The primary functions of cardiovascular system is to provide an adequate supply to all cells of the body, of materials needed for their proper function and to carry away the west product generated for their metabolism. It is a very well organised transport system of the body. By this system the blood being circulated within a closed system under different pressure gradients, which is creates by the pumping mechanism. Here the heart acts as the central pump.
The cardiovascular system includes the following:
All above the four are differ in structures as well as in functions. The blood volume in our body is limited, but it has to perform unlimited amount of work as a continuous process. Thus we can easily come to the conclusion that the same quantity of blood must be used over and over again. The total blood volume of our body can carry about 1200 ml of oxygen, and this amount can meet up the oxygen needs of the body for about five minutes only. So blood must be re-oxygenated and sent back to the tissue at every five minutes.
Blood get reduced in the tissues and oxygenated in the lungs. Consequently, it has to pass alternately through lungs and tissues and do opposite functions at these two places. So the circulatory system has been divided into two functionally opposite parts:
1) The systemic circulation – passing through the tissues.
2) The pulmonary circulation – passing through the lungs.
The above two systems again meet in the heart.
The circulatory system of man consist of a central pumping organ, i.e. Heart and a network of tube-like structures called blood vessels distributed all over the body. So the circulatory system is called the cardiovascular system.
The human heart is a hollow, cone shaped, muscular organ. An adult heart is weighs about 250-350g. Its upper broad end is called base that remains connected with large vessels and the lower part is tapering, the tip of which is apex. The heart lies in the thoracic cavity in between the two lungs, just beneath the sternum, and remains slightly inclined the left of the body. The apex of the heart lies about 9 cm apart from the midline, on the left side. The heart is enclosed by a covering of double layer membrane called the pericardium, the outer and inner layers are called parietal pericardium and visceral pericardium respectively.
The heart is the most important instrument of the cardiovascular system. The heart is divided into two compartments right and left which are further divided into two chambers each – the upper one known as auricle and the lower one as ventricle. Between each auricle and ventricle there is a non-return valve. The contraction and expansion of the heart give out two rhythmic sounds known as systole and diastole respectively. When heart contracts the pure blood is pushed from the left ventricle into the body through various blood vessels known as arteries. These arteries get further divided into smaller vessels – arterioles – and further into minute blood capillaries. It is in the capillaries that interchange of substances between blood and tissues takes place.
The impure blood carrying carbon dioxide and waste products returns to the heart into the right ventricle through blood vessels known as veins. To run the machinery of cardiovascular system the impure blood is pushed into the lungs through a pulmonary artery where the blood through its haemoglobin exchanges its carbon dioxide for oxygen and gets purified and returns to the heart through the pulmonary vein. Thus the simultaneous actions of supply of pure blood to different organs, receiving back of impure blood from the organs into heart, sending out the blood into lungs for purification and returning of the purified blood back to heart are carried out as a continuous process of cardiovascular system. We shall gradually go for the details of the system in our upcoming following chapters.