Controlling ventilation rate
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Flip to reveal answersWhich gas does the body monitor to control breathing rate?
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Question
Which gas does the body monitor to control breathing rate?
Answer
**Carbon dioxide (CO₂)** — not oxygen. A rise in CO₂ is the main signal that speeds up breathing.
Question
Define ventilation rate.
Answer
The **number of breaths taken per minute** (together with how deep each breath is).
Question
What is a chemoreceptor?
Answer
A **sensor that detects a chemical change** — here, a rise in blood CO₂ (and the fall in pH it causes).
Question
Where are the chemoreceptors that monitor blood CO₂?
Answer
In the **medulla** of the brain and in the walls of the **aorta and carotid arteries**.
Question
What is the control centre for breathing, and what does it do?
Answer
The **medulla** (in the brainstem) — it sends nerve impulses to the breathing muscles to set the ventilation rate.
Question
Which muscles act as the effectors that change breathing?
Answer
The **diaphragm and intercostal muscles** — they make breathing faster and deeper.
Question
How does a rise in blood CO₂ affect ventilation rate?
Answer
Ventilation rate **increases** — chemoreceptors detect the rise and the medulla speeds up breathing to exhale the extra CO₂.
Question
How does faster breathing bring blood CO₂ back to normal?
Answer
Faster, deeper breathing **exhales more CO₂**, so blood CO₂ (and pH) fall back to the normal level.
Question
Why is the control of ventilation an example of negative feedback?
Answer
The response (faster breathing, which removes CO₂) **opposes** the change (rising CO₂), returning CO₂ to its set point.
Question
What happens to breathing when blood CO₂ falls below normal?
Answer
Chemoreceptors are stimulated **less**, the medulla **slows breathing down**, so less CO₂ is exhaled and CO₂ rises back to normal.
Question
How does rising CO₂ affect blood pH?
Answer
It **lowers** blood pH (makes the blood more acidic), because dissolved CO₂ forms acid.
Question
On a graph of CO₂ against ventilation rate, what is the trend?
Answer
As CO₂ **increases**, ventilation rate **increases** — a positive correlation.
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Topic 3.6 hub
Integration of body systems
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