CHAPTER 7(b) - DISSOCIATION CURVE

OXYGEN DISSOCIATION CURVE OF HAEMOGLOBIN

-Gaseous diffuse  from high partial pressure to low partial pressure
-In inhaled air, the partial pressure of o2 is high but the partial pressure of co2 is low
-oxygen diffuse into the alveolar blood capillaries and co2 diffuse out into the alveolus

LOADING AND UNLOADING OF GASEOUS

-When haemoglobin associates with o2, it undergoes change in shape
-Helps a faster intake of the next oxygen molecule
-The last one is 700 times faster than the first (cooperativity)
-Reverse happens when oxygen dissociates with haemoglobin at a site where the partial pressure of oxygen is low.
-At first, small decrease of Po2 will lead to a big drop of oxygen saturation of haemoglobin
-It then gets harder and harder to remove the oxygen from haemoglobin

DISSOCIATION CURVE

-The haemoglobin can be 95% saturated with oxygen even at a very low Po2(10kPa)
-This is known as oxygen loading
-The partial pressure of oxygen in the lung is 13kPa
-The affinity of haemoglobin for oxygen also lowered by
 (a)2-3-DIPHOSPHOGLYCERATE-product of RBC
 (b)high temperature
-In the respiring cells, the partial pressure of oxygen is very low and oxygen will dissociate from haemoglobin supplying oxygen to the cells

CHANGES BY Pco2

-when the partial pressure of co2 increase or pH decrease will shift the dissociation curve to the right.
-lowering the affinity of haemoglobin for oxygen
-causes oxygen to dissociate from oxyhaemoglobin
-phenomenon is known as BOHR SHIFT

CHANGES BY HIGH TEMPERATURE

-Same goes when the temperature of body increase
-curve shift to the right
-this result in release of more oxygen particularly in vigorous activity

OXYGEN DISSOCIATION CURVE OF MYOGLOBIN

MYOGLOBIN

-Myoglobin is made up of one polypetide chain with a signle iron containing prosthetic group  attached to it
-each myoglobin binf with single oxygen molecule to form oxymyglobin
-the myoglobin dissociation curve is hyperbolic in shape
-this shows that myglobin has higher affinity for oxygen and combines more readily
-but releases it only when the partial pressure of oxygen is low
-myglobin is an oxygen store in muscle

OXYGEN DISSOCIATION CURVE OF FOETAL HAEMOGLOBIN (HbF) AND ADULT HAEMOGLOBIN (HbA)

-During the foetal development , the foetus in the mother's womb is able to obtain the oxygen
-from the mother through increased maternal blood supply to the placenta
-HbF has higher affinity for oxygen than the HbA

HbF VS HbA

-HbF has higher affinity than HbA
-Means hat HbF can easily saturated with oxygen even at low partial pressure
-ensures a sufficient and efficient oxygen supply to the foetus

DOUBLE BOHR EFFECT

-In the maternal blood, there is a high Pco2 which helps to release oxygen
-in the foetal blood , the partial pressure of co2 is low
-so in the foetal ,increase the binding of haemoglobin to oxygen
-taking up more oxygen easily
-this phenomenon is known as double bohr effect
-this causes the curve shifted in the opposite direction
-HbA to the right
-HbF to the left