The Lungs and Disease


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  • The Lungs and Disease
    • Structure of the Gas Exchange System
      • The lungs
        • The trachea is the main tube into the lungs, it branches off into two bronchus.
        • The bronchus split into smaller tubes called bronchioles. At the end of the bronchioles there are tiny air sacs called alveoli.
      • The Diaphragm
        • The diaphragm is a flat muscle that lies at the bottom of the thorax.
        • When the diaphragm contracts and relaxes it changes the volume and pressure of the lungs
        • It helps with inspiration and expiration.
    • The Mechanism of Breathing
      • Ventilation
        • Inspiration
          • 1. The intercostal and diaphragm muscles contract
          • 2. The ribcage moves upwards and outwards and the diaphragm flattens. This causes the volume of the thorax.
          • 3. As the volume of the thorax increases the pressure decreases (to below atmospheric pressure).
          • 4. Air flows into the lungs.
          • Inspiration is an active process so it requires energy.
        • Expiration
          • 1. The intercostal and diaphragm  relax.
          • 2. The ribcage moves downwards and inwards and the diaphragm becomes curved again.
          • 3. The thorax volume decreases, this causes the air pressure to increase (abouve atmospheric pressure).
          • 4. Air is forced out of the lungs.
          • Expiration is a passive process so it doesnt require any energy.
      • Pulmonary Ventilation = Tidal Volumes x Ventilation Rate
    • Gas Exchange in the Lungs
      • Features of an efficient gas exchange system
        • A thin exchange surface
          • If there is a short diffusion pathway then substances will diffuse across the membrane quicker.
          • The alveoli and capillaries are only one cell thick.
        • Large surface area
          • There are many tiny alveoli in the lunge to provide a large surface area.
          • A larger surface area means that more of the substance can diffuse over the membrane in the same amount of time. This increases the rate of diffusion.
        • Steep concentration gradient
          • Blood is constantly flowing through the capillaries so blood low in oxygen is always being brought to the lung and blood high in oxygen is being taken away, to the heart.
            • The concentration of oxygen in the blood near the alveoli need to be kept low to maintain the concentration gradient, this will mean oxygen will diffuse in to the blood.
          • We are always breathing in and out so air that is high in carbon dioxide is leaving the lungs and air high in oxygen is being brought into the lungs.
            • If the is a higher concentration of oxygen in the alveolus than the capillary then it will diffuse down the concentration and into the capillaries.
            • If the concentration of carbon dioxide is kept low in the alveoli then it will diffuse out of the blood.
        • Moist surface
          • The alveoli are moist with mucus so that gases can dissolve before diffusing.
      • Alveoli
        • there's a huge number of alveoli in the lungs, which means there is a big surface area for the exchange of oxygen.
        • The alveoli are surrounded by a network of capillaries, which gives them a good blood supply.
        • Oxygen diffuses out of the alveoli, down its concentration gradient, across the alveolar epithelium and the capillary endothelium and in the the hemoglobin in the blood
        • Carbon dioxide diffuses out of the blood, down its concentration gradient, and is breathed out.
        • Each alveolus is made from a single layer of flat cells called the alveolar epithelium
    • Lung Disease
      • Tuberculosis
        • Tuberculosis causes fibrosis.
        • When someone becomes infected with tuberculosis, immune system cells build a wall around the bacteira in the lungs.
          • This forms hard small lumps known as tubercles.
        • If the bacteria enters the blood stream they can spread to other parts of the body.
        • Infected tissue within the tubercles dies and the exchange system is damaged.
        • TB is transmitted by droplet infection. this can be by coughing and sneezing.
        • Symptoms include a persistent cough, coughing blood, chest pains, shortness of breath and fatigue.
        • Many people lose weight due to loss of appetite.
      • Fibrosis
        • Fibrosis is the formation of scar tissue i the lungs.
        • Scar tissue is thicker and less elastic than normal tissue.
          • The lungs are less likey to expand and they cant hold as much air.
        • Tidal volume is decreased and it is harder to force the air out of the lungs.
        • Symptoms include shortness of breath, a dry cough, chest pain, fatigue and weakness.
      • Asthma
      • Emphysema
        • Caused by smoking or long term exposure to air pollution.
        • Particles can become trapped in the alveoli which causes inflammation. This attracts phagocytes which produce an  enzyme that breaks down the elastin.
          • Elastin is a protein found in the wall of the alveoli. This means the alveoli cant return to their original shape and air remains trapped.
        • Destruction of the alveoli walls reduces the surface area so the rate of diffusion decreases.
        • Symptoms include shortness of breath and wheezing.
        • People with emphysema have an increased breathing rate as they try to get enough oxygen.

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