Page 307 - Anatomy and Physiology of Farm Animals, 8th Edition

292 / Anatomy and Physiology of Farm Animals

clinical cases to stimulate erythrocyte need for iron on a daily basis. Iron from the
circulation also accumulates in the liver in a
VetBooks.ir production in both humans and animals. retrievable storage form, ferritin.
However, an antibody response to the
After the protein and iron are removed
human molecule occurs in more than
25% of animals, and these antibodies from hemoglobin, a green pigment, biliver­
neutralize endogenous erythropoietin din, remains. This is reduced to bilirubin
as well as the rhEPO. The inappropriate (a yellowish pigment), which is transported
use of rhEPO has been reported in normal to the liver in combination with blood
human athletes in an attempt to increase albumin. The liver conjugates it; then it
their exercise capacity. The potential passes to the gallbladder in the bile and
for abusive use in animal athletes also finally to the intestine, where most of it is
exists. reduced to bilinogens. These are either
Mature erythrocytes of mammals have excreted in the feces (giving the brown
no nuclei. Immature forms in the bone color to feces), or reabsorbed into the blood
marrow do have nuclei, but these are lost and then excreted in the urine as uro­
during the latter stages of development. bilinogen. The reduction in the intestine is
The appearance of large numbers of nucle- accomplished by resident microorganisms.
ated erythrocytes in the circulation is an
indication that immature forms are being Clinical Conditions and Procedures
inappropriately released from the bone Involving Erythrocytes. Icterus ( jaundice)
marrow. In birds and reptiles, nuclei nor- is a syndrome characterized by a yellowish
mally persist in the red cells throughout discoloration of skin, mucous membranes,
the life of the cells. and/or sclera. It results from accumulation
Typically, erythrocytes circulate for only of bilirubin in the blood and may be caused
3 to 4 months after their release from the by liver damage, by occlusion of the bile
bone marrow. The removal and recycling of ducts, or by an increased rate of erythrocyte
senescent erythrocytes is one function of a destruction. In case of either liver damage
group of specialized cells, the monocyte– or blockage of the bile ducts, the bile
macrophage system (formally known as pigments are not secreted into the intestine
the reticuloendothelial system). The mac- but are resorbed into the circulatory
rophages of this system are found fixed or system, causing icterus. When blood
in residence in several sites throughout the damage is excessive, as in some parasitic
body but are especially prevalent in the blood diseases, such as anaplasmosis, the
spleen and liver. These macrophages are bile pigments are liberated into the blood
derived from circulating monocytes, hence faster than the liver can conjugate and
the name of the system. The macrophages secrete them, and icterus results.
phagocytize intact erythrocytes or cellular Hemolysis is the breakdown of erythro-
debris and hemoglobin that are released cytes and the release of hemoglobin.
when erythrocytes disintegrate in the Bacterial or plant toxins, snake venoms,
blood. The macrophages degrade the glo- blood parasites, and hypotonic solutions can
bin portion of hemoglobin and release the cause so much hemolysis that the hemo-
resulting amino acids into the circulation. globin in plasma produces a reddish color,
Iron is removed from the heme portion and the condition is called hemoglobine­
and released into the blood, where it is mia. The hemoglobin can then be excreted
transported in combination with a protein, in the urine, and this is termed hemoglobi­
transferrin. Cells that require iron have nuria (red water). Hemolysis can also be
cell membrane receptors that bind trans- produced in a blood sample by physically
ferrin, and this is the means by which cells disrupting the erythrocytes (e.g., forceful
can take up iron from the circulation. This and rapid expulsion of blood from a syringe).
includes hematopoietic cells in the bone Hemagglutination is clumping of eryth-
marrow, which have the highest metabolic rocytes. Erythrocytes have membrane pro-