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All 12 Flashcards — Alveoli and the mammalian lung
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Question
What is an alveolus?
Answer
A tiny **air sac** in the lung where **gas exchange** between air and blood takes place.
Question
Which two gases are exchanged at an alveolus, and in which direction?
Answer
**Oxygen** diffuses from the air into the blood; **carbon dioxide** diffuses from the blood into the air.
Question
List the adaptations of an alveolus for gas exchange.
Answer
**Large surface area**, wall **one cell thick** (short diffusion distance), **moist lining**, and a **rich blood supply**.
Question
Why are there millions of tiny alveoli rather than one large sac?
Answer
Many tiny sacs pack a **huge total surface area** into the chest, and surface area controls how fast gases diffuse.
Question
What is the function of a type I pneumocyte?
Answer
It is a **thin, flat cell** forming most of the alveolar wall, giving a **short diffusion distance** — it is the gas-exchange surface.
Question
What is the function of a type II pneumocyte?
Answer
It **secretes surfactant** onto the moist alveolar lining.
Question
What is the function of a phagocyte in the alveolus?
Answer
It **engulfs and digests** pathogens, dust and debris that are breathed in, keeping the surface clean.
Question
What is surfactant?
Answer
A fluid secreted by type II pneumocytes that **lowers the surface tension** of the moist alveolar lining.
Question
What is the role of surfactant? (2 marks)
Answer
It **lowers surface tension**, so alveoli **do not collapse** on exhalation and the lungs are **easier to inflate**.
Question
Why does a thin alveolar wall help gas exchange?
Answer
A wall **one cell thick** gives a **short diffusion distance**, so gases cross the wall quickly.
Question
Why does a rich capillary network help gas exchange?
Answer
It keeps a **steep concentration gradient** by carrying gases away, so diffusion stays fast.
Question
Predict the consequence of destroying the type II pneumocytes.
Answer
**No surfactant** is made → surface tension stays high → **alveoli collapse** → reduced gas exchange.
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Topic 2.6 hub
Gas exchange
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