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26. What parts does the circulatory system comprise? What is its function?

The circulatory system, the chief transport system of the body consists of three essential parts: the blood, the heart, blood vessels and lymphatic system.

The human heart consists of four chambers, two atria and two ventricles, each made of several layers of cardiac muscle arranged in circles and spirals. During the contraction phase, called the systole, blood is pumped out of the left ventricle into the aorta and then the arteries which carry blood to all parts of the body, and out of the right ventricle into the pulmonary artery and then the lungs. Used blood carrying carbon dioxide is returned to the right atrium through veins to the vena cava during the diastole or relaxation period and newly oxygenated blood returns from the lungs to the left atrium. Valves control the flow of blood from one part of the heart to another.

Arterioles are small arteries and venules are small veins. These two systems are joined by capillaries, the smallest blood vessels. In total there are 70,000 miles of blood vessels in the circulatory system.

The blood which runs through the circulatory system is made up of two parts, plasma and blood cells. Plasma is composed mostly of water and waste substances.

27. Speak on the composition of blood, types of cells in the blood, their functions.

The blood which runs through the circulatory system is made up of two parts, plasma and blood cells. Plasma is composed mostly of water and waste substances.

The corpuscles are cells and are divided into red corpuscles and white corpuscles.

The red corpuscles are minute, disc-shaped bodies. In one cubic millimeter of blood there are about 5,000,000 red corpuscles. Hemo­globin is the coloured pigment in the red corpuscles. It possesses the power of combining with oxygen throughout the body to the tissues. The red corpuscles are, therefore, the oxygen carriers of the body. The white corpuscles or leukocytes are larger than the red cells but less numerous; only 6,000-8,000 in each cubic millimeter of blood.

Leukocytes. About 65 per cent of all white cells are leukocytes.

The function of leukocytes is primarily that of protecting against infection. After the skin is pierced and the wound becomes infected, leukocytes from all the body are attracted to this place.

Lymphocytes. These cells, which comprise about 35 per cent of the white cells, have a nucleus which practically fills the cell.

They are produced in lymph nodes scattered throughout the body; the tonsils are examples of lymph nodes. They are thought to live only a few hours.

28. What are the types of blood? Give short characteristics to main types. Which blood type is most useful for emergencies?

Each person has a particular blood type, depending on the detailed composition of the blood. There are four main types, labeled A, B, O or AB and more than 200 minor types known.

Forty-six per cent of people are blood group O, 42 per cent group A, 9 per cent group B and 3 per cent group AB. The definition of these groups is based on the presence or absence of two chemicals, or agglutinates, A and B. Blood group O contains neither agglutinogen.

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