human gas exchange

• Trachea

  • The trachea is the entrance to the human gas exchange system.
  • When you breathe in, air flows through the trachea.
  • Ridges of cartilage surround the front of the trachea to provide protection and structure.
  • There is no cartilage at the back of the trachea so that the oesophagus (the tube where food travels) is not constricted.
• Bronchi

  • The trachea divides into two bronchi.
  • Air flows along each bronchus to a lung.
  • The bronchi are made from cartilage and smooth muscle.
• Bronchioles

  • Each bronchus divides into many smaller bronchioles.
  • The many bronchioles branch throughout the lungs into small air-sacs called alveoli.
• Alveoli

  • The alveoli are sacs that fill with air when you breathe in.
  • Oxygen in the alveoli diffuses into the bloodstream and carbon dioxide in the bloodstream diffuses into the alveoli.
  • There are millions of alveoli in the lungs
  • The alveoli provide a large surface area for gas exchange.
• Control of ventilation

  • Ventilation is controlled by the ribcage, intercostal muscles and the diaphragm.
  • When you breathe in, these structures move to allow the lungs to fill with air.
  • When you breathe out, these structures move to allow air to leave the lungs.
• alveoli:

  Capillaries

  • Each alveolus is surrounded by a network of capillaries.
  • The many capillaries provide a large surface area for gas exchange between the alveoli and the bloodstream.
• alveoli:

  Alveolar epithelium

  • The epithelium is made up of a single layer of epithelial cells that line the walls of the alveoli.
  • The epithelium provides a very short diffusion distance from the alveoli to the capillaries which maximises the rate of gas exchange
• alveoli:

  Concentration gradient

  • The capillaries supply carbon dioxide to the alveoli and oxygen is rapidly carried away from the alveoli.
  • The quick transport of gases in the bloodstream maintains a steep concentration gradient of oxygen and carbon dioxide.
  • The steep concentration gradient allows quick diffusion of gases into and out of the bloodstream.
• • Adaptations of alveoli for gas exchange
  • Network of capillaries
  • Large surface area
  • Maintain steep concentration gradient
  • Epithelium of alveoli
  • Short diffusion distance