 Here everybody, Dr. O here. We just got on talking about diffusion, which is the movement of a solute from high to low concentration. The solute in this picture would be a little purple dots, we'll call it, we'll say they're glucose. Now we're going to talk about osmosis, which is really the diffusion of water. So if diffusion is the movement of solute from high to low concentration, osmosis is the movement of solvent, the water, from an area of high to low concentration. Now the textbook definition of osmosis is the movement or diffusion of water across a semi permeable membrane, and that's the key thing, because they look at this picture here on the left. If you were going to, if you remove that semi permeable membrane, I hate saying that one, then we wouldn't need osmosis. Diffusion would work. The high concentration of glucose, those purple dots on the right side would diffuse across and things would become balanced. But now we have a membrane that won't allow solutes through, but will allow water, the solvent through. The water can still travel through this membrane. So instead of solutes moving from right to left, what you see is water doing the opposite, moving from left to right. That's why I like to look at osmosis as the diffusion of water. But here's the simplest way to remember osmosis, water follows solutes. You show me any picture, I'll show you some more pictures throughout here. You show me any picture, I'm going to look where's the solute. That's the direction water's going, because water's going to follow solute. Osmosis is a passive process, meaning it does not require energy. You can't stop water from moving. It's going to go wherever it wants. All right, so whenever we're talking about osmosis or the diffusion of water, you have to look at these three terms here. Isotonic solutions, hypertonic solutions, and hypotonic solutions. An isotonic solution is going to mean basically same tension, same tone, same concentration. So you're going to have the same amount of solute inside and outside the cell. So they both have 20% solute, 80% water. Notice here that the key is there's no net movement of water, not no movement of water. You can't stop water from moving. Water's going to go where it wants. But notice the arrow going out and arrow going in. So no net movement of water. In the middle, you have a hypertonic solution. There's more solute outside the cell than inside the cell, which means there's more water inside the cell than outside the cell. So water's going to move from where there's a lot of water to where there's less water. But the key to remember, water follows solutes. Look at the picture. There's more solutes outside the cell. Water goes that direction. A hypertonic solution will cause your cells to shrivel up or crenate. We use this with food. Look at your canned peas or whatever. They have salt in them or your canned fruit has sugar in them. That creates a hypertonic environment that shrivels up bacteria. It's called plasma lysis. Stops them from dividing. That's what keeps our canned goods safe or one of many things it does. So that's a hypertonic solution. We'll come back to a human example in a moment. Hypotonic solution, there's actually going to be less solute in the solution than there is inside the cell. So notice with this picture here, there's more solute inside the cell, 20%, than there is outside the cell, 10%. So since water follows solutes, water is going to rush into that cell, causing it to swell and potentially even lice or burst. So that is an isotonic solution, hypertonic solution and hypotonic solution. Let's go ahead and look at an example. So keeping, having the right amount of water in our body and having it in the right place is very, very important. We're going to cover fluid balance and electrolyte balance in detail later. But real quick example here, about two thirds of your body's water is inside your cells and about one third outside your cells, maybe 60, 40. But there's supposed to be more water inside your cells than outside your cells. And this is an oversimplification, but hopefully it helps. Sodium is mainly outside your cells and pulls water out of your cells. Potassium is mainly inside your cells and pulls water into your cells. So if you eat a diet high in sodium and low in potassium, which is very common because sodium's in processed foods and canned goods and potassium's in fresh produce. So if you eat a diet high in sodium and low in potassium, you're going to have more solute outside your cells than inside your cells, which is why high sodium, low potassium diet can pull water out of your cells, creating these shriveled up, creanated cells. But then you're going to have more extra cellular fluid. So a high sodium, low potassium diet can lead to edema, the accumulation of fluid between your cells. So puffy face, puffy ankles, whatever, and hypertension. Too much fluid inside your blood, increasing blood in your plasma, increasing blood volume and blood pressure. So edema and hypertension are examples of things that can occur if you create a hypertonic environment inside your body. On the flip side, if you eat a low sodium, high potassium diet, which is definitely more rare, or if you consume way too much water over hydration can actually kill you. Or if you're sweating a lot. So let's say you're a roofer and it's humid and you're sweating a lot or you're training outside and you're sweating a lot. Remember, you don't lose water when you sweat. You lose sweat and sweat is full of solutes as well. So if you're drinking water, but you're sweating out water plus all these solutes, you can create a situate, a hypotonic environment where you've got a whole bunch of water and not enough solutes. So let's look at what would happen there. Let's just say you were on a low sodium, high potassium diet. Or you're on a high potassium diet and you're losing a bunch of sodium from sweat. Well, that's going to create an environment where you have a hypotonic solution. More potassium inside your cells than sodium outside your cells. Water's going to rush into your cells and that's going to create these swollen cells. It actually causes a condition called hyponatremic, low sodium encephalopathy. So your brain cells can swell. So I had a friend that was like that. They were training for a marathon. They were sweating thousands of milligrams of sodium away but only drinking water almost killed them. Or if you hear about people that drink so much water they die, same condition. Hyponatremic encephalopathy can be caused by creating a hypotonic environment in your body. So this is not an interesting class. This is not health advice but generally speaking if you want to create the right balance between your cells and the rest of your body I usually tell people consume around 3,200 milligrams of sodium a day. I know it's higher than the government recommendations but I think that's a pretty sound number. And then the RDA for potassium is 4,700 milligrams a day. So give or take those are pretty decent numbers. All right, that's osmosis plus some real world examples of why it matters. I hope this helps. Have a wonderful day. Be blessed.