The control of respiration seems to be based on the following factors: a) An intrinsic rhythm of the respiratory neurones of the medulla oblongata. This rhythm is dependent upon oxygen supply to the neurones involved. It is regulated by both reflex and chemical mechanisms. b) The chemical regulation of respiration concerns the hydrogen ion content of the respiratory neurones which in turn is dependent upon the carbon dioxide tension of the blood and the rate of flow of blood through the medulla. Variations in blood oxygen tension under normal conditions are not thought to be concerned with direct regulating effects on the respiratory neurones. The control of respiration seems to be based on the following factors: a) An intrinsic rhythm of the respiratory neurones of the medulla oblongata. This rhythm is dependent upon oxygen supply to the neurones involved. It is regulated by both reflex and chemical mechanisms. b) The chemical regulation of respiration concerns the hydrogen ion content of the respiratory neurones which in turn is dependent upon the carbon dioxide tension of the blood and the rate of flow of blood through the medulla. Variations in blood oxygen tension under normal conditions are not thought to be concerned with direct regulating effects on the respiratory neurones. The Chemical Control of Respiration As already pointed out the role of anoxemia is concerned with a direct depressing influence of oxygen lack on the respiratory cells of the medulla, and an opposing excitatory effect upon chemoreceptors in the carotid body whose stimulation results in reflex augmentation of respiration. The respiratory neurones of the medulla, however, are extremely sensitive to variations in the CO2 tension of the blood and somewhat less so to any other acids. In both cases the stimulatory effect concerns

1. DR FAKHAR UN NISA
Transport of CO2

2. LEARNING OBJECTIVES
 At the end of lecture Students will be able to
 Discuss the diffusion of CO2 from tissue cells
to lungs due to partial pressure difference.
 Describe different chemical forms in which
CO2 is transported.
 Discuss Chloride shift & reverse Chloride
shift.
 Describe carbon dioxide dissociation curve.
 Explain Haldane effect.

3. TRANSPORT OF CARBON DIOXIDE IN THE
BLOOD
 carbon dioxide can usually be transported in far greater
quantities than oxygen because it is 20x more soluble than
oxygen .
 carbon dioxide in blood has a lot to do with the ACID-
BASE BALANCE of the body fluids.
 Normally 4 ml of carbon dioxide is transported from the
tissues to the lungs in each 100 ml of blood .
4 ml/100ml of blood
November 20, 2023
3

4. TRANSPORT OF CO2
 CO2 is produced in tissues as a result of
metabolic activity.Diffusion of CO2 occurs as
a result of pressure gradient from tissues to
Lungs alveoli.
 pCO2 in cells = 46 mm Hg
 In interstitial fluid of tissues = 45 mm Hg
 In arterial blood = 40 mm Hg

5. TRANSPORT OF CO2
40 mm Hg blood
45 mm Hg Interstitium
46 mm Hg
Cell

6. TRANSPORT OF CO2

8. 3 CHEMICAL FORMS OF CO2 IN BLOOD:
Dissolved in plasma
= 7%
As bicarbonate
in plasma = 70%
As carbamino proteins
= 23%

9. 1-DISSOLVED IN PLASMA = 7%
The amount of carbon dioxide dissolved in the fluid
of the blood at 45 mm Hg(venous blood) is
about 2.7 ml/dl(2.7 volumes per cent).
The amount dissolved at 40 mm Hg(arterial blood)
is about 2.4 ml/dl,
or a difference of 0.3milliliter/dl.
Therefore, only about 0.3 milliliter of
carbondioxide is transported in the dissolved
form by each100 milliliters of blood flow.

11. 2--CHLORIDE BIOCARBONATE
SHIFT/HAMBUERGER S PHENOMENON--RBCS AT
TISSUE LEVEL
 CO2 combine with H2O in blood plasma to form H2CO3 ,but this
process is slow as no carbonic anhydrase is absent here.
 Reaction of Carbon Dioxide with Water in the Red Blood Cells-
Effect of Carbonic Anhydrase
 CO2+H2O H2CO3
carbonic anhydrase, catalyzes ( about 5000-fold).
the reaction occurs very rapidly in the red blood cells within
fraction of a second.

