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ERYTHROCYTES [RBCs]
Lecture – 2
Dr. Zahoor Ali Shaikh
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ERYTHROCYTES
• 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.
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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.
HEMOGLOBIN FUNTIONS
• Transports O2.
• Also transports CO2.
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HEMOGLOBIN FUNTIONS (cont)
• 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 [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.
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ERYTHROPOIESIS [RBC FORMATION]
• 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.
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CONTROL OF ERYTHROPOIESIS (cont)
• 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?
Answer
• 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.
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RBC BREAKDOWN (cont)
• From Heme, iron is released and passes back to
blood. Porphyrin portion of heme 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 ?
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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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THANK YOU