blood plays most important role. In a human body there has a quite bit of blood that is about 5 litres, weighing about 1/13 of the total body weight. The blood carries nutrition and oxygen to all the cells and tissue of the body. It is not possible without this vital fluid to feed all of the organs of the body. Blood is a salty taste red fluid. Apparently it is a red fluid, but when viewed in the microscope, it is seen to contain different types of cells floating in a liquid called plasma. The cells are known as red blood cells, and white blood cells which are divided further into different type of cells. The quantity of red blood cells which are also known as erythrocytes in a healthy person is about 4 to 5 million per cubic millimetre of blood. The red colour of the blood is due to a pigment which contains iron named the haemoglobin . Without the red blood cells it will be impossible for the blood to carry oxygen which is mainly due to to the haemoglobin which have a property to absorb oxygen in the lungs.
The white blood cells in human circulatory system which are medically known as leucocytes, and number of which varies from 5000 to 9000 per cubic millimetre. The lymphocyte perform the protective function of the body, that means, the destroy bacteria and other harmful particles which may damage or interrupt the function of the body or the organs of the body. Blood also contains varying amounts of salts like potassium, sodium etc. and also some carbohydrates proteins etc.
The blood vessels which carry the pure oxygenated blood to different organs are called the arteries , where as the blood vessels which bring impure blood from different organs called the veins. One of the important phenomena associated with this important fluid is that of clotting of the blood. The body which take the responsibility of clotting the blood called the platelet . The substance called fibrinogen in the blood plasma for which due to a cut or injury would leads to continuous oozing of blood from the blood vessels leading ultimately to death. Platelet is the substance which is marvel in nature changes into fibrin after coming in contact with the air and entangles the blood cell into a clot which is very important for the human circulatory system.