6.4 Gas Exchange (Core)

Assessment Statements:

6.4.1 Distinguish between ventilation, respiration and gas exchange.

6.4.2 Explain the need for a ventilation system.

6.4.3 Describe the features of alveoli that adapt them to gas exchange.

6.4.4 Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli.

6.4.5 Explain the mechanism of ventilation of the lungs, in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles.

Ventilation

The flow of air in and out of the alveoli

Two stages: inhalation and exhalation

Lungs are not muscular and cannot ventilate themselves

The thorax moves and changes size, due to the action of two sets of muscles: the intercostal muscles and the diaphragm.

Gas ExchangeThe diffusion of gases (oxygen and carbon dioxide)

Two sites for gas exchange:

● Alveoli: Oxygen diffuses into the blood from the alveoli and carbon dioxide diffuses from the blood into the alveoli

● Tissues: Oxygen diffuses from blood into the cells and carbon dioxide diffuses from cells to the blood

Gas Exchange in Alveoli

Cell Respiration

●Aerobic respiration uses oxygen in the mitochondria and produces carbon dioxide

● Anaerobic respiration does not use oxygen but still produces carbon dioxide

Why do we need a ventilation system?To maintain a concentration gradient for diffusion

Air is constantly being refreshed in the lungskeeping the concentration of oxygen high and

carbon dioxide low

At the same time bllood is constantly carrying away oxygen and bringing new carbon dioxide

Both gases diffuse down their concentration gradient from high to low concentration

Watch the animation and summarise the process of ventilation

Features of alveoli for gas exchange

Large numbers of alveoli gives large surface area for gas exchange

Single layer of flattened cells in

wall of alveoli

Surrounded by dense network of

capillaries

Short distance for diffusion of gases

Oxygen dissolves in thin film of moisture on inside of alveoli - this

aids diffusion

The Ventilation Systemintercostal muscles

bronchi

bronchiolesheart

ribs

alveolusdiaphragm

Review