The primary function of blood is to deliver O2 and energy to the tissues, and remove CO2 and waste products. It is also important for the defence and immune systems, regulation of temperature, and trans- port of hormones and signalling molecules between tissues. Blood consists of plasma (Chapter 2) and blood cells. Red blood cells contain haemoglobin and transport respiratory gases (Chapter 28), whereas white cells form part of the defence system (Chapter 10). In adults, all blood cells are produced in the red bone marrow. Normal values for cell counts, haemoglobin and proportion of blood volume due to red cells (haematocrit or packed cell volume; estimated by centrifuging a blood sample) are shown in Figure 8a. Platelets are discussed in Chapter 9.
Plasma contains several important proteins (Fig. 8b), with a total concentration of 65–83 g/L. Most, other than γ-globulins (see below), are synthesized in the liver. Proteins can ionize as either acids or bases because of the presence of both NH2 and COOH groups. At pH 7.4 they are mostly in the anionic (acidic) form. Their ability to accept or donate H+ means they can act as buffers (Chapter 36). Plasma proteins have important transport functions, as they bind many hormones (e.g. cortisol and thyroxine) and metals (e.g. iron). They are classified into albumin, globulin and fibrinogen fractions. Globulins are further classified as α-, β- and γ-globulins. Examples and their major functions are shown in Figure 8b.