CO2 is transported in the blood in four ways: dissolved, as carbonic acid, as bicarbonates, and as carbamino compounds. CO2 is produced during aerobic metabolism and must be transported to the lungs to be eliminated. It diffuses from tissues into blood and from blood into the alveoli due to partial pressure gradients. In the blood, CO2 is carried as bicarbonates through a chloride shift that maintains electrolyte balance. The CO2 dissociation curve shows the relationship between CO2 levels in blood and partial pressure of CO2. Haldane effect causes more CO2 to be released from blood into alveoli in the presence of oxygen. Hypercapnia occurs when arterial CO

1. TRANSPORT OF
CARBONDIOXIDE IN BLOOD

2.  CO 2 is a by product of aerobic metabolism
in mitochondria.
 CO 2 readily hydrate to form carbonic acid,
so
it
can
be
a
source
of
significant
acidosis if allowed to accumulate.
 Thus it is very important to eliminated it
from the body.
 There
is
continuous
gradient
for
CO 2
tension from mitochondria to cytoplasm,

3.  In arterial blood the vol of CO 2 is 48 ml%
and PCO 2 is 40 mmHg
 In venous blood, the vol of CO 2 is 52ml%
and PCO 2 is 46 mmHg.
 Each 100 ml of venous blood release 4 ml
CO 2 while passing through lungs.
 CO is 5 L/min  CO 2 eliminated from body
is
4 x 5000
= 200ml/min

4. EXCHANGE OF CO 2 BETWEEN BLOOD AND
TISSUE
1. Diffusion of CO 2 from tissue into blood :

5.  PCO 2 is high in cells (46
mmHg
due
activity.
to
PCO 2
metabolic
is
arterial
blood is 40mmHg
 Pressure
mmHg
is
diffusion
gradient
of
responsible
of
CO 2
6
for
from

6. 2. Diffusion of CO 2 from blood to Alveoli :

7.  PaCO 2 in alveoli is 40 mmHg PCO 2 in blood
is 46 mmHg.
 The
pressure
gradient
of
6
mmHg
is
responsible for diffusion of CO 2 from blood
into alveoli.
3. Diffusion of CO 2 for alveoli to atmosphere :
 In atmosphere PCO 2 0.3 mmHg whereas in
alveoli it is 40 mmHg. So, CO 2 leaves

8. TRANSPORT OF CARBON DIOXIDE
CO 2 is transported in blood :
i. Dissolved form (7%)
ii. Carbonic acid
iii.As bicarbonate (63%)
iv. As carbamino compound (30%)
i. Dissolved form :
 CO 2 diffuses into blood and dissolves in
plasma forming simple solution

9.  7% of total CO 2 is transported as dissolved
state in blood.
ii. Carbonic acid :
 Part of dissolved CO 2 in plasma, combines
with water to form carbonic acid.
 This reaction is very slow and is negligible.

10. iii.As Bicarbonates :
 63% of CO 2 is transported as bicarbonate.
 From plasma, CO 2 enter RBC. Inside RBC, CO 2
combines with water to form carbonic acid.

11.  Carbonic acid is very unstable. Almost all
carbonic acid formed in RBC dissociate
into bicarbonate and H + ion.

se conc of bicarbonate inside RBC
causes diffusion of bicarbonate ion into
plasma.

12. Chloride shift :
 NaCl in plasma dissociate into Na + and cl
ions. When HCO 3 move out of RBC into
plasma, to maintain electrolyte balance Cl
move into RBC.
 This is called chloride shift as hamburger
phenomenon.
 H+ ion are buffered by Hb inside cell.
 HCO 3 combines with Na + ion in plasma to
form NaHco 3 and this form is transported in

13. Reverse chloride shift :
 Bicarbonate has to be reverted back into
CO 2 , which has to be expelled out.
 When blood reaches alveoli, NaHCO 3 in
plasma dissociate into Na + and HCO 3 . HCO 3
moves into RBC and Cl moves out of RBC
into plasma. This is called reverse chloride
shift.
 At same time, O 2 enters RBC and displace
H + from Hb. H+ then combines with HCO 3 to

14. iv. As Carbamino Compound :
 30% of CO 2 is transported as carbamino
compound.
 CO 2 combines with Hb to form carbamino
hemoglobin.
 CO 2 combines with plasma protein to form
carbamino protein.
 Carbamino
hemoglobin
protein
together
are
and
carbamino
called
carbamino

15. parameter
Arterial blood
Venous blood
Pco2
40 mm Hg
45 mm Hg
Dissolved CO2
27ml/l
29ml/l
Total CO2
content
Blood volume
490ml/l
530ml/l
1.25 l
3.75l
Volume of CO2 613ml
1988ml

16. CO 2 Dissociation Curve
 Amount
combining
of
with
CO 2
blood
depends upon the PCO 2 .
 The
relationship
between
PCO 2
and
quantity
of
CO 2
combined with blood is
demonstrated
curve
called
by
a
CO 2
:

18.  CO 2 content is 52 ml% when PCO 2 is 46
mmHg. It becomes 70ml% when PCO 2 is 100
mmHg.
 Combination of more amount of O 2 with Hb
displace CO 2 from Hb. This effect is called
Haldane’s effect.
 So, excess of oxygen content in blood
causes shift of CO 2 dissociation curve to
right.
Cause for Haldane’s effect :

19. Significance of Haldane’s effect :
 Haldane’s effect is essential for the
release
of
CO 2
from
blood
into
alveoli.
 It is essential for uptake of O 2 by
blood.

20. CO 2 on
CO2 unloads O2 from Hb (Bohr Effect)
At any PO less O2 bound
O 2 Saturation 2 of Hb

21. HYPERCAPNIA

Hypercapnia is defined as an arterial
PCO 2 above 46 mmHg that does not
represent
compensation
metabolic alkalosis.
for
a

22. PHYSIOLOGICAL EFFECTS OF HYPERCARBIA
1) On CVS :
 Causes direct depression of both cardiac muscle
and vascular smooth muscle, but at same time it
cause
reflex
stimulation
of
sympathoadrenal
system.
 Moderate
increase
to
severe
hypercapnia
results
in
HR and myocardial contractility with
consequent
stroke vol and cardiac output, while
systemic vascular resistance is reduced.

23. 2) Respiratory system :
 The
max
stimulatory
respiratory
PaCO 2 of about 100mmHg .
result in two fold
effect
is
by
Of 5 mmHg PaCO 2 can
in minute ventilation.
 With higher PaCO 2 stimulation is reduced and at
extremely high level respiration is depressed and
later ceases.
 Hypercapnia causes broncho dilation in both
healthy persons and patients with lung diseases.

24. 3) CNS :
 Cerebral blood flow α PaCO 2 between 20 –
80
mmHg.
Blood
flow
changes
12ml/100g/min per mmHg change in PaCO 2

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