Biology of Disease

protein called transferrin and stored in the liver and spleen cells in a storage
protein called ferritin (Figure 13.4 (A)and(B)). Excessive breakdown of Hb
produces more bilirubin than can be excreted and this accumulates in the
tissues causing jaundice (Chapter 11).

BLOOD CELLS AND PLATELETS

CZhhVg6]bZY!BVjgZZc9Vlhdc!8]g^hHb^i]:YLddY (),

Monocyte

Neutrophil

Basophil

Eosinophil

Lymphoid

stem cell

Pluripotent

stem cell

Myeloid

stem cell

Mast cell

Nucleated

reticulocyte Erythrocyte

Megakaryocyte

Platelets

Eosinophil

progenitor

Granulocyte-

monocyte

progenitor

Pre-B cell

Pre-NK cell NK cell

T cell

B cell

Basophil

progenitor

Thymus

0.0025

mm^2

0.04 mm^2

Counted Not counted

Hemocytometer

Thick cover slip

Blood sample

of 0.1 mm

depth

Figure 13.2 Origin of the cells of the blood. All of the cells of the blood, as well as the
platelets, originate in the bone marrow where progenitor stem cells divide and differentiate to
produce the different cell types. The process of differentiation is controlled by growth factors.
SeeChapter 4for more information on lymphocytes (natural killer (NK), T and B cells).

Figure 13.3 Counting blood cells using a

hemocytometer. Blood is diluted and then pipetted

into a glass chamber of known volume. The

number of cells within the indicated grid is counted

under the microscope and this number, multiplied

by the dilution, gives the number of cells in the

blood sample. Different dilutions need to be

done for erythrocytes and leukocytes. In hospital

laboratories cells counts are done automatically

using instruments called cell counters.