What is the main function of the alveoli?
Gas exchange — swapping oxygen (O₂) and carbon dioxide (CO₂) between the air and blood.
How does a large surface area help the alveoli function?
Millions of alveoli increase surface area, allowing faster and more efficient gas exchange.
Why are the alveolar walls only one cell thick?
To shorten the diffusion distance, speeding up gas exchange.
Why do alveoli have a moist lining?
Oxygen must dissolve in moisture before diffusing — this makes gas exchange more effective.
What is the benefit of alveoli being surrounded by a rich capillary network?
It maintains rapid diffusion of oxygen into blood and carbon dioxide out of blood.
How do ventilation and blood flow maintain a steep concentration gradient in the alveoli?
Fresh air keeps O₂ high in alveoli, while blood flow carries oxygen away — keeping levels low in blood.
Why do alveoli contain elastic fibres?
They stretch during inhalation and recoil during exhalation, helping efficient movement of air.
What are the overall adaptations of the alveoli?
Large surface area, thin walls, moist lining, extensive blood supply, steep concentration gradient, and elastic fibres.
What is the function of capillaries?
Allow exchange of oxygen, carbon dioxide, nutrients, and waste with tissues.
What structural features do capillaries have?
Walls one cell thick; very small lumen.
Why are capillary walls one cell thick?
To allow rapid diffusion of substances.
What is atherosclerosis?
The buildup of fatty deposits (plaques) inside arteries.
What is the first step in plaque formation?
Damage to the artery lining (endothelium).
Which cholesterol enters the damaged artery wall?
LDL (“bad cholesterol”).
What cells ingest LDL and become foam cells?
Macrophages.
What is a fatty streak?
A buildup of foam cells underneath the artery lining.
What forms over a fatty streak to create plaque?
A fibrous cap.
How do plaques cause CHD?
They narrow the artery and reduce blood flow to the heart muscle.
What happens if a plaque ruptures?
A blood clot forms, which can cause a heart attack or stroke.
