whenever we eat foods that are high in protein such as this uh delicious deer sausage I'm eating right now our body has to take those proteins and break them down or digest them into their amino acids we can then take those amino acids and absorb those into the villis of our small intestine and therefore into our bloodstream then they'll travel to the liver or our liver can reassemble those amino acids into all the different proteins that our body needs in order to function so in this video we're going to take a look at that whole process from digesting the proteins into their individual amino acids and small peptides all the way to absorbing those into the anas sites of the Villi of the small intestine and therefore into the bloodstream so let's uh jump to the Whiteboard and get started get me some more of that before we go so let's start by taking a look at an intestinal villis these are going to be little folds in the small intestine and they're made of a couple different things we got inas sites all of these inas sites also have something called micro Villi on the surface this is going to increase the surface area of these absorptive cells and that increased surface area will help to absorb more as well as digest or break down molecules more we also have goblet cells the goblet cells are going to be creating a mucus layer now since we're absorbing these molecules into the bloodstream we're going to need some arteries and veins that are running through the villis of the small intestine so artery In Vein and then of course a capillary the capillaries are where we're actually going to absorb these nutrients into the bloodstream for circulation now that's true for the amino acids from proteins as well as the monosaccharides from the sugars that we eat for the fatty acids from the fats that we eat that's going to have happen in a Lac teal or a lymph vessel and there'll be one of these lact teals going up into each of the Villi of the small intestine now I've got one Villa strong here of course we have many Villi in the small intestine and so you see a second one that got drawn in the diagram here so here we have the anas sites that we zoomed in on we're going to have a capillary that's running nearby so we can see where these molecules are going to go and we're taking a look at protein digestion and absorption so let's talk about what proteins are actually going to get broken down the first and most obvious is going to be the dietary proteins these are going to be proteins that we eat such as in the sausage that I ate in the intro of the video but the dietary proteins that we eat actually don't account for the majority of the proteins that we're breaking down in this process we also have proteins that are called endogenous proteins and endogenous proteins are going to be proteins that are already in the body that we need to kind of recycle we need to break them back down so we can build them into new proteins and use them again we don't want to waste all of these proteins and amino acids and stuff that we have in the body those endogenous proteins come from a few different sources one we have have all these digestive enzymes in our small intestine and digestive enzymes are actually proteins so when we break these other proteins down it's actually proteins breaking down other proteins we also have some of these ocytes or cells that are lining the small intestine they're going to die over time as all cells do and they get sort of softed off into the lining in the small intestine and we'll break those down and we got to recycle all of those proteins and there's just other plasma proteins that kind of live in the small intestine that we're going to be breaking down as well so we've got all these proteins that we need to digest or break down so let's talk about the structure of a protein in general now proteins of course are going to be chains of amino acids they're going to be connected by these bonds these are peptide bonds between each amino acid and if you notice in the diagram I've got them as different colors because not all amino acids are the same we've got lots of types of amino acids now all amino acids have the same general structure they're going to have an alpha carbon this main carbon kind of in the center here they're going to have an amine group that has a nitrogen and some hydrogens and it's going to have a carbox o ilc acid group with another carbon a couple oxygens as well and then there's going to be a side chain or an R Group which could be a lot of different things and this determines the identity of the amino acid so different types of amino acids have different R chains that are attached to that Alpha carbon but they all have this structure and they're all going to be connected to each other through peptide bonds which is where the carboxilate acid group of one amino acid is going to be bonded to the amine group of another amino acid creating that peptide bond now in this diagram I have what 10 amino acids bonded together in reality proteins have maybe thousands and thousands of amino acids bonded together so proteins are these huge complex molecules but I'm not going to draw that many amino acids on my diagram it's going to get a little out of hand if I do so what I'm going to do is I'm going to put a dotted line and another amino acid here and that just means that this continues on for however big that protein is and these giant