TRANSPORT MECHANISMS FOR OXYGEN ::
Transport of O2 from the lungs to the tissues and vice versa is done by haemoglobin Haemoglobin combines with O2 to form oxygenated haemoglobin or oxyhaemoglobin when haemoglobin looses its oxygen it is known as reduced haemoglobin Oxygenation is a reversible loose combination of O2 with Hb
formation of oxyhaemoglobin and reduced haemoglobin or the loading and unloading of oxygen from the tissues depends on (a) po2 (b) pCo2 and (c) Body temperature It is the characteristic property of haemoglobin that it quickly looses oxygen if pO2 is 40.6 mmhg However if pO2 is above 80 mmHg there occurs 100% saturation of haemoglobin with O2 and no further loading of O2 occurs after this This relation between saturation of haemoglobin with O2 can be illustrated by a curve oxygen dissociation curve
The oxygen dissocitaion curve is shifted to left if pCO2 or temperature is decreased Since decrease in pCO2 is associated with decrease in [H+] (or increase in pH) oxygen dissociation curve is shifted to left This effect is referred to as the Bohr s effect
Transport of carbon dioxide : Venous blood carries about 52 cc% of CO2 whereas arterial blood carries about 48 cc% of CO2 Thus about 4cc%CO2 is released in lungs by deoxygenated blood and from the tissues 4cc%CO2 by the oxygenated blood
under normal conditions of temperature and pressure only 2.7ml of CO2 is carried in physical solution i.e as H2CO3 majority of CO2 is carried by blood as bicarbonate when CO2 enters the blood chloride ion from plasma entres the red blood cells while Na+ is left behind when CO2 escapes from blood chloride ions leave the cells enter the plasma and combines again with Na+ This phenomenon is known as chloride shift it is the major transport mechanism for CO2 transport (45.7ml of CO2 is being transported by this mechanism) Apart of CO2 (3.7 ml) is also transported as carbamino compound which is formed when NH2 radical of proteins (plasma proteins or globin of haemoglobin ) combines with one molecule of CO2 (as free gas) This process does not require the enzyme carbonic anhydrase (Hence it can not be inhibited by cyanide poisoning )
0 Comments