The Respiratory System

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  • Created by: ernily
  • Created on: 21-04-15 20:03

Lung Function

  • Ventilation: Breathing in and out.
  • Inspiraton:
    • The intercostal and diaphragm muscles contract.
    • This causes the ribcage to move upwards and outwards, and the diaphragm to flatten.
    • The volume of the thorax increases, and lung pressure decreases.
    • This causes air to flow into the lungs.
  • Expiration:
    • The intercostal and diaphragm muscles relax.
    • The ribcage moves downwards and inwards.
    • The volume of the thorax decreases, and lung pressure increases.
    • This causes air to be forced out of the lungs.
  • Factors Affecting Gas Exchange:
    • Large Surface Area: There are a huge number of alveoli in the lungs.
    • The alveoli are surrounded by a network of capillaries.
    • Short Diffusion Pathway: Oxygen diffuses out of the alveoli, across the alveolar and capillary endothelium, and into haemoglobin.
    • Carbon Dioxide diffuses into the alveoli from the blood and is breathed out.
    • Steep Concentration Gradient: Increases the rate of diffusion.
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How Lung Disease Affects Function

  • Pulmonary Ventilation: The volume of air taken into the lungs in one minute.
  • Tidal Volume: The volume of air in each breath.
  • Ventilation Rate: The number of breaths per minute.
  • PV (dm3min-1) = TV (dm3) x VR (min-1)
  • Pulmonary Tuberculosis:
    • Caused by mycobacterium tuberculosis.
    • When infected, the immune system cells build a wall around the bacteria.
    • This forms hard lumps called tubercles.
    • The infected tissue in the tubercles dies, damaging the gas exchange surface.
    • The tidal volume decreases.
    • TB also causes fibrosis, which further reduces the tidal volume.
    • Symptoms include: cough, chest pains, shortness of breath, and fatigue.
  • TB is transmitted by droplet infection; sneezing, coughing, etc.
  • It's spread in areas with poor hygiene and crowded living.
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How Lung Disease Affects Function

  • Fibrosis:
    • Scar tissue forms on the surface of the lungs as a result of infection or exposure to toxic substances.
    • The scar tissue is thicker and less elastic than normal tissue.
    • This means that the lungs are less able to expand, and they can't hold as much air.
    • This causes the tidal volume to decrease. It is harder to ventilate the lungs due to the loss of elasticity.
    • Diffusion is slower, therefore gas exchange is slower.
    • Symptoms include shortness of breath, dry cough, chest pain, fatigue, and weakness.
    • A person with pulmonary fibrosis will have a faster breathing rate in order to try to get enough air into the lungs to oxygenate their blood.
  • Asthma:
    • A person's airways become inflamed due to an allergic reaction.
    • The bronchioles contract and mucus is produced.
    • The airways constrict, so airflow is severely reduced.
    • This makes it difficult to breathe properly, so gas exchange is reduced.
    • Symptoms include wheezing, a tight chest, and shortness of breath.
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How Lung Disease Affects Function

  • Emphysema:
    • This is a lung disease caused by smoking or air pollution.
    • It causes inflammation, which attracts phagocytes that break down the elastin of the lungs.
    • Loss of elastin means that the alveoli can't recoil, so air remains trapped in them.
    • The alveoli walls are destroyed, which reduces the surface area of the lungs, and so the rate of gas exchange decreases.
    • Symptoms include wheezing, shortness of breath, and increased breathing rate as the patient attempts to ventilate their lungs.
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