Section 4 - Structure of the Thorax

Question 1

In the lungs, where does gax exchange take place?

Answer 1

In millions of tiny air sacs, called alveoli

Question 2

What 3 adaptions do alveoli have that increase the diffusion rate?

Answer 2

• The walls of the alveoli consist of a single layer of thin, flattened, epithelial cells. Diffusion happens faster when molecules only have to travel a short distance.
• Diffusion is faster when there’s a bigger difference in concentration between two regions. The blood flowing through the rich network of capillaries around the alveoli carries away the oxygen that has diffused through the alveolar walls. This ensures that there’s always a higher concentration of oxygen inside the alveoli than in the blood. The reverse is true for carbon dioxide.
• The alveolar walls are fully permeable to dissolved gases. Oxygen and carbon dioxide can pass easily through the cell membranes of the epithelial cells.