Gas exchange at the alveolus

Overview

Recall questions on the structure of the alveolar wall and the capillary beside it, the short diffusion path, the surfactant and the moist lining, and how the blood supply and ventilation together maintain the gradient.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   How does mass flow of air help gas exchange in the lungs?

   Model answer

   Breathing brings a bulk flow of fresh air to the alveoli, which keeps alveolar oxygen high and carbon dioxide low and so maintains the diffusion gradients.

2. 2

   How do the alveoli provide a large surface area for gas exchange?

   Model answer

   There are several hundred million small alveolar sacs in the lungs, and together their walls add up to a very large total area.

3. 3

   Name the tissue that forms the wall of an alveolus.

   Model answer

   The alveolar wall is formed of simple squamous epithelium.

4. 4

   Name the tissue that forms the wall of a blood capillary surrounding an alveolus.

   Model answer

   The capillary wall is formed of simple squamous endothelium.

5. 5

   Why is the barrier between alveolar air and the blood so thin?

   Model answer

   It consists only of a flattened alveolar epithelial cell and a flattened capillary endothelial cell, so the diffusion path is less than a micrometre.

6. 6

   Why is the outer surface of an alveolus kept moist?

   Model answer

   Oxygen and carbon dioxide must dissolve in the film of fluid before they can diffuse across the alveolar wall.

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