Tissues in the gaseous exchange system

• Alveoli compromises

  • squamous epithelial surrounded by blood capillaries reducing the diffusion distance
  • the walls contain elastic fibres

  -> stretches during inspiration but recoils to push air out during expiration

  • the alveoli walls are one cell thin
• Similarities + differences between the Trachea, bronchi and bronchioles

  • bronchioles are much narrower than bronchi
  • the larger bronchioles may have some cartilage
  • the walls is made of elastic fibres
  • the smallest bronchioles end up in clusters of alveoli
• the airways

  • large enough to allow sufficient air to flow without obstruction
  • be supported by cartilage to prevent collapse when the air pressure is low during inspiration
  • be flexible in order tom allow movement
  • airway is lined by ciliated epithelium , keeping lungs healthy ; goblet cells in the epithelium release mucus , trapping pathogens and the cilia sweeps up the mucus to the airway where it is swallowed

  glandular tissue in the loose tissue also produces mucus
• The trachea and bronchi

  • trachea and bronchus has similar structure; bronchi is much narrower
  • these airways are supported by rings of cartilage that are c-shaped which allows flexibility and space for food to pass down the oesophagus
• The bronchioles

  • much more narrower than bronchi
  • larger bronchioles have cartilage whilst small ones don’t
  • the wall is mostly comprised of smooth muscle and elastic fibres
  • the smaller bronchioles end up in clusters of alveoli
• Smooth muscles and elastic fibres

  • smooth muscle can contract

  →this action constricts airway and makes lumen narrower

  • constriction of lumen restricts flow of air to and from alveoli

  →constriction of lumen is important when there are harmful substances in air :

  • the contraction of smooth muscle and control of air flow is not a voluntary act and may occur as a result of an allergic reaction
  • when muscle contracts, it deforms the elastic fibres; as the muscles relax, elastic fibres recoil and this acts to dilate the airway [elastic fibres recoil to reduce the size of alveoli during expiration]