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Respiratory system
L4
Faisal I. Mohammed, MD, PhD
Yanal A. Shafagoj MD, PhD
University of Jordan
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Transport of Oxygen and Carbon Dioxide

Oxygen transport
 Only about 1.5% dissolved in plasma
 98.5% bound to hemoglobin in red blood cells
 Heme portion of hemoglobin contains 4 iron
atoms – each can bind one O2 molecule
 Oxyhemoglobin
 Only dissolved portion can diffuse out of blood
into cells
 Oxygen must be able to bind and dissociate from
heme
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Oxygen in blood:
Blood of a normal
person contains
about 15 gm of Hb in
each 100 ml of
blood.
Oxygen Hb
Oxygen in soln.
98.50%
Each gram of Hb can
bind with a
1.50%
maximum of 1.34 ml
of O2
OXYGEN IN THE BLOOD in Milliliters:
200 ml in 1litre arterial blood.
Relationship between Hemoglobin and
Oxygen Partial Pressure




Higher the PO2, More O2 combines with Hb
Fully saturated – completely converted to oxyhemoglobin
Percent saturation expresses average saturation of
hemoglobin with oxygen
Oxygen-hemoglobin dissociation curve
 In pulmonary capillaries, O2 loads onto Hb
 In tissues, O2 is not held and unloaded
 75% may still remain in deoxygenated blood
(reserve)
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Hemoglobin and Oxygen


Other factors affecting affinity of Hemoglobin for
oxygen
Each makes sense if you keep in mind that
metabolically active tissues need O2, and produce
acids, CO2, and heat as wastes
 Acidity (pH)
 PCO2
 Temperature
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Hemoglobin and 02 Transport



280 million
hemoglobin/RBC.
Each hemoglobin
has 4 polypeptide
chains and 4 hemes.
In the center of each
heme group is 1
atom of iron that
can combine with 1
molecule 02.
Insert fig. 16.32
Hemoglobin
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How does Hemoglobin carry Oxygen?

Hemoglobin exists in two forms:
 Oxyhemoglobin: HbO2
O2 + Hb
HbO2
 Iron in Hb binds to O2
 4 O2 molecules per Hb molecule
 Deoxyhemoglobin

The fraction of all the Hemoglobin in the form of
Oxyhemoglobin is expressed as Hemoglobin
saturation.
Hemoglobin

Methemoglobin:

Has iron in the oxidized form (Fe3+).

Lacks electrons and cannot bind with 02.


(continued)
Blood normally contains a small amount.
Carboxyhemoglobin:


The reduced heme is combined with carbon
monoxide.
The bond with carbon monoxide is 210 times
stronger than the bond with oxygen.

Transport of 02 to tissues is impaired.
Hemoglobin (continued)


Oxygen-carrying capacity of blood determined by its
[hemoglobin].
 Anemia:
 [Hemoglobin] below normal.
 Polycythemia:
 [Hemoglobin] above normal.
 Hemoglobin production controlled by erythropoietin.
 Production stimulated by PC02 delivery to kidneys.
Loading/unloading depends:
 P02 of environment.
 Affinity between hemoglobin and 02.
Oxyhemoglobin Dissociation Curve


Graphic illustration of the % oxyhemoglobin
saturation at different values of P02.
 Loading and unloading of 02.
 Steep portion of the sigmoidal curve, small
changes in P02 produce large differences in %
saturation (unload more 02).
Decreased pH, increased temperature, and increased
2,3 DPG:
 Affinity of hemoglobin for 02 decreases.
 Greater unloading of 02:
 Shift to the curve to the right.
Oxygen-hemoglobin Dissociation Curve
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Oxyhemoglobin Dissociation Curve
Insert fig.16.34
Effects of pH and Temperature



The loading and
unloading of O2
influenced by the
affinity of
hemoglobin for 02.
Affinity is
decreased when pH
is decreased.
Increased
temperature and
2,3-DPG:

Shift the curve to the
right.
Insert fig. 16.35
Effect of 2,3 DPG on 02 Transport


Anemia:
 RBCs total blood [hemoglobin] falls, each RBC
produces greater amount of 2,3 DPG.
 Since RBCs lack both nuclei and
mitochondria, produce ATP through
anaerobic metabolism.
Fetal hemoglobin (hemoglobin f):
 Has 2 -chains in place of the -chains.
 Hemoglobin f cannot bind to 2,3 DPG.
 Has a higher affinity for 02.
Inherited Defects in Hemoglobin Structure
and Function


Sickle-cell anemia:
 Hemoglobin S differs in that valine is substituted for
glutamic acid on position 6 of the b chains.
 Cross links form a “paracrystalline gel” within the
RBCs.
 Makes the RBCs less flexible and more fragile.
Thalassemia:
 Decreased synthesis of a or b chains, increased
synthesis of g chains.
Muscle Myoglobin

Red pigment found
exclusively in striated
muscle.
 Slow-twitch skeletal
Insert fig. 13.37
fibers and cardiac
muscle cells are rich in
myoglobin.
 Have a higher affinity
for 02 than
hemoglobin.
 May act as a “gobetween” in the transfer
of 02 from blood to the
mitochondria within
muscle cells.
 May also have an 02 storage function in cardiac muscles.
Bohr Effect




As acidity increases (pH
decreases), affinity of Hb
for O2 decreases
Increasing acidity enhances
unloading
Shifts curve to right
PCO2
 Also shifts curve to right
 As PCO2 rises, Hb unloads
oxygen more easily
 Low blood pH can result
from high PCO2
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Temperature Changes
Within limits, as
temperature increases,
more oxygen is
released from Hb
 During hypothermia,
more oxygen remains
bound
2,3-bisphosphoglycerate
 BPG formed by red
blood cells during
glycolysis
 Helps unload oxygen
by binding with Hb


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Fetal and Maternal Hemoglobin



Fetal hemoglobin has a
higher affinity for
oxygen than adult
hemoglobin
Hb-F can carry up to
30% more oxygen
Maternal blood’s
oxygen readily
transferred to fetal
blood
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Carbon dioxide in blood
CO2 produced by cells is carried by the blood in three forms
 In physical solution Plasma/Erythrocyte: 7%
 As Carbamino-Hemoglobin : 23%
 CO2 + Hb  HbCO2
 As Bicarbonate ions: 70%
 Mostly in the Erythrocyte which has the enzyme, Carbonic
anhydrase (Catalyses the formation of Carbonic acid 5000
times.)
 CO2 + H2O  H2 CO3 [H+] + [HCO3-]
Carbon dioxide in blood
transported from the body cells back to the
lungs (Tidal Co2) as:
Phy. Soln.
CarbaminoHb
Bicarbonate
7%
23%
70%
CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3
Chloride shift
 HCO3- accumulates inside RBCs as they pick up
carbon dioxide
 Some diffuses out into plasma
 To balance the loss of negative ions, chloride (Cl-)
moves into RBCs from plasma
 Reverse happens in lungs – Cl- moves out as moves
back into RBCs
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Thank You
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