Advanced Pathophysiology

Fluid Distribution Transcript

Okay, we're back. We just talked about systems in the body and how they help regulate fluid, or the main systems that help regulate fluid. Sometimes you might feel like, geez, I already know this, but that's good because that's just a refresher, reminding you of the things that are really important. Your book doesn't even talk about the systems overall and how they contribute to fluid.

I felt it was really important because it gives you a foundation. If you understand the systems and how they cause certain things to happen, if that system's broken, you can predict what's going to happen to the body. If you know the heart contributes to fluid and electrolyte movement by doing certain things, if the heart's broken, you can count on those things not happening. Or if I tell you that the kidneys are important for filtering the blood and the kidneys break, you know that the body's not going to be able to filter blood.

I keep reminding you of the special processes of systems and you see some symptom or sign in a client or a patient that says, hey, they're not filtering or, hey, they're not getting circulation. You can look right to the systems and pinpoint.

Now we're going to go in this section a little bit deeper. We're going to go from the systems. We're going to go down to specific areas of the body that are distributing the fluids, or where do they go. This picture is a reminder of the different things that water's there for, like helping protect the tissues, chemical reactions, to transport nutrients. Now we're going to go a little bit closer and actually look at the cells, the blood vessels and the interstitial space, the space between.

Some terminology you need to get familiar with. First is TBW means total body water. If you take all of the water in the body, the entire body, and you pulled every drop of water out and just left you as a pile of dust, where would that water be? Our total body water is going to be roughly about 60% of us. It's going to make about 60%.

Down here on the bottom, I put a rule of thumb that you might want to remember that 70 kilogram male, which is the average male, according to medicine, 60% of our body is going to be water. About 60% of that 70 kilograms is 42 kilograms, and instant conversion you can use is that when you see one kilogram, it's about one liter of water or vice versa. If we say that there are 40 liters of water in this person, that means that about 40 kilograms of that person are water, just a rule of thumb to remember.

If you were to guess the total body water, and you said, well, there's the space inside the cells. There's the space between the cells and there's all of the plasma. Where would you guess the most water in the body is going to be? Is it going to be in the cells? Is it going to be in the space between, or is it going to be in the plasma itself?

A lot of people automatically go for the plasma because we say, hey, there are roughly five liters of blood in a person. You can measure that. You can pour it into a container, but in reality, the bulk of all of the water in your body is in your cells. A trillion cells in your body, each having this little tiny microscopic droplet of water, makes up the bulk of your body. We're going to call that the intracellular fluid or the ICF, so just get familiar with the abbreviations.

Everything that's not inside of a cell is extracellular. The fluid that's inside the blood, the fluid and the space between the cells and the blood. That's all extracellular. Things like the vitreous humor or the aqueous humor in the eyes. That's extracellular, that's extra fluid. The fluid in your joints. Do you remember what it's called? Synovial, that's extra cellular fluid. It's outside the cells.

Those are all insignificant when you look at the grand scheme of things, but they're all really important at the same time. They have to be there otherwise you'd have problems, but when we look at the extracellular fluid, basically it's any compartment, lymph, synovial, intestines. What CSF? Cerebro spinal fluid. Would you die if you didn't have any? Yes, and you'd have a terrible headache on the way there, so you need these different things.

When we talk about the ISF, it means interstitial, which literally means between the space. The space between here, like the Dave Matthews' song, but this is interstitial. It's a space between the major areas. Then when we talk about intravascular, it means within the vessels, so don't forget inter means between, intra means within.

When you look at the distribution, like I said before, the total body weight, male versus female, you can see that with males, we have just a little bit more water in our body. Not huge amounts, but a little bit more water. Women have a little bit more solid in their body. So if you take and you split up our body proportions, remember this is proportional. We're not saying that a 250-pound, six foot-four man versus a five-foot, 103-pound woman. Obviously, this man has to have more water, but proportionately, per amount of water, substance in their body, proportionately men will have more. Women have less.

Then when you subdivide these fluids, we get split into the intracellular, which is within the cell, to the extracellular. Remember intravascular, interstitial, the aqueous humor, etc. We can subdivide those two main categories into the interstitial fluid and the plasma. A lot of people like to say, well, the plasma is where most of the water is in the body. But in reality, look at that, it actually represents one of the least amounts of the significant areas, so only about 20% of our water in our bodies and our plasma.

