Hello, chemists. We're going to have a quick video here on water. And when we talk about water, it's important for us as anatomists and physiologists because 70% of the adult mass, the adult's body mass is coming from water.
And water is going to do several really important things for our body. So one important feature is Water will act as a lubricant. Remember we talked about those fluid-filled body cavities when we were discussing chapter one, and we talked about, oh, this is really great because you encase the heart in a cavity, you encase the lungs in a cavity, and then the heart can move separately and the lungs can move separately, and that fluid in between reduces friction between. And that fluid then, of course, is a water-based solution. So that's one example.
We'll also think about water as an important cushion for the body. So even in that discussion of the pericardial cavity, which is that sac holding the heart or the pleural cavity, that sac that's holding the lungs, there is a little bit of shock absorption and protection that's happening with that fluid. We see this especially in the cranium.
So our brain is floating around in cerebrospinal fluid. Pretty much all the fluid of the body is water-based, right? And so this fluid is helpful in like making our brain buoyant. So it's not quite so heavy and hard to lug around.
But also as we move and shake and bounce and all that, we don't have to worry about our brain, our soft brain tissue smashing up against that hard. bone. So that's going to be an important feature.
We see water important in our joints, which we'll be talking about this semester. We'll see also that water is important heat sink. And what this is talking about is water's ability to absorb, absorb, and then dissipate heat. And so this is super important in how we cool our bodies.
So we can also talk about sweating as evaporative cooling. Those hottest water molecules are the ones that evaporate off of our skin, leaving behind the cooling, the cooler water molecules. And so there's water molecules as they leave and become gas and enter the atmosphere.
then is making our bodies cooler as a result of that. Another super deeper important feature is that water is what's called a universal solvent. And the term solvent means dissolver. This is such an important feature. And this is true.
Because water is polar. And remember, when we talk about solubility, likes dissolve likes. So polar water will dissolve polar molecules. So this is a really great test. Does sugar mix with water?
It does. Sweet tea, right? Hot.
Sweet coffee, right? Kool-Aid, right? And so sugar is polar.
So as a quick test, if you have something you don't know about, if you combine it with water and it mixes, then that tells you that it's polar. Polar water will also dissolve ions. And that's what we're going to be talking about next as salts. So we'll see that this is important too.
When we talk about polar water and water being polar, we're going to use these terms hydrophilic to mean like water loving. So anything that dissolves well in water, we can call hydrophilic. The opposite of this would be hydrophobic, which would be like water fearing.
So again, If you're unsure about something, combine it with water. And if it mixes, it's polar. And if it doesn't, it's not. So you've all heard the expression, oil and water don't mix. And why would that be?
You got it. Oil is nonpolar, so we can also talk about oil as being hydrophobic. I also want to mention some other terms while we're on this topic of solutions.
We have what's called a coiloid and we have what's called a suspension. Now, a coiloid is going to be a suspension of large molecules, usually proteins. that don't settle.
Milk is a great example of a colloid. So you can't see through milk. It's not transparent, right?
And what's going on with the milk is you have a lot of proteins and you have a lot of fats that are suspended in that milk. And that milk can sit in your refrigerator for a week and it's going to have that same coloration. Those proteins and those fats will continue to be suspended in that milk for the whole week, right? This is different from a suspension because in the suspension, it will settle out. So in both cases, we would not say that those molecules are dissolved.
We say that they're suspended in the water. In the case of the coiloid, that suspension is like a permanent, it's forever suspended. In the case of the suspension, it's temporary and it can settle out. So here, if you were to take a mason jar and scoop up some muddy lake water, and when you first do that, there's maybe a lot of mud and debris and the water is really cloudy. You let it sit overnight, you take a look at it the next day, and you'll see all that debris has settled to the bottom of the jar and you have some clear water.
in your jar. So that would be an example of a suspension where those things that are not dissolved are suspended but will settle out with time. These terms will be important as we move into future discussions.
The last important property or characteristic of water that we need to look at is that it is reactive and this gives us a whole conversation. So when we talk about water being reactive, we see that there's two important types of reactions that are involved with water, that water is involved with. We have a dehydration synthesis reaction. Y'all know that word dehydration means remove water and synthesis means to make. The very opposite of that is hydrolysis reaction.
And let's talk about each one of these. In a dehydration synthesis reaction, we can think about this in super generic terms. So we can say molecule A H plus molecule B O H react together to form something new.
AB, and in the process, pull out that water molecule. So a dehydration synthesis is removing two hydrogens and an oxygen. So you remove water, remove H2O, in order to perform anabolic reaction, right? Anabolic means building or making something new. So here we've removed the water and here we've made something new.
This is a dehydration synthesis reaction. Exactly the opposite of this is hydrolysis. Now, if you want to, you can mispronounce this word. You could say hydro as in water, lysis as in to break. So we're going to use this term lysis quite a lot in the course.
We can write this equation out, but notice we're going to go the opposite direction. So we're going to start with the molecule AB and we're going to combine it with water. And when we do that, what's going to happen is both the water molecule will split and the AB molecule will split.
And so now we end up with hydrogen from water pairing with that A and then the hydroxide group also from water pairing with that B. So here we are going to split. water.
And we're doing a catabolic reaction. right? Now, you're going to see the term hydrolyze used to describe that a process, a hydrolysis reaction has occurred.
So, if you hydrolyze something, that tells you that you're doing the catabolic reaction, specifically hydrolysis reaction. Now, hydrolysis reactions, we're doing all the time. This is a key part of our digestion.
So, when we eat food, right? And we mechanically break that down in our mouths, but we also start a chemical digestion. And those are going to be hydrolysis reactions.
So breaking down our food into basic units, those nutrients that we need is going to be hydrolysis. Those nutrients make their way from our small intestine to our bloodstream and out to our tissues. And then our cells will do a dehydration synthesis reaction in order to build the molecules that our cells need.
So both of these processes are happening in the body all the time. Okay, stay tuned for a quick discussion on salts and acids and bases coming up. And as always, take care of yourselves and each other.