Life span and Hemolysis of RBCs in animals
Life span of erythrocytes
| Cattle | Sheep | Goat | Horse | Dog | Cat | Pig | Poultry |
| 125-150 | 140-150 | 125-150 | 140-150 | 100-120 | 70-80 | 51-79 | 20-30 |
Site of destruction of erythrocytes
In most of the domestic animals bone marrow functions as a chief site of destruction of erythrocytes, whereas in man it is the spleen. In the birds liver acts as an organ of destruction of erythrocytes.
Hemolysis
The erythrocytes have a remarkable capacity to change their shape when they pass through the capillaries but they become less deformable when they reach the end of their life span.
Two types of destruction of erythrocytes takes place- Intravascular hemolysis and Extravascular hemolysis.
Intravascular hemolysis
About 10% of aged RBCs undergo intravascular hemolysis within the capillaries due to loss of compressibility of RBCs caused by increased membrane permeability and osmotic change.
When this occurs the hemoglobin is released, which combine with haptoglobulin which is removed by the cells of the mononuclear phagocytic system (MPS).
Extravascular hemolysis
About 90% of the aged RBCs are directly destroyed by the mononuclear phagocytic system (MPS).
The Hb and proteins are catabolised by the MPS cells. The MPS (also known as reticulo-endothelial system) includes the histiocyte or macrophages, stellate or Kupffer cells of the sinusoids of the liver, spleen, mononuclear cells of bone marrow and lymph nodes.
The globin of the Hb is degraded to amino acids and is reutilized. Iron removed from the heme is stored in the MPS cells in the form of ferritin or hemosiderinand utilised for the synthesis of hemoglobin or enters the plasma and combine with apotransferrin to form transferrin. The transferrin enters the bone marrow to produce more erythrocytes.
The heme is converted to bile pigments, biliverdin (a green pigment) and then reduced to bilirubin (a yellow pigment). The free bilirubin enters the plasma, binds with albumin and transported to liver. In the liver bilirubin is conjugated with glucuronic acid, secreted in bile to enter intestine. Large intestinal bacteria reduce the bilirubin to urobilinogen, most of that are excreted in feces in the oxidised form of urobilin or stercobilin which impart colour to feces.
Part of the urobilinogen is reabsorbed into the enterohepatic circulation and reexcreted in bile. Some of the urobilinogen in the plasma enters the kidneys to be excreted in urine as urobilin.
Globin protein portion of hemoglobin is broken down to amino acid and used in the formation of new hemoglobin or other proteins.
Hemolysis caused by external agents like
- Blood parasites: Babesiosis, theileriosis, trypanosomiasis and sarcocystosis.
- Chemicals: Copper, lead, nitrate and nitrite poisoning.