If you want deeper, looking deeper into the distribution, you can see a cell. One cell by itself is 85% water. Your liver, if we pull out of your body, it's 90% water. When you look at the brain, where's the brain on here? It's like 80… There we go, 85%. Your brain is just a big bag of water and fats, basically. Even bone, 35% water.

All right, so major factors that affect the distribution. First factor is going to be sex, and I already talked about this a little bit. You can see a normal male is about 60% water. A normal female is about 50% water. If it's a lean male, 70% water, lean female, 60% water, but look at obese. Here's normal to obese, what happened to their water concentration as they gained fat?

In other words, this normally 150-pound person, when they go up to 180, what actually happened to the water concentration in their body? It went down, which is super significant, and I'll talk about it in the next slide too. But when you gain fat, that means you have to lose water. Do fat and water get along? No, not at all. Fat and water don't get along. The more fat you have in cells or the fat you have in your body, the less water you hold in your body, which means you're getting… I'll leave it to the next slide.

A big thing to remember is that really after about 20% fluid loss, it's life threatening. If you hit one third flu loss, so at roughly 33%, you better be really careful. These people that are having an IV their arm. Pediatrics and other things, so babies, when they're first born, they're about 75 to 80% water. A lot more water, and actually about 24 hours after postpartum or after they're born, they lose about 5% of that water.

The big thing to remember here is that the more susceptible to dehydration. When they start losing water, and a large amount of their body's dependent on this high concentration of water, so they get dehydrated a lot easier. You also think of other things like drugs, that might be an environment, foods that they might be eating, different types of things that may affect the hydration too.

Then geriatrics, so the elderly population. With the elderly population, their body fluids start decreasing too. As they start dropping, that means that they're more susceptible to the hydration also. They get more fat, like I said here, the more fat you have, the less water you have. They have less muscle mass and muscles have a lot of water inside of them. Their kidneys don't work the way they used to, so they can't maintain water properly like they did before. Also, the brain starts aging too. So the hypothalamus, the water detector is starting to decrease.

Like I said before, when you think of fat, and these are big areas of fat, pockets of fat. When you look at a cell, a fat cell and adipose cell itself, you can see all this fat, all the water substance have to be smashed to the side. The big influence here is that if you have more fat, you have less water, which means you're easily dehydrated, and you also don't move watery-loving substances through your bodies efficiently. Another trick is that fat loving substances can hide in these fat tissues.

There's a huge difference when you're looking at body composition of somebody that has more adipose tissue on them versus somebody that has more lean tissue like muscle mass. Those muscles like to hold water, but you have to remember that these people with more fat get dehydrated a lot easier because the fat displaces water.

How does substances move between those compartments? You've got the blood, which remembers intravascular fluid. You've got the cell, which is the intracellular fluid. Then you have the interstitial, the in between. When you have control over somebody's body water, the only place you have direct control over is the blood. You put something in the blood, it has moved up by diffusion to the interstitial, and then by diffusion or pumps into the intracellular fluid.

When you look at these body compartments, they move back and forth. If the blood's low in water, it will pull it from the interstitial. Then the interstitials will, it pulls it from the cell and vice versa. If the blood's high in water in the blood. It goes to the blood to the interstitial and then the interstitial's high. Now it goes into the cell. Things shift between compartments and the primary driver is actually diffusion, whether it's the fusion of particles or diffusion of water.

Two keys to remember. When things are shifting, they try to stay electrically neutral. When a positive moves across a membrane, a negative will go with it. Or when a positive moves across a membrane, a positive will go the opposite way to keep it neutral, and we'll talk about this more in detail later. The other thing is osmosis. Water likes to distribute so it's evenly distributed across the different compartments. It's trying to hit equilibrium.

How do things move? I already said diffusion. Diffusion, the key to remember is it's always passive, no energy required. The other thing about diffusion is it always moves down a concentration gradient. It will always go from high concentration to low. Things are crowded. They don't like being crowded so they space out.

It's like people, if you had a little room with 500 people in it, and they're like 10 people in the hallway, people naturally want to diffuse out of the room and get out of there. The point where there are 250 here and 250 here, so they're evenly distributed. The movement's not that much. As a couple people start moving into this area, a couple of other people will start moving back into the other area. That's diffusion, high to low until it hits equilibrium.

