(3) Alveoli

Alveoli

Tiny sacs of lung tissue specialized for gas exchange between air and blood

Average Alveoli Diameter

200-300μm

Average number of Alveoli in an adult lung

300-500 million, increasing the rate of diffusion

Features of Alveoli

- Squamous epithelial

- Elastic Fibres

- Large surface area

- Thin layers

- Good blood supply

- Good ventilation

Why do alveoli have elastic fibres?

- Allows alveoli to expand and contract efficiently, accommodating the changes in lung volume without damage to the lung tissue.

- Elastic recoil helps squeeze air out during exhalation

Why is it beneficial that alveoli have a large surface area?

- It allows for a greater contact area between the air in the alveoli and the blood in the surrounding capillaries.

- This facilitates rapid and efficient gas exchange between the lungs and the bloodstream.

Why is it beneficial that alveoli have thin layers?

- Their walls are only a single epithelial cell thick

- Therefore there is a short diffusion distance between the air in the alveolus and the blood in the capillaries

Why is it beneficial that alveoli have a good blood supply?

Maintains a steep concentration gradient for CO₂ and O₂ between the air in the alveoli and the blood in the capillaries

Why is it beneficial that alveoli have good ventilation?

Breathing moves air in and out of the alveoli

This helps to maintain a steep diffusion gradient for O₂ and CO₂ between the blood and the air in the lungs.