exchange surfaces

• Small organisms have a large surface area to volume ratio
• Large organisms have a small surface area to volume ratio
• Specialised exchange surfaces:

  Increased surface area

  Thin layers

  Good blood supply

  Ventilation to maintain diffusion gradient
• Increased surface area provides the area needed for exchange and overcome the limitation of SA:V ratio of larger organisms.
• Thin layers means the distances that substances have to diffuse are short
• Good blood supply means the steeper the concentration gradient, the faster the rate of diffusion. Good blood supply also means substances are constantly delivered and removed from the exchange surface.
• Ventilation to maintain diffusion gradients, for gases a ventilation system helps maintain concentration gradients making the process more efficient.
• Nasal cavity:

  • a large surface area with a good blood supply, which warms the air to body temperature
  • a hair lining, which separates mucus, traps dust and bacteria, protecting delicate lung tissue
  • moist surfaces, increases humidity, reducing evaporation from exchange surfaces
• Trachea:

  • wide tube supported by incomplete rings of strong flexible cartilage, which stops trachea from collapsing
  • the trachea and its branches are lined with ciliated epithelium with goblet cells
  • goblet cells secrete mucus onto lining to trap microorganisms
  • the cilia moves the dust away and most goes into the throat and swallowed
• Bronchus:

  • trachea divides into left and right bronchus
  • similar structure to the trachea but smaller
• Bronchioles:

  • the smaller bronchioles have no cartilage rings
  • the walls contain smooth muscle, when the muscle contracts, the bronchioles constrict visa versa.
  • this changes the amount of air reaching the lungs
  • bronchioles are lined with a layer of flattened epithelium, making some gaseous exchange possible
• Alveoli:

  • tiny air sacs, main gaseous exchange surface
  • consists of a layer of epithelial cells along with collagen and elastic fibres
  • these elastic tissues allow the alveoli to stretch as air is drawn down
  • when they return to resting size, they squeeze air out... this is called elastic recoil.
• Inspiration:

  • diaphragm contracts, flattens and lowers
  • the external intercostals contract
  • ribs move up and out
  • volume of thorax increases, so pressure is reduced
• Expiration:

  • diaphragm relax and move up
  • external intercostals relax
  • ribs move down and in
  • elastic fibres in alveoli return to normal length
  • volume of thorax decreases, so pressure is greater than pressure in atmospheric air
• Exhaling using energy:

  • diaphragm & internal intercostal relaxes
  • ribs move up and out
  • rectus abdominus contract
  • external intercostals contracts
• erythrocyte = red blood cell
• Tidal volume is the volume of air breathed in and out in one breath at rest
• Vital capacity is the volume of air expired after one maximum inspiration
• Ventilation rate is the volume of air moved in and out in 1 minute
• Spirometer:

  • closed system so the patient must wear a nose clip
  • soda lime absorbs carbon dioxide, this means that the volume of air in the spirometer is reducing, therefore the line will fall.
• A simple spirometer consists of a weighted drum, containing oxygen inverted over a chamber of water, a tube connects the air filled chamber with subjects mouth and soda lime in the system absorbs the carbon dioxide breathed out.
• During inspiration:

  • air is removed from the chamber, the drum sinks and an upwards deflection is recorded on the paper on the rotating drum

  During expiration:

  • air is added to the chamber, the drum rises and a downward deflection is recorded
• Inspiratory reserve volume is the volume that can be breathed in by a maximum inspiration at the end of a normal inspiration
• Expiratory reserve volume is the volume that can be breathed out by a maximum effort at the end of a normal expiration
• Residual volume is the volume of air remaining in the lungs at the end of a maximum expiration