Some things can diffuse across the membrane, oxygen, CO2. They can slide right through. Other things diffuse through little tiny pores or holes, and other things have to diffuse based on transport. You might have a sugar particle out here, and it needs to get into the low concentration area, so it goes into the transporter, and it's like a little revolving door. It just kicks it in, no energy required. As soon as it sits in here, it just turns.

Then water, water slides for things called water pores or aquaporins. The other type of movement is called active transport, and active transport requires energy. Typically, when you see the active, you're going to see the word pump, like sodium potassium pump, hydrogen potassium pump, you'll see calcium pump. Lots of pumps going on, that means ATP is required.

Another process that requires energy is endo and exocytosis. Vesicular transport through the cell, moving that stuff out of the cell and ejecting it. Those are important processes you need to remember and how you can move things between membranes. For instance, a protein. A protein doesn't easily slide through a membrane, so it has to be eaten. It goes into the cell and then it can actually be exocytosed out the other side of the cell.

How we measure solutions, this section is really a basic terminology section, but how we measure solutions are in three ways. You had the osmolality, and the osmolality's talking about the number of particles per unit of weight of the solution. Typically when you see something like this, the 9% sodium chloride, this is actually an osmolality measurement. You might see as milligrams per 100 milliliters or milligrams per deciliter. It's the weight divided by the volume.

Another way that they measure it is osmolarity, and it's the number of particles per unit. The number of particles would be like, when it says, well, down here, 300 milliosmoles per kilogram, so it's number of particles per measurement. Another way we do it as milliequivalents, so milliequivalents, how many of these particles, how these particles actually bind to hydrogen, which is a little more complexity you need for this class.

If you go into pharmacology or chemistry, they'll talk about it more. When we measure, like we take a sample of plasma, we'll actually look at how many particles of sodium in a milliequivalents. We don't look at your blood as 0.9% sodium chloride, even though this is the same concentration of salt as the blood, we look at it in milliequivalents. We'll say you have 140 milliequivalents per liter of salt.

I put down here rules of thumbs you to remember. First, you want to remember that conversion of weight to water. When you're talking about a kilogram of water, how many liters of water is that? When I just set up here, I forgot what I already said, so I said something like 300 milliosmoles per kilogram. Well, it's the same as saying 300 milliosmoles per liter, so it's the same thing.

When you look at neutral saline solution, they have nine grams of sodium chloride dissolved in one liter of water and the measurement comes out to .9% weight per volume, which is a measurement of osmolarity. The .9%'s what you have to remember. An isotonic solution or a solution that's just like the body will have 0.9% salt or saline. 300 milliosmoles is the measurement for [inaudible 00:14:11] the blood. That's taking into consider, things like salt and potassium and chloride, and all these things. That's neutral or balanced. Then as we go into individual particles, we'll talk about those individually, like I just mentioned before, 140 milliequivalents for sodium.

All right, so why is it important? Because when you compare parts of the body, they use those measurements to compare. When you describe things in the body, very few things are a standard, and we just say it is because it is. It's like me asking, are you a tall person? Are you a short person? Are you old? Are you young? Is your nose too small? Is your nose large? Are you successful? Are you not?

We rate all those things by comparing it to others. Are you tall? No, I'm not tall, but yes, I'm tall for my family. Are you short? Well, yes, I'm short for the average person, but I'm tall for my family. We described comparatively. When you're talking about solutions in the body, we do exactly the same thing, we compare.

Here's three general rules. First, use the inside of the cell as the reference. If you're looking at red blood cells, the inside of the cell is the reference point. That's what you're measuring. If you're talking about a tissue, use the inside of the cell of that tissue as a reference point. Next, when we talk about the tonicity compared to the inside of the cell, we're referring to the solution around.

Typically, inside of the cell the tonicity is about 300 milliosmoles. It's actually 280 - 294, but we used 300 is an average range. If this inside is 300 milliosmoles and this outside is 300 milliosmoles, they are the same or iso. This solution out here is what we're trying to describe. We know what the cell is. We're describing a solution around it. Tonicity describes the extracellular fluid unless otherwise marked.

Isotonic means the cell is 300. The outside is 300 also. If you look at a solution that is hypertonic, hypertonic means more, tonicity refers to the solute. We're saying that this solution out here has more solute in it than inside the cell. If it has more solute when we're talking about osmosis, what's it have to have less of? It has less water.

