Movement of water through human skin?

[Cmac22]

I was not certain where to post this, sorry if this is not the correct place.

 

During breakfast the other day my friend randomly asked a question somewhere along the lines of "If you were to bathe in a pool of syrup, would you loose water through your skin?" i.e. through diffusion/osmosis. I found I was not able to come up with a satisfactory answer. Ultimately, I decided no, that there must be some barrier to prevent this, but i was not certain at all about this. My thought was, that if this was true, it would also mean that you would swell with water if you were swimming in a lake, which I feel does not happen, although I am not sure about this either.

 

After recently searching google, I still have no answer. The information I found was vague, ambiguous, and sometimes controdictory. Thus, I have turned to the forum to get a satisfactory answer.

 

Is water free to flow through your skin like this? If you sat in syrup (or salt water with a high enough concentation) for long enough, would you become dehydrated? would you die from it?

 

Thanks!

 

 

 

 

[AlphaZNV]

Shouldn't it be separated and therefor, different concepts apply?
As osmosis, the water diffusion, occurring within the body on a much smaller level between cells and therefor organs, will be efficient.

On a larger scale however (of the skin), with different factors and variables, different laws must apply.

The most basic being, as you scale up the level (volume etc.) of liquids, the size of the pores of the plasma membrane does not scale with and therefor, different laws must apply due to the variation of different variables (volume of liquid etc.) of factors, by constants (size of pores etc.).

 

The concept similar to the difference between an ant-sized insect and us, gravity stays at constant, whereby our variables changes, therefor affected by gravity differently to gravity affecting ant-sized insects with different variables (mass etc.).

This is only a speculation, don't take this too seriously without confirmation.

[Cmac22]

In reply to AlphaZNV:

 

Thanks for your input.

However, I do not think that some of what you have said is correct. you can think of the body as a system, with the skin as its external barrier, and the liquid you are swimming in as the external environment. The 'scale' does not effect the dynamics in the way you suggest. The pores do not change because the volume of the external liquid is so much larger.

 

Similarly, volume does not make a difference, per say. What matters is the gradients between the internal system (body) and the external environment, across the skin. Thus it is not volume that matters, but the concentration of solutes in the body and external liquid. Diffusion is governed by the same laws in both cases, save for things like active transport etc. inside the body. But in both cases the 'scale' is at the molecular level, i.e. the movement of water molecules and ions from one area to another.

 

However, some of the things you said about different factors and variables made me think, and here is what I have found. The skin consists of 3 main layers. From internal to external: hypodermis, dermis, epidermis. Blood vessels only extend to the top of the dermis layer. Thus, epidermis cells die as they migrate outwards because they have no access to blood vessels. As they die, the cytoplasm (and this water) is removed from the cells and replaced by the protein keratin. The epidermis functions as a 'waterproofing' layer.

 

The epidermis is typically 25-30 cells thick. the outermost layer(s) is called the stratum corneum, and is largely responsible for protection from the environment. It is an effective barrier against most nano sized particles. These cells are also surrounded by various proteins, which add to their adhesive and barrier functionality.

 

'Trans-epidermal water loss' or 'insensible water loss' is the term use to describe the loss of water to the environment via evaporation. (obviously evaporation is a little bit different, but I think the same principles still apply). The epidermis functions to minimize water loss with a low permeability. However, organisms have little control over 'trans-epidermal water loss'

 

What I take from these things is this: The skin functions to minimize the rate of diffusion/osmosis across it. It does this by blocking the movement of most nano sized particles, and by doing things such as keratinization. as you move to the outward layers of the epidermis, the cells contain less water. These things function to minimize the movement of water. There is little water to move, there is no blood circulation so there is no 'convection', and keratin help absorb/retain water(i think?).

 

Overall though, this does not really answer my question. It only shows that the movement of water through the skin is very slow, ostensibly. However, water does move through it, and defects in skin can cause dehydration issues etc. So how slow is slow? How long would you have to sit in pure water or some very solute heavy solution for effects to become dangerous, if ever?

[AlphaZNV]

So you are suggesting that on a different level, the same laws for which applies in the molecular level applies?

Of course, you mentioned different factors as well, such as different layers of skins, which in itself would be different variables affecting osmosis, with your knowledge in biology, you are currently supporting the theory that on different levels with difference variables, osmosis itself, will act very differently in contrast to osmosis on a molecular level.

Nonetheless, what I originally intend to suggest, is that the affect of osmosis (water diffusion, which we should all remember) is ultimately eliminated, as volume increase, so does the concentration gradient, given the same constant (which I'm sure you know). However, with the same constants that operate on a molecular level, such as the size of pores of the plasma membrane (which dictates many variables), the rate of diffusion in itself is ultimately eliminated.

We have to remember that syrup is of a much different molecule than water, and the osmosis in which you are attempting to apply is the osmosis on the molecular level.

Osmosis is essentially maintaining equilibrium, whereby both are given the same variables and constants, hence the result of equilibrium.

[Ringer]

Much of the water loss through skin is regulated through sweat glands. Since water isn't just free flowing throughout your body (it's contained in various places) there isn't an excess amount of water loss through the skin unless there isn't a source of hydration. The same way you can't get enough water to live by sitting in a pool, you won't lose enough water to die by sitting in anything (unless it makes you sweat a lot). Osmotic pressures won't have a large effect because of multiple barriers against water loss.

[Carlamast]

Similarly, volume does not make a difference, per say. What matters is the gradients between the internal system (body) and the external environment, across the skin. Thus it is not volume that matters, but the concentration of solutes in the body and external liquid. Diffusion is governed by the same laws in both cases, save for things like active transport etc. inside the body. But in both cases the 'scale' is at the molecular level, i.e. the movement of water molecules and ions from one area to another....

[Ringer]

Something I found while procrastinating:

http://www.pnas.org/content/87/10/3871.full.pdf