Human help: why do humans not swell and pop in hypertonic solutions? - Help.com

Because water moves out of the cell into the solution, causing the cells to shrink, not expand and pop.

That’s very true Cady…unless you’re a bubble head :D

ok, now how about for a hypotonic solution? I used to know this, but I forgot over the years.

Well, it would be quite the opposite in a hypotonic solution. Osmosis works in the other direction, so more liquid or solution or water or whatever, would be entering the cells and poofing up.

Now, isotonic. You go.

Yes, but I am just trying to recall the method of homeostasis used by our bodies to keep water from entering or exiting through our skin and other membranes.

Whatcha mean…exactly?

I mean, our bodies contain lots of salts and stuff. Our skin is a semipermeable membrane. When we step into a swimming pool, there is more salt and solids inside us than in the pool. So why don’t we fill with fluid and pop?

Well, you’ve got the understanding of this process backward. Let’s break it down to simple ideas.

You have a liquid (solution)
You have a cell.

When the solution contains a higher concentration of salts and other “stuff” than the cell does, those particles and liquid move inside the cell causing it to swell up.

If the solution contains a lower concentration than the cell, stuff moves out of the cell and shrinks.

So your example of a person in a pool…

We do contain more salts and stuff than the pool water, or bathtub water. And if you are in that water long enough, you start to shrivel up, not poof up. Check your hands after a long bath and notice how the skin on your fingers has wrinkled.

Here’s the basic stuff:

Diffusion is the movement of particles from a higher concentration to a lower one.
Osmosis is simply the diffusion of water.

Take a sponge, a dry one.
Get a bowl of water.
Dip one end of the sponge in the water and you see the water moves up the sponge.

That’s osmosis (diffusion) in action. The water is moving from an area of greater concentration (the bowl) to an area of lesser concentration (the dry sponge).

This is what we are talking about here except we are talking about cells and other liquids. Cells already contain a great amount of water.

So, cells don’t generally take in water or release water when placed IN water.
UNLESS, the water you place the cell in differs in “salt” concentrations. (I say salt here because salt is an easy example of what might be dissolved in the water.)

So, if you have two cups of water, for example. In one cup(1) you dissolve a large amount of salts (more than would be present in a cell). In the other cup(2), you leave the water as pure as possible.

Then you place a cell in both cups.

The cell that is placed in cup 1 will absorb the salty water and poof up.
This is a hypotonic solution example.

The cell that is placed in cup 2 will release water into the pure water and shrivel up.
This is a hypertonic solution example.

I hope this helps. This may be a really bad example and explanation but hopefully it kind of illustrates what I’m talking about.