Tuesday, October 12, 2010

How now to blow your cells up 101

Unfortunately, unlike plant, algal, fungal and bacterial cells, human cells just don't have a lot of strength behind them. They are weak, flexible and easily broken by the osmotic pressure occuring during Donnan Equilibrium. So, to maintain this equilibrium, the body has developed a method of being able to unsure that our cells don't swell up to the point that they burst, nor remove solution away to the point that the cells shrivel up like an old person. This solution - allow both the cell to swell and shrivel at the same time in such an equilibrium that neither burstage nor complete shrivelling occur. The cells allow for continuous pumping of the sodium ions by using metabolic energy. This creates a nonequilibrium system, but a steady state.

The text provides another example of this as the water fountain. Allow the fountain to keep running without a pump will cause it to eventually stop, but by using a pump, one can move the water back to the water source, and the cycle of fountain flow can continue.

Finally, the text eludes to some genetic defects which can interfere with osmoregulation. If one has spherocytosis, then their red blood cells become more permeable to sodium. Because the cells have to work a lot harder to remove the sodium, then it results in some cells surcoming to the eventual swelling and bursting. As the text says, "Entropic forces can kill"

Finally (this time it actually is finally) I was going to elude to action potentials. These are an example of continuous pumping of ions in and out of the cell but which can perform a useful action. Once a certain energy threshold has been achieved in the cells, a cascade of ions can be pumped in and out of the cell, allowing the muscle to perform useful work.


  1. It seems that animal cells would be most vunerable to extremely high or low concentrations of salt, as other cells have structural support like walls to protect them. I suppose this is why bacteria and animals evolved first, as they could survive in these conditions, and once they created less variable conditions, other cells were able to evolve.

  2. Plants don't shrivel but they do become flaccid. They use osmosis to contain enough water in their cells so that they can push against their walls. By doing so they remain rigid.

    A great (and messy) way of visualizing this is to drop A) a piece of meat then B) a carrot from a height. Obviously the meat will just squish into the floor, but the carrot will shatter into pieces! This is an effect of the rigidness of the wall.

  3. Shattering carrots sound cool! I tried to find a video on youtube, but I had no success. I guess that means we will have to do some experiments!