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Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter 7<br />

The Erythrocyte: Physiology, Metabolism,<br />

and Biochemical Disorders<br />

John W. Harvey<br />

Department <strong>of</strong> Physiological Sciences<br />

College <strong>of</strong> Veterinary Medicine<br />

University <strong>of</strong> Florida<br />

Gainesville, Florida<br />

I. INTRODUCTION<br />

A. Species Differences in Erythrocyte Shape<br />

B. Functions <strong>of</strong> RBCs<br />

II. HEMATOPOIESIS<br />

A. Stem Cells and Progenitor Cells<br />

B. Hematopoietic Microenvironment<br />

C. Hematopoietic Growth Factors<br />

D. Erythropoiesis<br />

III. DEVELOPING ERYTHROID CELLS<br />

A. Morphological and Metabolic Changes<br />

B. Iron Metabolism<br />

C. Hb Synthesis<br />

D. Reticulocytes<br />

E. Abnormalities in Erythroid Development<br />

IV. MATURE RBC<br />

A. Membrane Structure<br />

B. Shape and Deformability<br />

C. Blood Group Isoantigens<br />

D. Membrane Transport<br />

E. Metabolism <strong>of</strong> Adenine Nucleotides<br />

F. Carbohydrate Metabolism<br />

G. Embden-Meyerh<strong>of</strong> Pathway<br />

H. Diphosphoglycerate Pathway<br />

I. Hb Oxygen Affinity<br />

J. Pentose Phosphate Pathway<br />

K. Nature <strong>of</strong> Oxidants in Biology<br />

L. Metabolic Protection against Oxidants<br />

V. DETERMINANTS OF RBC SURVIVAL<br />

A. Oxidative Injury<br />

B. RBC Aging and Normal Life Spans<br />

C. Anemia <strong>of</strong> the Newborn<br />

VI. INHERITED DISORDERS OF RBCS<br />

A. Cytosolic Enzyme Deficiencies<br />

B. Membrane Abnormalities<br />

C. Miscellaneous Abnormalities<br />

REFERENCES<br />

I . INTRODUCTION<br />

Mammalian erythrocytes or red blood cells (RBCs) are<br />

anucleate cells that normally circulate for several months in<br />

blood despite limited synthetic capacities and repeated exposures<br />

to mechanical and metabolic insults. Their primary<br />

purpose is to carry hemoglobin (Hb), a heme-containing<br />

protein that accounts for more than 90% <strong>of</strong> the protein<br />

within RBCs ( Quigley et al. , 2004 ). The benefits <strong>of</strong> having<br />

Hb contained within cells, as opposed to free in plasma,<br />

include the much slower turnover in blood (free Hb has a<br />

half-life <strong>of</strong> only a few hours), the metabolic capability <strong>of</strong><br />

RBCs to maintain iron in Hb in the functional ferrous state,<br />

and the ability to control Hb oxygen affinity by altering the<br />

concentrations <strong>of</strong> organic phosphates, especially 2,3-diphosphoglycerate<br />

(2,3DPG). In addition, the presence <strong>of</strong> free<br />

Hb in plasma in concentrations normally found in whole<br />

blood would exert an osmotic pressure several times greater<br />

than that normally exerted by plasma proteins, pr<strong>of</strong>oundly<br />

affecting the movement <strong>of</strong> fluid between the vascular<br />

system and tissues.<br />

A . Species Differences in Erythrocyte<br />

Shape<br />

Most RBCs in normal dogs, cats, horses, cattle, and sheep<br />

occur in the shape <strong>of</strong> biconcave disks (discocytes). The<br />

degree <strong>of</strong> biconcavity is most pronounced in dogs and less<br />

so in cats and horses. RBCs from goats generally have a<br />

flat surface with little surface depression; a variety <strong>of</strong> irregularly<br />

shaped RBCs (poikilocytes) may be present in clinically<br />

normal goats ( Jain, 1986 ). The apparent benefit <strong>of</strong> the<br />

biconcave shape is that it gives RBCs high surface area-tovolume<br />

ratios and allows for deformations that must take<br />

place as they circulate.<br />

<strong>Clinical</strong> <strong>Biochemistry</strong> <strong>of</strong> <strong>Domestic</strong> <strong>Animals</strong>, 6th <strong>Edition</strong> 173<br />

Copyright © 2008, Elsevier Inc.<br />

All rights reserved.

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