proteins remember they're going to fold into all these really interesting and unique shapes that are going to allow them to do whatever their function is such as being an enzyme or being a transport protein or a pump or whatever they do all right so let's start breaking this protein down we've got a couple different enzymes we're going to do the first one I want to talk about is pepsin and pepsin is going to be found in the stomach it actually starts as an enzyme called pepsinogen that gen part just means it's an inactive form that can become an active form so pepsinogen will be converted into pepsin and that conversion from pepsinogen into pepsin is done by acid and so our stomach of course produces a lot of acid and that acid is going to convert the pep cinogen in the stomach into pepsin and so this is all taking place in the stomach we eat the food it travels down the esophagus comes into the stomach and that's where protein digestion is going to start to occur so I have acid converting pepsinogen into pepsin and it's going to start to break some of those peptide bonds in the amino acids so they get broken down kind of like you've got a big Lego structure and you're taking off piece by piece of that Lego structure the individual Lego bricks would be the amino acids and the whole structure would be like the protein in that metaphor so that's taking place in the stomach from the stomach the food will then move into the small intestine there's going to be pancreatic proteases in the small intestine or the duodenum of the small intestine that are going to further break down the proteins that we've eaten so this food is going to pass from the stomach into the small intestine you can see where the connection is going to be right there and that duodenum of the small intestine is connected to the pancreas the pancreas has cells that are going to produce all these pancreatic proteases the pancreas actually produces enzymes for carbohydrates as well as lipids to break them down further but you can see on here this pancreatic duct and the enzymes made by the pancreas are going to travel down the pancreatic duct into the duodenum of the small intestine where they're going to further break down those proteins into their constituent amino acids all right so pepsin in the stomach as well as pancreatic proteases released by the pancreas into the duodenum those are breaking down the proteins and so those will have broken the proteins down into their constituent amino acids here but that's not going to break it down into only amino acid there's still going to be some amino acids stuck together in what we call small peptides and we're talking like two maybe three amino acids still bonded together through a peptide bond so we kind of at two products at this point individual amino acids as well as small peptides here the individual amino acids they're ready to be absorbed into the anas sites and get them into the capillaries and therefore onto the liver but the small peptides they've got a couple more steps to go through before we get into that let me add a little bit more green of my mucus layer just to distinguish what's happening where everything in the white up here is taking place before we get to like the mucus layer of the small intestine everything below this is going to be taking place in the brush border basically like on or right up against those microvilli so the small peptides will be broken down by what's called Amino peptidases the amino there just means it's breaking it down from the Amin side remember how the amino acids have a carboxilic acid end or an amine end so these Amino peptidases are going to be breaking down or cleaving the peptide bonds starting with the amine end will work to break these small peptides into their individual amino acids but not every one of those are going to get broken down so we'll still have some left over small peptides and at this point we've got amino acids and small peptides ready to be absorbed into the ocytes so some of the small peptides have been broken down further into amino acids by the aminopeptidases and then we got some that have avoided getting broken down altogether they're still as small peptides we're going to absorb the amino acids as well as the smaller peptides into the anas sites but the small peptides once they get in there there'll be more enzymes is ready to break them down there's going to be the intracellular or in the cell peptidases now here's where the fun begins the absorption part now the mechanism here is a little bit complicated but I'm going to break it down step by step first thing we got to do is we're going to have to get this through the luminal or appical membrane we've got to get the amino acids small peptides through this luminal or appical membrane and then we'll have to get them through what we call the basil membrane and I'm going to separate this into the amino acids part as well as the small peptides part now in both of these they're going to use active transport but they're not going to use primary active transport the amino acids will use secondary and the small peptides will use tertiary active transport they'll all start with the same stage though the primary active transport part of this is going to be a sodium potassium pump that's going to be on the Bas of membrane of the ocytes and I've got one drawn right here but these are going to be sort of just lining this basal membrane