Question

What do you know about delivery of O2 and removal of CO2 from tissues (carbamate and bicarbonate)

Answer 1

Blood is the medium for transport of oxyzen and carbondioxide.

Transport of oxyzen :- About 97% of oxyzen is transported by RBCs in the blood.The remaining 3% of oxyzen is carried in a dissolved state through plasma.

●Transport by haemoglobin:- Haemoglobin is a red coloured iron containing pigment present in the RBCs .Oxyzen can bind with haemoglobin in a reversible manner to form oxyhaemoglobin.Each haemoglobin molecule can carry a maximum of 4 molecules of oxyzen.Binding of oxyzen with haemoglobin is primarily related to partial pressure of oxyzen. Partial pressure of co2 ,hydrogen ion concentration and temperature which can interfere with binding of haemoglobin.In the alveoli where is higher partial pressure of oxyzen ,low temperature ,lesser hydrogen ions concentration and lower temperature .All these factors are favourable for binding of haemoglobin with oxyzen.Now this oxyhaemoglobin molecule reaches to the tissue .In tissues low partial pressure of oxyzen, high hydrogen ion concentration and high temperature .These all conditions are responsible for dissociation of oxyhaemoglobin.Oxyhaemoglobin dissociates and releases 4 molecules of oxyzen at tissue level and haemoglobin released from tissues.Every 100 ml of oxyzenated blood can carry 5 ml of o2 to the tissues .

Hb_{4 + 4o2----------------------------------------Hb4o8}

Removal of carbondioxide : co2 is produced in body as an end product of cell respiration.100 ml of blood receives about 3.7 ml ofcarbondioxide .It is transported both by plasma and haemoglobin of blood.

●As carbamate :- About 23% of co2 is transported as carbaminohaemoglobin which is formed by combination of carbondioxide with amino group of globin part of haemoglibin.

These are formed at cellular level in presemce of low partial pressure ofoxyzen and low acidic haemoglobin.

As carbonic acid :- About 7% of carbondioxide is transported by blood as carbonic acid which is formed by dissolution of co2 in water.Each decilitre of blood transports about 0.3 ml of co2 in dissolved form.

Co2 + H2o ---------------–------------H2co3

This reaction mainly occurs in RBCs. It is catalysed by carbonic anhydrase which is stimulated by low po2 at cellular level.

This carbondioxide is transported from body tissues to lungs as sodium and potassium bicarbonates.Most of carbonic acid formed inside the RBCs dissociates into hydrogen and bicarbonate ions.Most of bicarbonate ions diffuse into the plasma.To maintain electroneutrality,equal amount of chloride ions diffuse inside the RBCs .This exchange of bicarbonate ions of RBC and chloride ions of plasma is known as chloride shift or Hamburger shift .This occurs in presence of special bicarbonate chloride carrier protein in the red blood cell.