mammalian gas exchange system

• gaseous exchange system is moist, so oxygen dissolves in water before dissolving into tissues.

  conditions idea for evaporation of water
• nasal cavity

  -large surface area with a good blood supply which warms the air to body temperature.

  -hairy lining= secretes mucus to trap dust and bacteria- protecting lungs from irritation and infection.

  -moist surface= increases humidity of air- reducing evaporation.
• trachea

  = main airway carrying clean, warm, moist air from the nose to the chest.

  -wide tubes supported by incomplete rings (so food can go down) made of strong, flexible c-shaped rungs of cartilage= stops trachea collapsing.

  -lined with a ciliated epithelium.

  -goblet cells= secrete mucus onto the lining of trachea.

  -cilia= beat and waft mucus away from lungs.
• bronchus

  -trachea divides to form left bronchus leading to left lung and the right bronchus leading to the right lungs.

  -have supportive rings (smaller)
• bronchioles

  -bronchus divide to form many bronchioles

  -have no cartilage rings

  -walls contain smooth muscle= when it contracts the bronchioles constrict

  -when it relaxes, bronchioles contract- this changes the amount of air reaching the lungs.

  -lined with thin layer of flattened epithelium= more gas exchange
• alveoli

  = tiny air sacs

  -layers of thin, flattened epithelial cells, along with collagen and elastic fibres= allows alveoli to stretch as air is drawn in and they return to existing size and help squeezes air out= elastic recoil.
• adaptations of alveoli

  • large SA (300-500million)
  • thin layers
  • good blood supply
  • good ventilation
• alveoli

  alveoli