6.8 Exchange of gas in the lungs

Question 1

How is a diffusion gradient maintained in the alveoli?

Answer 1

• movement of the external medium (air) and the internal medium (blood). Since the alveoli are located inside the body, the external medium moves by ventilation (breathing)
• around each alveoli is a network of pulmonary capillaries with walls only one cell thick.

Question 2

Why is the diffusion of gases between the alveoli and blood rapid?

Answer 2

• RBCs are slowed as hey pass through pulmonary capillaries, allowing more time for diffusion
• Distance between alveolar air and RBCs is reduced as RBCs are flattened against capillary walls
• Walls of alveoli and capillaries are thin, reducing diffusion distance.
• alveoli and pulmonary capillaries have a large combined surface area.
• breathing constantly ventilates the lungs, and the heart action constantly circulates blood around the alveoli, ensuring a steep conc. gradient
• blood flow through the pulmonary capillaries maintains gradient