Breathing and Gas Exchange

  • Created by: Harry
  • Created on: 15-05-14 10:09

Diagram of the gas exchange system


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Aspects of the gas exchange system

  • Diaphragm + thorax: These two's actions allows the movement of air in and out of the lungs
  • Intercostal muscles: Two sets of muscles that join each rib to the next
  • Bronchal tree: Allows air passage into the lungs
  • Trachea: Aka. the windpipe => splits into two tubes called the bronchi (one for each lung)
  • Bronchioles: The smaller tubes of the trachea
  • Alveoli: The place where gas exchange takes place
  • Cartilage: Support airways and keep them open when we breathe in
  • Pleural membranes: Make a continuous envelope around the lungs => airtight seal
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How the ventilation of the lungs work

  • Inhaling: The outer intercostals contract + pull ribs up, the muscles of the diaphragm contract and increase of the volume of the chest occurs. Air then enters the lungs
  • Exhaling: The outer intercostals relax + internal intercostals constrict => ribs pull down and in. Diaphragm muscles relax + diaphragm goes back to its original shape.
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How gas exchange occurs in the alveoli

  • Alveoli must have a structure that brings air and blood very close together over a very large surface area
  • Blood is pumped from heart to lungs + passes through capillaries surrounding the alveoli
  • The blood has come in from the respiring tissues of the body where it has given up some of its oxygen to cells + gained carbon dioxide
  • Around lungs, blood is separated from air inside each alveolus by two cell layers (cells making up wall of alveolus and capillary wall itself)
  • Because air in alveolus has higher conc. of oxygen than blood entering the capillary network => oxygen diffuses from air across wall of alveolus and into the blood
  • At same time there is more carbon dioxide in blood than in lungs => means there is a diffusion gradient for carbon dioxide in the other direction => carbon dioxide diffuses the other way, out of blood and into the alveolus
  • Blood which has flown through capillaries + heart gains oxygen + loses CO2
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The effects of smoking on lungs and tissues

  • Is linked to emphasemia, lung caner and bronchitis, alongside being a contributer to coronary heart disease
  • In the tranchea and bronchi of a smoker, cilia are destroyed by chemicals in cigarette smoke => reduced no. of cilia
  • Reduced no. cilia means mucus is not swept away from lungs but remains to clog air passages
  • Emphysema => Greatly reduces surface area for gas exchange => becomes inefficient 
  • Blood of a person with emphysema carries less oxygen -> may be unable to carry out exercise
  • Carbon monoxide => enters the bloodstream and interferes with the ability of carrying oxygen in the blood
  • Combines with the haemoglobin in the blood to form carboxyhaemoglobin => carries carbon monoxide in preference to oxygen => less gas exchange
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