Biochemistry of blood.
Respiratory function of
Pathobiochemistry of blood.
Red Blood Cells (erythrocytes)
The most numerous type in the blood.
•The erythrocytes doesn’t contain nucleus, chromatine
•The erythrocytes doesn’t contain mytochondrias, thus АТP
producing due to the anaerobic glycolisis till to the lactate
•The glycolisis has features. During it the 2,3 BPG will be
produced, not 1,3 BPG. This compound need for joining О2 to
hemoglobin: low concentration of 2,3 BPG will increase the
affinity hemoglobin (Нв) to О2.
• The PPP is the main path for producing of reductive
equivalents NADPН2 for taking part in glycolisis
Red blood cells are responsible for the
transport of oxygen and carbon dioxide.
In adult humans the
hemoglobin (Hb) molecule
consists of four
two alpha (α) chains of
141 amino acids and
two beta (β) chains of
146 amino acids
Each of these is attached
the prosthetic group heme.
There is one atom of iron at
the center of each heme.
One molecule of oxygen
can bind to each heme.
The reaction is reversible.
Transport of oxygen by hemoglobin
Hemoglobin has all the requirements of an ideal
-It can transport large quantities of oxygen.
-It has great solubility.
-It can take up and release oxygen at appropriate partial
-It is a powerful buffer.
Oxygenation and oxidation
• When hemoglobin carries oxygen, the Hb is
oxygenated. The iron atom in Hb is still in
the ferrous state.
• Oxidized hemoglobin is called Met-Hb; then
iron is in ferric state and the oxygen carrying
capacity is lost.
Oxygen Dissociation Curve
(ODC)• The ability of hemoglobin to load and unload
oxygen at physiological pO2 (partial pressure
• At the oxygen tension in the pulmonary
alveoli, the Hb is 97% saturated with oxygen.
Normal blood with 15mg/dl of Hb can carry
20ml of O2/dl of blood.
• In the tissue capillaries, where the pO2 is only
40mm of Hg, the Hb is about 60% saturated.
So physiologically, 40% of oxygen is released.
Oxygen binding to one subunit of Hb,
increases the affinity of the other subunits
for additional oxygens. In other words, the
first one is the hardest, the rest are easy.
Anaemia is a shortage of RBCs and/or the
amount of haemoglobin in them.
Carbon dioxide (CO2) combines with water forming
carbonic acid, which dissociates into a hydrogen ion
(H+) and a bicarbonate ions:
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3−
95% of the CO2 generated in the tissues is carried in
the red blood cells:
It probably enters (and leaves) the cell by diffusing
through transmembrane channels in the plasma
membrane. (One of the proteins that forms the
channel is the D antigen that is the most important
factor in the Rh system of blood groups.)
Once inside, about one-half of the CO2 is directly
bound to hemoglobin (at a site different from the one
that binds oxygen).
The rest is converted — following the equation above —
by the enzyme carbonic anhydrase into
bicarbonate ions that diffuse back out into the plasma
hydrogen ions (H+) that bind to the protein portion of
the hemoglobin (thus having no effect on pH).
Only about 5% of the CO2 generated in the tissues
dissolves directly in the plasma.
When the red cells reach the lungs, these reactions are
reversed and CO2 is released to the air of the alveoli.
The ability of hemoglobin to release oxygen, is affected by pH, CO2
and by the differences in the oxygen-rich environment of the lungs and
the oxygen-poor environment of the tissues. The pH in the tissues is
considerably lower (more acidic) than in the lungs. Protons are
generated from the reaction between carbon dioxide and water to form
CO2 + H20 -----------------> HCO3- + H+
This increased acidity serves a two fold purpose.
- First, protons are lower the affinity of hemoglobin for oxygen,
allowing easier release into the tissues. As all four oxygens
are released, hemoglobin binds to two protons. This helps to
maintain equilibrium towards the right side of the equation.
This is known as the Bohr effect, and is vital in the removal of
carbon dioxide as waste because CO2 is insoluble in the
bloodstream. The bicarbonate ion is much more soluble, and
can thereby be transported back to the lungs after being
bound to hemoglobin.
- If hemoglobin couldn’t absorb the excess protons, the
equilibrium would shift to the left, and carbon dioxide couldn’t
In the lungs, this effect works in the reverse
direction. In the presence of the high oxygen
concentration in the lungs, lead to the proton
affinity decreasing. As protons are shed, the
reaction is driven to the left, and CO2 forms as
an insoluble gas to be expelled from the lungs.
The proton poor hemoglobin now has a greater
affinity for oxygen, and the cycle continues.
Effect of BPG
pO2 (mm Hg)
0 20 40 60 80 100 120 140 160
pO2 vs p50=8
pO2 vs p50=26
Hb + BPG
BPG is the main
player in Hb
further to right
Myoglobin and Hemoglobin
Mb is monomer, Hb is a tetramer (ex. a2b2).
