hello and welcome to the last digestion video we are going to take a look at chemical digestion and the enzymes and the substrates that they act on and and will be done with digestion all right so here's what I need you to know so first of all carbohydrates come in three different versions they come in they're single monomers so um if you go back to chemical or I mean uh um amp1 in cell chemistry hopefully you learned that the single units of carbohydrates are monosaccharides so glucose is the important one that we need to know disaccharides are when you put two monosaccharides together so sucrose and maltose so the things that need to be digested will be the disaccharides and then the polysaccharides they're going to be starches and cellulose and those ones need to be especially the starches absolutely have to be broken down into whoops it okay there could go into their individual glucose molecules for absorption or absorption all right so um and then the disaccharides will be broken down into their individual monosaccharides but glucose starch cellulose those are the ones that we really want to talk about or that we want to remember and where do we digest carbohydrates oral cavity and small intestine okay we're going to use it are we going to use celery amylase in your mouth to start breaking the bonds between the glucose molecules within a starch it is inactivated by the low pH of the stomach so as soon as you swallow that always shut off that digestion and since um you only hold your food in your mouth for a short period of time they're um you're only digesting a very small portion of the carbohydrates that you consume and most of our diets are carbohydrate-based not many of us eat more fats in proteins than carbs unless you're specifically on a ketogenic diet or something like that a specific low carb diet okay so we have no new carb enzymes from the stomach and then we have to start up that carbohydrate breakdown when we get to small intestine so we're going to secrete pancreatic amylase from the pancreas it's part of our pancreatic juice I'm just going to finish digesting um no you're not going to finish digesting the starch we are going to um do a lot of the digestion so um the starch molecules into individual glucoses but there's still one more enzyme or a type of enzyme that needs to be used and so we'll look at those in just a sec all right so pancreatic amylase is going to keep breaking down the starches so here shows what pancreatic amylase is going to do so pancreatic amylase produced by the pancreas secret in the small intestine Here Comes those partially digested starches and then our disaccharides of lactose and sucrose so pancreatic amylase continuous digestion starch began in the oral cavity of salivary amylase now we get down to disaccharides so this is a small for the most part as pancreatic amylase it can pop off individual glucose molecules but I'm still going to have some of these disaccharides and pancreatic amylase will not work on a disaccharide then we need to use brush border enzymes so in the wall so in the Villi in the microvilli and the mucosa of the small intestine there will be the enzymes and so the enzymes we're going to have you may be familiar with that one lactase because that's what people who are lactose intolerant are missing I do not express the lactase enzyme we do early on in our life but then it shuts down and really it's supposed to shut down it's supposed to be um done by the time we get weaned when we're two years old about and we don't rely on on breast milk anymore but that's when our our lactase should stop being expressed but um so people who are lactose intolerant really are what the way it's supposed to be the rest of us who are not who can still eat dairy products and ice cream and butter and all that kind of stuff um we are the mutants and I say we because I am not lactose intolerant and so we can still digest that as if we were infants so um okay so lactase maltase and sucrase will be the brush border enzymes that we will find along the microvilli the villain and microvilli of the um of the small intestine duodenum okay and so it says brush border enzymes are responsible for the digestion of disaccharides so this next slide shows some dextrinase glucoemylase maltase and then the next slide will also this is using a couple to get down to individual glucose molecules here's just one so if I take lactose and the presence of lactase we'll break down glucose to galactose and sucrose sucrase glucose and fructose um only brush border enzymes are required to digest lactose and sucrose we don't need the amylase because they're sugars they're not starches um so there's that okay um so then we're going to absorb the monosaccharides we're going to absorb the glucose we're going to take it to the liver and then fructose and galactose which are other monosaccharides are going to be converted to glucose because that's what we use in the um cellular respiration right in that's our substrate that we use is glucose now glucose will be taken up for energy of course by our