This document discusses oxygen and carbon dioxide transport in the blood. Oxygen is transported primarily by binding reversibly to hemoglobin in red blood cells. The oxygen dissociation curve represents the relationship between oxygen content of blood and the partial pressure of oxygen. Carbon dioxide is transported as dissolved CO2, bicarbonate ions, and carbamate compounds. The Bohr and Haldane effects alter hemoglobin's oxygen affinity in response to changes in pH, CO2, and oxygen saturation levels to facilitate oxygen delivery and carbon dioxide removal in the tissues.

1. OXYGEN AND CARBONDIOXIDE
TRANSPORT
Dr. Midhun Mohan K
Junior resident
MD Pulmonary Medicine
Govt. Medical college trivantrum

2. OXYGEN TRANSPORT
• Dissolved form
• In combination with Hb

3. • Oxygen is relatively insoluble in aqueous solutions like blood.
• Oxygen binds reversibly to haemoglobin, enabling the transport of
significant amounts of oxygen.
• Approximately 20ml/100ml of blood at a haemoglobin concentration of
15g/100ml.
• (1 gm Hb carry 1.34 ml of O2 )

4. OXYGEN DISSOCIATION CURVE
• Represents the relationship between the oxygen content of blood and
the partial pressure of oxygen to which is exposed.
• The standard ODC demonstrates the effects of O2—Hb interaction at
standard PH (7.40),temperature(37oC ),and atmospheric pressure (760
mm Hg).

6. • ODC is S or Sigmoid shaped owing to changes in oxygen affinity of
unbound heme groups following the binding of oxygen to another
heme group in the same haemoglobin molecule.
• Changes in affinity brought about by changes in quarternary structure
of haemoglobin that accompanies O2 binding.

7. • The flatness of the curve in the arterial oxygen tension range is an
advantage.
• As long as arterial PO2 remains ≥60 mm Hg , reductions in arterial PO2
(as in lung diseases)will still allow for a relatively normal arterial O2
content.

8. • Once the partial pressure of oxygen reaches 90 to 100 mm Hg , there
is only minimal oxygen binding even at higher oxygen tensions (as the
Hb is almost completely saturated with bound oxygen).

9. Venous Blood
• Normal PO2 at rest is ~ 40 mm Hg.
• ~75% of maximum O2 capacity.

10. • At rest only 25% of oxygen is extracted from blood for metabolism.
• In tissues, the steep slope of the ODC between 20 and 60 mm Hg
facilitates the release of large amounts of oxygen into the tissues with
relatively moderate decrease in oxygen tension.

11. ALTERATIONS OF OXYGEN AFFINITY
Decrease O2 affiity increase O2 affiity
Rise in H+ Fall in H+
Rise in CO2 Fall in CO2
Rise in temperature Fall in temperature
Increase in 2,3DPG Decrease in 2,3DPG

13. • The degree of shift of the ODC is described by P50 (ie; the partial
pressure of oxygen required to saturate 50% of Hb).
• The normal P50 for human blood is 26.5 mm Hg.

14. CO POISONING
• Binding of CO to Hb interferes with oxygen binding and
produces a functional anemia.
• Binding of CO to Hb also increases the affinity of Hb for
oxygen, thus shifting the ODC to the Left.
• This increased affinity hinders the release of O2 in tissues.

15. BOHR EFFECT
• Shift of ODC produced by changes in PCO2 and PH is known as the
Bohr effect.
• Similar to 2,3-DPG, H+ and CO2 bind at sites different from the O2
binding site, decreasing oxygen affinity of Hb by changing it`s
configuration, thus facilitating release of O2.

16. • This effect is minimal at rest (2%-3%)because of the minute difference
in PH between arterial and venous blood (0.03-0.05 PH)units at rest.
• Becomes significant during exercise, with the addition of lactic acid,
from muscle to venous blood.
• This is an adaptive response for improving oxygen delivery at high
levels of exercise.