If I take this 300, that was in here and I raised up to 600, what did I just do to the water concentration? I reduced it. That's telling me that the water here is low. The water in here is still, remember, the same, the 300 milliosmoles. We're talking about high water compared to out here. The water races out and shrivels up the cell. The cell will shrink. It can't carry out its metabolic reactions and it dies. It's like shrinking bacteria to kill it when you cure meat.

The second solution is hypotonic solution. In hypertonic solution, I have less tonicity out here, so less solute out here, which means I have more water out here. Water wants to go from high concentration to the low, and the cell expands until it pops.

You can try this with a raisin. I love cooking raisins in my oatmeal because raisins are shriveled up. There's very little water inside of a raisin, but when you put it in the oatmeal with high water concentration and heat, that heat speeds up the diffusion, the water goes racing in, it swells the raisin until it's gigantic. Then when you bite into it, it pops, so kind of interesting fun application to real world, I guess.

Always remember what happens to a cell when you put isotonic solution around it, hypertonic solution or hypo. The reason this is important is because if you put isotonic solution to somebody's blood vessels, that's going to do what to the cells? If it's the same concentration, the water is the same concentration as the cells, it should stay the same.

If I put a hypertonic solution, so I put a really, really salt intense, or dense with salt solution into somebody's body, what's going to happen to their cells? It's going to pull the water out of the cells. They shrink like a raisin. If I put a hypotonic solution in somebody's body, that hypotonic means there's lots of water in that solution. It's going to race in the cells and swell them up.

A good application for hypertonic is if you were stranded on a deserted island and you drank the saltwater surrounding it. That salt is extremely high, it's hypertonic compared to your blood. When you put that saltwater in your GI tract, what's going to happen to the water in your body? It's going to be attracted to that saltwater, and your GI tract is going to dehydrate you and shrivel your cells up, and then you'll end up dying because of it.

Think quickly here, we've talked about organs. We've talked about the cell level and we've talked about some terminology. First, let's say you just ate a big bag of pretzels or a big pile of these salty pretzels like this, which actually makes me kind of crave it. You didn't lose any water, but why are you so thirsty? Think about this as a tissue level. What type of solution would this situation cause the blood to become? All that salt is going into your blood, is it becoming iso, hypo or hypertonic solution around your cells in your blood?

It's raising the solute, which means it's become hypertonic. When it's hypertonic, what's going to happen to your cells?0. They're going to start shrinking. Your cells at a cellular level start shrinking. Think about it a little deeper. As your cells start shrinking, your body doesn't want that, because your cells could possibly die.

What organs would detect the increased salt concentration? Salt concentration, we're talking about concentrations here, not volumes. Your blood volume might be just right, but you have high salt in it. Your hypothalamus has those osmoreceptors that detect the chains and concentrations. Now what organ, I think I may have just said that, hypothalamus has the osmoreceptors.

The hypothalamus is going to make you do two things. The first thing it's going to do is it's going to make you feel like you're thirsty, and you're going to start drinking water. You bring water in, what are you trying to do to your blood? You're introducing water to it because you have a lot of solute. You're diluting it down until it's isotonic again.

What other chemical will the brain release or the hypothalamus release to help you keep water in your body? Would it be aldosterone or ADH? It would be ADH, and this is a key. You're trying to keep water. You release ADH because trying to keep water. Do you want to keep salt? No, you don't want to keep salt because you have too much salt in your body now. Will your body start releasing aldosterone? No, because aldosterone will make you retain more salt. Your body's going to stop releasing aldosterone and let you secrete it and get it out of your body.

ADH is released, but not aldosterone. Don't think of them always being released at the same time. In fact, the hypothalamus doesn't release aldosterone, the renin–angiotensin–aldosterone system does. In other words, how would the kidney respond to this? Number one is the kidney would start retaining water, keeping water, because ADH is telling it to. But the kidney will not release renin. If it doesn't release renin, you don't turn on the angiotensin-aldosterone system, which means that you don't start releasing aldosterone, which means you're going to get rid of sodium.

The kidneys respond by letting the sodium pass straight out into your urine, but the water starts being retained. What would happen to your urine? Would you be making lots of it? No, you wouldn't. You wouldn't be making very much urine. What would you know about the urine now? It's going to be very concentrated. They'll be a darker color, which is a sign that you're dehydrated, so just think of the pathways. Think of the cell, what's going to happen in the cell, what's going to happen to the tissue, what's going to happen to the organs.