cells um by the liver it's going to be converted to glycogen and it can also be converted to Fat we only store so much glycogen and then that extra carbohydrates yep gets turned into fat and then we store that we'll put triglyceride is what it's going to get turned into and then we store it in our adipose stored in adipose tissue all right now what about cellulose we do not have the enzymes to break down cellulose we can chew it up but it'll just be like a mulch you know and then um what that does is add the bulk to our digestive system and and that's what stimulates the mass movements that go through the colon if you have a low fiber diet you do not your colon doesn't want to contract very much and so you need to have a high fiber diet to move that stuff out of there and reduce your risk of colorectal cancer all right celiac disease okay so this is an autoimmune disease um is triggered by uh Pro gluten the protein in wheat Ryan barley stimulates a mutant and this is the thing so my son is gluten intolerant but he doesn't he he doesn't um his immune system has not attacked his digestive tract and so it stimulates in a room response immune response that damages the Villi so you know your Villi go like this okay so that's what the inside of the small intestine of a non-celiac person looks like this is what the inside of a Celiac person so this is nons this is normal non-celiac this is celiac we it just strips those microvilli or those Villi and so now can you absorb no so you get abdominal pain diarrhea and here's this is the big thing I'm not getting nutrients out of my food because it can't absorb it so I have to have something that's gonna um not trigger my autoimmunity all right proteins so proteins are made of amino acids they're going to be linked together by peptide bonds and then when we digest it then we want to just reduce it back to our individual amino acids so um okay broken down my enzymes targeting that peptide bond that's fine now protein enzymes have to be released as inactive and inactive enzymes that will be activated so like I said before prevents the enzymes from breaking down proteins in cells that produce the enzyme so pepsin in the stomach must be uh secreted as pepsinogen and then the proteases in the small intestine no from the pancreas sorry they go into the small intestine okay all right so we are not going to do protein breakdown in the mouth because the pH is too high so we need a low ph that will convert pepsinogen it's inactive precursor into active pepsin okay so when hydrochloric acid released from the parietal cells changes pepsinogen into pepsin and then it also so here's what a protein looks like it's hard for an enzyme to get to those peptide bonds like that so instead we denature the protein I should have made a little squiggly there we go and so we're going to have individual amino acids hooked together and so pepsin is going to come in here and break those bonds and actually it's just going to like break it here and here and here and here so you're breaking it into polypeptides into chunks then we get when we leave the stomach and we go into the small intestine so now we've got to neutralize that acid because the enzymes trypsinogen chymotrypsinogen and pro-carbox peptidase those will be deactivated in a in a acidic environment so we have to um uh uh we have to neutralize the chyme so that's when the bicarbonate from the from the pancreas comes in to neutralize it now trypsinogen trypsinogen is going to be released first and it's inactive form and our small intestine is going to make an enzyme called enteropeptidase and what that's going to do is oh it's right there activates trypsinogen to trypsin okay so once you turn on trypsin then trypsin is going to turn on these two guys it's going to turn on chymotrypsin leave that in and then cut the pro off so whenever you see Pro in front of an enzyme or in front of a word or you see ogin on the end that sits inactive form and we have to convert it to its active form so trypsin is gonna it's gonna be positive feedback so once you start to make the trips and then you're going to make more from the chemical or from the trypsinogen and then we activate chymotrypsin and then we activate the carboxypeptidase okay and so um these are going to break bonds between specific amino acids so you get those polypeptide chains then carboxypeptidase doesn't care what he's going to do is just cut make a cut at the carboxyl in so on amino acid every uh oh that doesn't have a charge yet every amino acid has this on the end and so it's going to break the bond here to whatever else is Downstream from here so we're just going to cut here and then we're going to cut here and here and here all the way down so we're going to pop off individual amino acids with carboxypeptidase except trypsin and chymotrypsin are going to cut it into chunks then we're going to finally break it down when when we um my so when the trypsin and chymotrypsin have cut it down into when there's just two amino acids together then we're going to use this dipeptidase called Amino