Erythrocyte/RBC of Animals

Erythrocyte/RBC of Animals

Functions of erythrocytes

Transport hemoglobin which in turn carries oxygen from the lungs to the tissues.

RBCs contain large quantity of carbonic anhydrase which catalyzes the reversible reaction between carbon dioxide and water. Thereby makes it possible for the water of the blood to transport enormous quantities of carbon dioxide from the tissues to the lungs in the form of bicarbonate.

Hemoglobin in the cells is an excellent acid base buffer. Therefore, the RBCs are responsible for most of the acid base buffering power of whole blood.

Shape of RBC

• The mammalian RBCs are usually non-nucleated and non-motile cells, biconcave circular disc with central pale spot. Its shape differs in various species of animals:
  1. Dog, Cow, Sheep: Markedly biconcave.
  2. Horse and cat: Shallow concaving,
  3. Goat: Very shallow or flat surfaced erythrocytes.
  4. Camel and Deer: Elliptical and sickle shaped.
  5. Cold blooded animals (amphibians and birds): Elliptical and nucleated.

Significance of biconcavity of RBCs

RBC of animals increase the surface area thus facilitating the exchange of oxygen and carbon dioxide carried by the RBCs.

Structure of RBC

The cell membrane of RBC is made up of lipids (lecithin, cephalin and cholesterol) and glycoprotein encloses a spongy inner structure called the stroma.

 The RBC membrane protein, Spectrin forms the inner lining of the membrane, whereas the outer layer is formed by glycoproteins, have the blood group antigens. The cell membrane is highly permeable to lipid soluble substances, glucose, urea and water.

 Hemoglobin is deposited in the inter-spaces of the spongy stroma. The surface of mature erythrocyte is smooth, while the immature RBCs have relatively rough surface.

Size of RBC

Average diameter of RBC ranges from 4.1 to 7.5 µm

Surface area‚ varies from 57-67m² / kg body weight in mammals. It is lowest in goat (lesser diameter) and highest in man (greater diameters).

Composition of erythrocytes

Erythrocyte contains 62 – 72% water and 35% solids. Of the solids, 95% is contributed by Hb and the remaining 5% by cell and stromal protein, lipids, phospholipids, cholesterol, cholesterol esters, neutral fat and vitamins.

RBC metabolism

Energy is required for RBCs to-

1. To maintain the shape and flexibility of the cell membrane.
2. To preserve high K⁺, low Na⁺ and low Ca⁺⁺ ions within the RBCs against the concentration gradient of these ions of plasma.
3. To maintain iron in ferrous (Fe⁺⁺) state (to reduce ferric to ferrous state, NADH and NADPH are required).
4. To generate reduced glutathione (anti-oxidant); this helps to maintain the ferrous state.
5. To generate 2,3 Diphospho glycerate (DPG) for O₂ dissociation.
6. Mitochondria are absent in mature erythrocytes. These cells derive their energy from glucose metabolism via anaerobic Embden- Meyerhoff (EM) pathway (90%) and oxidative pentose cycle (10%) which produce NADH and NADPH. Kreb’s cycle is very much reduced in activity.

Concentration of RBCs

The concentration of RBC depends on various factors such as interspecies, intraspecies and diurnal variation, age, sex, environment, exercise, nutritional status, climate and altitude.