ERYTHROCYTES [RBCs]

Dr. Shaikh Mujeeb AhmedAssistant ProfessorAlMaarefa College

HMIM BLOCK 224

Objectives

• Know the normal range of RBCs.• Enumerate different functions of hemoglobin.• Know the sites of erythropoiesis in different

stages of life.• Stages of erythropoiesis & the requirements.• Explain the clinical conditions related to

erythropoiesis.

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ERYTHROCYTES

• Normal RBC count - 5 million per cubic millimeter (mm3) of blood.

• Male – 5 – 5.5 / mm3

• Female 4.5 – 5 / mm3

• RBC contain hemoglobin which carries O2.

• Main function of RBC – O2 transport, also CO2 transport.

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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.

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HEMOGLOBIN

• 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 α chain [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.

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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.

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HEMOGLOBIN[cont]

• It appears reddish when combine with O2, e.g. Arterial blood.

• It appears bluish when deoxygenated, e.g. venous blood.

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HEMOGLOBIN FUNTIONS

• 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.

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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.

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ERYTHROPOIESIS• Formation and maturation of RBCs.• 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.

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ERYTHROPOIESIS

• 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.

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IMPORTANT

• If we need bone marrow sample for examination, we usually take from iliac crest or sternum.

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MAJOR STEPS IN ERYTHROPOIESIS

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ERYTHROPOIESIS

• As RBC matures, it involves - reduction in size - disappearance of nucleus - acquiring of hemoglobin

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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.

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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.

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IMPORTANT

• 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.

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TEST YOUR KNOWLEDGE

Q . In case of hemorrhage [blood loss], what will happen to rate of Erythropoiesis ?

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

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TEST YOUR KNOWLEDGE

Q. 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.

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RETICULOCYTES

• It is immature erythrocyte.• Normal reticulocyte count 0.5 – 1.5% in blood.• Increased reticulocyte count in blood indicates

high rate of erythropoietic activity.

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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.

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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.

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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

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I Thank Dr. Zahoor for this lecture