Humans

• How is a concentration gradient maintained in the lungs?

  Ventilation by a tidal stream of air. This means that air is constantly replenished.
• Features of the trachea which support its function:

  1. Rings of cartilage prevent the trachea from collapsing when air pressure falls.
  2. Tracheal walls are lined with cilia which waft mucus containing dirt and pathogens up towards the mouth.
  3. Goblet cells produce mucus.
• Features of the bronchi which support their function:

  1. Contain some cartilage but less as they get smaller.
  2. Produce mucus to trap dirt and pathogens- produced by goblet cells.
  3. Have cilia to move dirt-laden mucus towards the throat.
• Feature of bronchioles related to function:

  Walls are made of muscle lined with epithelial cells so they can constrict to control the flow of air in and out of the alveoli.
• Features of alveoli related to gas exchange:

  1. Millions of them - large surface area.
  2. Lined with a thin alveolar epithelium that is one cell thick - short diffusion pathway.
  3. Surrounded by capillaries - good blood supply.
  4. Between them there is collagen (for structure) and elastic fibres (stretch and recoil during breathing).
• TIREDVP pneumonic:

  T- thorax

  I- internal intercostals

  R- ribs

  E- external intercostals

  D- diaphragm

  V- volume

  P- pressure
• What is the diaphragm?

  A sheet of muscle that separates the thorax from the abdomen.
• What are internal intercostal muscles responsible for?

  Forced exhalation e.g. exercise, shouting
• What is the relationship between internal and external intercostal muscles?

  They are antagonistic.
• Describe and explain the mechanism which causes inspiration:

  • Diaphragm contracts and moves down
  • External intercostal muscles contract, internal intercostals relax
  • The ribs move up and out
  • Volume of thorax increases so pressure decreases
  • Atmospheric pressure is greater than pulmonary pressure, so air moves into the lungs down a pressure gradient
• Describe and explain the mechanism which causes *forced* expiration:

  • The diaphragm relaxes and moves up
  • * Internal intercostals contract * and external intercostals relax
  • Ribs move down and in
  • Volume of thorax decreases so pressure increases
  • Pulmonary pressure is greater than atmospheric pressure so air is forced out down a pressure gradient
• What is the pulmonary ventilation rate?

  The total volume of air that is moved into the lungs in one minute.
• Equation and units for PVR:

  PVR = TV X BR

  dm3min-1 = dm3 X min-1
• Define tidal volume:

  The volume of air normally taken in at each breath at rest
• Define breathing rate:

  The number of breaths taken in one minute.