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Week6 RBC:an explanation on the process of RBC formation
1. Course Title: PHS 213 – HUMAN PHYSIOLOGY I
TOPIC: RED BLOOD CELL (RBC)
2. OUTLINE
Introduction
Morphological features of RBC
RBC count
Erythrocyte Sedimentation Rate (ESR)
Structural adaptation of RBC
Functions of RBC
Production of RBC (Erythropoiesis)
Regulation of RBC production
Haemoglobin and transport of Oxygen
Destruction of Senile RBC
Clinical Correlates
3. Introduction
Recap
Composition of Blood:
1. Cellular components - RBC (Erythrocytes), WBC (Leucocytes),
Plateletes (Thrombocytes)
2. Plasma- water (98%), ions, plasma proteins (albumin, globulin,
fibrinogen)
Functions of blood
Packed Cell Volume (PCV)/ Hematocrit value
4. Morphological features of RBC
Biconcave disc and non-nucleated
Diameter = 7-8 µm, thickness = 2.1 µm, Surface
area= 130 µm2, Volume= 80-100 fL (femtolitres,
10-15 L)
Each RBC contains approximately 30 pg
(picogram 10-12) of Hb
5. RBC Count
Male: 4.3 – 5.3 x 10 12 / L (130 – 150g Hb)
Female: 3.8 – 4.8 x 10 12 / L (110 – 140g Hb)
Newborn: 7 – 8 x 10 12 / L
6. Erythrocyte Sedimentation Rate (ESR)
The rate at which the erythrocytes settle down.
Importance: Indirect way to diagnose certain chronic inflammatory diseases such
as: tuberculosis and arthritis
Factors influencing ESR
RBC size and count
Plasma proteins
pH of blood plasma
Lipidemia
7. Factors that can accelerate ESR
Physiological factors: Gravidity, menstruation
Pathological factors: tumor, liver diseases
Values: Male = 2 - 5 mm/h
Female = 3 -8 mm/h (less RBC, more fibrinogen)
8. Structural adaptation of RBC
The shape of RBC has three important adaptations:
• Diapedesis: Flexibility; ability to squeeze through narrow capillaries without
disrupting its cell membrane
• Faster rate of gas exchange in and out of the of the cell due to the greater surface
area and shorter distance to the central region (when compared to a sphere of
same volume)
• Reduces wall tension as the cell swells after taking up CO2 from the tissue
9. Functions of RBC
O2 and CO2 transport
Buffer by regulating ECF pH
Blood group determination
10. Production of RBC
The production of RBC is called erythropoiesis.
It is produced in the bone marrow under the control of erythropoietin; a hormone majorly
synthesize in the peritubular capillaries of the kidney in response to local hypoxia
In fetus, erythropoietin is majorly synthesize by the liver
The production takes approximately 7 days
Lifespan of RBC is approximately 120 days and is removed from the circulation by macrophages in
the bone marrow, liver or spleen
14. Haemoglobin and transport of oxygen
Haemoglobin (Hb) is the constituent of the red blood cell that combines with oxygen.
Consists of two parts; The haem and the globin.
Haem is a complex of a porphyrin ring and iron in the ferrous (Fe2+) state.
Iron is an essential part of haemoglobin and its deficiency due to dietary inadequacy or
loss through chronic haemorrhage leads to anaemia
The haem is conjugated with globin, a polypeptide consisting of four subunits
15. The amount of oxygen the blood carries is described as the oxygen content of blood
Vast majority of oxygen is carried bound to haemoglobin and a very small amount is dissolved in the
plasma. The total amount of oxygen carried by blood can be obtained by adding these two amounts
Under physiological condition, the haemoglobin is almost fully saturated with oxygen as blood leaves the
lungs, and each gram of Hb contains 1.39ml of oxygen
However, by the time it reaches the systemic circulation this amount has fallen slightly due to the addition of
a small volume of venous blood from the pulmonary and coronary circulations
Therefore in the arterial circulation, one gram of Hb is around 98% saturated and contains 1.34ml of oxygen
16. The amount of oxygen dissolved in the blood is proportional to the partial pressure.
At 37 degrees Celcius (body temperature), 0.23ml oxygen dissolves in each litre of
blood per kPa. Therefore the O2 content of blood can be calculated from the equation
below:
O2 content of blood (L) = (Hb x 1.34 x SaO2) + (0.23 x PaO2)
= (150 x 1.34 x 98%) + (0.23 x 13)
≈ 20.3 ml/L
17. Oxygen combines reversibly with the ferrous ion in the haemoglobin molecule to form
oxyhaemoglobin. Hb + O2 ↔ HbO2
In the lungs, where the partial pressure of oxygen is high, the forward reaction
oxygenating haemoglobin is favoured
Hb + O2 HbO2
In the tissues where the partial pressure of oxygen is low the reverse reaction reducing
haemoglobin is favoured.
