Biology of Disease

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.

Plasma Concentration

[Total protein]/gdm^366

[Fibrinogen]/gdm^3 3.1

[Albumins]/gdm^3 32.6

[Globulins] (excluding fibrinogen)]/gdm^3 30.1

Cells and platelets Number

Erythrocytes

male / dm–3

female / dm–3

4.4 5.9s 1012

3.8 5.2s 1012

Leukocytes / dm–3 4

11 s 109

Platelets / dm–3 2.5 5.0s 109

*Blood volume of 78 and 66 cm^3 kg–1body weight in males and females respectively

Table 13.1Composition of the blood*

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.

13.2 Blood Cells and Platelets

All of the cells of the blood originate from pluripotent stem cells in the bone

marrow (Figure 13.2). Chemical signals, such as cytokines (Chapter 4), direct

primordial stem cells to develop in different ways to produce erythrocytes,

leukocytes of various types, and megakaryocytes, which are the precursors

ofplatelets.

Normoblasts are erythroid cells that arise from divisions of pluripotent stem

cells. Eventually these lose their nuclei giving rise to reticulocytes, which

contain mRNAs for globins and are still able to synthesize hemoglobin (Hb),

and which are the precursors of the erythrocytes. The reticulocytes circulate in

the blood for 1 2 days before maturing to erythrocytes, and normally constitute

1

 2% of the circulating red cells. Erythrocytes are the most numerous cells

in the blood. Adult males and females have erythrocyte counts of about 5.5

and 4.8 s 1012 dm–3, respectively. The number of cells in a given volume of

blood can be determined using a hemocytometer (Figure 13.3). About 2 s 1011

mature erythrocytes are formed daily. They have no nuclei or other organelles

and are biconcave in shape (Figure 13.1). Erythrocytes circulate for about 120

days and are then removed from circulation and destroyed by macrophages in

the liver and spleen. Hemoglobin is the red protein found in the erythrocytes

that carries dioxygen (O 2 ) and which also plays an important role in buffering,

maintaining the pH at 7.4 p 0.1 (Chapter 9). The iron-containing heme

is removed from the Hb of defunct erythrocytes and its porphyrin ring is

converted to bilirubin, which is excreted in the bile. The iron is conserved

and recycled (Box 13.1). Iron circulates in the blood attached to a transport

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B)

Figure 13.1 (A) Shows the appearance of a

normal blood smear when examined with a

microscope. The erythrocytes predominate with

the occasional leukocyte being visible. (B) The

erythrocytes are biconcave in shape and their

centers appear lighter in color.

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