Ventilation
Laura Armstrong
Teacher
Recall Questions
This topic requires prior knowledge of lung anatomy. You can test your knowledge on this below.
What is ventilation?
Ventilation is the process of moving air in and out of the lungs, maintaining a steep concentration gradient for gas exchange.
What is the role of the diaphragm in inhalation?
The diaphragm contracts and flattens during inhalation, increasing thoracic volume and decreasing pressure, allowing air to enter the lungs.
How does oxygen move from the alveoli into the blood?
Oxygen diffuses across the alveolar epithelium and capillary endothelium into the blood, moving down its concentration / diffusion gradient.
Topic Explainer Video
Check out this @LauraDoesBiology video that explains ventilation or read the full notes below. Once you've gone through the whole note, try out the practice questions!
What is Ventilation?
Ventilation is the process of inspiration (inhalation) and expiration (exhalation) to maintain a concentration gradient for gas exchange. It relies on pressure changes in the thoracic cavity due to the actions of the diaphragm and the intercostal muscles.
Mechanism of Ventilation
1. Inhalation (Inspiration) – Active Process
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External intercostal muscles contract → ribs move up and out
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Diaphragm contracts and flattens
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Thoracic volume increases → pressure decreases below atmospheric pressure
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Air moves into the lungs down a pressure gradient
Requires energy (active process)
2. Exhalation (Expiration) – Passive Process
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External intercostal muscles relax → ribs move down and in
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Diaphragm relaxes and returns to dome shape
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Thoracic volume decreases → pressure increases above atmospheric pressure
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Air is forced out of the lungs
Passive process (except during forced expiration)
3. Forced Expiration – Active Process
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External intercostal muscles relax → ribs move down and in
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Internal intercostal muscles contract, pulling the ribs further down and in
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Diaphragm relaxes and returns to dome shape
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Abdominal muscles contract, pushing the diaphragm further up
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Thoracic volume decreases rapidly → pressure increases above atmospheric pressure
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Air is forced out quickly (there is a steeper pressure gradient)
Used during exercise, coughing, or when blowing up a balloon!
Key Terms
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Ventilation: The movement of air into and out of the lungs.
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Thoracic cavity: The chest cavity containing the lungs.
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Diaphragm: A sheet of muscle involved in breathing.
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Intercostal muscles: Muscles between the ribs that aid breathing.
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Pressure gradient: Air moves from high to low pressure.
- Forced expiration: Actively pushing air out using internal intercostal muscles and abdominal muscles.
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Exam Tip
Common mistake: Many students forget to mention that internal intercostal muscles contract during forced expiration, while external intercostal muscles contract during inhalation. Always describe the specific muscles involved in each process.
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Describe the process of ventilation, including how both inhalation and exhalation occur. (6 marks)
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During inhalation, the external intercostal muscles contract, pulling the ribs up and out.
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The diaphragm contracts and flattens, increasing the thoracic volume.
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This decreases the pressure inside the lungs, drawing air into the lungs down a pressure gradient.
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During exhalation, the external intercostal muscles relax, causing the ribs to move down and in.
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The diaphragm relaxes, returning to a dome shape, decreasing thoracic volume.
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This increases pressure inside the lungs, forcing air out down a pressure gradient.
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!