hi i want to talk to you a little bit more about ph in the body and how this relates to buffer systems first it's important to recognize something very important and that is the ph is not the same throughout your entire body and you you can probably already guess this when we talk about stomach acid we can assume that has an acidic ph but you can probably guess that your blood is not acidic so ph differs or varies throughout the body let's write that and you've also learned in the previous video that buffers are used to keep ph relatively constant buffers do not keep ph neutral so i often hear people use the term that buffers neutralize ph i think of neutral as being the true definition and that is that neutral ph is 7.0 there is almost nowhere in your entire body that is exactly ph 7.0 and that ph differs throughout your body i want to tell you a story about the digestive system to illustrate this example one thing you really need to realize is that in the human body and in all biological systems ph must remain relatively constant in order for proteins to function correctly and the reason for this is proteins have a very specific three-dimensional shape and if the three-dimensional shape of that protein changes the function of that protein changes okay so proteins have a very specific three-dimensional shape change in shape is going to cause change in function in fact change in shape usually means it doesn't function at all what are some things that can change the shape of a protein we're going to learn a lot about protein shape and the importance of protein shape this semester one thing that can change protein shape is just having the wrong recipe for how to make that protein to start with and we'll learn about that when we learn about the dna because that dna influences that the other thing that can change the shape of a protein is a process called denaturation also pronounced denaturation sometimes when a protein becomes denatured it means that the shape has changed it's sometimes even shown as kind of an unraveling of the of the shape of that protein some things that can cause that shape to change are changes in ph changes in temperature changes in salinity which is the level of salts changes in ph are what we're talking about here the reason you need ph to stay relatively constant in your body is because changes in ph can cause your proteins to not function correctly okay so let's just draw an illustration of a pretend protein shape so this is a protein every protein is a chain of amino acids and it's going to have a very specific way that it folds into this three-dimensional shape okay so this is a protein and that's its three-dimensional shape a change in ph is going to change the shape of that protein and it's probably not going to function correctly anymore once that shape changes that's why we need to keep ph relatively constant we need to keep it normal whatever normal is for that area of the body so the ph of your stomach is obviously very different from the ph of your mouth so the goal of buffers is to keep ph normal whatever normal is for that area of the body and that changes throughout the body so the ph of your mouth is dramatically different than the ph of your stomach than the ph of your small intestine i want to just quickly show you a diagram sorry i'm going to go into my photos really fast and this is a diagram of the digestive system and you can look up these values they differ depending on what website you look at they're a little bit different site to site but this is you know roughly what the ph is it differs person to person but the key point here is that the ph differs so if you look at the ph in the saliva it's dramatically different from that of the stomach especially the lower stomach you can see ph 1.5 to 4 in the lower stomach and then again it goes back up in the duodenum which is that first part of the small intestine and then in the lower small intestine it differs in the large intestine so when you eat your food you chew it in your mouth and it mixes with the saliva that's going to be a different ph than what the food achieves when it hits your stomach what does this have to do with this class and what you need to know i'm not going to talk in detail about the function of the digestive system but i want you to realize ph varies throughout the body buffers need to keep ph constant whatever is normal for that area of the body i want to talk a little bit about enzymes though in the small intestine so you eat your food you chew it you swallow it it goes to the stomach and then you can see that according to this that the food remains in the stomach for about one to three hours it can remain in there for up to around four hours why is this why is it that the stomach doesn't just re release all of that food directly into the small intestine there's a very important reason for that and it has to do with ph in fact ph is going to regulate food moving from the stomach to the small intestine let's go back to the notes and just talk a little bit about the function of the small intestine in digestion okay so this first part of your small intestine the duodenum is the first part of the small intestine there are several um pronunciations also you can call it duodenum i don't know everybody has a preference for how they pronounce that but this is where your chemical digestion takes place what this means is you're going to take the big food molecules and break them down into smaller food molecules so they can be absorbed in the lower part of the small intestine so the first part of your small intestine is for the chemical digestion to take place the rest of the small intestine all that that loopy increased surface area folding folding folding and then folding within the folds that is all for absorption into the bloodstream of everything you digested in that first part of the small intestine how does chemical digestion take place it takes place with enzymes enzymes are a category of proteins so that means those enzymes have a specific three-dimensional shape and that means that those enzymes only function at a certain ph a certain temperature a certain salinity in fact it's