Gas exchange

• Cell respiration


  The process of cells getting energy by oxidizing food
• Cells need continuous supply of oxygen to respire
• The waste product of respiration is CO2 and it needs to be removed from the body
• Gas exchange


  The process of exchanging gases between blood and air in the lungs

  
• Ventilation


  The process of moving air in and out
• Gas exchange system/ventilation system


  Highly specialized structure for ventilation
• Components of the human gas exchange system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Lungs

  
• Lungs


  • Enclosed in the thorax/chest by ribcage and a muscular sheet of tissue called diaphragm

  
• Ribs


  • Joined to each other by muscles called intercostals muscles
• Breathing in


  1. Air enters nose or mouth

  2. Passes down the trachea

  3. Trachea splits into two bronchi

  4. Each bronchus divides into smaller bronchioles

  5. Bronchioles ending at alveoli

  
• Trachea and bronchi


  • Contain rings of cartilage to support the airways and keep them open

  
• Pleural membranes


  Thin, moist membranes that separate the thorax from the lungs
• Pleural cavity


  Space between the two pleural membranes filled with pleural fluid
• Airways


  • Lined with cells that secrete mucus to trap dirt and bacteria, and have cilia to sweep the mucus out
• Ventilation


  Moving air in and out, requires a difference in air pressure
• Breathing in


  1. External intercostal muscles contract, moving ribcage up and out

  2. Diaphragm muscles contract, moving diaphragm down

  3. Increases volume of thorax, decreases air pressure, air rushes in

  
• Breathing out


  1. Internal intercostal muscles contract, moving ribcage down and in

  2. Diaphragm muscles relax, moving diaphragm up

  3. Decreases volume of thorax, increases air pressure, air rushes out

  
• Alveoli


  • Thin-walled, moist, large surface area, concentration gradients for efficient gas exchange

  
• Gas exchange in alveoli

  1. Oxygen diffuses from alveoli into blood

  2. Carbon dioxide diffuses from blood into alveoli

  
• Oxygenated blood leaves the capillaries and flows back to the heart, which then pumps it around the body