Alveoli: Adaptations for Gas Exchange

Alveoli

Tiny air sacs in the lungs where gas exchange occurs

Gas exchange

Movement of oxygen into the blood and carbon dioxide out of the blood

Large surface area

Many alveoli provide a huge area for diffusion

Thin walls

One‑cell‑thick walls for fast diffusion

Moist lining

Allows gases to dissolve before diffusing

Good blood supply

Dense capillary network maintains steep concentration gradients

Steep concentration gradient

Difference in gas concentration that drives diffusion

Elastic fibres

Allow alveoli to stretch and recoil during breathing

Capillaries

Tiny blood vessels surrounding alveoli

What is the main function of alveoli?

Gas exchange

Why do alveoli have a large surface area?

To increase the rate of diffusion

Why are alveoli walls one cell thick?

To shorten the diffusion distance

Why do alveoli have a moist lining?

To dissolve gases for easier diffusion

Why are alveoli surrounded by capillaries?

To maintain steep concentration gradients

What gas diffuses from alveoli into the blood?

Oxygen

What gas diffuses from the blood into the alveoli?

Carbon dioxide

Why is a steep concentration gradient important?

It speeds up diffusion

What maintains the steep concentration gradient in alveoli?

Continuous blood flow

What role do elastic fibres play?

Help alveoli expand and recoil during ventilation

Why is diffusion fast in alveoli?

Large surface area, thin walls, moist lining, good blood supply

What happens to oxygen once it enters the blood?

It binds to haemoglobin in red blood cells

Why is the alveolar surface moist but not flooded?

Enough moisture for diffusion without blocking air flow