Red blood cells or erythrocytes

Erythrocytes are the functional component of blood involved in the transportation of gases and nutrients throughout the human body.

1. Red Blood Cells or Erythrocytes Amjad Khan Afridi Chapter # 08

2. Erythrocytes Also called Red Blood Cells Have no nucleus Thin plasma membrane A  lipid bilayer  membrane covers the cell’s  cytoplasm Do not have cell organelles Shaped as a biconcave disk Primary component hemoglobin (Hb) 7.5 µm in diameter Erythrocytes are the functional component of blood involved in the transportation of gases and nutrients throughout the human body.

3. Because of the lack of a nucleus, erythrocytes cannot divide and thus need to be continually replaced by new cells synthesized in the red bone marrow. The lifespan of red blood cells is about 120 days, and the development of red blood cells from stem cells occurs in about seven days via the process of erythropoiesis.

4. Structure of Erythrocytes The mature human erythrocyte has a biconcave, discoid shape and is anucleated . They are approximately 7.5 μm in diameter, 2.6-μm thick at the rim, but only 0.75-μm thick in the center. The biconcave shape of the cell provides a large surface-to-volume ratio and facilitates gas exchange.

5. The average concentration of erythrocytes in the blood is approximately 3.9-5.5 million per microliter ( μL , or mm 3 ) in women and 4.1-6.0 million / μL in men. Erythrocytes are quite flexible, which permits them to bend and adapt to the small diameters and irregular shape of the blood vessels.

6. The plasmalemma (Plasma membrane) of erythrocyte, consists of about 40% lipid, 10% carbohydrate, and 50% protein. A phospholipid bilayer membrane supports the structure of the RBC & also covered the cytoplasm of RBC, which is maintained by a network of proteins that make up the cytoskeleton.

7. The cytoskeleton is composed of proteins like spectrin , actin, band 3 ( anion exchanger-1) , protein 4.1 ( Beatty's Protein) , and ankyrin , which allows for cellular structural integrity as well as malleability. The cytoplasm of erythrocytes lacks all organelles but is densely filled with hemoglobin, which allows the transportation of respiratory gases.

8. The RBC membrane contains integral and  peripheral proteins . Integral proteins distinguish individuals in the form of A, B, O, and AB blood types. They also support the internal structure and bind hemoglobin. Peripheral membrane proteins are found on the inner side of the membrane and help to make the red blood cell extremely elastic.

9. Functions of Erythrocytes RBCs transport oxygen from the lungs to the peripheral tissues to assist. The cells also collect the generated carbon dioxide from the periphery and return it to the lungs for elimination from the body.

10. 10 th January, 2022