a very narrow range of ph temperature and salinity at which these enzymes will function correctly so these enzymes function in a narrow range of ph i'm just listing ph because that's what we're talking about today if the ph changes significantly those enzymes become denatured and they don't function correctly so drastic change in ph enzymes change shape and we call that denaturation denaturation enzymes don't function correctly chemical digestion does not take place well here's the problem the problem is you eat the food okay you chew it in the mouth so it's going to be mixing with your saliva so this is you know going to be about ph let's just say 6.8 just 7.4 it's going to go down your esophagus and it's going to mix with the acid in your stomach so the stomach is pretty low ph let's just say ph one to two again you can you can look up these values i don't want you to necessarily memorize the values i just want you to realize how significantly the ph changes even just within one system of your body really acidic food one of the rules of that acid is to kill pathogens in your food this is actually part of your barrier defenses in your immune system so one of the things that really protects us from pathogens is the stomach acid that kills these pathogens it also helps start protein digestion nevertheless that food mixes with acid in the stomach but really to break down that food into the smaller molecules that need to get absorbed into the bloodstream it needs to go to the small intestine and remember that first part is called the duodenum so this is the first part of the small intestine and this has a much higher ph let's say ph 7.4 to 7.8 so we have this really acidic food now getting dumped into the duodenum this is where the digestive enzymes come in where do these enzymes come from i'm going to actually write digestive enzymes these digestive enzymes are coming from the pancreas into the duodenum if we just dumped all of that acidic food straight into the small intestine you could not digest your food it would completely denature all of those enzymes instead what's going to happen is the food is going to get slowly pulsed into the duodenum a little bit at a time the amount of food that enters is 100 based on ph so here's what's going to happen okay small amount a food moves from the stomach into the small intestine which i'm going to now abbreviate as i so we don't have to write out small intestine throughout this entire story and the way that food is going to move in is due to opening i have some circular muscles that control food moving in and out it's called a sphincter and this particular one is called the pyloric sphincter opening and closing of that is 100 regulated by ph so you have ph sensors that are going to allow just a certain amount to come in so the foods coming from the stomach is going into the duodenum when that opens up and allows it to come through and then it immediately closes when the ph gets too low here okay so ph is high acidic food comes in the ph is going to temporarily drop and when it drops it's going to close that off it won't open again until the ph comes back up to normal then it will open and let it a little bit more through but now we have this acidic food in there how do we get the ph back up the way we get the ph back up is before these digestive enzymes can come in we need to send in a buffer okay otherwise what would happen is as soon as that acidic food hits the small intestine it would denature all of the digestive enzymes and it would just move through and you'd never you would never make use of that food you would never break it down you would basically just get rid of it as a waste product so as soon as that food moves in a buffer is pumped in to the si from the pancreas and that buffer is oops this is misspelled come on and that buffer is bicarbonate ions recall the carbonic acid buffer system remember the general equation remember reversible arrows these are the bicarbonate ions what happens is if you pump in a bunch of bicarbonate ions it's going to tie up all of this hydrogen and shift the whole thing this way so increasing the ph remember if we tie up all these free hydrogen ions then they're not free in the solution to make it more acidic so the way to bring up the ph is to pump in a bunch of bicarbonate ions tie up all the free acid and that food that just got pumped from the stomach and bring that ph back up so a little bit of food comes in closes off doesn't let more in we're gonna pump in some buffer okay so the ph increases okay now digestive enzymes are going to be pumped in from the pancreas to the small intestine you don't want those enzymes coming in until we get the ph back up the way we do that is with a buffer so buffers are a very important part of your digestive process without buffers coming in first you would not be able to break down your food because those digestive enzymes would become denatured so now once those digestive enzymes come through start working on that little bit of food that food's going to start moving down okay now a little bit more food can be brought in pyloric sphincter opens when the ph gets back up to a certain level let's a little bit more food in closes off when the ph gets too low in the small intestine more buffer is going to come in more digestive enzymes than come in and that just keeps going until all the food has left your stomach so anywhere from one to four hours on average for that to happen depending on the size of your meal again if all of that food just came straight from the stomach to the small intestine all of your digestive enzymes would become denatured due to that change in ph you would not be able to chemically digest and absorb your food i hope that helps and you should know this story in case there is an essay question slash short answer question on the exam this is an excellent example of two things one is that the ph differs throughout the body two buffers serve to keep ph relatively constant changes in ph can denature proteins and cause them to not work correctly and in the case of the digestive system changes in ph can denature the enzymes and not allow you to digest your food