gas exchange

• Gas exchange surfaces

  • Large surface area
  • Thin walls
  • Good ventilation
  • Good blood supply
• Structures in the human breathing system

  • Lungs
  • Cilia and mucus
  • Goblet cells

  
• Cilia

  Tiny hairs on the end of epithelial cells that beat and push mucus up the passages
• Goblet cells

  Mucus-producing cells that are shaped like a goblet or cup
• Mucus

  Traps particles, dust and pathogens and prevents them from getting into the lungs
• Cilia beat and push mucus up and away from the lungs
• External intercostal muscles

  Pull the rib cage up
• Internal intercostal muscles

  Pull the rib cage down
• Diaphragm

  Thin sheet of muscle that separates the chest cavity from the abdomen
• Inhalation

  1. Diaphragm contracts and flattens

  2. External intercostal muscles contract to pull ribs up and out

  3. Increases volume of chest cavity

  4. Decreases air pressure in lungs

  5. Air is drawn in
• Exhalation

  1. Diaphragm relaxes and moves upwards

  2. External intercostal muscles relax so ribs drop down and in

  3. Decreases volume of chest cavity

  4. Increases air pressure in lungs

  5. Air is forced out
• Internal intercostal muscles can also contract to pull ribs down and in for forced exhalation
• Forced exhalation allows a greater volume of gases to be exchanged
• Alveoli

  • Many rounded alveolar sacs for large surface area
  • Thin, single cell layers to minimise diffusion distance
  • Ventilation maintains high oxygen and low carbon dioxide
  • Good blood supply
  • Moisture on surface aids diffusion
• Smoking

  Causes chronic obstructive lung disease, coronary heart disease, and increased cancer risk
• Chemicals in cigarettes

  • Tar
  • Nicotine
  • Carbon monoxide
• Nicotine

  Narrows blood vessels, increases blood pressure and heart rate
• Carbon monoxide

  Binds irreversibly to haemoglobin, reducing oxygen-carrying capacity of blood
• Tar

  Carcinogenic, contributes to chronic bronchitis and emphysema
• Breakdown of alveoli in emphysema reduces surface area for gas exchange
• Effect of exercise on breathing

  1. Frequency increases to provide more oxygen and remove carbon dioxide

  2. Breathing rate remains elevated after exercise to repay oxygen debt from anaerobic respiration
• Fitness and breathing rate

  • Unfit individuals have higher resting breathing rate, faster increase during exercise, and longer recovery time