This document discusses the transport of carbon dioxide in the body. It notes that CO2 is produced during cellular respiration and diffuses into tissue capillaries before being transported back to the lungs. CO2 is transported in three forms: dissolved in plasma, as bicarbonate ions, and bound to hemoglobin. The majority (70%) is transported as bicarbonate ions via reactions that involve carbonic anhydrase. Transport is facilitated by pressure gradients and the Haldane effect, which enhances CO2 unloading in the lungs and loading in tissues. Hypoventilation and hyperventilation can disrupt acid-base balance by altering CO2 levels.

1. Transport of
Carbon Dioxide
Dr. Sai Sailesh Kumar G
Assistant Professor
Department of Physiology
RDGMC

2. Why to remove CO2
 To maintain PH, acid-base balance

3. Transport of Co2
 In the tissues, oxygen reacts with various food stuffs to
form large quantities of C02.
 This Co2 enters the tissue capillaries and is
transported back to the lungs.
 Co2 like oxygen, combines with the chemical
substance (Hb), that increases the Co2 transport 15-20
folds.

4. Transport of Co2
 Transport of Co2 is not a problem even in the most
abnormal conditions.
 Co2 can usually be transported in far greater quantities
than can oxygen.
 Under normal resting conditions, an average of 4 ml of
carbon Dioxide is transported from tissues to the lungs
in each 100 ml of blood.

5. Diffusion of CO2
 When oxygen is used by the cells, all of it becomes CO2 and
increases intra cellular PCO2
 Due to pressure gradient, CO2 diffuses from cells into tissue
capillaries
 In the lungs, it diffuses from pulmonary capillaries into the alveoli
and expired
 Each point of the process, CO2 diffuses exactly opposite to the
diffusion of O2
 CO2 diffuses 20 times rapidly than O2.
 The pressure difference required for CO2 transport is very less
when compared to O2

6. CO2 Pressures
 Intra cellular PCO2 is 46 mmHg
 Interstitial PCO2 is 45 mmHg
 Thus there is only 1 mmHg pressure difference
 PCo2 of arterial blood entering tissues is 40 mmHg
 PCo2 of venous blood leaving tissues is 45 mmHg
 PCo2 of blood entering pulmonary capillaries at arterial
end is 45 mmHg
 PCo2 of alveolar air is 40 mmHg
 Thus there is pressure gradient of 5 mmHg

7. CO2 Pressures
 Pulmonary capillary blood entering the lungs at
arterial end has PCo2 of 45 mmHg
 Alveolar PCO2 is 40 mmHg
 CO2 diffuses so rapid
 Pulmonary capillary blood pCO2 becomes 40 mmHg
before it has passed more than about one third
distance through the capillaries

9. Chemical forms in which Co2 is
transported
 Co2 diffuses out of the tissues in dissolved molecular
Co2 form.
 On entering the tissue capillaries, Co2 initiates a host
of almost instantaneous physical and chemical
reactions.
 These Physical and chemical reactions are essential
for the transportation of Co2.

10. Dissolved state
 Small portion of Co2 is transported in dissolved state to the lungs
 PCo2 of venous blood is 45 mmHg
 PCo2 of arterial blood is 40 mmHg
 The amount of Co2 dissolved in the fluid of blood at 45 mmHg is
about 2.7 mL/DL.
 The amount of Co2 dissolved in the fluid of blood at 40 mmHg is
about 2.4 mL/DL.
 The difference is 0.3 mL. That is only 0.3 mL of Co2 is transported
in dissolved form by each 100 ml of blood flow.

11. Bicarbonate form
 The dissolved Co2 in the blood reacts with water to form carbonic acid
 This reaction occurs so rapidly in RBC (fraction of second)
 The protein required for this reaction is carbonic anhydrase (present in
RBC)
 In another fraction of second, the carbonic acid formed in RBC,
(H2Co3), dissociates into hydrogen and bicarbonate ions (H+ and
HCO3-). This step occurs with out enzymes
 Most of the hydrogen ions combines with hemoglobin in the RBC (Hb
is a powerful acid-base buffer)

12. Fate of Bicarbonate ions
 Many bicarbonate ions diffuse from RBC into plasma
 At the same time chloride ions diffuse from plasma into RBC
 This diffusion is made possible by presence of bicarbonate-
chloride carrier protein in RBC membrane (Band 3 protein)
 This is called chloride shift or Hamberger phenomenon
 Followed by this, water enters RBC (water shift)
 This is the reason for larger size and high chloride content of
RBC in venous blood than arterial blood

13. Chloride shift

14. PCV of venous blood is more
 RBC of venous blood has high volume
 More water

15. Bicarbonate form
 70% of Co2 transport occurs in this form
 In lungs, chloride shift will reverse and releases CO2
 When carbonic anhydrase inhibitor (Acetazolamide)
is administered to an animal to block the action of
carbonic anhydrase in RBC
 Co2 transport from the tissue becomes so poor
 Raise in PCo2 up to 80 mmHg (normal PCo2 is 45
mmHg)

