Events in inhalation

7

Carbon dioxide gas diffuses from the plasma into the alveolar air

3

The volume of the thorax increases

6

Air enters from the higher pressure outside to the lower pressure inside. Oxygen moves by diffusion into the alveoli and from there into the red blood cells of the capilalries

1

During inhalation the diaphragm contracts, causing it to flatten and move downwards

8

Steep concentration gradients of oxygen and carbon dioxide between air and blood are maintained by the circulatory system and ventilation

2

The external intercostal muscles contract, the internal intercostal muscles relax and the rib cage moves upwards and outwards

5

The lungs are pulled out when the thorax expands and the pressure inside them falls

4

The pleural membranes provide an air tight seal between the inside of the rib cage and the outer surface of the lungs and transmit any changes in volume of the thorax to the lungs