MICROANATOMY

Detailed explanation-1: -And the fact that they are permeable means that it is much easier for the gases to diffuse from the capillaries into the cells and vice versa. We have therefore determined that the correct answer is (E). It is important for capillaries to have thin, permeable walls to allow substances to diffuse into and out of cells.

Detailed explanation-2: -The walls of the alveoli and capillaries are permeable. What does this mean? Substances can pass through them.

Detailed explanation-3: -Oxygen breathed in from the air passes through the alveoli and into the blood and travels to the tissues throughout the body. Carbon dioxide travels in the blood from the body’s tissues and passes through the alveoli to be breathed out.

Detailed explanation-4: -Adaptations of the alveoli: Moist walls-gases dissolve in the moisture helping them to pass across the gas exchange surface. Permeable walls-allow gases to pass through. Extensive blood supply-ensuring oxygen rich blood is taken away from the lungs and carbon dioxide rich blood is taken to the lungs.

Detailed explanation-5: -The alveolar wall is impermeable to albumin and the oalb value for that structure must be 1.0. For alveolar walls it is also relevant to calculate oNa, since Na is the most abundant plasma solute and one to which alveolar walls have only a low permeability.