We can sum up the functions of blood as follows.

a) We know blood transports oxygen and carbon dioxide, thus playing a vital role in respiration. We also carry dissolved food from the small intestine to the tissues, besides transporting hormones. Antibodies and other secretions to various parts o the body. Waste materials formed in the tissues are carried by blood to the respective sites from where they are expelled.

b) Blood is the body’s major weapon of the Defence against infections. Its ability to coagulate protects us from blood loss.

c) Blood regulates the balance of water in our tissues. It makes in excess water, if any, from our cells and also provides them with water when they need it. Our body temperature, too, is regulated by blood. By constant circulation, it distributes and helps out the heat produced in our tissues.

Blood vessels

Blood is carried to different parts of the body n tube like structures called blood vessels. These are of varying thickness, with diameters ranging from 0.001 mm to 1 cm. there are there kinds of blood vessels.


These carry blood from the heart to the other parts of the body. The pumping of blood by the heart into these vessels creates considerable pressure on their walls. They are able take this pressure because their walls are thick.


These carry blood from various parts of the body to the heart. Veins are wide and their walls are thinner than those of arteries. Blood flows through them with less pressure than through the arteries. Veins have valves to prevent blood from flowing back. The blood vessels you see under the skin are veins. You can not see arteries as they lay deeper inside.


Arteries branch into smaller vessels, the finest of which are capillaries. The fact that these are very small makes is possible for them to reach all parts of our tissues. Their thin walls allow oxygen and other materials to diffuse from the blood into the cells. They also allow the capillaries to take up carbon dioxide and other materials from the cells, and carry these into the veins after joining up to from larger and larger vessels.

It is through the capillaries that oxygen and carbon dioxide pass in and out of the alveoli and cells. Capillaries are also involved in the absorption of digested food in the small intestine, its assimilation in the cells, and the filtration of wastes in the kidneys.

The hear

The heart is a muscular organ located between the lungs. It is surrounded by a protective double-membranes bag called the pericardium. The space between the membranes is filled is filled with pericardial fluid, which functions as a shock absorber. An adult’s heart measures 12 cm in length and 9 cm in breadth, and weighs about 300g.

As you know, the heart is made of specialized muscles called cardiac muscles. These work without rest and keep the heart functioning throughout our lifetime. The heart pumps averages of 5 L of blood per minute.

The heart consists of four chambers. The two upper chambers are called the right auricle and the auricle, and the two lower chambers are called the right ventricle and the left ventricle. The walls of the auricles are thin, wile those other ventricles are thick. The auricles are also called atria.



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