When you consider that about 60% of your body weight is made up of water, it stands to reason that our bodies need regular replenishment of fluids to keep every system – all the biochemical processes – in the body functioning properly.
The glass of water that you drink ends up in the gut, which actually refers to the 8 – 9 meter long gastro-intestinal tract (GIT), that starts in the mouth and ends at the anus. However, the glass of water and other fluids that you drink are not the only source of fluids in the GIT – on average the daily water balance of about 9 litres in a healthy adult GIT consists of the following:
- oral intake (water, beverages, water in food) – 2 litres
- saliva – 1,5 litres
- gastric juice – 2,5 litres
- bile – 500 ml
- pancreatic juice – 1,5 litres
- intestinal secretions – 1 litre
And where does it all go to?
- small intestinal absorption accounts for 7 litres (78%)
- colonic absorption for 1,9 litres (21%)
- about 100 ml (1%) ends up in the stools
The water that gets absorbed has many important functions, says the Harvard Medical School:
- “carrying nutrients and oxygen to your cells
- flushing bacteria from your bladder
- aiding digestion
- preventing constipation
- normalizing blood pressure
- stabilizing the heartbeat
- cushioning joints
- protecting organs and tissues
- regulating body temperature
- maintaining electrolyte (sodium) balance.”
Dehydration can easily occur when you lose too much water from your body without replacing it. Mild dehydration means you have lost up to 5% of your body fluids, and can already result in an imbalance in the body’s equilibrium. Moderate or long term dehydration can result in the slowing of metabolism, increased cholesterol levels, a rapid heart rate and low blood pressure. Acute and severe dehydration can be life threatening with symptoms such as delirium and unconsciousness.
Being thirsty is usually the first sign that your body needs water. Another easy sign to determine your levels of hydration is to look at the colour of your urine. When the body is getting sufficient fluids, the urine is light in colour and free of odour. However, when the body is not getting sufficient fluids, the urine can be more concentrated – dark yellow in colour, with an increase in odour. (Please note that certain supplements or types of medication can affect the colour of urine.)
(The biochemical processes in the body need water, not the extra burden of all the sugar in sweetened drinks!)
We mentioned earlier that about 60% of body weight is made up of water, about 42 liters in a 70 kg male. But where does all this water hide away?
- 67% in the intracellular fluid compartment (the fluid in the cytoplasm of all cells in the body). (Intra means internal – inside the cells in this case)
- 33% in the extracellular fluid compartment (which is separated by the cell plasma membrane from the intracellular fluid compartment). (Extra means external – outside the cells in this case.)
- The extracellular fluid compartment is subdivided into the intravascular compartment, and the extravascular compartment.
- The intravascular compartment contains the fluid inside the body’s blood vessels, called the plasma. The plasma is the fluid portion of blood, while the rest of the blood is made up of red blood cells, white blood cells, and platelets. The average human body carries about 5 liters of blood.
- The extravascular compartment is separated from the intravascular compartment by the lining of the walls of the capillaries. The extravascular compartment is further subdivided into two compartments, namely interstitial fluid and transcellular fluid.
- Interstitial fluid “bathes” the cells and tissues in the body.
- Transcellular fluid is found in small amounts in various areas in the body, for example cerebrospinal fluid that “bathes” the brain and the spinal cord, lymph fluids, and synovial fluid found in the joints.
After a full circuit in the blood vessels of the body, the returning blood is carrying waste products. The kidneys then have a mammoth task to remove these waste products from the plasma, by filtering the total amount of plasma in the body about 50 times a day! These waste products are byproducts of normal metabolism in the body and are ultimately removed from the body through the urine. The filtered plasma gets reabsorbed back again into the bloodstream inside the kidneys.
How much water should you drink? Published September 2016. Harvard Health Publishing, Harvard Medical School.
7 Science-based health benefits of drinking enough water. Published 4 June 2017. Healthline. (www.healthline.com)
Body fluid compartments of a 70-kg adult male. Published 14 November 2015. Physiology Web. (www.physiologyweb.com)
How dehydration affects your brain function. Dr Mercola. (www.drmercola.com)
6 Reasons to drink water. Last reviewed 8 may 2008. WebMD. (www.webmd.com)
Medical Physiology. A systems approach. Physiology handbook by Hershel Raff and Michael Levitzky. Published by McGraw Hill, 2011.