peptidase which is a brush border enzyme so this is going to be in the wall of the small intestine in the most microvilli and then it will pop off those last amino acids so split these two bonds into individual amino acids or free amino acids then we're just going to absorb them we're just going to go through our little Transporters and and and make what we're going to make so either going to make new proteins or we can take those proteins and convert them to glucose in our liver if we are eating a low carb low carb high protein diet because you're probably wondering well where's the glucose coming from for cellular respiration if I'm not eating carbs it's from the proteins that you're eating um your liver will convert it to glucose we call that glucose we already talked about this in the um endocrine system we're going to talk about cortisol and um glucagon gluconeogenesis so that's making new glucose from proteins and fatty acids all right so here's trypsinogen chymotrypsinogen procarbox peptidase so anaeropeptidase is going to be secreted by this epithelial cell and it's going to come out and then we get trypsin and then trypsin will will make more of itself and then chymotrypsin carbox peptidase so now we're cutting it down into pep dipeptides and amino peptides oh well in peptides and then in our brush border we're going to have dipeptides and aminopeptidase that are going to break them down so um here's where the carboxypeptidase works can you see it's where the carboxyl group is and aminopeptidase cuts things between the amine group and the central carbon of an amino acid so that's how that works um no not the central carbon the cart between the amino acid so it's amino acid on one side the amine group and then the carboxyl group on the other all right IQ care I care but it's okay I just need you to know um these come out of the pancreas so these three guys come out of the pancreas inactive enteropeptidase kicks in trypsin and trypsin turns on everybody else and then they may they cut down peptides and amino acids and then we've finished the job with the dipeptidases like Amino peptidase that's in the brush border okay we're almost done so lipids not water soluble highly variable yeah they come in different forms so the two forms that we need to be aware of are triglycerides so this is our fats that we eat so if we're eating anything that's fat plant fat animal fat um we're gonna have a glycerol and Three fatty acids that need to be broken apart so we have enzymes that are going to break the bonds between the glycerol and the Three fatty acids this is what it looks like so glycerol is a three carbon molecule and then I'm going to have a fatty acid chain so I'm going to have carbons to do forever okay and so each one of these and there'll be Bonds in between I just didn't draw them in okay so each one of these is a fatty acid so what we're going to do with lipase is break this bond in here so we're going to break that um spawn so that we can absorb those okay cholesterol does not need to be broken down for absorption we're just going to absorb it in its whole cholesterol State all right so how are we going to break it down well we make two enzymes one in our mouth and one in our stomach called lingual lipase in our mouth and gastric glyphase in our stomach um so saliva and then Chief cells now they only break down about 30 percent of the triglycerides that we eat and so what that diglyceride would look like is here's our glycerol so there would still be carbon here and a carbon here I mean a fatty acid here and then there'd be this fatty acid by itself and that's what that does so it's not that important I usually don't even worry about the fact that there is some lipase in your mouth and some lipase in your stomach this is what do we worry about so how do we break down lipids in our small intestine we're going to use pancreatic lipase so that's going to be produced by the pancreas and released into the duodenum and it's going to break down glycerides into a monoglyceride and two fatty acids so here is what a monoglyceride looks like so it's going to be a glycerolin one fatty acid and then I'm going to have a fatty acid here and a fatty acid here all right now what has to happen first is that we need to emulsify our fat so if we have a little cruet of oh I think that was pretty good almost fairly uniform anyway so I have Italian dressing here are my seasonings down here at the bottom here's my water here's my oil right oil sits on top of there this is my H2O my vinegar vinegar and my seasonings down there okay so what do you have to do to get this all interspersed you have to Shake It Up so segmentation is going to shake it up then I want the oil to not separate out and so I never want the oil so you know once you're done shaking it oh that's a stupid looking one um here's going to be your water and you know how you have all those little fat droplets in there now once you shook up the Italian dressing okay that's we want them to stay this means that they have been mixed up and we want to emulsify them which means