DISORDERS OF THE BLOOD
Blood is a protein-rich fluid called plasma in which erythrocytes and leukocytes, sometimes called red and white blood cells respectively, and platelets are suspended (Figure 13.1). The cells constitute about 40–45% of the volume of the blood. The blood is pumped around the body by the heart through the arteries that supply the capillaries and is returned to the heart in the veins . The main functions of the blood are to distribute oxygen, nutrients and hormones and other signaling molecules between tissues and to remove carbon dioxide and other waste products. Plasma contains the proteins of the clotting system and of the immune systems.
Plasma is blood from which the cells have been removed. It contains a range of plasma proteins in addition to the clotting and immune system proteins mentioned above, nutrients, such as glucose, waste materials, for example urea, and a range of electrolytes in solution. If it is allowed to clot, the clear straw-colored liquid remaining after removal of the clot is called serum. The composition of the blood and the plasma is given in Table 13.1.
In a text of this size it is not, of course, possible to discuss each type of blood disorder and attention will focus only on the major types of diseases likely to be normally encountered.