16
Gas Transport Prof. K. Sivapalan
Gas Transport
Prof. K. Sivapalan
Gas Transport 2
Transport of gases in Blood
2013
Gas Transport 3
• Iron atoms in Hb bind reversibly with O2- Oxygination.
• 4Hb + 4O2 ↔ Hb4O8
• Oxygen dissociation curve illustrates the relation of PO2 to saturation.
• The sigmoid curve is the result of changing affinity of Hb to oxygen.
• When fully saturated, 1 g Hb carries 1.34 ml oxygen
Reaction of Oxygen with Haemoglobin
2013
Gas Transport 4
Factors Affecting the Affinity of Haemoglobin to Oxygen
• Factors that reduce the affinity [shift the curve to right, increase P50]
– Rise in temperature
– Fall in pH
– Rise in 2,3-biphosphoglycerate
• P50- partial pressure at which 50 % haemoglogin is saturated.
2013
Gas Transport 5
Reaction with CO
• Carbon monoxide reacts with haemoglobin in the same way as oxygen but the affinity is 250 times more.
2013
Gas Transport 6
2,3- Biphosphoglycerate
2013
• It binds to β chain of deoxy haemoglobin• Alkalinity, thyroid hormone, androgens and
growth hormone increase it.• Exercise causes increase in 60 minutes but it
may not occur in trained athlets.
Gas Transport 7
Color Changes of Haemoglobin
• Haemoglobin is blue
• Oxyhaemoglobin is pink
• Cyanisis- blue discolorization dueto deoxigination.
• It becomes apperant if deoxy haemoglobin is more than 5g/dl
• Carboxy haemoglobin is cherry red
2013
Gas Transport 8
Transport of Carbon Dioxide
• Considerable amount of CO2 remains dissolved in plasma.
• CO2 enters red cells and carbonic anhydrase catalyses formation of Hydrogen and bicarbonate.
• CO2 reacts with NH2 in proteins [haemoglobin and plasma proteins] to form carbamino compound.
2013
Gas Transport 9
• The dissociation of carbonic acid formed in red cells as H+ and HCO3
- will not proceed unless at least one is removed.
• The Hb is a good buffer and takes up H+ and the reaction continues.
• The resulted HCO3- concentration rises and difuses
into plasma.
• The electrical in-equilibrium drags Cl- into red cell.
• This increases osmolality and the red cell volume increases.
• 70 % of the CO2 is transported as HCO3-
Bicarbonate Formation and Chloride Shift
2013
Gas Transport 10
Summary of CO2 in DL blood
Arterial Blood [PCO2- 40 mm
Hg]
Added in tissues/
removed in lungs
Venous blood [PCO2- 46 mm
Hg]
Dissolved 2.6 mL 0.4 mL 3.0 mL
Carbimino compound 2.6 mL 0.8 mL 3.4 mL
Bicarbonate 43.8 mL 2.5 mL 46.3 mL
Total 49.0 mL 3.7 mL 52.7 mL
pH 7.4 7.362013
Gas Transport 11
Carbon Dioxide Dissociation Curve
2013
Gas Transport 12
Interaction of Oxygen and Carbon Dioxide with Haemoglobin
• Increase of CO2 promotes dissociation of O2- Bohr Effect.
• Oxygination tends to displace CO2 from blood- Haldane effect.
• Oxy haemoglobin is more acidic – Less tendancy to form carbamino
compounds.
– Less tendancy to accept hydrogen ion.2013
Gas Transport 13
Summary of Changes in Lungs
• Oxygen up take- 250 ml/min.
• Carbon dioxide output- 200 ml/min.
• Respiratory exchange ratio- – CO2/O2 = 200/250 =0.8
• Oxygen uptake is facilitated by carbon dioxide dissociation and carbon dioxide dissociation is facilitated by oxygenation.
2013
Gas Transport 14
Physiologic Shunt of Venous Blood
• Drainage of small amounts of bronchial blood into pulmonary vein
• Left ventricular blood draining into the chamber directly.
• The result is blood in aorta with 95 % saturation of oxygen.
2013
Gas Transport 15
• The cells are using oxygen and the partial pressure is very low.
• The cells are producing carbon dioxide and the partial pressure is high.
• The gases diffuse according to the Partial pressure difference through the tissue fluid.
• Higher temperature, higher PCO2, more acidity facilitate de-oxigenation and deoxigenation facilitates CO2 reaction with haemoglobin
Exchange in Tissues
2013
Gas Transport 16
Supply of Oxygen
• When tissue metabolism increases, the tissue partial pressure falls.
• Slight fall in partial pressure results in dissociation of more oxygen from haemoglobin.
• Myoglobin in muscles releases oxygen when the partial pressure is very low.
2013
