Essential idea: The lungs are actively ventilated to ensure that gas exchange can occur passively.
Two processes maintain the concentration gradients between the blood and the alveolar air to ensure that diffusion of both oxygen and carbon dioxide can occur: firstly circulation of the blood brings a constant supply of high carbon dioxide, deoxygenated blood to the alveoli. Secondly the diaphragm (above) and intercostal muscles constantly increase and decrease the volume of the lungs to cause ventilation to occur, this is turn ensures a supply of high oxygen, low carbon dioxide air to the alveoli. The muscles cause the lungs to increase and decrease in volume by contractions. You can clearly see the striations in the diaphragm muscle tissue above. The striations help the muscle tissue to contract and relax.
Understandings, applications and skills
| 6.4.U1 | Ventilation maintains concentration gradients of oxygen and carbon dioxide between air in alveoli and blood flowing in adjacent capillaries. |
| 6.4.U2 | Type I pneumocytes are extremely thin alveolar cells that are adapted to carry out gas exchange. |
| 6.4.U3 | 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. |
| 6.4.U4 | Air is carried to the lungs in the trachea and bronchi and then to the alveoli in bronchioles. [Students should be able to draw a diagram to show the structure of an alveolus and an adjacent capillary.] |
| 6.4.U5 | Muscle contractions cause the pressure changes inside the thorax that force air in and out of the lungs to ventilate them. |
| 6.4.U6 | Different muscles are required for inspiration and expiration because muscles only do work when they contract. |
| 6.4.A1 | Causes and consequences of lung cancer. |
| 6.4.A2 | Causes and consequences of emphysema. |
| 6.4.A3 | External and internal intercostal muscles, and diaphragm and abdominal muscles as examples of antagonistic muscle action. |
| 6.4.S1 | Monitoring of ventilation in humans at rest and after mild and vigorous exercise. (Practical 6) [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.] |
[Text in square brackets indicates guidance notes]
Presentation and Notes
The presentation is designed to help your understanding.
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The 6.4 Gas exchange - the bottom line template can be used as a note construction template in itself or as a checklist if you are using your own or another template such as the Cornell style template.
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Nature of science
Obtain evidence for theories—epidemiological studies have contributed to our understanding of the causes of lung cancer. (1.8)
