6.8 Exchange of gases in the lungs

Question 1

Where is the site of gas exchange in humans

Answer 1

The epithelium of the alveoli

Question 2

What must occur to ensure a constant supply of oxygen to the body

Answer 2

A diffusion gradient must be maintained at the alveolar surface

Question 3

What ensures efficient transfer of materials across exchange surfaces

Answer 3

Thin, partially permeable and have a large surface area.

There also has to be movement of both the environmental medium and internal medium

Question 4

Why is diffusion between the blood and alveoli very rapid

Answer 4

1. Red blood cells are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
2. The distance between the alveolar air and red blood cells is reduced as the red blood cells are flattened against the capillary walls
3. the walls of both alveoli and capillaries are very thin and therefore the distance over which diffusion takes place is very short
4. Alveoli and pulmonary capillaries have a very large total surface area
5. Breathing movements constantly ventilate the lungs, and the action of the heart constantly circulates blood around the alveoli. Together, these ensure that a steep concentration gradient of the gases is maintained
6. Blood flow through the pulmonary capillaries maintains a concentration gradient