Plan
► Concept of blood. Composition of blood. Functions of blood.
► Modern concept of immunological properties of blood. Theory of blood groups. Rules of blood transfusion (hemotransfusion).
► Hemostasis (arrest of bleeding). Types of hemostasis.
Concept, Composition, Functions of Blood
Blood is a component of the internal environment of the body. Blood is often viewed as a kind of tissue in which interstitial fluids predominate over cell elements. In this context blood is regarded as a kind of a biological fluid. The ratio of cell elements to the liquid portion of blood is termed hematocrit. Cell elements account for 40-48%, and the liquid portion accounts for 5260% of the total blood volume. The liquid part of blood is plasma.
Cell Composition of Blood (Formed Elements of Blood)
Blood consists of the following cells: erythrocytes (red blood cells - RBCs), leukocytes (white blood cells - WBCs) and platelets, or thrombocytes.
Erythrocytes (RBCs) are non-nucleated cells. They contain hemoglobin protein, which gives the blood red color. Hemoglobin participates in transport of gases - O2 and CO2. There are from 4 500 000 to 5 000 000/1 mm3, or 4.5-5.0 × 1012/l of RBCs in human blood.
Leukocytes (WBCs) are cells of the white line of blood. There are from 6000 to 8000/1 mm3, or 6.0-8.0 × 109/l WBCs in blood. Leukocytes have a non-uniform composition: 63% of them are granulocytes (containing granules in the cytoplasm), and 37% are agranulocytes (containing no granules). Granulocytes include neutrophilic, basophilic and eosinophilic cells (neutro-phils, basophils and eosinophils, respectively). Agranulocytes are lymphocytes and monocytes.
Thrombocytes are small blood platelets produced by cells of the bone marrow and playing an important role in hemostasis and thrombosis. It is thrombocytes, or platelets, that maintain fluid condition of blood, provide lysis of formed thrombi and protect vessel wall against injury. Blood contains 180-320 × 109/l platelets.