Respiratory System – Part 2

How do we breathe?Key starting points:

Lungs are in their own air-tight space

Diaphragm powers breathing…With some help from the intercostal

muscles around the ribcage

Which set of lungs has a bigger volume?

How does the thoracic cavity change size?

How do you know when to breathe?

Involuntary in humans, but can be controlled consciously if we try (partial conscious control)

Carbon dioxide and hydrogen ion levels control when you breatheOxygen levels only control breathing during very

low oxygen situations

The breathing centre of the brain senses these levels and sends signals to the muscles

5. Diaphragm lowers, rib cages lifts Low pressure

6. Air flows in alveoli stretch

7. Stretch receptors signal the medulla to stop the signal to contract

8. Medulla stops sending the message to contract

9. Relaxation of muscles The lung space shrinks High pressure

10. Air flows out

1. CO2 levels rise

2. Chemoreceptors sense increased CO2

3. Send signal to medulla oblongata in brain

4. Medulla sends nerve signal to diaphragm and rib muscles to contract

How much can you breathe in/out?

Definitions:

Tidal volumethe amount you exchange in a normal breath

Inspiratory reserve volumethe maximum you can breathe in

Expiratory reserve volumethe maximum you can breathe out

Residual volumethe air left in your lungs when you breathe out

Vital capacitythe maximum volume you can breathe in and out