chapter one General General physiology will focus on the first section from the big picture physiology medical course in Step One review second edition textbook and the first section of chapter one is about homeostasis and this is how the body systems uh work to regulate the conditions within within the organism the human body homeostasis the term basically means the maintaining of a stable internal environment which is going to require multiple organ systems reacting to some change and they react in a way to restore the natural condition or the normal range whatever it's set for in whatever condition you're talking about one way that is accomplished is by something called negative feedback loops or negative feedback control the negative feedback control is a way that a body can react to a change so in most conditions what you have to understand is that all the conditions how they in the body have a very narrow range there's a table at the very bottom that we can look at and go over but you want to just at least glance and see what the normal ranges are for some of the conditions in the human body we'll give examples as I go through so a negative feedback control system has a few uh specific points to it and all of these work together in conjunction with each other to return the body to its normal range for whatever reason um it has been bumped out of that normal range so in the first example that I'll give you we'll talk about blood glucose levels and in this condition this helps you to have a good idea of how something is restored by turning something off or opposing the stimulus going against the stimulus so we'll give you example it'll help you the first thing to know is that there is always a set point value or a normal range so for this example we'll just use the fact that um blood glucose levels will go with 90 milligrams per 100 mils that is the standard blood glucose level we have these things in the body called sensors they will monitor that blood glucose level and then we have a comparator and effectors which will carry out a response when the levels go up or down depending on what scenario occurs so we'll start with our first example here and with this one we'll have us eating sugar cookies and when you eat the sugar cookies that is the stimulus the digestion process will increase the blood the glucose level in your bloodstream and then we have sensors or these things called receptors that will recognize there is an increase in the blood sugar the comparator is going to be our beta cells they are found in the pancreas and they will produce insulin which then will allow the effectors which are our body cells or liver cells um to take up that glucose and as the cells take up the glucose we can lower our blood glucose levels and by lowering them we have opposed the stimulus we've gone against the stimulus done the opposite of what the stimulus was and again the stimulus was an increase in our blood glucose levels so that is where we get this negative feedback loop there are other things called positive feedback loops as well but in this scenario I'm giving you a negative feedback loop so we get back to the normal conditions and stays there for a period of time until there's another scenario in some cases if you don't eat for a long period of time we will get the stimulus to be the opposite of this it'll be a lower blood glucose level because you haven't eaten for 12 hours or 15 hours or 20 hours our receptors will recognize that that the blood glucose level is uh lowered and it needs to be restored because it's going below this 90 milligrams per 100 mils and then the pancreas cells will then respond by producing glucagon and that will obviously go impact the liver cells if you've learned about this and it'll restore it by increasing blood glucose levels by breaking down glycogen in our storage in our liver storage so that's another example it can go both ways and there's examples for all of them I will leave this one here for you because this is going to be very important as we move through each of the courses medphys one through three you will have to be able to understand these negative feedback loops and how the body restores itself to balance when things are out of the normal range so with this one this is using the control of blood pressure as an example you want to walk yourself through this one and see if you can map out how you can restore your blood pressure when it increases or you can go ahead and do when it decreases again you should start with a set point and go from there the next part of this chapter just goes over the internal environment and this is going to go over our body fluids and the importance of body fluids within um the within the human body there is an Optimum fluid level for inside of our cells as well as outside of our cells so we have two very specific areas here we have intracellular fluid and then we have extracellular fluid when it says intracellular fluids that's the fluid that's found inside all of our cells that would make up the cytoplasm the extracellular fluid is going to be any of the fluid that's found outside the cells and then also the fluid found in our blood stream which makes up our blood plasma so we have two different components to this extracellular fluid and it's called interstitial fluid and blood plasma I have an image coming up in a second that I'll show you this internal environment in the body is very important for bathing ourselves and keeping a fluid balance which also helps to keep anything dissolved in that fluid any electrolytes or proteins that happen to be dissolved in any of those fluids in a correct balance so they're sort of pushing against each other equally and they're not diffusing into one area of the body extracellular fluid or intracellular fluid in too much of in too much of an imbalance so we want to work on that and make sure we understand the diffusion in osmosis that occurs between all these things and what's dissolved in are fluids so down here at the bottom the volume of a total body water is about 60 percent in men and then 50 in women so there will always be a slight difference you do have to keep that in mind when you're looking at the male and female bodies sixty percent of the total body water is found as intracellular fluid and the 40 other 40 is going to be our extracellular fluid again I'll have an image in a second but we also have to consider is that 80 percent of the extracellular fluid is going to be the interstitial fluid 20 is going to be in the blood plasma we also have to take into consideration the other things that are found dissolved such as sodium chloride salt potassium are also dissolved that help to make up the osmolarity of our blood and as are in our fluids interstitial fluid is similar in composition to plasma accept the fact that