Human gas exchange

• Parts of the respiratory system

  • Trachea
  • Bronchi
  • Bronchioles
  • Alveoli
  • Capillary network
• Alveoli


  Tiny sacs with many structural adaptations to enable efficient gas exchange, such as their thin walls and large surface area to volume ratio.
• Bronchi


  The plural of Bronchus. The left and right bronchi are at the bottom of the trachea and are similar in structure, but narrower. The bronchi lead to bronchioles.
• Trachea

  The airway that leads from the mouth and nose to the bronchi. The trachea is lined with mucus-secreting Goblet cells and cilia. The cilia sweep microorganisms and dust away from the Lungs
• Lungs

  Central part of the respiratory system and where gas exchange takes place
• Capillary network


  An extensive network of capillaries surrounds the alveoli and are an exchange surface between the lungs and the blood.
• Bronchioles


  Narrow tubes (less than 1mm) which carry air from the bronchi to the alveoli. As they are so narrow, they have no supporting cartilage and so can collapse.
• Why are the lungs (gas exchange system) located inside the body?

  1. air is not dense enough to support and protect these delicate structures
  2. the body would lose a lot of water and dry out
• What does the Ciliated epithelium have on their surface ?

  • Each cell has small projections of cilia which sweep mucus, dust and bacteria upwards and away from the lungs and the epithelium itself
• Ciliated epithelium

  A specialised tissue found along the trachea down to the bronchi
• What does the ciliated epithelium consist off?

  Basement membrane

  goblet cell

  nucleus

  micro villi
• Mechanism for breathing

  To maintain diffusion of gases across alveolar epithelium air is constantly moved out of the lungs. (This process is known as breathing or ventilation)
• Inspiration

  when air pressure of the atmosphere is greater than the air pressure inside the lungs air is forced into the lungs
• Expiration

  When the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs
• Inspiration

  • breathing in is an active process (uses energy)
  • the external intercostal muscles contract while the intercostal muscles relax
  • the ribs are pulled upwards and outwards, increasing the volume of the thorax
  • the diaphragm muscle contracts, causing it to flatten which also increases the volume of the thorax.
  • increase in volume of thorax leads to a decrease in pressure in the lungs
  • atmospheric pressure is now greater than pulmonary pressure and so air is forced into the lungs
• Expiration

  • breathing out is mostly a passive process (does not require energy)
  • the internal intercostal muscles contract, while the external intercostal muscles relax
  • the ribs move downwards and inwards, decreasing the volume of the thorax.
  • diaphragm muscle relaxes and forms a dome shape
  • decrease in volume of thorax leads to an increase in pressure
  • the pulmonary pressure is now greater than that of the atmosphere and so air is forced out of the lungs.