2.6.3Additional lessons
Mechanism of Ventilation — IB Biology SL Revision Notes & Topical Questions
5 min read 5 parts Lesson 29 of 142
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.
Part 1 of 5Inspiration
1
The external intercostal muscles contract, pulling the ribcage up and out.
2
The diaphragm contracts and flattens, which increases the volume of the chest cavity.
3
The larger volume lowers the pressure inside the lungs below atmospheric pressure.
4
Air flows from the higher pressure outside into the lungs until the pressures are equal.
5
Inspiration is an active process because it requires muscle contraction and energy from ATP.
Part 2 of 5Expiration
Passive expiration
- Passive expiration At rest the external intercostal muscles and the diaphragm relax, and the elastic lungs recoil to reduce volume.
Diaphragm
- Diaphragm On relaxation the diaphragm returns to its dome shape and pushes up into the thorax.
Pressure rise
- Pressure rise Lower volume raises the pressure inside the lungs above atmospheric pressure, so air flows out.
Forced expiration
- Forced expiration The internal intercostal muscles contract to pull the ribs down and in, and abdominal muscles push the diaphragm up.
Antagonistic muscles
- Antagonistic muscles The external and internal intercostals oppose each other, so one set moves the ribs up and the other moves them down.
| Stage | Intercostals | Diaphragm | Volume | Pressure |
|---|---|---|---|---|
| Inspiration | External contract | Contracts, flattens | Increases | Decreases |
| Passive expiration | External relax | Relaxes, domed | Decreases | Increases |
| Forced expiration | Internal contract | Pushed up | Decreases more | Increases more |
Part 3 of 5Ventilation Rate
Ventilation maintains the concentration gradient of gases at the alveoli.
Ventilation Rate
Ventilation rate
- Ventilation rate The number of breaths per minute, which can be counted over one minute.
Tidal volume
- Tidal volume The volume of air taken in with each breath at rest.
Minute ventilation
- Minute ventilation The total volume of air moved per minute, found by multiplying ventilation rate by tidal volume.
Exercise
- Exercise Muscles need more oxygen, so both rate and depth of breathing increase.
Part 4 of 5Worked Example
Question
- At rest a person takes 15 breaths per minute with a tidal volume of 500 cm³.
- Calculate the minute ventilation in cm³ and in dm³.
- Minute ventilation = ventilation rate × tidal volume.
- 15 breaths per minute × 500 cm³ = 7500 cm³ per minute.
- 1 dm³ = 1000 cm³, so 7500 cm³ = 7.5 dm³.
Answer Minute ventilation is 7500 cm³ per minute, which is 7.5 dm³ per minute.
Part 5 of 5Exam Checklist & Tips
2.6.3 – Key Points for the Exam
- Inspiration Breathing in, caused by contraction of the diaphragm and external intercostals.
- Expiration Breathing out, which is passive at rest.
- Antagonistic muscles Muscles that produce opposite movements, such as the internal and external intercostals.
- Ventilation rate The number of breaths taken per minute.
Common Mistakes
- Saying air is sucked in because the lungs expand on their own; muscles change the volume first.
- Stating that the diaphragm relaxes and flattens during inspiration; it contracts and flattens.
- Mixing up pressure and volume, as lower volume increases pressure.
- Describing quiet expiration as an active process using internal intercostal muscles.
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