21

THE BLOOD AND ITS DISORDERS

The blood is the sticky red fluid circulating in our veins and arteries. Its main functions are: transport of oxygen, carbon dioxide, foodstuffs and hormones, defence against infections, and regu-lation of pH and temperaturę.

The blood is a connective tissue. There are four primary constituents in the blood. They are: the fluid matrix called the plasma and three types of cells,namely, erythrocytes, leukocytes, and thrombocytes. Plasma is the fluid matrix of the blood. It is colourless and contains seven classes of substances: water, salts, proteins, carbohydrates, wastes, gases and hormones. Water constitutes 91 per cent of plasma. Other materials are dissolved or suspended in this water. Plasma takes part in transport of some substances.

Erythrocytes or red blood cells (RBC) are discoid, non-nucleated cells. They contain the red pigment and protein called haemoglobin. The human blood comprises 4.4 to 5 million red blood cells per cubic millimetre. Erythrocytes carry oxygen from the lung capillarieś to the body cells and carbon dioxide in the opposite direction. Oxygen combined with haemoglobin gives the blood dark bluish red colour.

Fig. 7. The blood cells.

Leukocytes or white blood cells (WBC) are ameboid, nucleated cells. They are larger than erythrocytes. Their number is about 8,000 per cubic millimetre. There are two main groups of leukocytes: the granulocytes (granular leukocytes) which have granules in their cytoplasm and agranulocytes (non-granular leukocytes) which have no granules in their cytoplasm. Granulocytes are basophils, eosinophils and neutrophils. Agranulocytes are lymphocytes and monocytes. In generał, leukocytes form the defensive mechanism of the body; they are part of the immune system. They ingest bacteria and produce antibodies against pathogenic organisms.

Thrombocytes (blood platelets) are the smallest cells in the blood. They are non-nucleated and discoid in shape. The blood contains approximately 300,000 thrombocytes per cubic millimetre. They are mainly concemed with blood coagulation or blood clotting.

Lymph is aliąuid which consits of blood plasma, leukocytes aiidprotein. The function of lymph is similar to that of blood. It circulates among the body tissues carrying oxygen and food. It also collects the waste materials from the cells.    ,

E. Donesch-Jeżo - English for Medical Students and Doctors - 1

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