22 June 2013

#81 Gaseous exchange, role of mucus and cilia

Gas exchange usually involves 2 or more gases transferred in opposite directions across a respiratory surface.

1. Structure of the breathing system: the larynx, trachea, bronchi,  bronchioles, alveoli and associated capillaries.

Credit: biology-forums.com

2. Gaseous exchange relies on diffusion. To be efficient, the gaseous exchange surface must: 

- thin – shorter distance to diffuse
- moist – allow gases to dissolve
- large surface area
- have a concentration gradient across surface – maintained by movement of air and transport/ use of gas.

These features are present in gills (fish) and alveoli (lungs).

3. The role of mucus and cilia

- Inside the nose, thin turbinal bones are covered with a layer of cells. Some of which are goblet cells.

- Goblet cells produce a liquid (water + mucus) ---> evaporate ---> moisten nose.

- Cilia: tiny hair-like projections; constantly moving

- Bacteria + dust particles are trapped by cilia and mucus as to not move further inside the gas exchange system.

Try this
State how each feature labeled on the diagram of an alveolus makes the process of gaseous exchange efficient. [5 marks]


Wall of alveolus – one cell thick (or very thin) so that diffusion happens quickly.

Moist surface- allow O2 to dissolve making diffusion faster.

Blood is moving – so that’s  concentration gradient is maintained for O2 and CO2

Wall of capillary – one cell thick (or very thin) so that’s diffusion happens quickly.

Red blood cells – contain haemoglobin to transport O2 away from the lungs. 

Video: Gas exchange

Video: Functions of Cilia and Goblet Cells