Digestive System 9, Digestive enzymes full detailed lecture

so having considered mechanical digestion in the previous video we're now going to go on and think about chemical enzyme based digestion and there's three main types of enzymes found in the gastrointestinal tract protease is lipases and amylases so these are the three main classifications of enzymes and this isn't surprising really because protease is so the gada is on the end means enzyme A's and A's and then the first part of the word usually describes the substrate that the enzyme works on so coati protease you can see that's going to ease or be an enzyme for protein lip fat lip lip is to do with fat so lipase they will digest fats and amylase is amylase is related to carbohydrates so these are the carbohydrate digesting enzymes so most of the enzymes that would come across the vast majority of digestion is done by enzymes in these three categories so any enzyme that breaks down proteins as a protease any enzyme that breaks down fats or lipids is a lipase and any enzyme that breaks down carbohydrates is a amylase so now we want to go on and think about the components of the gastrointestinal tract and the enzymes that are present there and we're going to start off by thinking about the saliva glands and the saliva glands are going to produce saliva now there's three main pairs of saliva glands two parotid glands two submandibular glands and two sublingual saliva glands so if you think about a face to have your drawings better than mine there we have our person in in profile now the paratus library glands ever put the the sort of side of the head here around it going up to the bottom of the year so this is the area here of the parotid salivary glands and then coming around here underneath the tongue so of course the tongue is in the mouth terms in there and lingual means to do with the tongue so the sublingual saliva glands are going to be under the tongue so the sublingual are going to be there sublingual glands there in red in this case and then the submandibular saliva read lungs as the name would suggest under the mandible not more lateral this sort of position here and of course there's two of these two of these and two of these so parotid sublingual and submandibular saliva glands one gland on each side there in tears now what a lot of people don't appreciate is that in the mouth in the oil of submucosa the several hundred other smaller saliva glands as well but the most of the saliva is produced in these three pairs of saliva glands and of course you might have heard of a condition that's common in childhood called infective parotitis you might have heard that that is called mumps or infective parotitis and certainly i remember as a child being very ill that very swollen parotid slide redlines recorded mumps because it's a virus it's a viral infection and it causes swelling of the parotid glands usually it's worse on one side but it can involve both parotid glands and the patients very generally unwell what we used to call general malaise I felt ill for days with this and fever as well and one of the things about mumps is it is very contagious it's spread by respiro tree droplet infection I've got a relatively long incubation period but the thing about mumps is the reason it's a problem is it can have complications there can be sequelae so it can lead to meningitis pancreatitis inflammation of the heart deafness testicular information which can result in problems with fertility it can affect the ovaries as well so be grateful that we're living in the phase of the the measles mumps rubella and the mumps vaccines and we see much less of this condition now but most of the time these glands are happily producing saliva are going into the mouth via their ducts the juice and saliva as we noted on a previous video under the influence of their parasympathetic nervous system now in terms of the function of saliva well the saliva is doing is the saliva amylase is the main digestive enzyme in saliva and what will that that will do is will convert starch which is a polysaccharide starch is the most common form of carbohydrate in our diet so potatoes bread pasta rice or very high in starch and it will break those down into a mostly it breaks them down into the disaccharide maltose so it starts that digestion of starch and molto's another small sugar units maltose is actually a two sugar unit is also breaks it down into some three sugar units and when the saliva is swallowed with the food bolus this can actually carry on working for about an hour in the fundus of the stomach until eventually is neutralized by gastric acid because this likes a relatively alkaline environment and of course the medium in the stomach is acid and the acidity in the stomach will come to neutralize the saliva amylase and you can kind of do a test for this yourself so if you get a bit of bread put it in your mouth that contains starch of course and if you sort of chew it up a bit and swill it around your mouth if you don't swallow it then the saliva amylase is going to progressively break the starch down into maltose now the starch doesn't taste sweet whereas the molto's does taste somewhat sweet so it can start to taste sweet as you leave in your mouth for longer as the saliva amylase is working now so that's the main enzyme and saliva the saliva amylase but there is another enzyme and saliva and that's called lingual lipase lingual lipase and lingual again means tongue so this is from the lingual glans in the tongue and this actually doesn't work in the mouth but it's swallowed in the food bolus and the lingual lipase is actually activated by the acidic environment in the stomach because we know this idea the enzymes only work in a particular pH environment and the lingual lipase likes it acidic so once it's swallowed it's activated and there'll be some activation