1. 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

2. Which set of lungs has a bigger volume?

3. How does the thoracic cavity change size?

4. 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 breathe Oxygen levels only control breathing during very low oxygen situations The breathing centre of the brain senses these levels and sends signals to the muscles

6. 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

7. How much can you breathe in/out?

8. Definitions: Tidal volume the amount you exchange in a normal breath Inspiratory reserve volume the maximum you can breathe in Expiratory reserve volume the maximum you can breathe out Residual volume the air left in your lungs when you breathe out Vital capacity the maximum volume you can breathe in and out