Body fluids and electrolytes

by: Dr Matt & Dr Mike's Medical YouTube

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[2.27]
so let's very quickly talk about body fluids now if you have a look at an average male of about 70 kilograms and how to look at the water inside their body the fluid inside their body it would constitute about 65% of their body mass okay now this percentage is body fluid per centage depends upon certain physiological characteristics for example females tend to have less body fluid percentage and individuals who are carrying far more fat on their body have less as well now this is because if you compare fat and muscle fat carries a lot less water compared to muscle so that's the reason why now if you look at infants you'll find that they have a higher body flood percentage and if you look at the elderly they have a lot so it's very important to understand body fluid differences between individuals and what's supposed to be a normal body fluid percentage now of this fluid so basically water with some solutes mixed thing of this fluid where is it actually sitting and that's what we're going to focus this particular video on so there's two major compartments that body fluids sit within now these compartments are called the intracellular compartment and the extra cellular compartment but first let me show you where they're partitioned so first we follow the dorsum cells up so one cell to cell 3 cells for example and the most to draw blood vessel here what you'll find is that you have fluid that sits within the cell fluid that sits outside in between the cells and fluid that sits within the blood vessels so there's three different places for fluid to sit now the floor that sits within cells is called intracellular fluid makes sense ICF so let's write that down ICF is intra silly well fluid and fluid that sits outside the cell is called extracellular fluid so that means the fluid between the cells and fluid within the blood vessel and ECF is extracellular fluid


[147.85]
now that means that extracellular fluid is broken into two sub compartments so what you find is first of all the fluid between the cells is called interstitial fluid okay so fluid between the cells is called interstitial fluid so let's label that so fluid sitting between the cells is called interstitial fluid and fluid that sits within a blood vessel is called blood plasma


[196.15]
so you can break this up into interstitial fluid and blood plasma now why is this important it's important because extracellular fluid meaning fluid within the interstitial between cells and the blood plasma they talk to each other but how does this work well you know that when it comes to blood vessels that a large artery will break into a smaller arteriole which are then branch into a capillary bed and at the capillary bed you'll find little holes so capillaries are porous and these pores let this fluid and some solutes come in and out so that means there's some holes here in this blood vessel and that allows for certain fluids and solutes that come out and also to come back in okay so that means that whatever fluid is in the ECF meaning in the interstitial is going to be easily exchangeable with the fluid in the blood plasma okay now again why is this important well because whatever concentration of stuff or solutes is sitting here between the cells is going to be the same concentration of solids in your blood plasma exceptions include red blood cells white blood cells and some proteins okay these are too large usually to go out or in to these blood vessels okay but what does get exchanged here well very importantly the substances or solutes that gets exchanged between the interstitial and the blood plasma include all the different ions of the body okay so what I want to do is list or label the important islands of the extracellular fluid and then label the important ions of the intracellular forward okay so either the extracellular food well they include sodium calcium chloride and bicarbonate so these are some of the major extracellular cations positive charged ions and anions negative charged ions so what are the most common or most abundant intracellular cations and anions well just get rid of that well the most abundant intracellular cation is potassium okay there's also magnesium for the anions there's a phosphate and there's negatively charged proteins okay so what you can see is two most abundant extracellular cations meaning the two most abundant positively charged ions that sit outside the cell is sodium and calcium the two most abundant intracellular cations is potassium magnesium the two most abundant extracellular anions chloride bicarbonate and the two most abundant intracellular anions is phosphate and proteins now remember that this partition is important because they're not easily exchangeable why because all cells are surrounded by a phospholipid bilayer that means a fatty layer this fatty layer remember does not like charged substances ions by definition are charged which means they get repelled so the potassium inside cannot just diffuse out it bounces off the walls and remains inside the sodium it's outside cannot just diffuse it in a bounce off the walls and stay outside they need certain channels to let them throw so that means that the concentration of sodium outside will not be reflected by the concentration of sodium inside and the concentration of potassium inside will not be reflected by the concentration outside however because the blood plasma or the blood vessel does allow for exchange between the interstitial and the blood plasma that means that whatever concentration of sodium is in the interstitial that will be the concentration of sodium in the blood vessel so for example the fold to just extend this blood vessel out the concentration of sodium outside the cell is going to be the same concentration of sodium in the blood vessel the concentration of calcium outside the cells can be the same concentration calcium in the blood vessel and same with chloride and bicarbonate the clinical significance of this is when you test a patient's blood serum for electrolytes for example you take it from their blood okay so you draw it out of here and what is it measuring while it's gonna tell you sodium concentration of calcium chloride and bicarbonate and so forth and potassium and you may think but potassium is in the cell well yes but there is some potassium outside and it's going to be a reflection when you take this blood and measure it's going to be a reflection of what's happening between the cells as well whatever the concentration is here is the concentration here now again this is important because even though these ions are not exchangeable so I'm going to now wipe this off and redraw it so


