Gas exchange

Nature of science:

Obtain evidence for theories—epidemiological studies have contributed to our understanding of the causes of lung cancer. (1.8)

• 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.

Applications and skills:

• Application: Causes and consequences of lung cancer.
• Application: Causes and consequences of emphysema.
• Application: 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)

• Syllabus and cross-curricular links:
• Biology
• Topic 1.4 Membrane transport
• Topic 1.6 Cell division
• Topic 6.2 The blood system
• Physics
• Topic 3.2 Modelling a gas

Aims:

• Aim 8: The social consequences of lung cancer and emphysema could be discussed.

• 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.