Ganong's Review of Medical Physiology, 23rd Edition

524
SECTION VI
Cardiovascular Physiology

compete with O
2
for binding to deoxygenated hemoglobin,
decreasing the affinity of hemoglobin for O
2
by shifting the
positions of the four peptide chains (quaternary structure).
The details of the oxygenation and deoxygenation of hemo-
globin and the physiologic role of these reactions in O
2
trans-
port are discussed in Chapter 36.
When blood is exposed to various drugs and other oxidizing
agents in vitro or in vivo, the ferrous iron (Fe
2+
) that is nor-

mally in the molecule is converted to ferric iron (Fe

3+

), form-

ing

methemoglobin.

Methemoglobin is dark-colored, and

when it is present in large quantities in the circulation, it

causes a dusky discoloration of the skin resembling cyanosis

(see Chapter 36). Some oxidation of hemoglobin to methemo-

globin occurs normally, but an enzyme system in the red cells,

the dihydronicotinamide adenine dinucleotide (NADH)-

methemoglobin reductase system, converts methemoglobin

FIGURE 32–3
Development of various formed elements of the blood from bone marrow cells.
Cells below the horizontal line are
found in normal peripheral blood. The principal sites of action of erythropoietin (erythro) and the various colony-stimulating factors (CSF) that
stimulate the differentiation of the components are indicated. G, granulocyte; M, macrophage; IL, interleukin; thrombo, thrombopoietin; SCF, stem
cell factor.

IL-1

IL-6

IL-3

Hemopoietic

stem cell

Bone marrow

lymphocyte

precursor

GM-CSF GM-CSF

IL-5

GM-CSF

thrombo

GM-CSF

erythro

Megakaryocyte

M-CSF G-CSF

Neutrophil Eosinophil Basophil

Polymorphonuclear

cells

Tissue

macrophage

BT

Lymphocytes

Red blood Platelets

cell

Juvenile

Monocyte

Segmented

Monocyte

Reticulocyte

Late normoblast

IL-4

IL-3

C o m m i t t e d s t e m c e l l s

(progenitor cell)

Bursalequiv. Thymus

GM-CSF

G-CSF

SCF