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Diffusion

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xlouisex | 22:42 Fri 24th Nov 2006 | Science
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Can anyone give me an example of diffusion in the body??
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Oxygen and carbon dioxide pass across the alveolar wall between the alveolar lumen and the capillary blood by passive diffusion.

Absorption of alcohol from the gastrointestinal tract into the bloodstream.

The passage of oxygen, carbon dioxide, some minerals and urea diffuse across the chorionic villi of the placenta into the foetus.

Drug absorbtion via the stomach wall into the bloodstream.

Absorption by cells of water from lymph when the percentage of salt is less in the lymph than in the cells.

Prof, I thought that if it was water it was osmosis, diffusion was gas related ?
I'd be the first to agree that all this can be confusing Dreddnaught. Let me try to explain (if the alcohol in my bloodstream will allow!)

Diffusion may be defined as the movement of molecules from a region of high concentration to one of lower concentration due to random molecular motion.

Diffusion of gases in other gases is most rapid and is indeed the most commonly cited form of diffusion. However, diffusion of solutes in solvents can also occur, and solids are capable of diffusing into each other, although at extremely slower rates than gases.

The rate of diffusion of molecules from any region in a substance is proportional to the concentration of the molecules in that region. In turn, the rate of diffusion into that region is proportional to the concentration of molecules in the surrounding area. What this means in practice is that the net flow is from regions of higher concentrations to regions of lower concentrations.

When a soluble salt, such as copper sulphate is dissolved in water, it may be considered to have diffused into that medium. Water evaporates into the air, which is another form of diffusion. Some types of polymers will migrate or diffuse into one another when kept in close proximity. There are even some elements that diffuse into each other under the right conditions.

Osmosis is solutions is essentially the retention of a solute behind a membrane which the solvent has passed through.
Using radioactive oxygen (O15), carbon monoxide and carbon dioxide with external counting over the chest, it is possible to measure perfusion and diffusion per unit of lung volume. Patients with mitral stenosis, particularly those with high pulmonary artery pressures, may show a higher blood flow through the upper zone of the lung than the lower. This distribution of blood flow is the reverse of that found in normal subjects. The observed changes in blood flow are consistent with the radiological and pathological changes in the pulmonary vascular tree in mitral stenosis.

ps. still like walkers crisps although they do taste a bit gooey
theprof. once again your answer has given us excellent info.
crete you indiscrete
Thanks crete.

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