Overall, the result is increase water in the body, increased volume, but a decreased salt concentration because you're trying to bring it back to isotonic. All right, the pathophysiology dehydration symptoms, definitely remember the keys to dehydration. What happened in hydration is that lots of causes can happen. You can be sweating crazy. You can have a fever, which causes you to sweat, which causes you to breathe heavy, to blow out lots of hot air. It's full of water.

Burns can do that. They suck water out of your skin. Hemorrhages, that's isotonic fluid loss. You're completely just bleeding the blood out, vomiting, diarrhea, all good examples. You can think of the different organs. When you're thinking about the organs, make sure you know how they contribute to the fluid. Do they add fluid to the body, or do they take it away? What happens if you turn either of those up? What happens if you add too much water, or you take too much away?

Anyway, you have these causes of fluid loss here. What's going to happen to your blood? Let's say you're losing pure water, not lots of solutes. What's going to happen to your blood? If you're losing pure water, the blood becomes hypertonic and dehydrates the cell. What if you're vomiting or hemorrhage, actually a good example, vomiting, hemorrhaging. You're losing electrolytes and losing water.

What happens to the tonicity change of the blood? If you're losing electrolytes and water, the blood stays isotonic but the problem is that you have less volume. Now, it works on pressure. The low pressure in your blood pulls water and electrolytes from the interstitial fluid, and the low pressure and interstitial fluid now pulls water from the cells. It's an isotonic change, but the problems, the outcomes, are just as bad. You don't have water. You don't have moisture in your cells. Your cells start drying out. They start shrinking.

You can look at this as not being one specific thing, and that's why I left it blank. If you have different situations, like if you're urinating a lot of really dilute, urine out, you're losing lots of water, but not lots of electrolytes, so you'd be becoming hypertonic. If you're bleeding, you're losing isotonic fluids. You can still get dehydrated, but it's isotonic fashion.

Sometimes it may be confusing, but I left these blank so that you can look at what is the primary cause and then work from there. It's like sweating. If you're sweating a lot, you're losing electrolytes, sodium, potassium, chloride, you're losing water. The blood's still isotonic, but you have very little fluid volume, which is your problem. Your organ cells will start shrinking just the same.

Mild dehydration is when you lost about 2% of your body weight of water, so about one to two liters, not talking blood because one to two liters of blood is significant. When we're talking about one, two liters of water, we're talking about evenly distributed water from the body. Your skin starts getting a little bit dry. It may get a little thick. If you start pulling up on your skin, like pinching it, pulling it upwards, it might stay in that shape, and it's a sign that you're getting dehydrated.

You might get really tired. You might start getting headaches. You're not getting good, adequate flow and water to the brain in other words. Then constipation, why would you get constipation? It's because the GI tract is trying to compensate and is trying to pull more water in, which makes your feces more dense.

Severe dehydration is when it's over 5%, so about three to five liters of water is lost from your body. At this point, you're going to stop sweating. You might be hot, but you're not going to be sweating because why would you not want to sweat when you're dehydrated? Because you'd lose more water. The body's trying to compensate, but now you have another problem. Your body's getting too hot.

This low skin turgor is talking about pulling your skin up. It should snap back normal shape. If it stays up, then that means you're dehydrated. Then if you keep pushing this over 20%, it's possibly fatal. When it's over 30%, you're dangerously low and you need an IV in your arm.

Then, like I said, this is dense, bulk information, but don't give up your thinking. When you have a situation, you have to run through your mind all the possibilities, eliminate the ones that don't work and keep the ones that do work. Look at the problem, what organ's not working appropriately?

Then here's the question for this set. Question number three, so what situation could have caused dehydration due to the integument? In other words, tell me what the integument system could do that makes you lose a lot of water that causes dehydration? What could be happening in the kidneys that would make you lose a lot of water and become dehydrated? What's something that could be happening in the circulatory system that's making you lose lots of water that makes you be dehydrated? What's something that could be happening in the nervous system, maybe hormones or behavior you're doing, that would make you lose water? What would be happening in the GI tract that makes you lose water?

I'm hoping these all are making sense to you, and then for your own use, you might want to go back and say, well, what could be happening here that causes over hydration? Or how do you get the water? Hit the pause here. This is the last of this video, and I'll see you on the next video.