Monday, June 25, 2007
Teaser Appetizer: Why Does BIL Drink Water?
On Saturday morning, when I entered my kitchen to make tea for my brother-in-law (BIL) - who was visiting for the long weekend - I found him sitting at the kitchen table, looking intently at a row of glasses of water: eight of them, filled up to the rim.
“No thanks, I will not have tea. I'd rather have this water.” He declared.
“All eight of them?” I sounded surprised.
“ To flush the toxins, that is how many you need.” he said.
“Eight glasses can’t flush your sins.” I teased BIL, the hedge fund manager.
“I said toxins, not sins.”
I sat there and watched him with curiosity: his eager gulps of the first glass waned into reluctant slurps of the fourth and forced sips of the last.
Relishing my tea, I envisioned the silent journey of this water through his body.
The water falls into BIL’s stomach, which absorbs some and pushes the rest into the intestines. The surface of the small intestines sucks it up – not like a sponge, but by actively creating an osmotic gradient. (Water travels by osmosis from lower osmotic concentration to higher. The amount of dissolved solutes in water determines its osmolality; more solute concentration generates higher osmolality.) The cells lining the intestinal lining actively absorb sodium ions (salt) and extrude them into the microscopic space between the cells, which creates a higher sodium concentration in this area. Water permeates into this space from the intestinal lumen by osmosis and then leaks into the blood stream meandering in the minute capillary blood vessels.
BIL’s intestine must cope with the massive deluge; about 90% percent of water will enter the blood circulation through the small intestine. The permeability and absorption of water will decrease as it travels to BIL’s colon.
Blood circulation carries water to the farthest cells and inundates them. The cells have been used to this; they remember the times when they drifted alone in the oceanic soup four billion years ago. After many mutations and missteps they evolved a wall around them – the cell membrane – to protect them from the surrounding poisons and maintain their internal chemical tranquility, which includes maintaining a normal osmolality of 285 to 290 mili-Osmols. The cell walls maintain this constant osmolality by rejecting the entry of sodium into the cell and preventing the escape of potassium and phosphate from inside.
When BIL’s consumed water arrives, it dilutes the fluid surrounding the cell and drags down the osmolality. The cell membrane lets only the water permeate into its interior thus maintaining the osmotic equilibrium. The dehydrated cells will keep the water but the already hydrated cells reject excess water.
Water also reaches BIL’s brain and heart - the two organs with sensors, which detect water load.
The hypothalamus part of brain senses variations in osmolality (solute content) and in response secrets a chemical messenger: anti diuretic hormone (ADH), which regulates the volume of urine excretion. An excess of ADH decreases and lack of ADH increases the urine production.
The heart has pressure sensors, which read the volume of circulating water and produce another chemical – natriuretic peptide - in response. Higher circulating water volume induces this peptide, which in turn coerces the kidneys to get rid of excess water.
BIL’s water binge does two things: it decreases the blood osmolality and increases the circulating volume. This shuts down production of ADH and enhances the manufacture of the peptide form the heart. Consequently, kidneys oblige and get rid of the excess water.
That is exactly what I observed. BIL got up after the 4th glass - and a few more times later- to ease himself. The water had flooded BIL’s kidneys; ADH from the brain and the peptide from the heart had assaulted his kidneys and poor BIL had to frequent the toilet.
I visualized the nephrons of BIL’s kidneys in overdrive. Nephron is the filtering and urine-manufacturing unit in the kidney. And there are 1.4 million of them. This exquisite, intelligent, U shaped microscopic tube is the final arbiter of the water volume in BIL’s body.
BIL’s water filters into one end the nephron, travels through the U loop and trickles out at the other end into to the urine collecting system. Since BIL has excess water in his body, each nephron makes more urine and the union of 1.4 million members of the urine production trade sends BIL to the toilet frequently.
The nephron has the ability to respond to the sum of blood volume or pressure, sodium concentration and the quantities of floating ADH. Through these mechanisms, it can produce varying volumes of urine of different solute concentrations. The function of the kidneys is to excrete solutes unwanted by the body and the water serves as a solvent carrier.
Kidneys have a maximum ability to excrete up to 1200 mili-Osmols (mOsm) of solutes per Kg of water. BIL has to eliminate, an average of 600 mili osmols (mOsm) of solute daily. Since the maximal urine concentration is 1200 mOsm/kg water, the minimal urine volume BIL needs to make is 500 ml to excrete 600 mOsm. With BIL’s normal kidneys, mere 500 ml should be enough to “ flush the toxins – and sins.” But BIL just inundated his poor unsuspecting kidneys with eight glasses of water and the penance for this ‘sin’ is the trip to the toilet.
BIL’s body handled the flood better than Bush managed Katrina. Water gushed to the heart, which pumped it vigorously to the farthest crevices of the body. As it traveled farther it slowed to a trickle, then seeped through the accommodating tissues and finally permeated into the cells. BIL’s body fluid regulatory apparatus sensed the deluge and the sirens went off.
OK, eight glasses is no Katrina, but we will agree BIL did it better than Bush.
Let us also be fair to BIL: 60% of his body weight is water and a mere loss of ten percent can be lethal. Water still surrounds and nourishes each cell, like it did when the cell was a complete organism in the waters of early evolution. When we left the oceans to venture onto land, we carried our share of water with us. The distribution of solutes and water is of utmost importance to normal cell function.
BIL maintains the volume of water in his body with exquisite precision of thirst, intake, absorption and excretion. His kidneys, hypothalamus, heart, cell membranes and the thirst mechanism work in unison and simultaneously.
On a normal day, he looses about 1500 ml in urine and another 500 to 1000 ml in breath, sweat and stools. He needs to replenish this by drinking 2 to 3 liters of water daily.
Should BIL drink plain water or a sports beverage?
Water is the osmotic slave of salt and follows sodium with utmost fidelity. BIL does need some sodium in his guts for efficient absorption of water and to absorb sodium the intestinal cells need a little sugar. Water with a dash of sugar and a pinch of salt will suffice. Sugar exceeding 8% of the beverage may actually slow the water absorption.
Here is a recipe: one liter of water; 1/3 cup of sugar; ¼ teaspoon of salt; add lemon or orange flavor; refrigerate and drink. This is the cheap homemade ‘Gatorade’. (BIL can use the other expensive one just for the ceremonial drenching of the coach.)
But BIL being a hedge fund manager lives by the dictum: nothing succeeds like excess; moderation is a fatal habit.
He inundates his cells in water with an atavistic compulsion and like so many other beliefs; he holds that drinking eight glasses of water in the morning cleanses the depths of his interior. It would be more physiological, if he spread his drinking through out the day.
BIL cannot drink water in the morning to hedge against the dehydration of the evening.
Posted by Shiban Ganju at 12:01 AM | Permalink