we are going to keep them suspended within the water so in order for us to digest our food we do segmentation to stir it all up and now we're going to emulsify those fat droplets so here's what happens with the emulsification so we're going to use um no well that's a bummer because I thought I had a picture of how that works all right so let me just show you how that works so I'm going to have a fat droplet now I'm gonna have a fat globule so this is a fat globule so I'm going to shake it all up break it into little pieces into individual little fat droplets then in my bile I'm going to have an amphipathic molecule which means it's polar on one side and nonpolar on the other just like in our cell membrane those are amphipathic molecules called bile salt so on the bile salt there's going to be some nonpolar non-polar which will attract to the lipid so I'm going to put lipid lipid lipid these are all fat droplets then on the other side of the molecule that's polar that will form water molecules we'll stick around it and so now you've got these um bile salts here that are then surrounding this water droplet no this fat droplet and then making sure that it stays separate from everybody else because as soon as it hooks up with another lipid then it's going to just stick all together in the film on top of the water so the non-polar Tails line up around the fat droplet with the heads towards the aqueous fluid we're not going to worry about micelles okay um and then what's that going to do now is that lipase pancreatic lipase can come in and break up so it allows greater access of the pancreatic lipase to break up the triglyceride and that's it and then this part right here salts recovered by active transport in the night in the last portion of the ilium that's that 95 percent of our bile salts we reabsorb and we only lose five okay so um that's it we are not going to do um the exact process because we have to it's a little complicated to get those lipids through the epithelial cells so we're not going to worry about micelles so this right here my cells and we're not going to worry about chylomicrons either all we're going to do is say that when lipids are absorbed they enter the lacteals which are the lymphatic capillaries of the intestine and then they enter the blood and deliver liberal lipids to the liver and other tissues and that's all that we're going to say so if we look at this picture here's all our fats we want to break it up into bile salts I mean not break it up break it up into little droplets and so we're going to stick bile salts all around on the outside here to keep that little droplet suspended and then the triglyceride in the presence of pancreatic amylase is going to get broken down into the monoglyceride and the two free fatty acids and then we'll absorb it into the lacteal we're not going to worry about chylomicrons and in my cells and then triglyceride molecules um uh absorbed into lactals and that's all you need to know we're not going to worry about nucleic acid digestion and that because we don't use that as food so just to pass or just to finish this off so water absorption so the small intestine absorbs almost all ingested water so eight out of nine liters is absorbed by our small intestine I like to do the 6500 did 6500 and 1700 but whatever the large intestine absorbs some the rest is passed in feces so it's between 1 and 300 MLS that we get in our year not in our urine hope we get more than that in our feces we get more than that we have diarrhea less than that constipation and it's just absorbed across the epithelium and into the blood vessels via osmosis okay electrolytes we have um uh uh some Transporters for you know sodium and potassium and and such for our electrolytes so small intestine absorbs almost all electrolytes absorption is unregulated depends on how many you eat okay so it's dependent on your diet iron though has controlled absorption we're not going to worry about hepsiden um at all so worry about that okay and then vitamin absorption the fat soluble vitamins have to be absorbed with the lipids okay so they're going to be absorbed into the lacteals into lacteals so a d e and K are fat soluble vitamins but the vitamins B and C they absorb through diffusion and active transport because they are water soluble so they're going to go into the capillaries into the blood capillaries um B12 vitamin B12 is large so we need some endocytosis going on in order to have that happen remember this this is really the only thing that your stomach does that you absolutely can't replace or have somebody else down the line do it so making that intrinsic factor from the parietal cells in the stomach will allow vitamin B12 to be absorbed and without it you will be vitamin B12 deficient we'll have to give you infusions of vitamin B12 into your bloodstream into an IV and not um oral you will not be able to take any oral vitamin B12 and that Brands is the end of the digestive system and thanks for making it through this journey with me and we'll pick you up on the urinary system in the next module