we have lots of these and they're going to be pumping sodium out and potassium in they're going to use ATP to do that which is why this is active transport it has to use energy so we'll consume the ATP and in the process of consuming the ATP we pump a sodium out and a potassium in technically we're pumping three sodiums out and two potassiums in every time we use one ATP what this does is create a concentration gradient of sodium we pumped so much sodium out of the cell they we have very little sodium inside the anas sites we have lots of sodium outside the anas sites in the Lumen of the small intestine and molecules tend to flow from a high concentration toward a low concentration and that gets rid of the concent ation gradient but we can use that gradient to power the secondary and tertiary aspects of this process so we have a concentration gradient of sodium very lad of sodium inside lots of sodium outside and that's going to allow us to do this next stage this is going to be a sorter meaning that it's moving two molecules in the same direction it's going to use the sodium concentration gradient to bring sodium in and every time it bring sodium in it's going to bring amino acids in so we see that here the sodium travels in and that's going to pump in an amino acid no ATP is involved in that particular step the ATP the energy was consumed in the first step the sodium potassium pump creating the sodium concentration gradient now as the sodium flows from its high to low concentration that concentration gradient is going to be used to pump in amino acids and so we'll go ahead and keep doing that each time we bring in amino acid we're going to be sending more sodiums in but I just didn't animate that in this uh drawing here so that's how we get amino acids into the anas site through secondary active transport primary active transport is using the sodium pottassium pump to create the sodium gradient and then secondary is going to be using that sodium gradient in order to pump in the amino acids the other thing we got to do is bring in the small peptides and like I said we're going to use tertiary active transport so let's add in a couple proteins here and remember these pumps the sodium pottassium pump the sorter for amino acids and sodium as well as these new ones I'm drawing in these are all proteins themselves proteins are the pumps and enzymes in our body so this is going to be a co-transporter for hydrogen ions and small peptides and we've got another one we need to add which is going to be an antiporter antiporter meaning that they're transporting things in opposite directions the sodium potassium pump was another antiporter this antio is going to bring sodium in and pump hydrogen out so let's talk about this three-step process here the sodium potassium pump is pumping sodium out so we have a concentration gradient for sodium lots of sodium outside very little sodium inside the next step is going to be to use the sodium and hydrogen antiporter it's going to use the concentration gradient for sodium to power it and that's going to be pumping hydrogen out of the cell so sodium travels in and that pumps hydrogen out of the cell so then at this point we've got a concentration gradient for hydrogen we've pumped out lots of hydrogen so we have hydrogen outside very little hydrogen inside right here and we can then use that hydrogen concentration gradient to pump in the small peptides so the hydrogen will come in going from a high concentration to a low concentration and that's going to pump in these small peptides so hydrogen coming in small peptide coming in and we'll do that with more hydrogen to bring in our other peptides so we've got all these small peptides pumped in through this tertiary active transport mechanism again pump sodium out then use the concentration gradient to pump hydrogen out then use the hydrogen concentration gradient in order to pump the small peptides into the cell now we'll use those intracellular peptidases to break these small peptides down into their amino acids so we're going to break those down using the intracellular peptidases now at this point we've broken kind of everything down into amino acids we've had multiple rounds of these peptidases to break down the proteins and the small peptides down in the amino acids there will be a small a small small percentage of these small peptides left over that still never got broken down and we can actually bring those into the capillary as well but that's a very very small percentage most of this has been broken down into amino acids now we got to get the amino acids from the osy through the basil membrane into the capillary and we'll do that through passive transport through facilitated diffusion these amino acids aren't going to pass just directly through the membrane they're going to pass through a protein Channel I've got three drawn in right here and so those amino acids are going to pass through those protein channels to get out of the ocytes and then from there they'll passively transport between the gaps in the cells of the capillaries to get into that capillary and therefore into the vein which is going to connect with some other veins and go up through the hepatic portal vein into the liver the liver then is going to take these amino acids and reassemble them into the different proteins that our body needs so that'll be the next place that they go and then from there