Haemoglobin

Red blood cells contain haemoglobin

• 4 subunits each contain a polypetide protein and heam group and heam group has an affinty for oxygen.

Taking up oxygen

• Oxygen absorbed by the blood enters the blood plasma then enters the blood plasma then enters the red blood cells. Here taken up by the haemoglobin.
• Oxygen molecules leave so a steep diffusion gradient created
• Diffusion gradient allows more oxygen to enter the cells

Releasing oxygen

• cells need oxygen for aerobic respiration there oxyhaemoglobin must release oxygen this is called dissociation

unloading occurs in tissue capillaries where;

• pp02 is ------ low
• pco2 is ------ high
• blood ph ----- lower
• temperature ----higher Tt is difficult for the third oxygen molecules to diffuse and associate with the last heam group so therefore it is difficult to gain 100% saturation of all the heamoglobin molecules. Even when oxygen tension is very high so therefore the curve levels off when saturation becomes 100%.

Carbon dioxide can be transported in 3 different ways;

• 5% is dissolved directly in to the plasma
• 10% combined directly is with haemoglobin to form a compound called Carbamniohaemoglobin
• 85% is transported in the form of hydrogen carbonate ions (hco3-)

Hydrogen carbonate ions are formed;

co2 diffuses into the blood some enters the red blood cells and combines with water to form carbonic acid which is catalysed by carbonic anhydrase

co2 + H2O -------------> H2OC03

Co2 + H2o -------------> H2Co3

the carbonic acid dissociates to release H ions and hydrogencarbonate Hco3-

H2Co3 -------------> Hco3- + H+

• hydrogen carbonate ions diffuse out of the red blood cell into the plasma
• Charge inside the red blood cell maintained by the chloride shift
• the H+ ions can become acidic so it is taken up by haemoglobin to produce Haemoglobinic acid. Haemoglobin acts as a Buffer!

Increased ppco2, lower ph and increased temperature all have the effect to push the curve to the right more is unloaded which is the Bohr effect

• Haemoglobin has a lower affinity for oxygen as the oxygen is trying to supply the body with more oxygen
• more Co2 is gained as the body is respiring
• Oxygen is needed to the respiring tissues
• LESS AFFINITY for oxygen as it gives it up!