16. Carbonic anhydrase
 Enzyme present at
1. Gastric mucosa- for formation of HCl
2. RBC – for formation of CO2 transport
3. PCT of kidney – for sodium absorption
4. Eye – For production of aqueous humor
5. Pancreas – speed up the reaction (combination of
water and CO2)

17. Carbonic anhydrase blocker
 Acetazolamide
 Treatment of glaucoma
 Acetazolamide tablets given
 This drug is used in past as diuretic

18. Carbaminohemoglobin form
 Transport of CO2 in combination with hemoglobin and plasma
proteins
 CO2 reacts directly with amine amine radicals of hemoglobin
molecule to form carbamino hemoglobin (CO2 Hgb)
 This does not require enzymes
 Reduced hemoglobin more readily form carbamino hemoglobin
 This combination is reversible so that the CO2 can be
released into alveoli where PCO2 is lower than the pulmonary
capillaries
 2,3 DPG depress the formation of carbaminohemoglobin

19. Carbaminohemoglobin form
 Small amounts of CO2 also reacts in the same way with
plasma proteins in the tissue capillaries
 This reaction is much less significant
 The quantity of the plasma proteins in the blood is only
one-forth as great as the quantity of hemoglobin
 30% of CO2 is transported in carbaminohemoglobin form
 1.5 mL of Co2 is transported in carbaminohemoglobin
form in 100 mL of blood

20. Chloride shift at the level of lungs

21. Carbon dioxide dissociation
curve
 PCO2 on x-axis
 Volumes % of CO2 on y axis

23. Haldane effect
 Favors CO2 unloading or loading by change in the
pressures of oxygen
 Oxygen pressure changes help loading/ unloading of
CO2
 High oxygen pressure helps unloading of CO2
(lungs)
 Lower oxygen pressure helps loading of CO2
(tissues)
 Haldane effect is reverse of Bohr effect

24. Haldane effect
 When there is high PO2 (lungs =104 mmHg)
 Oxygen binds with hemoglobin
 Hemoglobin becomes more acidic
 Hemoglobin releases hydrogen ions
 Hydrogen ions reacts with bicarbonate ions
 Formation of H2CO3
 Dissociation of H2CO3 into H2O and CO2
 CO2 unloaded (enters alveoli)

25. Haldane effect
 At the level of tissues
 PCO2 is 45 mmHg
 PO2 is 40 mmHg
 Lower PO2
 Favors loading of CO2
 This causes 52 volumes % of CO2 to be loaded

26. Haldane effect
 At the level of lungs
 PCO2 is 45 mmHg
 PO2 is 40 mmHg (imagine no change in pO2)
 No Haldane effect
 This causes decrease in the % volumes of CO2 to
50 ( from 52 to 50)
 Only 2 volume % is unloaded with out Haldane effect

27. Haldane effect
 At the level of lungs
 PCO2 is 45 mmHg
 PO2 is 104 mmHg
 Higher PO2
 Favors unloading
 The volume % of CO2 decreases to 48 (from 52 to 48)
 4 volume % of CO2 is unloaded
 Haldane effect doubles the loading (tissues)/ unloading
(lungs) of CO2

28. Respiratory exchange ratio
 R = Rate of Co2 output/ rate of O2 intake
 100 ml of blood transports 5 ml of oxygen from lungs to
tissues
 100 ml of blood transports 4 ml of Co2 from tissues to
lungs
 R= 4/5 =0.8
 If the individual is on a normal diet (carbohydrates,
proteins and fat)

29. Respiratory exchange ratio
 If the diet has only carbohydrates then R = 1
 If the diet has only fat then R= 0.7
 When oxygen is metabolized with carbohydrates, one
molecule of carbondioxide is formed for each molecule
of oxygen consumption
 When oxygen reacts with fat, large share of oxygen
combines with hydrogen ions to form water instead of
Co2

30. Hypoventilation
 Depression of respiratory center
 Damage of nerve supply to respiratory muscles
 Myasthenia gravis
 Dysfunction of lung mechanics such as chest wall
injuries
 Kyphosis, scoliosis
 Airway obstruction
 Hypoxia

31. Hypoventilation
 Causes decrease in the Po2
 Increase in the PCO2 (hypercapnia)
 Leads to respiratory acidosis
 This is compensated by kidney
 Renal HCO3- retention
 Excretion of hydrogen ions
 Acid-base balance

32. Hyperventilation
 Increased alveolar ventilation rate more than rate of
production of CO2
 PCO2 becomes below normal.. Seen in
1. Cardiac failure
2. Anxiety
3. Hepatic failure
4. Use of drugs such as salicylates
5. Fever
6. Pregnancy

33. Hyperventilation
 PCO2 becomes below normal
 Decreased ventillatoy drive
 Temporarily caused apnea
 CO2 buildup during apnea
 Restore ventilation drive
 Chronic hyperventilation leads to respiratory alkalosis
 Compensated by renal retention of hydrogen ions and
excretion of HCO3-

34. Apnea
 Temporary cessation of breathing
1. Voluntary apnea
2. Sleep apnea
3. Drug induced (opiate toxicity)
4. Mechanically induced (strangulation)
5. Deglutition apnea
6. Adrenalin apnea

35. THANK YOU