08 Respiration and Circulation - part 09 - Red blood corpuscles / Erythrocytes

 


08 Respiration and Circulation - part 09 - Red blood corpuscles / Erythrocytes


Red blood corpuscles / Erythrocytes :
  • Most abundant cells in the human body. 
  • Circular, biconcave and enucleated (in camel and llama they are nucleated).
  • Red colour or RBCs is due to an oxygen carrying pigment, the haemoglobin, in their cytoplasm. 
  • In males, their average number is about 5.1-5.8 million/mm3 (per μL) and in females about 4.3-5.2 million/mm3. This is called total RBC count. 
  • The average life span of RBCs is 120 days. 
  • The process of formation of RBCs is called erythropoiesis.
  • RBCs are produced from haemocytoblasts / reticulocytes. 
  • The erythropoeitic organ of the foetus is the liver and spleen and in the adult, it is mainly the red bone marrow. 
  • Vitamin B12, folic acid and heme protein are required for production of RBCs.
  • The old and worn out RBCs are destroyed in the liver and spleen (graveyard of RBCs). 
  • Condition with increase in the number of RBCs is called polycythemia and with decrease in number of RBCs is called as erythrocytopenia. 
  • The hormone erythropoietin produced by the kideny cells stimulates the bone marrow for production of RBCs.
  • Mature erythrocyte is devoid of nucleus, mitochondria or other membrane bound cell organelles. 
  • Its cytoplasm (stroma) is rich in haemoglobin and O2 carrying proteinaceous pigment that gives red colour to the RBCs and blood. 
  • It also contains an enzyme, carbonic anhydrase.
  • Erythrocytes are responsible for -  
  1. Transport of respiratory gases O2 and CO2
  2. Maintaining pH and 
  3. Viscosity of blood. 
  • They also contribute in the process of blood clotting.
  • The hematocrit is ratio of the volume of RBCs to total blood volume of blood. 
  • It is different for men and women.
Do U Know ?
  • Each erythrocyte approximately contains 270 million molecules of haemoglobin.
  • Normal content of haemoglobin in blood of men is about 14 – 17 gm% and in women it is about 13 – 15 gm%. 
  • Condition with less number of RBCs or less amount of haemoglobin or both is called as anaemia.
  • Each molecule of haemoglobin is a protein-iron complex. 
  • It consists of four polypeptide (globin) chains 2 alpha and 2 beta chains. 
  • An iron – porphyrin (haem) group is attached to each chain and all four chains are bound together. 
  • Each haem group can carry one O2 molecule and thus one haemoglobin molecule can carry four O2 forming oxyhaemoglobin. 
  • CO2 interacts with amino acid residues of globin chains and forms carbaminohaemoglobin. 
  • After haemolysis, haemoglobin is broken down.
  • Its globin part is broken to recycle the amino acids. 
  • Iron of heme group is stored as ferritin in the liver 
  • Porphyrin group of heme is converted into green pigment biliverdin and then into red-orange coloured bilirubin. 
  • These pigments (mainly bilirubin) are added to bile and finally removed out of body along with faeces.

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