Osmosis

Khannie

So I've done a bit of reading. Enough to ask a stupid question....

So water passes through the wall of the small intestine and into the blood stream through osmosis, right?

I read the wikipedia page on osmosis and it seemed to me that the rate of absorption *should* be best if the water in the intestines is pure water, but I know from experience (and some reading) that when a small amount of glucose and even smaller amount of salt are disolved in water that the rate of absorption is better.

Can someone explain this to me?

GLaDOS

Possibly something to do with the ion pumps which affect water absoption (Cholera affectss these and leads to massive dehydration). Just a guess however.

Kevster

Isn't it the large intestine where water absorption occurs? It's what makes our faeces become more 'solid' (or, to be correct, more viscous). Maybe it occurs in the small intestine too, if I'm to believe what you're saying! As with any osmotic system, the movement of water is surely controlled by electrolytes like, for example, sodium, potassium, etc? The cells lining the gut have probably evolved to retain a certain amount of such electrolytes to keep things in check (re movement of water).

In this case, if you intake ****loads of salty water, for example, you might just end up doing the reverse of what should happen - i.e. you'll extract water from your body and thi will flush out your guts?

Kevin

concussion

Some studies have shown that the best gastric uptake is obtained with concentrations of glucose in the range of 6-8%. I'll post the relevant articles when I get a chance, in the mean time some info can be found on the Defence Science and Technology Organisation website. Cold liquid was also shown to cause increased uptake when compared to warm.

http://www.dsto.defence.gov.au/

ngoyvaerts

Don't quote me on this, but water follows salt. So due to the osmotic pressure intercellularly, the salt is exchanged into the cells and the water follows. I believe it's due to the K+/Na+ pump. So 3 Sodiums for 2 potassiums.

Bloody Nipples

Yeah the salt ions are pumped across which changes the osmolarity of the cytoplasm. Water flows from regions of hight solute conc. to low so it crosses the cell membrane into the cell.

And in humans isn't water uptake mainly down to the aquaporins AQP 1 and 2?

Khannie

concussion wrote: »

Some studies have shown that the best gastric uptake is obtained with concentrations of glucose in the range of 6-8%. I'll post the relevant articles when I get a chance, in the mean time some info can be found on the Defence Science and Technology Organisation website. Cold liquid was also shown to cause increased uptake when compared to warm.

http://www.dsto.defence.gov.au/

Thanks for that. I had a look on the dsto website. Couldn't find much...I think because there's a *lot* on there.

My own reason for asking was for post-weigh-in rehydration. I want to get myself back to normal hydration levels as quickly as possible. My current plan is to use dioralite / oral rehydration therapy (this isn't an industry secret or anything) and that works well. As with all things though, it leads me to curiosity on how I can improve it.

I had heard that cold liquids help, but only because you're inclined to drink more of them. I'm working off specific volumes of liquid anyway so I drink what I tell myself I should.

Any links or further information anyone has would be most welcome.

Doyler92

Kevster wrote: »

Isn't it the large intestine where water absorption occurs? It's what makes our faeces become more 'solid' (or, to be correct, more viscous). Maybe it occurs in the small intestine too, if I'm to believe what you're saying! As with any osmotic system, the movement of water is surely controlled by electrolytes like, for example, sodium, potassium, etc? The cells lining the gut have probably evolved to retain a certain amount of such electrolytes to keep things in check (re movement of water).

In this case, if you intake ****loads of salty water, for example, you might just end up doing the reverse of what should happen - i.e. you'll extract water from your body and thi will flush out your guts?

Kevin

On our course we saw how the small intestine has adapted for absorption eg large surface area and lots of villi. So it may be the large intestine also but I'm nearly sure it's the small. I presume absorption means water though but I'm open for correction.

GLaDOS

Doyler92 wrote: »

On our course we saw how the small intestine has adapted for absorption eg large surface area and lots of villi. So it may be the large intestine also but I'm nearly sure it's the small. I presume absorption means water though but I'm open for correction.

Small intestine is designed for absorbing nutrients mostly, though it can absorb water as well. Large intestine absorbs water from the undigested matter that is left after the small intestine is through with it.

That was my take on it anyway.

Piste

There are sodium/glucose cotransporters in the small intestine and nephron of the kidney. They pretty much do exactly what it says on the tin; they transport sodium along with glucose through the apical membrane of the cell from the lumen of the intestine or nephron. The movement of sodium through the SGLT "drags" water as it's osmotically active.

Khannie

Ok, that would explain how dioralite (glucose + salts) restores water so quickly. I had read that the surface area of the small intestine was very large alright.

So at this point I have 2 more things I'm looking to find out:
1) What is the sweet spot (no pun intended) for glucose + salts to minimise the time it takes for water absorption?
2) I have read studies which indicate that glycerine can also help absorption rate (and duration of retention, weirdly). Is this by the same method? I mean....would adding glycerine to a glucose + salt mix further enhance the rate of absorption?

I realise that I'm into the realm of very seriously fine tuning here, but the body is in an unusual state when you step off the scales after a weigh in; Dehydrated, completely empty stomach, probably empty (or close to it) intestines. If nothing else this is just "interesting".

locum-motion

Khannie wrote: »

...1) What is the sweet spot (no pun intended) for glucose + salts to minimise the time it takes for water absorption

One sachet of Dioralyte dissolved in precisely 200ml of water is the 'sweet spot'. That's the reason that the instructions specify 200ml.

youllneverknow

if you read what osmosis is its the movement froma high concentration of water to a low concentration of water
putting salt in the water raises the concentration of water

Khannie

locum-motion wrote: »

One sachet of Dioralyte dissolved in precisely 200ml of water is the 'sweet spot'. That's the reason that the instructions specify 200ml.

Are you sure? Dioralite is supposed to maximise fluid replacement, not necessarily its speed of delivery.

Nice tone in that post btw. :rolleyes:

concussion

Here you are

Review of methods of improving the intake and absorption of water into the body by the use of alternative supply methods and/or additives

http://www.dsto.defence.gov.au/publications/scientific_record.php?record=3984

Khannie

Nice one. Thanks very much.