The Lungs

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  • The Lungs
    • Air can pass into the lungs through the nose and along the trachea, bronchi and bronchioles
      • All features adapted for their function in gas exchange
        • Reach the alveoli, wall of the alveoli are the surface where the exchange of gases takes place
    • Lungs are protected by they ribs
    • Gas exchange in the lungs
      • Gases can pass both ways through the thin alveoli walls
        • Oxygen passes from the air in the alveoli to the blood in the capillaries
        • Carbon dioxide passes from the blood to the alveoli
    • Adaptions for gas exchange
      • Large surface area - provides more space for molecules to pass through, small alveoli but there **** so many creating the large surface area
      • Barrier permeable to O2 and CO2 - the plasma membranes that surround the thin cytoplasm of the cell form the barrier exchange. These readily allwo diffusion of O2 and CO2
      • Thin barrier to reduce diffusion distance:
        • Alveolus wall is one cell thick
        • Capillary wall is one cell thick
        • Consist of squamous cells
        • Capillaries are narrow so the RBC are squeezed against the capillary wall making them closer to alveoli
        • Capillaries are in close contact with the alveolus wall
      • Maintains the diffusion graident
    • Requirments of airways:
      • Must be large enough to allow sufficient air to flow without obstruction
      • Strong enough to prevent collapsing when the air pressure is low.
      • Must be flexible to allow movement
      • Must be able to stretch and recoil
    • Trachea and bronchi
      • Have releatively thick walls, several layers of tissure
        • Much of walls is made of cartilage in the form of C-rings
          • Less regular in the bronchi
        • Layer of 'loose tissue' - glandular tissue, connective tissue, elastic fibres, smooth muscle and blood vessels
        • Inner lining is an epithelium layer that has two types of cell, cilia (ciliated epithelium) and among them are goblet cells
    • Bronchioles
      • Narrower than the bronchi
      • Larger bronchioles may have some cartilage, but somaller ones have no cartilage
      • The wall is made mostly of smooth muscle and elatsic fibres
      • The smallest bronchioles have clusters of alveoli at their ends
    • Role of tissue
      • Smooth muscle -  can contract, constricting the airways
      • Cartilage - structural role, supports trachea  and bronchi holding them open prevents collapse when the air pressure is low during inhalation.
        • Doesn't form  a complete ring so there is flexibility in the airways
      • Elastic fibres -   as the smooth muscle relaxes the elastic fibres recoil to their original shape
      • Goblet cells and glandular tissue - secrete mucus to trap tiny air particles
      • Ciliated epithelium - Cilia move in a synchronized  pattern to waft the mucus up the airway to the back of the throat


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