they can enter into our blood circulation and get where they need to go the amino acids as well as the monosaccharides from the sugars that we eat the carbs that we eat those are all going to end up to the liver right after this process the lipids that we eat will work a little bit different they'll go into a lacal or a lymph vessel and so they'll actually bypass the liver in their initial go through through the circulatory system so they work a little bit different but that's the general overview of the process of breaking down or digesting proteins into small peptides in am acids and then getting those amino acids and small peptides into the osy and then bringing those amino acids into our capillaries that's a lot of information let's do a recap of this whole process and then at the end of the video you'll have a chance to pause it and practice this yourself so we've got dietary proteins and endogenous proteins dietary proteins are the ones that we eat endogenous proteins are the ones that are already in our body already in our small intestine pepsin from the stomach and pancreatic proteases which are secreted by the pancreas and then are going to in the duodenum or dadum of the small intestine those are both going to be breaking these proteins down one into their small peptides as well as into individual amino acids now the small peptides then are going to be broken down into amino acids by aminopeptidases those are going to be found on the surface of the microvilli of our anas sites as well as some just in the brush border and the mucus and then some of those small peptides will avoid um just by happen stance will'll avoid the aminopeptidases and the pepsin and all those they won't get broken down and we're going to bring those into the anas sites as well now we're going to use active transport to bring amino acids and small peptides into the anas sites that's going to use secondary or tertiary active transport for the amino acids we use secondary active transport where it's going to start with the sodium potassium pump it's going to consume ATP in order to pump sodium out potassium in that's going to create a concentration gradient for sodium meaning there's very little sodium inside of the cell lots of sodium outside of the cell now and then our amino acid and sodium sorter is going to use that sodium concentration gradient to bring sodium in and therefore an amino acid in the sodium is powering that pump and each time a sodium comes in that's bringing an amino acid into the cell so let's bring all the rest of those amino acids in here so we've used that sodium concentration gradient to power the secondary active transport pump right here and again that secondary one's not using ATP we use ATP in the first step and then the second step we don't need ATP again now for the small peptides we're going to use tertiary active transport the first step is going to be that sodium pottassium pump again using ATP to pump sodium out we now have a sodium concentration gradient the sodium is going to flow down the gradient from high to low concentration and that's going to cause the hydrogen to be pumped out as that happens we're creating a hydrogen concentration gradient we have lots of hydrogen outside very little hydrogen inside that hydrogen ion concentration gradient is then going to power this sorter here where we're bringing hydrogen into the cell and small peptides into the cell the hydrogen is powering this pump and bringing in those small peptides there's going to be more peptidases inside the cell we call them intracellular peptidases and those are going to break down those small peptides into their amino acids now we have a lot of amino acids inside of the cell we've got to get those out so those are going to pass through protein channels through facilitated diffusion and then finally there's going to go into the capillary well then they'll travel through veins into the liver where they can be processed and like I said it's a somewhat complex process if you're trying to learn this stuff really well for a test that sort of thing I highly recommend that you take a moment pause the video see if you can talk all the way through this whole process and explain it yourself then you know that you know it pretty well here's the first diagram I also have a second diagram with less detail on it to make sure that you know it really well no labels or anything on here pause the video see if you can do it using this less um labeled diagram before we go special thanks to these awesome patrons from my patreon through their support I'm really able to make better videos I can spend more time doing this I can upgrade my equipment that sort of thing my patrons also get access to all the diagrams and their full resolution as well as some other resources but really honestly most of the people on this list are supporting it because they uh believe in free online educational content and want to support the channel so huge thanks to this group of people if you want to know more about this stuff I have other digestive system videos including a carbohydrate digestion video I'm working on a lipid digestion video so check those out down here in one of these Corners I always get mixed up on that there's a link to a playlist um where you can access the rest of those videos so yeah thanks for watching good luck learning anatomy and physiology and I'll uh see you in the next video bye