interstitial fluid will not have any proteins that'll be the one difference with that so as we go down here I want to show you the example that I have in the images that I have for you and then I will go over this highlighted area here for you in a second to give you a little example that you can look over um with this one this is a picture this is from your book and I decided to draw something a little different here for you just because it gives you a little bit better idea than that picture so what we'll look at the specifics can be found in the picture that's fine I have it drawn right next door with all these pictures for you so right here in the blue area that I'm outlining in Black that's one cell that one cell has obviously all of the organelles inside that a cell would have and then there's cytoplasm in there out here this green box here is going to be what we call the interstitial fluid that's going to be the fluid that's between cells and between the cells and the capillary which is what this is supposed to be right here and that is supposed to be a blood vessel and inside that is the blood plasma so we've got fluid in a couple different areas here and this is what we're working with when we're talking about fluid moving from one place to another so think about conditions of being over hydrated or under hydrated those can be very serious conditions because this water balance between these three specific areas will change and in some cases it can be an extensive change which is not good so furthering with our notes from that chapter it talked about the fact that there's this intracellular fluid and if we look at the diagram that will be these areas right here it talks about intracellular fluid and the whole entire body being about 25 liters we then have this bracket here that talks about what extracellular fluid is extracellular fluid will consist of the interstitial fluid that's between the cells in the green box here and in the blood plasma which is in the capillaries that also surround all all of the cells in this given area you can see it gives a number of about 16 liters between all of those where do we get the 16 liters in blood plasma and blood the plasma makes up about three liters give or take depending male female female Etc and then interstitial fluid is all the fluid in between is about 13 liters so that's where you get that 16 liters from so that's just again a broad overview of the liquid that's found the fluid that's found in all these different areas but then we have to take into account before we can talk about blood and or liquid moving from one place to another or diffusing one place to another we have to take a look about all those things that are dissolved in the extracellular fluid so in this case we have right here this I'm outlining it purple here and it's going to differ a little bit between each but all these different areas have um sodium potassium chloride and they may or may not have protein but all of the things dissolved again in a state of balance or homeostasis they should have a given amount of those ions dissolved or proteins dissolved in the fluid and it gives us something called osmolarity with all of that so if we look at them and you can take a look at the sodium and how it's either similar or different how the potassium is close similar in again the extracellular fluid the numbers are going to be similar but they're not going to be similar with the intracellular fluid just because that's what keeps everything in balance and diffusing and and the osmosis going from one place to another with the blood plasma and interstitial fluid the osmolarity is very similar we got that number of 285 so that is in our extracellular fluid that we keep in mind that we have this number this total number of 285 and in the intracellular fluid which is in the cytoplasm they also have 285. but they're equal so that water can keep moving um you know a dynamic equilibrium water is going to keep moving as long as everything is the same so as long as what's dissolved in the liquid keeps the concentration of these liquids the same things just move you know happily back and forth but what happens when you start losing a lot of water when you start losing a lot of water especially from your extracellular fluid if you start losing a lot of fluid that means the sodium the potassium the chloride those become more concentrated because there's less liquid so that's going to impact the fluid movement from intracellular to potentially the extracellular or vice versa from extracellular all the way to intracellular depending on what's happening with the the loss of liquid so when you go back to the notes Here it states that in order for um when a patient is hemorrhaging they need to lose about five liters of extracellular fluid before the blood plasma volume decreases by one liter and that again that's a lot of loss um and again if a continual loss is going to create a very severe situation for the patient but what you have to understand in order for someone to lose a liter of blood plasma they do have to lose five liters of extracellular fluid so if you go back to the image for that just so you can see that is saying right here that you have to lose about five liters of this fluid for the blood plasma to drop by one liter so you have to lose a great deal of liquid in the interstitial fluid in order for that to happen but once that does happen you have to understand the body has to compensate for that and that's where we're going to have to make sure we either restore it through intravenous fluids or the person is going to have a severe event where do these numbers come from where does the 5 liters and then losing one liter of blood plasma come in it comes in because of these numbers the osmolarity and because of the amount of liters of liquid in each area there's basically a five to one relationship between these numbers so where there's a five to one relationship that just means that 13 liters is to 285 as 25 liters is 28 285 as 3 liters is to 285. they're all related this number and the 2 85 that creates a relationship which makes we have a homeostasis event or a balanced event happening but when you start losing things will change so it's always like a five to one relationship so five layers of liquid in the interstitial area will result in a one liter drop in blood plasma and then to restore this if you read the second part of the notes how do you Rectify this situation you need to replace that one liter of plasma and then that will again allow us to restore that five liters of lost extracellular fluid that has occurred so that is where an isotonic saline would be infused which would help to restore that balance so that's where this picture goes over it just gives you an example of that and then the section stops before we get to week two