transport of carbon dioxide

DR NILESH KATE

MBBS,MD ASSOCIATE PROF

DEPT. OF PHYSIOLOGY

TRANSPORT OF CARBON DI-OXIDE.

OBJECTIVES. Diffusion of CO2 in blood. Transport of CO2 in blood. Release of Co2 in lungs. Other facts about CO2 transport.

Wednesday, May 3, 2023

INTRODUCTION. Transport occurs along conc

gradient Intracellular PCo2 – 46 mm

Hg Interstitial fluid PCO2 – 45

mm Hg Arterial blood – 40 mm Hg venous blood Pco2 – 45 mm

Hg Alveolar air Pco2 – 40 mm

Hg.


CO2 transport From cell into interstitial

fluid against difference of 1 mm Hg.

From interstitial fluid to tissue capillaries against 5 mm Hg.

From venous blood to alveolar air against conc difference of 5 mm Hg.


DIFFUSION OF CO2 IN BLOOD. Intracellular PCO2 46

mm Hg. Interstitial fluid PCO2

45 mm Hg. So CO2 transfer in conc

difference of 1 mm Hg.


TRANSPORT OF CO2 IN BLOOD.

In Dissolved form

In Bicarbonate form.

In Carbamino compound form.


IN DISSOLVED FORM Venous blood with PCO2 45

mm Hg contains 2.7ml/100ml CO2 in dissolved form.

Arterial blood with PCO2 40 mm Hg contains 2.4ml/100ml CO2 in dissolved form.

0.3 ml/100 ml transferred 7 % of total transport.


IN BICARBONATE FORM (70%) Chloride shift or

Hamburger phenomenon.


IN CARBAMINO COMPOUND FORM (23%)

In plasma – CO2 combines with amino group of

plasma proteins – forms Carbamino proteins.

Co2 +PrNH2 Pr.NH.COOH

In RBC – combines with amino group of Hb – forms

Carbamino Haemoglobin

CO2 + HbNH2 Hb.NH.COOH


IN CARBAMINO COMPOUND FORM (23%)

This combination of CO2 with Hb – Reversible

Slower than reaction of CO2 with water bcoz more

CO2 transported as Bicarbonates (70%) than

carbamino compounds (23%)


CARBON DIOXIDE DISSOCIATION CURVE

Relationship between PCO2 & total CO2 content.

Relationship is nearly linear over wide range of PCO2


FACTORS AFFECTING CO2 DISSOCIATION CURVE

OXYGEN DPG BODY

TEMPERATURE.


OXYGEN Deoxyhaemoglobin is

capable of loading more Co2 than oxyhaemoglobin.

Also oxygenation of Hb in lungs increases Co2 unloading – Haldane Effect.


OXYGEN Blood with PCO2 40 mmHg

reaching the tissue is capable of drawing CO2 more at PO2 40 mm Hg than at PO2 100 mmHg. So dissociation curve shift to left in tissue.

Blood with PCO2 45 mmHg reaching the lung is capable of leaving CO2 more at PO2 100 mm Hg than at PO2 40 mmHg. So dissociation curve shift to right in lungs.


DPG 2,3- DPG competes

with CO2 for same site on Hb in reduced blood so decreases formation of carbamino-Hb.

So shifts curve to Right decreasing CO2 carrying capacity.


BODY TEMPERATURE. Causes curve to shift to left. Increasing carrying capacity.


RELEASE OF CO2 IN LUNGS. Venous blood with PCO2

45 mm Hg & PO2 40 mm Hg contains CO2 52ml/100 ml.

Alveolar air with Pco2 40 mmHg, PO2 100 mmHg contains CO2 48ml/100ml.

So total diffusion of 4 ml/100 ml.


RELEASE OF CO2 FROM CARBAMINOHAEMOGLOBIN INTO PLASMA

O2 enters the RBC & convert Deoxy Hb – to Oxy Hb which has low affinity for CO2 & releases co2 from Carbamino-haemoglobin into plasma.

HALDANE EFFECT


RELEASE OF CO2 FROM CARBONATE INTO PLASMA

Oxyhemoglobin is strong acid – increases H+ ion conc – to neutralize HCO3- ions enters RBC & Cl- ions leaves RBC

Reversal of chloride shift.


DIFFUSION OF CO2 FROM PLASMA TO ALVEOLI

PCO2 of plasma of Pul arterial blood 45 mm Hg & PCO2 of alveolar air is 40 mm Hg.

So pressure gradient of 5 mm Hg Co2 transported from plasma to alveoli.


OTHER FACTS ABOUT CO2 TRANSPORT.

Comparison of different vehicles for CO2 transport.

Rate of total CO2 transport.

Changes in blood pH during transport of CO2

Respiratory Quotient. Definition Normal value Respiratory quotient depends upon the type of uel

consumed.


COMPARISON OF DIFFERENT VEHICLES FOR CO2 TRANSPORT.

Plasma – not good transporter (0.2ml/100 ml)

Bicarbonate also not a good transporter – beyond

PO2 40 mmHg no further transport of CO2

Whole Blood ideal vehicle


RATE OF TOTAL CO2 TRANSPORT.

At Rest – 4ml/100 ml from tissue to lungs so

200ml/min (with CO 5L)

Depending on severity up to 4L/min.

Change in pH is prevented by conversion of CO2 to

Bicaronate ions.


CHANGES IN BLOOD PH DURING TRANSPORT OF CO2

Arterial pH – 7.4 Venous blood – 7 Fall due to formation

of carbonic acid. During exercise excess

change in pH is prevented by blood buffers.


RESPIRATORY QUOTIENT.

Definition – it is defined as the ratio of the rate of

CO2 excretion & rate of O2 consumption/min

RESPIRATORY EXCHANGE RATIO

Can be easily estimated by knowing amount of O2

removed from inspired air to amount of CO2 added

to the expired air per min.


RESPIRATORY QUOTIENT. Normal value –

4ml/5ml = 0.8 Respiratory quotient

depends upon the type of fuel consumed. Carbohydrate as entire

source – ratio is 1 Proteins & fats as

source <1, only fats 0.7


Thank You

transport of carbon dioxide

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