The Respiratory System

• Nasal cavity


  Large cavity that connects external environment with the pharynx
• Function of nasal cavity

  1. Warming and moistening air

  2. Preventing epithelial damage
• Nasal cavity


  • Allows air from the external environment to be warmed and moistened
  • Respiratory tissue is delicate so this prevents damage from microbes and air dehydrating the epithelium
• Nasal cavity


  • Hair and mucus trap dirt particles and microbes before they enter the lungs
• Pharynx


  Passage for food and air
• Larynx


  Vocal cords supported by cartilage
• Function of larynx


  Sound production as air moves out of the lungs
• Trachea


  Tube from pharynx to bronchi - supported by C shaped rings of cartilage
• Function of trachea


  1. Cartilage holds the trachea open for air movement

  2. Ciliated epithelium along its length cleans the air with mucus
• Bronchi and Bronchioles


  Branching tubes within the lungs leading to tiny air sacs called alveoli
• Alveoli


  Site of gas exchange in the lungs, surrounded by capillaries for efficient oxygen and carbon dioxide exchange
• Pleura


  Membrane covering the lungs and lining the chest cavity. Contains pleural fluid that helps the lungs expand and contract during breathing
• Diaphragm


  • Sheet of muscle which separates the thoracic cavity from the abdominal cavity
  • Aids in the ventilation of the lung
• Intercostal muscles


  • Muscle found between ribs
  • Aids in the movement of the ribs for the ventilation of the lungs
• Ventilation


  The process by which air is moved into and out of the lungs
• Inspiration


  1. Take air into lungs

  2. Pressure of air in lungs must be less than atmospheric pressure outside body

  3. Increase volume of chest cavity by diaphragm flattening and rib cages moving upwards

  4. Increased lung volume lowers air pressure inside lungs slightly below pressure outside
• Expiration


  1. Breathe out

  2. Diaphragm and external intercostal muscles relax, diaphragm bulges more into chest cavity and rib cage moves downwards, reducing the volume of the chest cavity and that of the lungs

  3. Air pressure in lungs is greater than pressure outside, air flows out through trachea and nose until pressures are equal
• What features do lungs have that are suited for gas exchange?

  1. The alveoli give the lungs a huge surface area
  2. Each alveoli is well supplied with blood vessels
  3. The walls of the alveoli are very thin, so that gas molecules do not have far to travel
  4. The lungs are positioned deep inside the body to prevent excessive evaporation.  The membrane must be moist  because gases can only diffuse when they are dissolved in fluid
  5. The lung volume can be changed by movements of the respiratory muscles, so that air is  made to flow into and out of the lungs