Question

4a. Given the same PO2 gradients (e.g. PO2 of environment = 100 mm Hg and PO2 of blood = 40 mm Hg), the fish gill is able to extract a higher % of available O2 than can the mammalian lung. Provide two reasons for the difference in efficiency of O2 extraction between these two respiratory systems.

4b. Given the same PO2 gradients (e.g. PO2 of environment = 100 mm Hg and PO2 of blood = 40 mm Hg), the bird lung is able to extract a higher % of available O2 than can the mammalian lung. Provide two reasons for the difference in efficiency of O2 extraction between these two respiratory systems.

Answer 1

4a. Gills are more efficient than lungs of mammals because they have a high surface area relative to size/ volume. Gills are highly folded structures which ensures that water passes through each wall of the capillary making sure that oxygen is extracted from almost all the water that passes through.

4b. The difference in the efficiency of respiratory system of mammals and birds can be explained by the difference in the ventilation of the gas-exchanging tissue which has a flow-through pattern in the birds but is reciprocating in the mammals.As a result mammals have a reduced alveolar and arterial oxygen tension, a potential for uneven ventilation, and relatively large terminal air spaces. The pulmonary capillaries of birds are much thinner and have more uniform walls, with a more efficient cross-current pattern of gas-exchange, and the bird has separated the ventilatory and gas exchange functions.These differences make the respiratory system of birds more efficient than that of mammals.