Summary

Summary

Blood is a type of connective tissue. It consists of RBCs, WBCs, and platelets suspended in a liquid plasma, called the extracellular matrix. The RBCs, WBCs, and platelets are collectively described as formed ele-ments, but the blood also contains a liquid portion that transports­ these elements. The RBCs or erythrocytes are mostly developed in the red bone marrow. They are primarily involved in the supply of oxygen and nutri-ents to the body tissues. Hemoglobin is responsible for cellular transport of oxygen and carbon dioxide, with most oxygen being bound to hemoglobin. Anemia signifies the blood’s inability to carry enough oxygen. Other conditions involve excessive RBC destruction, or excessive RBC production. The WBCs or ­leukocytes protect the body against disease. Of the leukocytes, B cells are responsible for humoral immunity, and T cells are responsible for cell-mediated immunity. The platelets are vital for blood coagulation. Plasma suspends the cells and platelets of the blood.

Blood transports substances between body cells and the external environment. Blood plasma trans-ports gases and nutrients, helps maintain stable pH, and helps regulate fluid and electrolyte balance. Hemostasis is the stoppage of bleeding and involves the steps of blood vessel spasm, platelet plug forma-tion, and blood coagulation. It helps to maintain a stable internal environment. Blood clotting factors are known as procoagulants.

Blood can be typed on the basis of cell surface antigens. The ABO blood group concerns the presence or absence of antigens A and B. The Rh blood group concerns the Rh antigen, which is present on the RBC membranes of Rh-positive blood, but is negative in Rh-negative blood. The preferred method of blood transfusion is the use of packed red blood cells, in which most leukocytes and plasma have been removed from whole blood. Effects of aging on the blood include conditions such as decreased hematocrit, increased risk of thrombi or emboli, pooling of blood in the legs, ane-mias, clotting disorders, and chronic leukemias.