17. • The deoxygenated haemoglobin is a stronger base and is capable of
buffering more H+ produced during exercise.
• Approximately half of the hydrogen ions released in aerobic
metabolism are buffered in this manner.

18. CARBON DIOXIDE TRANSPORT
• Carbon dioxide is primarily the by-product of aerobic metabolism.
• It is also generated through the buffering of hydrogen ions (H+) from
organic acids, such as lactic acid and ketoacids.
• This buffering occurs through chemical reaction of H+ ions with
intracellular and extracellular bicarbonate ions (HCO3-).

19. • The CO2 produced by these reactions diffuses into capillary blood and
is carried in both chemical combination and physical solution to the
lungs.

20. • Carbon dioxide is transported in three forms in blood:
 Dissolved CO2
 bicarbonate ions
 carbamate compounds.
• The partial pressure of CO2 is low in arterial blood eventhough the total
quantity of CO2 is more than twice that of O2 in arterial blood.

21. THE CARBON DIOXIDE DISSOCIATION CURVE
• The CO2 dissociation curve is very steep.
• As a result, the difference in partial pressures of CO2 between arterial
and venous blood is small when compared to the large arterial–
venous differences in blood PO2.

23. DISSOLVED CO2
• CO2 is 20 times more soluble in aqueous solution than oxygen.
• Only 5% of total CO2 content in blood exists in dissolved form (in
plasma and red cell water) hence is insufficient to facilitate transport
of all the CO2 produced by metabolism.

24. • Only dissolved CO2 crosses the alveolar- capillary membrane.
• Therefore each molecule must be converted into dissolved form for
excretion by ventilation.
• The quantity of dissolved CO2 is directly proportional to the PCO2 in
blood

25. BICARBONATE
• Carbon dioxide combines with water to form carbonic acid, which at
normal PH dissociates into hydrogen and bicarbonate ions.
CO2 + H2O H2CO3 H+ + HCO3
-
• pKa= 6.1

26. • The natural rate of formation of carbonic acid from CO2 and water is
slow.
• Under the influence of the carbonic anhydrase enzyme in the cytosol
of erythrocytes, this reaction is increased (approx. 15,000 times).

27. Two isoenzymes of CA
CA- II is therefore responsible for almost all the CO2-bicarbonate catalysis in
vivo.
CA-I CA-II
High concentration in
erytrocytes
Lesser Conc.(1/6)
Inhibited by intracellular Cl- ions Not inhibited
Lesser intrinsic activity 7 times more intrinsic activity

29. CARBAMATE
• >10% of all CO2 binds to Hb as carbamate.
• These are salts of carbamic acid, formed by the reaction of CO2with
terminal amino groups α and β chains of Hb.
• Deoxygenated Hb binds more CO2 than oxygenated Hb, thus more
CO2 (8 times) can be carried in venous blood at any given PCO2 than in
oxygenated blood.

30. HALDANE EFFECT
• Oxygenated blood at any partial pressure of CO2 contains less total
CO2 content than deoxygenated blood at the same partial pressure.
This is known as the Haldane effect.
• Transport of CO2 in blood as bicarbonate or carbamate is dependent
upon the state of hemoglobin oxygenation.
• These changes are described as “oxylabile.

31. • Changes in configuration of the hemoglobin molecule accompanying
the release of oxygen facilitate binding of CO2 to hemoglobin as
carbamate,that is, oxylabile carbamate formation.
• Formation of both bicarbonate ions and carbamate compounds
releases large quantities of hydrogen ions which need to be buffered
effectively to promote CO2 transport.

32. • Deoxygenated Hb is a stronger base than oxyhaemoglobin and hence
effectively buffers excess H+ produced.
• Haldane effect has a far greater physiological effect on gas transport
than does the Bohr effect.

33. • Without Haldane effect, the difference between arterial and venous
CO2 tensions would be approximately twice the normal value, thereby
increasing tissue PCO2
• Haldane effect accounts for 40% to 50% of total CO2 exchange.