The respiratory system is adapted for gas exchange between the air and blood. Oxygen diffuses into the alveoli and into blood capillaries, while carbon dioxide diffuses out. The diaphragm and intercostal muscles drive breathing by expanding the lungs to inhale air and relaxing to exhale. Gas exchange occurs through the thin walls of alveoli surrounded by capillaries, allowing oxygenation of blood and removal of carbon dioxide.

1. The breathing system RESPIRATORY (LUNG)
SYSTEM

3. The intercoursal muscles, attached between the ribs, move the rib cage
up and down
The diaphragm is a sheet of muscle at the base of the rib cage
Cillia in the nose warms the air allowing it to absorb into the blood
quicker
each alveolus is covered in a net of thin-walled (one cell thick) blood
capillary

4. Alveolus structure
Oxygen diffuses through the alveolus & capillary linings and attaches to
red blood cells
At the same time, carbon dioxide diffuses from the plasma into the
alveolus
Diffusion is the movement of molecules from a region of high
concentration to a region of lower concentration

5. Alveolus
structure

6. Preventing infection
The lining cells of the nose, trachea and bronchi produce a sticky mucus
that traps dust and germs
White blood cells in the alveoli can engulf bacteria and foreign matters

7. How are the lungs adapted for their function
Alveoli have a large surface area
Short distance between air and blood
1 cell thick
Rich blood supply
Walls of alveoli are elastic

8. Composition of air in the lungs (% volume)
Inhaled air Exhaled air
Oxygen 21 16
Carbon dioxide 0.04 4
Nitrogen 79 79
Water vapour Varies saturated

9. Inhaling (inspiration)
The brain sends signals to the rib muscles and diaphragm to contract
The ribs are pulled up and out, and the diaphragm flattens downwards
The volume of the chest increases
Air pressure drops in the lungs
More air drawn into the lungs and alveoli

10. Gas exchange in the lungs & tissue

11. Transport of oxygen in the blood
Red blood cells have haemoglobin in them
Red blood cells carry 97% of the oxygen
The other 3% is carried in the plasma

12. Transport of carbon dioxide
Most is carried in the plasma as bicarbonate ions or as dissolved carbon
dioxide
A small % is carried by the red blood cells

13. Exhaling
The rib muscles and diaphragm relax, springing back to their original
position
Air pressure in the lungs increases
Air is pushed out from the alveoli

14. Voice box
Made up of two sheets of muscles
Vibrates as the air passes between them
Produce sounds & speech, in co-operation with our mouth, tongue and
teeth
We breath automatically by involuntary reflex action
Controlled by medulla oblangata of the brain

15. Role of the brain in breathing
Mostly our breathing rhythm is unconsciously set by the brain
We can voluntarily change the rate at which we breath
You can’t hold your breath forever
Your brain won’t let you

16. Why can’t you stop breathing?
When you hold your breath
Carbon Dioxide levels rises in your blood
This triggers the medulla oblangata in your brain to make you breath
You end you gasping for breath

17. Breathing disorders
Asthma – inflammation & constriction of bronchi
Bronchitis
Emphysema – destruction of alveoli
TB – elasticity reduced (bacteria)
Pneumonia – fills with fluid

18. Asthma
Cause: narrowing of the bronchioles due to some irritant (dust mite, pollen,
cold virus). Sufferer finds it difficult to inhale oxygen
Prevention: removing the offending agent
Treatment: inhalers