11.1.8Gas Exchange in Humans
Volume and Pressure Changes in the Lungs — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 5 parts Lesson 4 of 4 Unit quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Section 1 of 5Breathing In (Inhalation)
Air always moves from a region of higher pressure to a region of lower pressure.
1
The diaphragm muscle contracts and flattens, moving downwards, which increases the volume of the chest cavity.
2
The external intercostal muscles contract, pulling the ribcage upwards and outwards, which increases the volume further.
3
As the volume of the thorax increases, the air pressure inside the lungs falls below atmospheric pressure.
4
Air is pushed into the lungs by the higher pressure outside until the pressures are equal.
Section 2 of 5Breathing Out (Exhalation)
Normal breathing out at rest is largely a passive process.
1
The diaphragm relaxes and returns to its domed shape, which reduces the volume of the chest cavity.
2
The external intercostal muscles relax, so the ribcage moves downwards and inwards under its own weight.
3
The volume of the thorax decreases, so the pressure in the lungs rises above atmospheric pressure.
4
Air is forced out of the lungs until the pressure inside has fallen to the same level as outside.
Section 3 of 5Antagonistic Muscles and Exercise
Antagonistic pair
- Antagonistic pair The internal and external intercostal muscles work against each other, as one set pulls the ribs up and the other pulls them down.
Forced exhalation
- Forced exhalation During exercise the internal intercostal muscles contract, pulling the ribs down and in more strongly, so more air is forced out.
Abdominal muscles
- Abdominal muscles These also contract during forced breathing and push the diaphragm upwards, further reducing the volume of the chest.
Why it matters
- Why it matters More carbon dioxide is produced in active muscles, so faster and deeper breaths remove it and bring in more oxygen.
Rate and depth
- Rate and depth During exercise both the rate and the depth of breathing increase.
| Feature | Inhalation | Exhalation |
|---|---|---|
| Diaphragm | Contracts and flattens | Relaxes and domes upwards |
| External intercostals | Contract | Relax |
| Ribcage | Moves up and out | Moves down and in |
| Thorax volume | Increases | Decreases |
| Lung pressure | Falls below atmospheric | Rises above atmospheric |
Section 4 of 5Exam Wording
Exam Wording
Terms
- Terms Inspiration means breathing in and expiration means breathing out, and they are the same as inhalation and exhalation.
Cause and effect
- Cause and effect Always link the muscle action to the change in volume, then to the change in pressure, then to the direction of air movement.
Common slip
- Common slip Do not say that the lungs pull air in;
- the lungs have no muscle, and air moves because of the pressure difference.
Section 5 of 5Exam Checklist & Tips
11.1.8 – Key Points for the Exam
- Diaphragm A sheet of muscle separating the thorax from the abdomen.
- Intercostal muscles Muscles between the ribs that move the ribcage.
- Antagonistic muscles Muscles that work in opposite directions to each other.
- Atmospheric pressure The pressure of the air outside the body.
- Forced exhalation Active breathing out using the internal intercostal muscles.
Common Mistakes
- Saying the diaphragm moves up when it contracts, whereas it flattens and moves down.
- Stating that air enters because the lungs expand actively, when it enters because pressure falls.
- Mixing up which set of intercostal muscles raises the ribs; the external muscles raise them.
- Describing a decrease in volume as causing a decrease in pressure, when the pressure rises.
Last updated:
\n