Tissues in the gaseous exchange system

• Trachea

  Structure:

  • Have C-shaped rings of cartilage rather than a complete ring.
  • Large/wide lumen
  • Between the ciliated epithelium there are goblet cells and mucous glands.
  • The wall of the trachea contains smooth muscle and elastic fibres.

  
• Function:

  • The C-shaped rings ensure the trachea doesn't collapse and allows flexibility and to prevents friction from rubbing the oesophagus close behind.
  • The goblet cells secrete mucous onto the lining to trap dust and microorganisms, preventing them from entering the lungs.
  • The elastic fibres can deform and recoil back to original size.
  • Smooth muscle contracts or relaxes
  • Constricts airways when contracts
  • Dilates when relaxes
• Bronchi

  Structure:

  • Thinner walls and a smaller diameter
  • Cartilage doesn’t form a C-shape, can form full rings, and can also form irregular blocks.
  • Lined with ciliated epithelium goblet cells and mucus glands
  • Smooth muscle and elastic fibres.

  
• Function:

  • The Goblet cells secrete mucus onto the lining to trap dust and microorganisms, preventing them from entering the lungs.
  • The elastic fibres can deform and recoil back to the original size.
  • The smooth muscle involuntarily contracts.
• Bronchioles

  Structure:

  • Narrower than the bronchi.
  • Larger bronchioles may have some cartilage but smaller ones have no cartilage. They're comprised mostly of smooth muscle and elastic fibres.
  • Lined with ciliated epithelium but do not contain any Goblet cells.
  • Vary in size and structures, they get smaller as they get closer to alveoli.

  
• Function:

  • When the smooth muscle contracts, the bronchioles contract.
  • When it relaxes, the bronchioles dilate.
  • This changes the amount of air reaching the lungs.
  • The flattened epithelium making some gaseous exchange possible.
• Alveoli

  Structure:

  • The alveolar wall consists of a single layer of epithelium.
  • There's an extensive capillary network.
  • Capillary wall is one cell thick.
  • Both walls consist of squamous cells- this means flattened or very thin.
  • Watery fluid lines the alveoli, facilitating gas exchange.

  
• Function:

  • Large surface area provides more space for molecules to pass through.
  • Thin barrier to reduce the diffusion distance and increase rate of diffusion
  • A good blood supply helps to maintain a steep concentration gradient, so that the gases continue to diffuse.
  • Moisture allows gases to dissolve so they can diffuse quickly.