Transport of carbon dioxide

physio

1. TRANSPORT OF CARBON DI-OXIDE. Department of Physiology BDS I 23 rd June 2020

2. OBJEC T IV E S . Diffusion of CO2 in blood. Transport of CO2 in blood. Release of Co2 in lungs. Other facts about CO2 transport.

3. INTRODUCTION .      Transport occurs along conc gradient I ntracellular 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.

4. 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.

5. 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.

6. Transport of co2 in blood. In Dissolved form In Bicarbonate form. In Carbamino compound form.

7. 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.

8. In bicarbonate form (70%)  Chloride shift or Hamburger phenomenon.

9. 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

10. 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%)

11. Carbon dioxide dissociation curve Relationship between PCO2 & total CO2 content. Relationship is nearly linear over wide range of PCO2

12. Factors affecting co2 dissociation curve Oxygen Dpg Body temperature.

13. Oxygen Deoxyhaemoglobin is capable of loading more Co2 than oxyhaemoglobin . Also oxygenation of Hb in lungs increases Co2 unloading – Haldane Effect.

14. OX Y G E N   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.

15. 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.

16. Body temperature . Causes curve to shift to left. Increasing carrying capacity.

17. 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.

18. 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

19. 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.

20. 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 Co 2 transported from plasma to alveoli.

21. Other facts about co2 transport. Comparison of different vehicles for CO 2 transport. Rate of total CO 2 transport. Changes in blood pH during transport of CO 2 Respiratory Quotient. Definition Normal value Respiratory quotient depends upon the type of uel consumed.

22. 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

23. 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.

24. 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.

25. 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.

26. 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

27. Thank You