11. Gas exchange in humans

• Gas exchange surfaces:

  • thin surface: short distance to diffuse (one cell thick)
  • large surface area: more alveoli
  • good ventilation: regular fresh air supplies keep up concentration gradients for oxygen and carbon dioxide
  • good blood supply: gases can be carried to/from that need/produce them
• Gas exchange diagram:

  A) Larynx (voice box)

  B) trachea (windpipe)

  C) bronchus

  D) bronchiole

  E) aveoli

  F) ribs

  G) external intercostal muscle

  H) internal intercostal muscle

  I) diaphragm

  
• Functions of structure of the lungs:

  • cartilage (in trachea): prevent trachea from collapsing during the absence of air and protect it by keeping it open
  • ribs: protect vital organs & blood vessels, expand & contract for efficient breathing
  • intercostal (internal/external muscle): situated between the ribs that create & move the chest wall
  • diaphragm: produce volume & pressure changes in the thorax, leading to the ventilation of the lungs
• Test for CO2: add CO2 through limewater, +ve result = turns cloudy
• Composition of breathing dry air:

  -inspired air (same as gas in atmosphere):

  • oxygen: 21%
  • CO2: 0.04%
  • nitrogen: 78%
  • water vapour: lower

  -expired air:

  • oxygen: 16%
  • CO2: 4% - due to exhalation of air from body
  • nitrogen: 78%
  • water vapour: higher
• Physical activity on breathing:

  • increase breathing - more respiration - higher CO2 concentration in blood (hypothalamus detect lack of oxygen --> increase in breathing rate)
  • tissue respire at higher rate: change in breathing volume & rate help keep CO2 concentration and pH safe
  • breathing depth increases
• Inspiration:

  • external intercostal muscle contract - pull ribcage upwards & outwards
  • diaphragm muscle contract - diaphragm moves downwards, volume of thorax increase
  • atmospheric pressure > pressure in thorax
  • air moves into the lungs
• Expiration:

  • external intercostal muscles relax -ribcage falls downwards & inwards
  • diaphragm muscles relax - return to dome shape, volume of thorax decreases
  • atmospheric pressure < pressure in thorax
  • air moves out of the lungs
• Role onto exchange system:

  • internal intercostal muscles are used in coughing & sneezing
  • mucus & cilia: goblet cells produce sticky mucus to trap & eliminate particulate matter & microorganism
  • ciliated cells: have cilia, little hairs that sweep/beat in both directions to brush mucus up the lungs into the mouth