Friday, March 3, 2017

Water physiology

Water physiology
Drinking water (without some electrolytes and glucose-not simple sugars) alone for me is un-physiological.
This was the basis of formulation of rehydration fluid by our (National Formulary-Headed by Professor Senaka Bible) yesteryear physicians.
I may be wrong but Pediatrician Prof. Sanath Lamabadusuriya PhD thesis in London was (somewhat) related to Rehydration Fluid.
This formula has saved millions of sick people including children.
This is not an attempt to revisit that history but to pen down water metabolism (physiology) in a few lines.
I looked at all my physiology and medical books (huge volumes) and I could not find a succinct account on water metabolism.
As a last resort I browsed the web (content reproduced below) and it was no better except the lively web discussion.
No human can (rats in the desert can live longer) survive threee days without water.
There are centers in the brain that drive thirst and make somebody to crave for water if deprived of water completely.
That is also not my point of view here.
All these people who for political stunts (reasons) fast are scoundrels who cheat gullible masses and drink lot of sugary drinks and man can go on for three months of (absolute) starvation of solid food.
Let me come to the statement that drinking water alone is unphysiological.
There is only one place in the gastrointestinal tract that can absorb pure water (without electrolytes).
That is anatomically situated, not in the top end but in the bottom end.
It is the large intestine and rectum.
That is why rectal enema is saline based and never water.
In an old sick patient water enema can kill and cause water intoxication.

Water intoxication
Water intoxication can occur in a variety of different clinical settings but is generally not well recognized in the medical literature. The condition may go unrecognized in the early stages when the patient may have symptoms of confusion, disorientation, nausea, and vomiting, but also changes in mental state and psychotic symptoms. Early detection is crucial to prevent severe hyponatraemia, which can lead to seizures, coma, and death.
However, it is almost impossible to become water intoxicated by drinking water unless one is psychotic.
Many moons ago when I was working abroad I had a similar case.
The first thing I do when working abroad is, to find a difficult case generally neglected by the majority (patient is expected to die) and solve it on my own accord.
In this case very old gentleman 80 plus and supposed to have pneumonia.
Treated adequately with antibiotics but almost unconscious.
Generally old people present with confusion (not unconscious) with ill defined infection but this case had been adequately treated.
I ordered a repeat X-ray and it was all clear.
Looked at the basic biochemistry to see water intoxication (with hyponatraemia) with a saline drip running.
I asked the relatives what I should do?
They wanted their grandpa home.
I said give me two weeks and asked the nurse to take the drip down and leave the cannula.
They were hesitant but I said you have to follow my instructions.
Asked them to repeat blood chemistry twice a day and nothing by drip or mouth for two days.
In two days he woke up from slumber but still dazed.
Biochemistry marginally improved but not isotonic.
I told the nurses, he will ask for something to drink tomorrow give him a strong cup of coffee or tea and call me if he vomits.
In five days he recovered but disorientated.
I got friendly with him and the entire family and he went home in six weeks.
On the Christmas day he was admitted with broken hip.
I immediately transferred him by plane to the regional center where he had the hip replacement.
Mind you he broke his other hip within three months.
This was the only case who had bilateral hip replacement in my tenure in there.
He was doing OK when I left but he could not remember me (the family was very close to me) very well with all these medical misadventures. 
Coming to my bone of contention back; 
If one drinks large amount of water without food (it does not matter drinking water before or after a meal) one has to spend extra energy to absorb it and excrete the excess by the kidneys.
That is my bone of contention.
However, it may lower the risk of stone formation in the kidney.
All these physiological processes (water conservation or water excretion) need potential energy and we call it homeostasis.
What I am trying to say is if one is not feeling thirsty, do not drink water as a drill but always associate drinking water with food that helps digestion in many ways. 
It does not matter one drinks water soon before or soon after a meal or with the meal.
What I am against is drinking water as a drill which stresses the intestinal physiology (needs potential energy to excrete the excess of water).
Of course, if the water is retained that means there is water deficit to begin with but we cannot do that mental arithmetic ourselves but the the brain (pituitary does it automatically for us) does it for us.

Both hunger and thirst are physiological reactions to body's deficit in sugar or water.
No volition is implied here.

