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Diffusion and osmosis

Diffusion and osmosis. Diffusion is the process by which the molecules of a substance transfer through a layer or area Diffusion is affected by: tension gradient (dependent on solubility) characteristics of membrane molecular size. Graham’s law of diffusion.

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Diffusion and osmosis

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  1. Diffusion and osmosis Diffusion is the process by which the molecules of a substance transfer through a layer or area Diffusion is affected by: tension gradient (dependent on solubility) characteristics of membrane molecular size

  2. Graham’s law of diffusion Rate of diffusion is inversely proportional to the square root of the molecular weight of the substance 1 D αMwt

  3. Osmosis is the movement of a solvent across a semi-permeable membrane. This generates an osmoticpressure

  4. Osmotic pressure 1 mol of particles of solute at 0oC in 22.4 litres generates an osmotic pressure of 1 atmosphere or 101.325 kPa

  5. Osmolality is the number of osmoles / kg water or solvent Osmolarity is the number of osmoles / litre of solution

  6. Osmolarity can be calculated by adding the molarities in simple solution • Ringer lactate solution has total molarity of 278 mmol/l ≡ 278 mosm/l • Most body fluids have osmolarity around 300 mosm/l

  7. Plasma/interstitial fluid osmotic pressure • plasma – electrolytes constitute 99% of osmolarity – pl. proteins only 1%! • capillaries – albumin and globulin have oncotic pressure of 3.5 kPa • interstitial fluid almost protein-free, so pl. proteins determine oncotic pressure

  8. Measurement of osmolality • Osmometer which uses the colligative properties of a solution depression of freezing point depression of SVP raising of boiling point

  9. Azeotrope is a mixture which vaporises in the same proportions as the volume concentrations of the components in solution • one part ether/two parts halothane • 96% ethanol/4% water

  10. Vaporisers A vaporiser is a device for adding clinically useful concentrations of anaesthetic vapour to a stream of carrier gas • drawover vaporiser • plenum vaporiser

  11. Vaporisers The SVP of volatile anaesthetics at room temperature is many times greater than that required to produce anaesthesia, so the gas flow to the vaporiser is split into two streams

  12. Modern vaporisers designed to solve following problems • flow dependence through vapouriser • back pressure effect • temperature control • full saturation

  13. Humidity Absolute humidity is the mass of water vapour present in a given volume of air Relative humidity is the ratio of the mass of water vapour in a given volume of air to the mass required to saturate that given volume of air at the same temperature

  14. Relative humidity (RH%) RH = actual vapour pressure saturated vapour pressure or • RH = SVP at dew point SVP at ambient temperature • principle of Regnault’s hygrometer

  15. Humidifiers • HME artificial nose or condenser humidifier • HMEF bacterial filter included • water baths at 40 – 45oC • cascade humidifier

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