[548.12]
let's just focus on sodium and potassium so even though this sodium cannot get inside the cell and this potassium cannot go outside the cell what can actually be transferred between the two is water okay now remember if diffusion cannot occur osmosis will if there's a concentration gradient either side okay so think about it if a patient had altered electrolytes okay now firstly it's important for you to be aware that overall remember I said you get sodium you've got calcium you've got my carbonate and you've got flora and I said inside the cell you've got all the potassium magnesium phosphate and negatively charged proteins well did you know that the concentration of all these solids inside the cell should match the concentration of the science outside the cell and the concentration is dropping stuff 290 you need to remember this number 290 merely osmoles now that just means basically the concentration of solutes in one liter of fluid that's what that means and it's 219 millions miles that's outside the cell and that's inside the cell as well now let me very quickly tell you how we got to this calculation you will not need to know this for the exam but how do we get to 290 well one of the calculations we can use is this you can do so you can calculate the osmolarity osmolarity by taking two times the concentration sodium plus 2 times the concentration of potassium plus the glucose concentration plus the urea concentration this will give you 290 in a normal individual milliosmoles so for example 2 times so what should be the normal concentration of sodium in the blood around about 135 millimoles per liter what should be the concentration of potassium in the blood well about 5 millimoles per liter what should be the concentration of glucose in the blood and about 5 millimoles per liter what about urea well that's also run about five million moles per liter well what happens when you add this up 2 times 135 is 207 plus 2 times 5 is 10 plus 5 plus 5 what do we get 270 plus ten is 280 plus another 10 290 million smiles so that means so when could this change well if I increase the amount of sodium if I increase the amount of potassium or glucose or urea remember these are just substances or solutes dissolved in the fluid so we can change this concentration right here by changing the concentration of these Salyers okay now in the next video i'm going to talk about what happens in the body when this concentration changes so for example i'm going to prep the next video by telling you let's just say that you haven't drunk water for about 12 hours what do you think happens if you don't drink water for 12 hours that means that your body uses water up right it's going to excrete it in your urine and fecal matter while you breathe and so forth and it's going to use it to make energy okay which means the fluid in your body particularly the fluid in your extra cellular fluid drops but what about the song is well an actual factory of solids all remaining around about the same it's just that the water level drops so if you were to I was thinking about as though it's in a bucket and here we've got all the solids inside of this water and this is normal so you're not thirsty you're hydrated this is how you want to be perfect let's just say you start to become dehydrated and you're not drinking any water while the floor drops are the solutes stay the same so what happens the fluid level drops but now you've got the same amount of solid is what happens to the concentration of that fluid well firstly it's not very good but the concentration goes up so that means 290 million bottles may move its way up to 320 miles for example now look at that if you have 320 million moles concentration outside the cell compared to 290 inside so there's a concentration difference and you know that when there's a concentration difference things want to balance themselves out and you think that sodium will want to diffuse in and calcium one diffusing and they do that they can't because of the plasma membrane so what happens water will try and balance it out and just remember water will go wherever there's a higher concentration of solutes where's the higher concentration of solutes outside the cell so that means water from inside the cell moves out what do you think that means to the cell it shrinks remember I told you my semester but when it self shrinks is called the crow nation okay now I'm gonna tell you in the next video



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