Human respiratory system

• What is the airtight compartment that encloses the lungs called?

  Thorax
• What are the main components of the human respiratory system?

  • Intercostal muscles
  • Pleural membranes
  • Bronchioles
  • Larynx
  • Alveoli
  • Rib
  • Chest cavity
  • Diaphragm
• What is the function of the trachea in the respiratory system?

  It transports air to the bronchi
• What is the role of the alveoli in the respiratory system?

  They are the site of gaseous exchange
• How do mammals ventilate their lungs?

  By negative pressure breathing
• What happens to the intercostal muscles during inspiration?

  They contract, raising the ribcage
• What occurs to the diaphragm during expiration?

  It relaxes and curves upwards
• What are the steps of ventilation in mammals?

  1. Inspiration: Intercostal muscles contract, diaphragm flattens
  2. Thorax volume increases, pressure decreases
  3. Air enters lungs, lungs expand
  4. Expiration: Intercostal muscles relax, diaphragm curves upwards
  5. Thorax volume decreases, pressure increases
  6. Air is forced out of lungs
• What is the gas exchange surface in mammals?

  Alveoli
• Why do alveoli have thin walls?

  To provide a short diffusion path
• What maintains a steep concentration gradient for diffusion in the alveoli?

  Oxygenated blood is carried away
• What chemical covers the surface of each alveolus?

  Surfactant
• What is the purpose of surfactant in the alveoli?

  To prevent alveoli from collapsing
• What is the approximate percentage of oxygen in inspired air?


  20.95%
• Why is the percentage of oxygen lower in alveolar air compared to inspired air?

  It mixes with air already in the lungs
• What are the gas compositions in inspired, alveolar, and expired air?

  • Inspired air: Oxygen 20.95%, CO2 0.04%, Nitrogen 79.01%
  • Alveolar air: Oxygen 13.80%, CO2 5.50%, Nitrogen 80.70%
  • Expired air: Oxygen 16.40%, CO2 4.00%, Nitrogen 79.60%
• What happens to carbon dioxide during respiration?

  It diffuses from blood into the alveoli
• What happens to nitrogen during respiration?

  It is neither absorbed nor used
• What happens to water vapor in the alveoli?

  It evaporates and is exhaled
• What is the role of moisture in the alveoli?

  • Keeps alveoli moist for gas exchange
  • Prevents alveoli from drying out
  • Facilitates diffusion of gases