Question

Gas Transport in the Blood. Efficient oxygen exchange requires the reversible binding of oxygen to hemoglobin. Describe the relationship between the partial pressure of oxygen in the blood and the oxygen saturation of hemoglobin. Include a labeled figure that clearly shows this relationship. Then, explain in detail the significance of the relationship by discussing what is seen in “average” body tissues and tissues that are metabolically active (name them). Then, explain in detail the significance of the relationship with respect to (modestly) high elevation. Lastly, describe in detail the additional factors that influence the loading and unloading of oxygen and explain their significance. Your explanations will need to include supporting evidence/facts/or conclusions. Be sure to explicitly state the significance in each case and support your statements. A significant number of points are awarded for doing so. For example for each section where you have to explain the significance try: “This is significant because…” then explain why it is important.

Answer 1

Oxygen-hemoglobin dissociation curve is the curve that demonstrates the relationship between partial pressure of oxygen and the percentage saturation of hemoglobin with oxygen. It explains hemoglobin’s affinity for oxygen. Normally in the blood, hemoglobin is saturated with oxygen only up to 95%. Saturation of hemoglobin with oxygen depends upon the partial pressure of oxygen. When the partial pressure of oxygen is more,
hemoglobin accepts oxygen and when the partial press-ure of oxygen is less, hemoglobin releases oxygen.

Normal Oxygen-hemoglobin Dissociation Curve

Under normal conditions, oxygen-hemoglobin dissocia-tion curve is ‘S’ shaped or sigmoid shaped. Lower part of the curve indicates dissociation of oxygen from hemoglobin. Upper part of the curve indicates the uptake of oxygen by hemoglobin depending upon partial pressure of oxygen.

P50---> P50 is the partial pressure of oxygen at which hemoglobin saturation with oxygen is 50%. When the partial pres-sure of oxygen is 25 to 27 mm Hg, the hemoglobin is saturated to about 50%. That is, the blood contains 50% of oxygen. At 40 mm Hg of partial pressure of oxygen, the saturation is 75%. It becomes 95% when the partial pressure of oxygen is 100 mm Hg

Factors Affecting Oxygen-hemoglobin Dissociation Curve -

Oxygen-hemoglobin dissociation curve is shifted to left or right by various factors:

1. Shift to left indicates acceptance (association) of oxygen by hemoglobin

2. Shift to right indicates dissociation of oxygen from hemoglobin. 1

Oxygen-hemoglobin dissociation curve is shifted to right in the following conditions:

i. Decrease in partial pressure of oxygen

ii. Increase in partial pressure of carbon dioxide (Bohr effect)

iii. Increase in hydrogen ion concentration and decrease in pH (acidity)

i v. Increased body temperature

v. Excess of 2,3-diphosphoglycerate (DPG) in RBC. It is also called 2,3-biphosphoglycerate (BPG). DPG is a byproduct in Embden-Meyerhof pathway of carbohydrate metabolism. It combines with β-chains of hemoglobin.

Significance at high altitude

At high altitude as barometric pressure decreases and there is decrease in po2 i.e. partial pressure of 02 while PCo2 and PH remain constant .In acclimatised individual Oxygen delivery to tissues is maintained by  Increase 2,3 DPG biphosphoglyceric acid that reduces the affinity of haemoglobin for Oxygen and increase in release of O2 at tissue levels leading to shift of curve towards right.

Significance at metablically active tissue

The Bohr effect enables the body to adapt to changing conditions and makes it possible to supply extra oxygen to tissues that need it the most.

For example, when Skeletal muscles are undergoing strenuous activity, they require large amounts of oxygen for cellular respiration, which generates CO2 (and therefore HCO3− and H+) as byproducts.

These waste products lower the pH of the blood, which increases oxygen delivery to the active muscles.

Under anaerobic conditions, muscles generate lactic acid so quickly that pH of the blood passing through the muscles will and which causes shift of curve towards right causing haemoglobin to begin releasing more oxygen.[