Lung Function

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  • Lung Function
    • Lungs are specialised Organs for gas exchange
      • As you breathe in, air enters the trachea
        • The trachea splits into two bronchi - one bronchus leading to each lung
          • Each bronchus then branches off into smaller tubes called bronchioles
            • The bronchioles end in small air sacs called alveoli - this is where gases are exchanged
              • The ribcage, intercostal muscles and diaphragm all work together to move air in and out
    • In Humans Gaseous Exchange Happens in the Alveoli
      • Lungs contain millions of alveoli - the gas exchange surface, Each alveolus is made from a single layer of thin, flat cells called alveolar epithelium
        • Alveoli are arranged in bunches at the end of bronchioles
          • They're surrounded by a network of capillaries, giving each alveolus its own blood supply
            • O2 diffuses out of the alveoli across the alveolar epithelium and the capillary endothelium and into haemoglobin in the blood
              • CO2 diffuses into the alveoli from the blood, crossing the capillary endotheliun then the alveolar epithelium. After entering the alveolar space its breathed out
    • The Alveoli are adapted for gas exchange
      • Alveoli have features that speed up the rate of diffusion so gases can be exchanged quickly
        • A thin exchange surface - the alveolar epithelium is only one cell thick this means theres a short diffusion pathway
        • A large surface area - the large number of alveoli means theres a large surface area for gas exchange
        • Theres also a steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries which increases the rate of diffusion
          • This is constantly maintained by the flow of blood and ventilation
    • The Gaseous Exchange System has different parts with different functions
      • Goblet cells secrete mucus. The mucus traps microorganisms and dust particles in the inhaled air stopping them from reaching the alveoli
      • Cilia on the surface of cells beat the mucus which move it upward away from the alveoli towards the throat, where its swallowed. This helps prevent lung infection
      • Elastic fibres in the walls of the trachea, bronchi, bronchioles and alveoli help the process of breathing out. On breathing in, the lungs inflate and the elastic fibres are stretched. Then, the fibres recoil to help push the air out when exhaling
      • Smooth muscle in the walls of the trachea, bronchi and bronchioles allows their diameter to be controlled. During exercise the smooth muscle relaxes, making the tubes wider. This means theres less resistance to airflow and air can move in and out of the lungs more easily
      • Rings of cartilage in the walls of the trachea and bronchi provide support. Its strong but flexible - it stops the trachea and bronchi collapsing when you breathe in and the pressure drops


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