Hb subunits are structurally similar to Mb, with 8
a-helical regions, no b-strands and no interior
Both contain one heme prosthetic group per
Both Mb and Hb contain proximal and distal
Affinity of Mb for oxygen is high, affinity of Hb for
oxygen is lower and more variable.
The iron atom may either
be in the Fe2+ or Fe3+
state, but ferrihemoglobin
cannot bind oxygen. In
temporarily oxidizes Fe to
(Fe3+), so iron must exist
in the +2 oxidation state in
order to bind oxygen. The
hemoglobin found in the
inactive (Fe3+) state by
reducing the iron center.
Sickle cell hemoglobin (HbS)
H b A 1
H b S
( h e t e r o z y g o u s )
S i c k l e c e l l t r a i t
H b S
( h o m o z y g o u s )
S i c k l e c e l l d i s e a s e
Polymerization of HbS
Association shown in
previous figure is
repeated over and over
to produce large, rod-like
aggregates that bind
oxygen poorly and distort
shape of erythrocytes.
Sickle cell trait is usually asymptomatic, but
strenuous exercise at altitude could elicit
sickling and destruction of erythrocytes.
This lowers serum Hb and hematocrit, while
raising Hb breakdown products such as
bilirubin, which can accumulate to form
Rare, since a-gene is duplicated (four genes per diploid
Usually more severe than b-thalassemia because
there is no substitute for b-gene in adults.
Almost all b- thalassemias are deletions
In α thalassemia intermedia (αo
appearance of HbH (β4)
In α thalassemia major (αo
), Hb Bart’s
(γ4) is predominant (usually lethal).
BPG is ineffective in HbH & Hb Bart’s.
More common, since β gene is present in only
one copy per chromosome.
Less severe than α thalassemia, since δ chain
can effectively substitute in adults.
The γ chain can also persist into adulthood
In βδ thalassemia major (βδ0
) excess α
chains do not form soluble homotetramers.
• Normal plasma bilirubin level ranges from 0.2-0.8
mg/dl. The unconjugated bilirubin is about 0.2-0.6
mg/dl, while conjugated bilirubin is only 0- 0.2.
• If the level of plasma bilirubin exceeds 1 mg/dl, the
condition is called hyperbilirubinemia.
• Levels between 1 and 2 mg/dl are indicative of
• When the bilirubin level exceeds 2 mg/dl, it diffuses
into tissues producing yellowish discoloration of
skin and mucous membrane resulting in jaundice.
• Van den Bergh test is a test for detection of
• Depending on the nature of the
bilirubin elevated, the condition
may be grouped into conjugated or
• Based on the cause it may also be
classified into congenital and
• They results from abnormal uptake, conjugation or excretion of
bilirubin due to inherited defects.
Here the defect is in conjugation.
In type 1 (Congenital non-hemolytic jaundice), there is sever
deficiency of UDP glucuronyl transferase.
The disease is often fatal and the children die before the age 2.
Jaundice usually appears within the first 24 hours of life.
Unconjugated bilirubin level increases to more than 20
mg/dl, and hence Kernicterus is resulted.
2- Acquired Hyperbilirubinemias
It is also called as neonatal hyperbilirubinemia.
In all newborn infants after the second day of life, mild jaundice
This transient hyperbilirubinemia is due to an accelerated rate of
destruction of RBCs and also because of the immature hepatic system
of conjugation of bilirubin.
In such cases, bilirubin does not increase above
It disappears by the second week of life.
3- Hemolytic Jaundice
A) Hemolytic Disease of the Newborn:
This condition results from incompatibility between
maternal and fetal blood groups.
Rh+ve fetus may produce antibodies in Rh-ve mother,
leading to Rh incompatibility.
When blood level of bilirubin is more than 20mg/dl, the
capacity of albumin to bind bilirubin is exceeded.
In young children before the age of 1 year, the blood-
brain barrier is not fully matured, and therefore free
bilirubin enters the brain (Kernicterus).
It is deposited in brain, leading to mental retardation.
B) Hemolytic Diseases of Adults:
This condition is seen in increased rate of
It usually occurs in adults.
The characteristic features are increase in
unconjugated bilirubin in blood, absence of
bilirubinuria and excessive excretion of UBG in
urine and SBG in feces.
Common causes are:
• Autoimmune hemolytic anemias.
• Toxins like carbon tetrachloride.
4- Hepatocellular Jaundice
• The most common cause is viral hepatitis,
caused by hepatitis viruses A, B, C, D, or G.
• Conjugation in liver is decreased and hence
free bilirubin is increased in circulation.
Jaundice• Conjugated bilirubin is increased in blood, and it is excreted in urine.
• UBG will be decreased in urine or even absent.
• Since no pigment are entering into the gut, the feces become clay colored.
• The common causes are:
1. Intrahepatic cholestasis. This may be due to cirrhosis or hepatoma.
2. Extrahepatic obstruction. This may be due to stones in the gallbladder or biliary
tract; carcinoma of head of pancreas.