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ERYTHROCYTES [RBCs]. Lecture – 2 Dr. Zahoor Ali Shaikh. ERYTHROCYTES. Normal RBC count - 5 million per cubic millimeter (mm 3 ) of blood. RBC contain hemoglobin which carries O 2 . Main function of RBC – O 2 transport, also CO 2 transport. STRUCTURE OF RBC.

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erythrocytes rbcs


Lecture – 2

Dr. Zahoor Ali Shaikh

  • Normal RBC count - 5 million per cubic millimeter (mm3) of blood.
  • RBC contain hemoglobin which carries O2.
  • Main function of RBC – O2 transport, also CO2 transport.
structure of rbc
  • RBC are biconcave discs 7.5 - 8 micrometer (µm) in diameter and 2µm thick at outer edge and 1µm thick at the center.
  • RBC membrane is flexible and can change as RBC pass through capillary with a narrow diameter of 5µm.
  • Hemoglobin is found only in RBC.
  • Normal Hemoglobin – 15 gram / dl .
  • Structure of Hemoglobin
  • It has two parts

1.Globin – protein has 4 polypeptide chain

2 αchain [141 amino acid in each chain]

2 β chain [146 amino acid in each chain]

2.Heme – 4 iron containing groups, each is bound to one polypeptide chain.

hemoglobin cont
  • Each iron atom present in Heme [iron is in ferrous state] can combine reversibly with one molecule of O2, therefore, each hemoglobin molecule can take four O2 molecules in the lungs.
  • 98.5% of O2 is carried in the blood bound to hemoglobin.
  • Hemoglobin is a pigment naturally colored because of iron content.
hemoglobin cont1
  • It appears reddish when combine with O2, e.g. Arterial blood.
  • It appears bluish when deoxygenated, e.g. venous blood.


  • Transports O2.
  • Also transports CO2.
  • Combines with H+ ion, therefore, plays part as buffer.
  • Combines with carbon monoxide (CO), therefore, can cause CO poisoning.
  • Nitric Oxide (NO) gas combines with hemoglobin and this NO is released at the tissues and causes vasodilation.
important note
  • RBC is mainly a plasma membrane having hemoglobin.
  • RBC has no nucleus and organelle.
  • Enzyme in RBC

- Glycolytic enzyme, it generates energy ATP for active transport at membrane.

- Carbon anhydrase enzyme for CO2 transport.

erythropoiesis rbc formation
  • In adult RBC are formed in bone marrow.

[Bone marrow is cellular tissue that fills the internal cavities of bones].

  • Bone marrow normally generates new RBC to replace old ruptured cells.
  • In the fetus – RBC formation takes place in yolk sac during first 03 months of life then liver and spleen up to 7th month of intrauterine life.
  • Bone marrow starts from 4th month till birth of baby.
erythropoiesis rbc formation1
  • In children, most bones produce RBC by red bone marrow then red bone marrow is replaced by fatty yellow bone marrow that does not produce RBC.
  • In adults, red bone marrow remains in sternum, ribs, vertebrae, pelvis, upper end of long bones e.g. femur, humerus.
  • If we need bone marrow sample for examination, we usually take from iliac crest or sternum.
  • As RBC matures, it involves

- reduction in size

- disappearance of nucleus

- acquiring of hemoglobin

nutrional requirement of rbc production
  • 1. Amino Acids – for synthesis of globin of hemoglobin.
  • 2. Iron – If iron deficiency, it causes microcytic hypochromic anemia [small RBC with less Hb].
  • 3. Vitamins – Vitamin B12 and folic acid for synthesis of nucleo protein. If less DNA metabolism affected and results in megloblastic anemia [mega means large].
  • 4. Trace elements – e.g. copper, zinc, cobalt
  • 5. Hormones – Cortisol, growth hormone.
control of erythropoiesis
  • It is done by Erythropoietin hormone.
  • Source of Erythropoietin – mainly kidney.
  • Erythropoietin is produced by the kidneys due to reduced O2 delivery to kidney.
  • Main stimulus for production of erythropoietin is hypoxia e.g. high altitude, anemia.
  • Hormone erythropoietin is secreted in blood and stimulates erythropoiesis in the bone marrow by acting on committed RBC.
  • Normal RBC count 5 millions / mm3.
  • In every person, 25 trillion – 30 trillion RBC are moving through our blood vessels.
  • Average life of RBC is 120 days.
  • RBC are replaced at average rate of 2 millions to 3 millions / sec.
test your knowledge q in case of hemorrhage blood loss what will happen to rate of erythropoiesis
TEST YOUR KNOWLEDGEQ . In case of hemorrhage [blood loss], what will happen to rate of Erythropoiesis ?

Answer: Rate of Erythropoiesis can be increased more than 6 times.

TEST YOUR KNOWLEDGEQ. When you donate blood, your circulating RBC supply is replaced in how much time?
  • During blood donation about 450ml of blood is donated.
  • Donated Plasma is replaced in 2-3 days.
  • RBC are replaced in 36 days [range 20–59 days], therefore, repeat donation of blood is recommended after 3 months.
  • It is immature erythrocyte.
  • Normal reticulocyte count 0.5 – 1.5% in blood.
  • Increased reticulocyte count in blood indicates high rate of erythropoietic activity.
synthetic erythropoietin
  • Synthetic erythropoietin is given to kidney failure patients or those patients under going chemotherapy for cancer as chemotherapy affects bone marrow and developing RBC.
rbc breakdown
  • Average life of RBC is 120 days then it is destroyed.
  • When RBC breakdown, they release hemoglobin.
  • Hemoglobin is taken by macrophages.
  • Hemoglobin is broken into heme + globin.
  • Globin is degraded into amino acids which are used.
  • From Hemoglobin, iron is released and passes back to blood. Porphyrin portion of hemoglobin molecule is converted into bilirubin.
  • Bilirubin is carried to liver [bound with albumin] and secreted in bile by liver.
what you should know from this lecture
  • Normal RBC count, Size, Shape and Function
  • Life Span of RBC
  • Erythropoiesis in Adults & Children
  • Nutritional Requirement for Erythropoiesis
  • Erythropoietin
  • Functions of Hemoglobin
  • Importance of Reticulocyte count in blood
  • Hemoglobin Breakdown