- Respiratory tract consists of: nostril, nasal cavity, pharynx, trachea, bronchi + bronchioles.
à to tissues.
- O2 + CO2 à low solubility in blood plasma
- CO2 à mainly transported as hydrogen carbonate ion (HCO3+).
(B) Gaseous exchange in mammals
- Blood carries CO2 in 3 forms:
· dissolved gas (8%)
· HCO3- ion in the plasma (73%)
· carbamino haemoglobin in the red blood cells (19%)
- A large amount of CO2
· combines with H2O in the red blood cells (RBC)
· to form carbonic acid (H2CO3)
· then ionizes to form H+ + HCO3-
- HCO3- from the red blood cell:
· diffuse out into the plasma.
· loss of negatively charge HCO3- from the red blood cell
· balanced by the inward diffusion of -ve chloride ions (Cl-) = chloride shift.
- In the lungs.
à PCO2 is lower than in the blood.
à CO2 diffuses out
à into alveoli.
- In the plasma:
1. dissolved CO2 diffuses out into the alveolar air.
2. Carbamino haemoglobin:
à form CO2 + haemoglobin.
3. Hydrogen carbonate ions (HCO3-):
à diffuse into the red blood cells
à reacts with H+
à form carbonic acid (H2CO3).
à form H2O + CO2
à CO2 diffuses out into the alveolar air
(C) Gaseous exchange in mammals
1. O2 = transported by the haemoglobin molecule in the red blood cells.
2. Each haemoglobin molecule à carries 4 mol of O2.
3. Each polypeptide chain contains:
6. The cooperative effect is reversible
à when one subunit of oxyhaemoglobin unloads its O2,
à other three quickly follow suit
à conformational change
à lowers its affinity for O2.
à when haemoglobin is exposed to a gradual increase of PO2,
à it absorbs O2 rapidly at first
à but more slowly as the PO2 continues to rise.
9. The % of O2 saturation of haemoglobin = 95%
à when blood flows through the lungs (PO2 = 105 mmHg).
10. The % of O2 saturation of haemoglobin = 70%
à when blood flows through a moderately active/resting muscle (PO2=40 mmHg).
11. As the blood from the lungs reaches the muscle at rest:
à 25% of the O2 carried in the heamoglobin is unloaded to the surrounding tissues
à for cellular respiration.
à 70% of the oxygen is still retained by the haemoglobin.
à when the blood flows through the active muscle at PO2 of 20 mmHg.
13. When the muscle is active:
à haemoglobin readily unloads 55% of the oxygen
à still retains 40%.
15. The increase of CO2 conc/decrease in blood pH:
à will induce haemoglobin to unload more O2.
16. Foetal haemoglobin:
à has a higher affinity for O2 than the maternal haemoglobin
à therefore, O2 dissociation curve lies to the left.
17. O2 must easily dissociate from the maternal haemoglobin to the foetal haemoglobin
à therefore, easily transferred from maternal to foetal blood.
à higher affinity for O2 than haemoglobin.
à Therefore, dissociation curve lies to the left.
19. In the muscle:
à O2 dissociates from haemoglobin
à transferred to myoglobin to be stored.