Erythropoiesis in Animals

Erythropoiesis in Animals

From stem cell, the formation of reticulocyte takes about 72 hours and conversion of reticulocyte to erythrocyte requires 48 hours. Thus RBC formation requires 5 days time.

Under appropriate stimulation, CFU-E progenitor cells produce proerythroblast. Hb synthesis begins in polychromatophil erythroblast and maximum synthesis occurs in orthochromatic erythroblast.

The metarubricyte ejects the nucleus to become the reticulocyte that contains some mitochondria, ribosomes and endoplasmic reticulum. In 1-2 days, they develop into erythrocytes and enter circulation. 

Regulation of erythropoiesis

The level of oxygen in the tissue is the principle regulatory factor of erythropoietic activity of the bone marrow. The kidney cells, during hypoxia, releases erythrogenin (erythropoietin releasing factor) from the glomeruli, which in turn acts on erythropoietinogen, an µ₂ globulin of plasma and converts it into free erythro­poietin (hemopoietin). Kidney produces 90% of erythropoeitin and liver produces about 10%.

• Erythropoietin as a hormone stimulates hemopoietic stem cells of bone marrow to produce the committed stem cells-proerythroblast, thus initiates erythropoiesis. It stimulates,
  1. The proliferation of rubriblast by mitosis in the developing rubricytes.
  2. Accelerates maturation of the rubricytic cells.
  3. Induces the release of reticulocytes into the circulation.

The role of vitamins and minerals in erythropoiesis

Vitamin B₁₂ and folic acid are essential for the maturation of erythrocytes. Vitamin B₁₂ is required for DNA synthesis and folic acid for RNA synthesis. Macrocytic anemia is a very common in Vitamin B₁₂ and folic acid deficiencies.

Thiamine (B1), Pantothenic acid, Nicotinic acid, Vitamin E and pyridoxine (B₆), riboflavin, biotin and ascorbic acid are essential for erythropoiesis. Deficiency of Vitamin B₆ causes microcytic hypochromic anaemia in pigs. Pantothenic acid deficiency results in deficiency of ALA synthatase in birds and animals. Normocytic anemia in swine and primates is due to Vitamin E deficiency.

Minerals such as iron, copper and cobalt are essential for erythropoiesis. Iron acts as an integral part of Hb which is absolutely essential for Hb synthesis. Copper acts as a co-factor in ALA dehydrase in Hb synthesis. It is part of the enzyme ferroxidase which is necessary for oxidation of ferrous iron to ferric form and is necessary for the incorporation of iron into Hb. Copper deficiency is common in pigs, which may interfere with Fe absorption and utilization. In ruminants cobalt plays a key role for the synthesis of Vitamin B₁₂ by the rumen bacteria which in turn is required for the normal production of erythrocytes.

RETICULOCYTE

A low percentage (1 to 3%) of erythrocytes in circulation has a network of bluish threads within the cell and is called reticulocytes. These cells are immature RBCs, which have entered into the circulation at times of need from blood forming tissues.

In some diseases or due to excessive loss of blood or destruction of RBCs, the reticulocytic number increases in circulation. These cells have less or no O₂ carrying capacity.