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Dehydration

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MatC
250735.  Mon Dec 31, 2007 8:42 am Reply with quote

MatC wrote:
“Chris Kelly, the ECB’s umpires manager, has asked all the counties to provide his men with fruit and sodium sports drinks during the tea interval. Tea and coffee are so last season. ‘We are trying to make the umpires aware that tea and coffee increase dehydration,’ Kelly said. ‘When you are dehydrated one of the first things that goes is your concentration, the next thing is your vision.’”
- Daily Telegraph, 18 May 2006.

... and thus are the Superstitions of Health built upon the Tales of the Wives of Old.


What makes this so fascinating - the ECB’s belief that drinking tea makes you go blind - from the point of view of an amateur historian of idiocy, is that it takes us back to the 18th-19th centuries, when drinking tea occupied a position roughly analogous to that occupied by masturbation in the 19th-20th, and smoking in the 20th-21st.

That is to say, tea was known to be both sinful and unhealthy. Admittedly, I’ve yet to find an 18th-19thC source for tea making you blind (as both masturbation and smoking have done since), but drinking the sinful stuff certainly was known for a 100% medical fact to destroy the digestion and to lead to loose morals. “Excessive” tea drinking - whatever that meant - was known to be fatal.

 
costean
261536.  Sat Jan 19, 2008 4:09 am Reply with quote

Quote:
“Chris Kelly, the ECB’s umpires manager, has asked all the counties to provide his men with fruit and sodium sports drinks during the tea interval."

It could be argued that fruit juice is not the best liquid to aid rehydration either. OK, this is splitting hairs and if the juice is part of an isotonic sports drink then it probably is effective. But, orange juice, on its own, is not as effective as water when it comes to hydrating the body (not in the longer term anyway).

Interestingly an experiment to test just this was carried out by Eddie McGee, a British Army survival instructor in the 60s/70s. Once, while serving in Cyprus he was asked to undergo an exercise to test whether it was possible for a man to survive for fourteen days on oranges alone.

He was very experienced in survival situations, was tested for allergies (too much vitamin C etc) and had medics on hand throughout.

Some days he ate just the fruit and other days he drank just the juice (this was left to him). By the fourth day he was experiencing unpleasant physical symptoms and by the fifth was craving fresh water. On the morning of the tenth day both he and the medics agreed that his body had taken enough. He was monitored in hospital for a couple of days and fully recovered shortly afterwards.

Eddie McGee wrote:
The reason I have mentioned this story … is that many times I have picked up survival books where quite openly it claims that man can go for twelve to fourteen days without any liquids at all and from thirty to thirty-five days without food. Well, you can say that I did not go without liquids for ten days, but I can say this that after the fourth day I craved fresh water and by the eighth day I was getting really desperate. Now I always teach my pupils, no more than three days for you.

Unfortunately the experiment did not go on to test the effects of just water/tea/coffee/beer etc. But, I think it is safe to conclude that he would have lasted longer if he had had only water to drink; although he would not have lasted as long with nothing at all. So while orange juice is certainly refreshing and undoubtedly would replace short-term liquid deficiencies it should not be used as the sole source of liquid over the longer term.

S:
No Need To Die, chap 4 – Eddie McGee (1978)

 
Bondee
261667.  Sat Jan 19, 2008 12:10 pm Reply with quote

costean wrote:
So while orange juice is certainly refreshing and undoubtedly would replace short-term liquid deficiencies it should not be used as the sole source of liquid over the longer term.


As my doctor informed me recently, when I was diagnosed with IBS, excessive quantities of vitamin C can have a laxative effect.

As I've been led to believe, midwives used to (maybe still do) tell mums to give their babies a bit of orange if they got a bit blocked up.

 
auron5500
265266.  Fri Jan 25, 2008 4:55 am Reply with quote

One thought that I'd had on the subject of hangovers (and I'm not a biologist so this is just a guess) is that it would be caused by a diversion of blood from other organs to the liver in order to help process the alcohol quicker.

The idea for this comes partly from trying to explain to someone why your mouth would become dry in the morning after a night of heavy drinking even though the alcohol would not severely dehydrate you and also the 'fight or flight' response in which blood is diverted from places like the stomach, intestines and bladder to the muscles so you can run faster or fight better. In these cases you may feel sick (from the stomach), having loose bowels (from the intestines) or become incontinent(sp?)(from bladder). The point here being that in the morning if you feel ill it is likely not to be trying to remove alcohol in the stomach but that there is not much blood going to the stomach because you are still trying to process the alcohol in the liver.

Like I said I'm not a biologist and this is just a guess but it seems to make sense to me. I'm sure a more informed person will look over this and tell me how wrong I am.

 
smiley_face
265336.  Fri Jan 25, 2008 7:24 am Reply with quote

Quote:
In these cases you may feel sick (from the stomach), having loose bowels (from the intestines) or become incontinent(sp?)(from bladder).