Hb + O2 HbO2
18. Thus, haemoglobin combines with oxygen in the lungs and releases it at the level
of the tissues
Both the oxygenation and reduction of haemoglobin are extremely rapid reactions
taking less than 0.01 seconds.
19. The relationship between the saturation of haemoglobin and the partial pressure
of oxygen in the blood is described by the oxygen dissociation curve.
A right shift in the curve means that haemoglobin releases its oxygen relatively
easily. This occurs during an acidosis (decreased pH)
A left shift in the curve means that haemoglobin accept more oxygen. This occurs
during an alkalosis (increased pH)
21. The dissociation curve can be shifted to the right or left by a number of factors.
The curve is shifted to the right by:
1. Increased hydrogen ions (reduced pH)
2. Increased carbondioxide
3. Increased temperature
4. Increased DPG (2,3 diphosphoglycerate)
22. DPG is formed in RBCs as a product of glycolysis. It is a highly charged ion and
when it combines with the beta chain of haemoglobin, it displaces oxygen.
During exercise there is an increase in temperature, hydrogen ions, CO2 and DPG
in the tissues, all the conditions associated with a rightward shift in the curve to
help deliver oxygen to the active muscles.
23. Fetal Haemoglobin (HbF)and Adult Haemoglobin (HbA)
HbA has two alpha and two beta globin chains
HbF is structurally different from the HbA; In HbF, the two beta chains are replaced by
two gamma chains.
This structural difference means that fetal haemoglobin binds less avidly with DPG and,
as we know, DPG reduces the amount of oxygen that combines with haemoglobin.
Consequently, HbF has a higher affinity for oxygen than adult haemoglobin which is
demonstrated by a leftward shift in the oxygen dissociation curve.
24. This difference in haemoglobin physiology enables the fetus to extract oxygen
from maternal blood at the placenta
Adult haemoglobin quickly replaces fetal haemoglobin after birth thus correcting
the position of the curve and allowing the baby to utilise oxygen normally.
2.5% of adult circulating haemoglobin is HbF.
25. Destruction of Senile Erythrocytes
Reticuloendothelial cells, particularly those in spleen destroy the senile RBCs and release hemoglobin and later
degrade the hemoglobins
The heme part of the hemoglobin is further broken down into free iron (Fe+3) and biliverdin; a green substance that
is further reduced to bilirubin (a bile pigment)
the iron enter into the blood circulation and return to the red bone marrow to be re-used for the synthesis of new
hemoglobin
If not needed immediately for this purpose, excess iron is stored in the liver
The iron of RBCs is actually recycled over and over again
The globin or protein portion of the hemoglobin molecule is also catabolized by proteases into constituent amino
acids to be reused for the synthesis of new hemoglobin in the bone marrow
26. The liver removes bilirubin from circulation and excretes it into bile.
The Bile is secreted by the liver into the duodenum and passes through the small
intestine and colon.
Bilirubin is therefore eliminated in feces, and gives feces their characteristic brown
color.
In the colon some bilirubin is changed to urobilinogen by the colon bacteria.
27. Destruction of Senile RBC (Adapted from Essential of Medical Physiology by K
Sembulingam)
29. Sickle cell Anaemia
This is a haemoglobinopathy with autosomal recessive inheritance.
The genetic defect leads to the substitution of valine for glutamine at position six
on globin’s beta chain, creating HbS rather than HbA
There are a number of genotypes that make up the range of patients suffering
from sickle cell disease. The two most common are:
1 HbSS – patients who are homozygous and have sickle cell disease
2 HbSA- patients who are heterozygous and have sickle cell trait
30. Sickle cell Anaemia (Cont’d)
At low partial pressures of oxygen (5-5.5kPa) deoxygenated HbS becomes insoluble
It forms long crystals called tactoids which cause red cells to become sickle shaped and
rigid
The distorted cell shapes and associated increased blood viscosity promote venous
stasis
This leads to local blood vessel obstruction causing ischaemia and tissue infarction.
These events are termed a sickle cell crisis
31. Sickle cell Anaemia (Cont’d)
These cells have a decreased survival time of only 10-20 days
Therefore, patients with sickle cell disease suffer from a chronic anaemia (haemolytic)
and are often jaundiced (due to conversion of haem to bilirubin).
Patients who have sickle cell trait are also at risk of a sickle cell crisis but only at very
low partial pressures of oxygen as their erythrocytes only contain 20 to 45% HbS
A sickledex test can confirm the presence of haemoglobin S and electrophoresis can
differentiate between trait and disease. Electrophoresis can also determine the
proportion of HbA to HbS in the blood.
32. Thalasseamia
It is an inherited disease of haemoglobin production. Patients with the disorder
have a reduced or absent production of globin chains
It is commonly found in people of Mediterranean origin.
