B11.1 Gas exchange in humans

What is the human breathing system?

• Organ system that allows body to obtain oxygen needed for aerobic respiration (needs O₂) and allows the body to remove the carbon dioxide (releases CO₂) produced as waste

Identify in diagrams and images the parts of the breathing system

• Alveoli are located at the end of the bronchioles, and they are surrounded by capillaries

• Remember: in diagrams, the sides of the lungs are reversed

What is the pathway of air through the respiratory system?

1. Nose/mouth: air enters the body through here

2. Larynx: directs air into trachea

3. Trachea: windpipe carries air into the lungs 

4. Bronchi: trachea splits into two main bronchi (one for each lung)

5. Bronchioles: bronchi branch off into smaller tubes called bronchioles

6. Alveoli: tiny air sacs surrounded by capillaries located at the end of bronchioles, this is where gas exchange happens

Describe the process of gas exchange in the alveoli

1. Air is inhaled through nose or mouth filling alveoli with air

2. There is a high concentration of oxygen in the alveolus, and a low concentration in the capillaries

3. Oxygen diffuses from high concentration in alveolus to low concentration in capillaries

4. Oxygen binds with haemoglobin which is then transported around the body and diffused into cells with low oxygen concentration so that they can use it for cellular respiration

Describe features of alveoli for efficient gas exchange

1. Have a large surface area: more space for gases to diffuse across

2. Thin: reduces diffusion distance, making gases like oxygen and carbon dioxide diffuse more quickly

3. Good blood supply: each alveoli has lots of capillaries surrounding it which transport blood 

4. Good ventilation with air: good supply of air supplied through breathing

What is the difference between expired and inspired air?

• Inspired air: the air you breathe in

  • More oxygen

  • Less carbon dioxide

  • Used for aerobic respiration

• Expired air: the air you breathe out

  • Less oxygen

  • More carbon dioxide

  • More water vapour because moisture evaporates from the cells of the gas exchange surface

Describe the link between physical activity and the rate and depth of breathing

1. When exercising, cells in the body respire more during periods of physical activity to provide the muscles with the energy needed

2. Since theres more respiration, more carbon dioxide is produced as a waste product

3. The brain detects increasing carbon dioxide rate in the blood

4. This triggers the body to respond by increasing rate and depth of breathing to expel carbon dioxide from the body

5. These changes also increase amount of oxygen obtained which is needed for aerobic respiration to continue