Little Physiology and Anatomy

The top end, the oesophagus cannot absorb anything including water.
The stomach, is the reservoir of food until partial digestion is carried out and has to secrete large amount of digestive secretions.
Upper intestine (duodenum and jejunum) also secrete large amount of digestive enzymes.
Lower intestine (about 22 feet in length -I could remember without referring) does most of the absorption including water (80%) and the digested food.

The small intestine in adults is a long and narrow tube about 7 meters (23 feet) long. The large intestine is so called because it is wide in diameter. However, it is shorter than the small intestine — only about 1.5 meters (5 feet) long.
Large intestine absorb 400 ml of water (20%).

Below is an interesting web interaction reproduced.

Water absorption occurs primarily in the
A. duodenum.
B. jejunum.
C. stomach.
D. large intestine.
E. mouth.

I thought small intestine can absorb water but Kaplan says large intestine is the right answer.
Can someone check this for me?

Yup. the small intestine absorbs sugars fats and protein.

The large intestine does the water absorption and K+ ions and B16 it think. But here are some notes I threw together from EK.
Hope it Helps.

My human physiology power power slides say it can also absorb water XD.

I don't know which one to follow.

The Large intestines main function is water absorption and electrolyte absorption. Remember that in the small intestine primarily the in the duodenum ( I forgot how to spell it) the body will absorb amino acids and sugars through the enterocytes directly into the blood stream. While the fatty acids will get absorbed into the enterocytes and then will be modified in the smooth ER where they are incorporated into chylomicrons (water soluble globules).

There really isn’t much water absorption in small intestine ... it was a question on my bio final... so I'm assuming.

A.. yes large intestine's main role is water absorption but it's only absorbing what's left over from small intestine. My whole class argued over this one.. so I remember this very well.

I'm pretty sure its the large intestine. The main function of the large intestine is to absorb the water from the material that comes in from the small intestine and make solid waste (feces).

Vitamin K and Water are absorbed within the LARGE intestine! Small intestine is primarily involved in absorption of nutrients.

Site of compaction = large intestine, so I think it's large intestine. If the small intestine was the answer..way too easy I think. 
Small intestine (jejunum). We JUST had a quiz on this today and that's the right answer.

Large intestine is the first answer that comes to mind.

Although my Physiology power points tell me that the small intestine reabsorbs 8500ml of water compared to 400ml in the small intestine.

Yeah, small intestine.
Note the difference between the two choices:
While most water is absorbed in the small intestine, that's not its primary function. The large intestine's primary function is water absorption, but it doesn't do the majority of that during the digestive process.

Also, if you look at the diagram, it looks as if the part where 8500 ml is being reabsorbed, it looks like that would be the jejunum.

I'm almost 100% sure that the discussion could have ended with this post.
Main function of Colon is water reabsorption, but most of water reabsorption is done in the small intestine.
Therefore its a major fuction of the large intestine.

Water ingested              2000 ml per day
Saliva                           1500 ml per day
Gastric Juice                 2000 ml per day
Bile                              500 ml per day
Pancreatic Juice           1500 ml per day
Upper Intestinal sectretions 1500 ml per day

Lower intestinal absorption 8500 ml per day
Colonic absorption              400 ml per day
Feacal Excretion                 100 ml per day

Water Metabolism
Chemical reactions take place in cells. Collectively these reactions together are called metabolism, i.e. all the chemical and physical processes within a cell. The chemicals involved are called metabolites. Water is a metabolite in many reactions, either as a reactant or as a product of reaction. For example, it's involved in photosynthesis, digestion and aerobic respiration.
Metabolic water refers to water created inside a living organism through their metabolism, by oxidizing energy-containing substances in their food. Animal metabolism produces about 100 grams of water per 100 grams of fat 42 grams of water per 100 g of protein and 60 grams of water per 100 g of carbohydrate.
Some organisms, especially xerocoles, animals living in the desert, rely exclusively on metabolic water. Migratory birds must rely exclusively on metabolic water production while making non-stop flights. Humans, by contrast, obtain only about 8-10% of their water needs through metabolic water production.
In mammals, the water produced from metabolism of protein roughly equals the amount needed to excrete the urea which is a byproduct of the metabolism of protein. Birds, however, excrete uric acid and can have a net gain of water from the metabolism of protein.

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