mammalian gas exchange system

• describe how gases pass through the lungs?

  Gases pass by diffusion through the thin walls of the alveoli. oxygen passes from the air in the alveoli to the blood in the capillaries. carbon dioxide passes from the blood to the alveoli. the lungs must maintain a steep concentration gradient in each direction in order to ensure that diffusion can continue,
• what is the significance of the large surface area of the alveoli?

  Individual alveoli are very small. they are so numerous so that the total surface area of the lungs is much larger than that of the skin. this allows for more gas molecules to pass at once
• What is the significance of the surfectant layer around the alveoli?

  This layer evaporates and is lost when we breathe out; the lungs must produce this layer so that the cohesive forces between molecules of water are reduced; if these forces were present, the alveoli would collapse.
• what are the adaptations of the alveoli that reduce the diffusion distance?


  The alveolus wall is one cell thick

  The capillary wall is one cell thick

  Both walls consist of squamous cells, they are either flattened or very thin.

  Capillaries are in close contact with alveolus walls

  Capillaries are so narrow that erythrocytes are squeezed against the capillary wall, making them close to the air in the alveoli and reducing the rate of flow.
• What is the significance of a good supply in terms of the alveoli?


  A good blood supply helps to maintain a steep concentration gradient. The blood system transports carbon dioxide from the tissues to the lungs, ensuring the concentration of carbon dioxide in the blood is higher than that of the air in the alveoli. The blood also transports oxygen away from the lungs, ensuring the concentration of oxygen in the blood is kept lower than that of the alveoli.
• describe what happens to the diaphragm when a mammal inhales.


  The diaphragm contracts moves down, and becomes flat- displacing the digestive organs downwards.
• Describe what happens to the external intercostal muscles when a mammal inhales.


  The external intercostal muscles contract, raising the ribs.
• Describe what happens to the volume of the chest cavity of a mammal when it inhales?

  The volume of the chest cavity increases
• Describe what happens to the pressure of the chest cavity when a mammal inhales?

  The pressure in the chest cavity drops below the atmospheric pressure
• Which way does are go when a mammal inhales?

  Into the lungs
• What happens to the diaphragm when a mammal exhales?

  The diaphragm relaxes and is pushed up by the displaced digestive organs underneath
• What happens to the external intercostal muscles when a mammal exhales?

  The external intercostal muscles relax, the ribs fall.
• What can the internal intercostal muscles do to force more air out of the lungs, when would this happen?

  If a mammal coughs, sneezes or exercises then the internal intercostal muscles can contract to help push more air out of the lungs forcefully.
• What happens to the volume of the chest cavity of a mammal when it exhales?

  The volume of the chest cavity decreases
• What happens to the pressure of the lungs in a mammal when it exhales?

  The pressure in the lungs increases and rises above the pressure in the surrounding atmosphere
• What direction does air go when a mammal exhales?

  Air moves out of the lungs.