Quite right. Which is why the term "shit scared" is really rather accurate.

As for the "diverting blood away from the liver", it's not one I've heard before, but I'll look into it now...

 
Jenny
265559.  Fri Jan 25, 2008 5:58 pm Reply with quote

That doesn't sound right to me - surely blood just, erm, circulates doesn't it? Wouldn't it have a predetermined circulatory path?

 
Davini994
265658.  Fri Jan 25, 2008 10:06 pm Reply with quote

Jenny wrote:
That doesn't sound right to me - surely blood just, erm, circulates doesn't it? Wouldn't it have a predetermined circulatory path?

Less blood goes to your extremities when cold though doesn't it?

 
barbados
265717.  Sat Jan 26, 2008 4:53 am Reply with quote

And apparently while exercising, which is why long distance runners and footballers wear gloves, even when it isn't really cold

 
smiley_face
265756.  Sat Jan 26, 2008 7:47 am Reply with quote

Blood flow to different areas of the body can be controlled. For instance, it doesn't matter what else happens, blood will keep flowing to the brain, since that's the most important organ in survival. The other two key organs are the heart (not too surprising) and the kidneys.

“Autoregulation” is one of the most important mechanisms in homeostasis. Its function is to maintain the flow of blood to different parts of the body in spite of changes in blood pressure. It does this in various ways.

One example is in the kidney, where a set of cells (called the macula densa) senses changes in the concentration of sodium ions and chloride ions. This is an indication of a change in blood pressure. As a result, the macula densa cells release chemicals known as prostaglandins. These are then detected by cells called granular juxtaglomerular cells which line the arteries supplying blood to the nephrons of the kidneys.

The juxtaglomerular cells then release a chemical called renin, which controls vasocontriction, (narrowing and widening of the arteries).
____________________________________________________________

It's then just a case of simple physics. If you put your finger over 90% of the outlet aperture of a tap, the water comes spurting out at high speed and pressure. This is because pressure is inversely proportion to area. Hence, if you narrow an artery when there is a lowered flow of blood, you can raise its pressure.

 
Jenny
265888.  Sat Jan 26, 2008 11:54 am Reply with quote

So how can the blood just not get to a certain part of the body under certain conditions that don't involve an artery or a vein being directly blocked?

 
auron5500
265903.  Sat Jan 26, 2008 12:16 pm Reply with quote

I would have thought that if a vein, artery or capillary if constricted without the heart pumping more forcefully wouldn't cause an increase in pressure as the blood would be more likely to go through an alternate, less constricted, route. i.e. the path of least resistance stuff

 
Davini994
265912.  Sat Jan 26, 2008 12:34 pm Reply with quote

I've never understood this on the show. If you get extremely drunk of an evening, the following morning I have an overwhelming desire to drink vast amounts of water, and am demonstrably dehydrated as evidenced by my first trip to the little boys room.

 
smiley_face
265915.  Sat Jan 26, 2008 12:46 pm Reply with quote

Jenny wrote:
So how can the blood just not get to a certain part of the body under certain conditions that don't involve an artery or a vein being directly blocked?

I'm not sure if I'm reading you correctly (I've just been stood on a freezing hockey pitch for 70 minutes and my brain has gone on strike), but is it that you're implying that you don't understand how the blood completely stops going to a particular part of the body?

In which case, (and I will need to triple check this), the fact is that blood never completely stops going to any part of the body, or else the cells in that part of the body will die from lack of oxygen. It's just that the movement of blood to certain parts of the body is prioritised at times.

 
Jenny
265934.  Sat Jan 26, 2008 1:33 pm Reply with quote

smiley_face wrote:


In which case, (and I will need to triple check this), the fact is that blood never completely stops going to any part of the body, or else the cells in that part of the body will die from lack of oxygen. It's just that the movement of blood to certain parts of the body is prioritised at times.


That was what I thought - that tissue would die if blood didn't reach it. However when you say that the movement of blood to certain parts of the body is prioritised, it makes me think of blood flow as being something quite chaotic with blood flowing in all sorts of different directions, whereas I had thought of it as following an orderly and predictable route.

 
smiley_face
265939.  Sat Jan 26, 2008 1:55 pm Reply with quote

It's not like there is one continuous tube flowing around the body - it's a complicated networking involving lots of branching out and later, merging again.

The blood from the heart which travels out through the aorta is almost immediately begins to branch into other main arteries, which carry the blood to the brain, liver, kidneys etc.etc.

The blood continues to branch out into smaller arteries, then arterioles (very small arteries), and then capillaries. Capillaries are the smallest blood vessels, with one-cell-thick walls, so oxygen diffuses out of the blood and into the tissues here. Similarly, CO2 enters the blood stream from the tissues here.

Having branched out, the blood in the capillary starts to merge with the blood from other capillaries into venules (small veins). Then the blood from this venule will merge with blood from others into a vein. The blood is then transported back to the heart again.

 

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