The science of saline – why can we drink pure water, but when we put water into our bodies in other ways, like an IV, must we add minerals to it?
In: 480
We normally pick up the required complement of sodium chloride from food, but people who require IVs are often also unable to eat at the moment.
In short, we can’t drink pure water either. Our bodies rely on electrolytes to function properly, and drinking ultra pure water would sponge those electrolytes out of your blood. Even filtered drinking water, which we would think of as “pure” contains enough trace elements of electrolytes to make it safe to drink.
[The TV show QI did a bit on this.](https://youtu.be/Ra0vcC476Rk)
Your blood has a salinity concentration of about 0.9%, this is why most IV fluids have a similar “salt” concentration. If you were to hypothetically flood someone with pure water through an IV, it would offset the natural gradient of 0.9% causing fluid to flow into your cells and cause extreme swelling.
Water wants to be evenly mixed with the salts and such that are around it. If you add a drop of food coloring to a glass of water, it will slowly move on its own until there is a uniform mixture.
Your blood is a salty fluid filled with balloons called cells. If you add plain water, the salty fluid just gets diluted, but water also moves into the balloons to dilute their contents. This causes the balloons to swell up and burst. The extra water would also leave the blood vessels and cause swelling in other places, which can be especially bad in the brain which doesn’t have room to expand because it’s surrounded by the skull.
Your stomach is a special place that is designed to take stuff from the outside and prepare it for your body to use. The cells are protected from being burst and it can buffer things a bit better. You can still mess it up with too much water (think gallons at once, but people have died from drinking too much water) but for everyday use it is safe.
It’s all about tonicity which is a fancy way of saying concentration of stuff (e.g., electrolytes). Nature likes for concentrations to be equal, so if you inject pure water into your veins, the water (no stuff) will enter your cells (lots of stuff) to try to equalize the concentrations. The problem is, if too much water enters your cells, they’ll burst and die. If you add enough stuff to the water so that the concentrations are equal, the water will stay in your veins without going into your cells.
If you have too much stuff in the water, you can also cause water to leave your cells (like pouring salt on a slug), which would cause them to shrivel up.
Water you drink is rarely pure. Tap water has different minerals in it. Ever heard about a state having “hard”
water in it? That because it has higher then average levels of calcium in it.
I have a DI system at work and run the water through 6 different filters in the system to try and get as close to pure water as possible and it’s tested every week for containments, from biological to chemical.
In chemistry, it’s not about the presence of a chemical in the water, but the concentration of the chemical.
You add salts(electrolytes) because your body needs them to carry out various functions. ATP (adenosine triphosphate, short term molecule for energy). generation for examples depends on sodium and potassium ion pumps.
Salt concentration can also have an effect on your blood pressure. So if you are directly injecting water, you don’t want to cause another problem by dropping(or raising I forget which I’m a chemist not biologist/physician) their blood pressure
When you ingest something, it goes through your digestive system, which processes it before it hits your blood stream. When you insert something directly into your blood, you are bypassing all those preparation systems. So it has to be very close to what your body already expected to see in those areas, because if not you will simply break the highly optimized machinery.
Actually pure water as in H2O is not the most suitable for drinking as it lacks minerals which are required to help maintain homeostasis. Pure water as the question implies would overtime takes minerals such as calcium out of your blood and eventually your bones leading to wakened bones. Sodium and potassium also plays a significant role in homeostasis which is why some bottled waters are supplemented with minerals. If as in pure water you meant treated to kill microbes then that’s a different issue and does not necessarily impact the salt and mineral balance of your blood the way pure water as in distilled water would.
I’m not entirely sure but I believe it would dilute the saline concentration already in your blood and that would cause a whole mess
By pure, do you mean reagent or HPLC grade water?
Latest Answers