12.  Dissociation of Carbonic Acid into Bicarbonate and Hydrogen
Ions
In another fraction of a second, the carbonic acid formed in the red
cells (H2CO3) dissociates into hydrogen and bicarbonate ions .
H2CO3 H+ + HCO3-
 Most of the H+ ions then combine with the hemoglobin in the red
blood cells because the hemoglobin protein is a powerful acid-base
buffer.
 Many of HCO3 ions diffuse from the red cells into plasma, while
chloride ions diffuse into the red cells to take their place.
 This is made possible by the presence of a special bicarbonate-
chloride carrier protein in the red cell membrane that shuttles
these two ions in opposite directions at rapid velocities.
 Thus, the chloride content of venous red blood cells is greater than
that of arterial red cells, a phenomenon called the Chloride shift.
November 20, 2023
12

13. CO2 CARRIAGE AT TISSUE LEVEL
November 20, 2023
13

14. 3-CARBAMINO COMPOUNDS WITH HB AND
PLASMA PROTEINS
3rd form in which carbon dioxide is transported is,
as Carbamino Hb.
carbon dioxide reacts directly with amine radicals
of the hemoglobin molecule and plasma proteins
to form the compound carbaminohemoglobin
(CO2Hb).
R—N---H +CO2---R---N---COOH
H H

15. RBCS AT LUNG LEVEL:
 When RBCs reach the lung, there is formation of
oxy-Hb, which is very strong acid (acids are
proton donors).
 It cannot hold Hydrogen ions any more, so that
they become separated.

17. CARBAMINO COMPOUNDS IN PULMONARY
CAPILLARIES
When blood  lung capillaries  combination of
oxygen with hemoglobin in the lungs causes the
hemoglobin to become a stronger acid.
the carbon dioxide that is present in the carbamino
form is released CO2 diffuses the respiratory
membrane  alveolar air  expired out.

20. NET TRANSPORT OF CARBON DIOXIDE
/100ML OF BLOOD
 4 ml of carbon dioxide is added to venous blood
/100ml/dl.
 In venous blood PCO2 is 45 mm Hg &
 in alveolar air, it is 40 mm Hg.
 So from venous blood, CO2 goes  alveolar
blood.

21. November 20, 2023
21
Carbon Dioxide Dissociation
Curve

23. SPECIAL FEATURES OF CO2
DISSOCIATION CURVE:
 Total blood CO2 depends
in all its forms on PCO2.
 Normal blood PCO2
range:
40 mm Hg in arterial
blood to
45 mm Hg in venous
blood
= very narrow range.

24. SPECIAL FEATURES OF CO2
DISSOCIATION CURVE:
 At tissue PCO2 is 46 mm/Hg
& Normal conc. of CO2 in
blood in all its different forms
is 52 ml/100ml.
 At alveoli PCO2 is 40
mm/Hg & content of CO2 is
50ml/100ml .
 Only 2% of this is exchanged
during normal transport of
CO2 from the tissues to the
lungs.

25.  This figure shows small portions of
two carbon dioxide dissociation
curves:
 (1) when the Po2 is 100 mm Hg,
which is the case in the blood
capillaries of the lungs
 now 48 volumes percent of carbon
dioxide combine with the blood.
 So total exchange of 4 volumes
percent of carbon dioxide occur
from tissue to lungs.
25

26. HALDANE’S EFFECT:
 In transport of CO2, Haldane’s effect is
important, i.e.,
 Binding of oxygen with Hb, displaces out
CO2.
 When O2 binds with Hb  oxy-Hb (strong
acid) is formed.It cannot hold H+  CO2 is
displaced out of blood.,
 So Haldane effect doubles the amount of
CO2 released from blood in the lungs

27. SIGNIFICANCE OF HALDANE’S EFFECT AT
LUNG & TISSUE LEVELS:
 At tissue level:
 When Hb gives up its
oxygen, it becomes a
weaker acid and accepts
the H ion.CO2 is
transported by the blood.
 At lung level:
 When oxygen binds with
Hb, Hb becomes strong
acid ,cannot hold H ion
any more.CO2 is
displaced out  alveolar
air.

28. BOHR EFFECT VS HALDANE EFFECT
 Bohr effect
 Increase in CO2 in the
blood  O2
displacement from the
Hb.
 It operates at tissue
level.
 Haldane effect
 Binding of O2 with Hb 
displace CO2 from the
blood.
 It operates at lung level.

29. RESPIRATORY EXCHANGE RATIO
 R= rate of carbon dioxide output/rate of
oxygen uptake
 When carbohydrate used R is 1.00
 When Fats used R = .70 ,
 as when O2 reacts with fats water is
produced instead of CO2.
 For a person who is on balanced diet R=
.825

30. LEARNING OBJECTIVES
 At the end of lecture Students will be able to
 Discuss the diffusion of CO2 from tissue cells
to lungs due to partial pressure difference.
 Describe different chemical forms in which
CO2 is transported.
 Discuss Chloride shift & reverse Chloride
shift.
 Describe carbon dioxide dissociation curve.
 Explain Haldane effect.