Laboratory 2-Function of Haemoglobin in Oxygen Transport –Human Physiology II
Laboratory 2- The Function of Haemoglobin in Oxygen Transport
1. Ventilation: exchange of air between atmosphere and alveoli by bulk flow
2. Exchange of O2 and Co2 between alveolar air and blood in lung capillaries by diffusion
3. Transport of O2 and Co2 between pulmonary and systemic circulation by bulk flow
4. Exchange of O2 and Co2 between blood in tissue capillaries and cells in tissues by
OXYGEN IN BLOOD IS CARRIED IN 2 FORMS
(1) Dissolved in blood
- at normal arterial PO2 of 100mmHg , only 3ml O2 can be transported in dissolved form for
every liter of blood (3ml O2/L blood)
(2) Chemically bound to haemoglobin
-98% of the O2 in the blood is carried in this manner
-Hb is an iron bearing protein molecule located within red blood cells (erythrocytes)
-Major function of Hemoglobin is O2 and CO2 Transport
STRUCTURE OF HEMOGLOBIN
~280 million Hb molecule are per erythrocyte. Hb molecule is a tetramer
of two alpha & two beta polypeptide chains (globin subunits).
Each of these four subunits in turn are associated with an iron-
containing heme group.. The iron portion of the heme groups interacts
with the O2.
Percent Hb Saturation (%SO ) is2a measure of the extent to which
Hb is combined with O2. It can vary from 0-100%. At 100%
saturation, the carrying capacity of Hb for O2 is 1.34 ml O 2gram Hb.
Hb is present in the blood in 2 forms
Combined with O2 = oxyHb (HbO ) 2 NOT Combined with O2 = reduced Hb
Law of Mass Action: If the concentration of the substance on one side of a reversible reaction
is increased , the reaction is driven towards the OPPOSITE side.
Hb + O2 <===> HbO 2
The relationship between blood PO2 and Hb saturation is depicted by sigmoidal (S-shaped)
curve known as the O -H2 dissociation curve Laboratory 2-Function of Haemoglobin in Oxygen Transport –Human Physiology II
The shape of this O 2Hb dissociation curve is important physiologically
Steep= Low PO2 values(10mmHg-60mmHg) ; values seen in systemic capillary blood
Plateau= Higher PO2 values (60mmHg-100mmHg); values seen in pulmonary capillaries at the
level of lungs. Hb saturation remains relatively constant.
Factors that determining the extent of Hb Saturation. PO2 of the blood is the principal
2.Acidity (decreased pH)
ALL THESE SHIFT THE to the Right At any given PaO2 the percent
3. Temperature saturation of Hb is reduced
4. 2, 3 diphosphoglycerate (2,3 DPG)
**AN INCREASE IN THESE 4 factors IS A RESULT OF INCREASED TISSUE
METABOLISM** Laboratory 2-Function of Haemoglobin in Oxygen Transport –Huma