Abnormalities of RBC Concentration in animals
Abnormalities of RBC Concentration in animals are Polycythemia, Oligocythemia and Anemia.
Polycythemia in Animals
It is otherwise known as erythrocytosis. It is a condition of increased number of RBCs in the circulation. It is of two types.
Physiological (secondary) polycythemia
An increase in RBCs occurs as a compensatory measure (in high altitude of 14000 to 17000 feet to compensate low PO2). Whenever tissues become hypoxic because of too little oxygen in the atmosphere, for example at high altitude or because of failure of delivery of oxygen in the tissues as in cardiac failure, then the blood forming organs automatically produce large quantities of extra RBCs i.e 30% above the normal.
Increased Hb requirement during heavy muscular exercise to meet increased oxygen demand. In sports animals (racehorse, hunting dogs) RBC elevation is a normal feature.
Increased environmental stress / temperature, the spleenic contraction, and increased RBC synthesis by the bone marrow cause increased number of RBCs into the circulation.
Hemoconcentration due to water loss that occurs in vomiting, diarrhoea, prolonged high fever and burns also causes polycythemia.
Pathological polycythemia
Due to decreased O2 supply to the tissue, chronic carbon monoxide poisoning, myeloid (bone marrow) cancer, pulmonary emphysema, repeated hemorrhage.
Polycythemia vera is the condition due to bone marrow cancer (myeloid leukemia). It occurs as a result of genetic aberration in the hemocytoblastic cell line that produces the blood cells.
Oligocythemia in Animals
Reduction in the number of erythrocytes in the circulation is called as oligocythemia. Oligocythemia in animals are two types-
Physiological oligocythemia
Physiological oligocythemia occurs due to hemodilution; RBC number per unit volume is reduced. Example: pregnancy.
Pathological oligocythemia
Pathological oligocythemia is also known as anaemia.
Anemia in Animals
Abnormal reduction in the number of the erythrocytes or the hemoglobin content in the blood or both.
Causes of Anemia
- Excessive whole blood loss occurs in hemorrhage or by blood sucking parasites (Hookworms, ticks), increased destruction of RBCs by the reticuloendothelial cells.
- Impaired RBC production and Hb synthesis, due to deficiency of Fe, Cu, Vitamin B12 and folic acid.
- Hemolytic:
- Disease caused by blood parasites, (babesiosis) or drugs like sulphanamides, antimalarial drugs and high doses of aspirin (analgesic)
Anemia due to defective blood formation
- Aplastic anemia
- It occurs due to lack of functional bone marrow caused by excessive x-ray treatment or bone marrow cancer, certain industrial chemicals, drugs etc.
- Anemic anemia
- Megaloblastic anemia:
- It is due to deficiency of iron, folic acid, Vitamin B12 (extrinsic factor) and intrinsic factor of the gastric mucosa.
- Microcytic and hypochromic anemia:
- It results due to deficiency of iron results in small sized, decreased number of RBCs and low Hb content.
- Macrocytic and hyperchromic anemia:
- Lack of extrinsic factor, the Vitamin B12 causes decreased number of RBCs, large sized RBCs and high Hb content because the erythroblasts cannot proliferate rapidly enough to form normal number of RBCs, the cells that are formed are mostly oversized, bizarre in shape and have a fragile membrane.
- Pernicious anemia:
- It occurs due to the deficiency of the intrinsic factor of the gastric mucosa that interferes with the Vitamin B12 absorption.
- Megaloblastic anemia:
Anemia due to excessive blood loss or increased RBC destruction
- Hemorrhagic anemia– Excessive blood loss due to accident, peptic ulcers etc.
- Hemolytic anemia– Following acute destruction of RBCs (haemolysis) the number of RBCs is below normal, but the RBC size and Hb content are normal, known as normocytic and normochromic anemia.
Causes
- Blood parasites: Eg. babesiosis, theileriosis and trypanosomiasis;
- Chemicals: Copper, lead, nitrate and nitrite.
Anemia due to abnormal structure of RBC
- In some hereditary diseases the defects are with the RBC membrane – e.g., sickle cell anemia, defects in the globin chain structure (thalassemia) or its synthesis or the deficiency of the enzymes of the RBCs energy system, the pyruvate kinase and glucose 6 phosphate dehydrogenase (G.6-PD).
- Sickle cell anemia:
- In this type of anemia the cells contain an abnormal type of hemoglobin called as Hb “S”. It is caused by abnormal composition of β chains of the hemoglobin.
- When this type of hemoglobin is exposed to low concentration of oxygen it precipitates into long crystals inside the erythrocytes. These crystals elongate the cell and it gives the appearance of sickle shape.
- The precipitated hemoglobin also damages the cell membrane so that the cells become highly fragile leading to anemia.
- Thalassemia:
- It is otherwise known as Cooley’s anemia or Mediterranean anemia. It occurs due to defect in the synthesis of α or β peptide chains to form hemoglobin or due to deficiency of enzymes of the RBC energy system, pyruvate kinase and G-6-PD thereby depressing the hemoglobin synthesis.
- Sickle cell anemia: