Gas Exchange

Question 1

Explain the process of intercostal muscles during inhalation

Answer 1

During inhalation the diaphragm contracts and flattens. The external set of intercostal muscles contract to pull the ribs up and out: This increases the volume of the chest cavity (thorax) Leading to a decrease in air pressure inside the lungs relative to outside the body
Air is drawn in

Question 1

Explain the process of intercostal muscles during exhalation

Answer 1

The diaphragm relaxes, it moves upwards back into its domed shape. The external set of intercostal muscles relax so the ribs drop down and in. This decreases the volume of the chest cavity (thorax). Leading to an increase in air pressure inside the lungs relative to outside the body
Air is forced out

Question 2

How are the alveoli suitable for gas exchange

Answer 2

There are many rounded alveolar sacs which give a very large surface area to volume ratio
Alveoli (and the capillaries around them) have thin, single layers of cells to minimise diffusion distance
Ventilation maintains high levels of oxygen and low levels of carbon dioxide in the alveolar air space
A good blood supply ensures constant supply of blood high in carbon dioxide and low in oxygen
A layer of moisture on the surface of the alveoli helps diffusion as gases dissolve