1. Gas Exchange
Topic 6.4

2. • 6.3 Gas Exchange
• Ventilation maintains concentration gradients of oxygen and carbon
dioxide between air in alveoli and blood flowing in adjacent
capillaries.
• Type I pneumocytes are extremely thin alveolar cells that are
adapted to carry out gas exchange.
• Type II pneumocytes secrete a solution containing surfactant that
creates a moist surface inside the alveoli to prevent the sides of the
alveolus adhering to each other by reducing surface tension.
• Air is carried to the lungs in the trachea and bronchi and then to the
alveoli in bronchioles.
• Muscle contractions cause the pressure changes inside the thorax
that force air in and out of the lungs to ventilate them.
• Different muscles are required for inspiration and expiration because
muscles only do work when they contract.

3. Applications:
•Causes and consequences of lung cancer
•Causes and consequences of emphysema.
•External and internal intercostal muscles, and diaphragm and
abdominal muscles as examples of antagonistic muscle action.
•Skill: Monitoring of ventilation in humans at rest and after mild and
vigorous exercise. (Practical 6)
Guidance:
•Ventilation can either be monitored by simple observation and simple
apparatus or by data logging with a spirometer or chest belt and
pressure meter. Ventilation rate and tidal volume should be measured,
but the terms vital capacity and residual volume are not expected.
•Students should be able to draw a diagram to show the structure of an
alveolus and an adjacent capillary.

6. Alveoli
• Microscopic sacs at the terminal ends of the
bronchioles
• Site of gas exchange in the lungs
• Consist of two cell types:
– The Type I pneumocytes are extremely thin alveolar
cells that are adapted to carry out gas exchange.
– Type II pneumocytes secrete a solution containing
surfactant that creates a moist surface inside the alveoli
to prevent the sides of the alveolus adhering to each
other by reducing surface tension.

7. The Type I pneumocytes are
extremely thin alveolar cells
that are adapted to carry out
gas exchange.
Type II pneumocytes secrete a solution
containing surfactant that creates a
moist surface inside the alveoli to
prevent the sides of the alveolus
adhering to each other by reducing

13. Effects of Emphysema:
Emphysema is a chronic lung disease. The large number of small alveoli
are replaced by a small number of much larger much less elastic air
spaces. These have much smaller surface area and so there is much less
gas exchange.
Symptoms are
breathlessness and
forced breathing it is
a type of COPD and
untreated can lead
can be fatal.

14. What causes Emphysema?
1.Constant inflammation that occurs to our lungs will cause infection.
2.Phagocytes remove bacteria and numbers increase.
3.Phagocytes release the protein digesting enzyme elastase on their way to reach
lungs from capillaries.
4.That enzyme destroys elastin in the walls of the alveoli.
5.The air spaces are bigger and less elastic.
Contributory factors:
•Cigarette smoking
•Air pollution
•Gender; men are more likely to develop emphysema than women
•People’s age; older age is a risk factor for emphysema
•Genetic factors