of the lingual lipase once it gets into the stomach and the action there is that triglycerides which I by far the most common fat in the diet are broken down into fatty acids and also into diglycerides so this is starting off this process of fat digestion and a diglyceride it is a glycerol molecule attached to two fatty acids so it's only cleaved off one of the fatty acids from the triglycerides which contain three fatty acids - a diglyceride which contains - but it's starting off this process but the majority of fatty digestion is carried out in the pancreas as well see later on in this video but this does start the process although it's not one of the major digestive enzymes that life depends on so there's our diagram of the digestive system that we now know and love so the foods going to be swallowed into the esophagus and it's going to enter into the stomach of course the stomachs the next part of the gastrointestinal tract so we go into the stomach and the digestive enzymes there are going to be produced by the gastric glands the gastric glands and the gastric glands are located in the gastric pits so what we have in the mucosa of the stomach is there are these gastric so that's the top of the mucosa there then there's like a pit there in the in the gastric mucosa and this pit opens out into two or three year gastric glands so that's the gastric pit within the gastric mucosa and these are gastric glands and of course all of this wall here is lined by cells as you would expect with glands that's got to be secrete of yourselves so there's numerous secreted cells in the walls of the gastric glands down here and also in the neck of the gastric pits up here now there's a lot of mucous secreting cells and they are they are the top of the pit appear to secrete mucus because we need a lot of mucus in the lining the gastrointestinal tract so these dream ones are our mucous secreting cells this is remarkably important because the pits themselves and the gastric lining needs to be subsidy essential that it's lined with mucus I've drawn it green but in practice it's actually a fairly clear because lining the stomach we have about one to three millimeters of alkaline mucous lining the surface mucosal cells of the stomach so there'd be further mucosal cells yeah and these are needs to be protected from the gastric juices so this will be the lumen of the stomach here that these cells need to be protected from because in the gastric glands we have another type of cell in the gastric glands and these are parietal cells and the parietal cells produce hydrochloric acid which goes up well the esters produce hydrogen ion and chloride ions but that they soon combine to form the HCL of hydrochloric acid so the gastric environment contains a lot of this very strong acid hydrochloric acid produced by these parietal cells and this is good because any unfortunate bacteria that are swallowed a fairly rapidly dealt with by this very acidic environment in the lumen of the stomach and as well as that in the gastric glands is another type of cell the cell type in the gastric glands and the product of these cells is a pepsinogen and these cells have drawn in blue are called the chief cells the chief cells and they produce pepsinogen and again this goes up into the gastric into the gastric lumen and the pepsinogen and the gastric lumen is converted to pepsin which is a protein digesting enzyme so what we see is we have hydrochloric acid and protein digesting enzymes now what are these cells made of that comprise the gastric mucosa well the fatty acids of course phospholipids are membranes but they're also made of protein so we don't want them getting digested by the protein digesting enzyme the pepsin we do not want them being eroded by this very strong hydrochloric acid so they need to be protected by this layer of mucus absolutely vital they need to be protected from this juice the gastric juice is sometimes called peptic juice but if there's a problem in the mucosa so there's a hole in the mucosa and can you see that means that these hydrate the hydrochloric acid in the pepsin can get down into the soft tissues and of course they will start digesting it and you'll get a hole or an ulcer caused by peptic juice and a hole or an ulcer caused by peptic juices a peptic ulcer and these can occur in the stomach they can occur in the duodenum and you can actually get regurgitation into the lower part of the esophagus for example in a condition like a hiatus hernia see so this particularly can be a problem if bacteria get into the under the mucous bacteria called Helicobacter pylori which can lead to this inflammation causing what is essentially a self digestive process there are actually some other cells in in the gastric pits not going to do those just now but the other main group of cells in the gastric pits are called G cells and they produce an endocrine gland called gastrin but these gastric juices coming out from the gastric pits from the gastric glands it can amount to 2 to 3 liters per day of gastric juices to facilitate the digestive processes in the stomach so let's think about what's happening now so these gastric glands as we've mentioned the chief cells in the gastric glands are producing pepsinogen and that's going to go into the gastric pits and out into the lumen of the stomach now we don't want an active protein digesting enzymes which pepsin is to be formed in the gland itself because the pepsin would immediately start digesting the protein of the gland that had just produced it so that would be terrible so we don't want so the gastric glands do not produce pepsin they produce pepsinogen which is a pro enzyme now just before we go on we notice that pepsin doesn't end in A's but it is an enzyme and the reason for this is this was discovered before it was internationally agreed that all enzymes would end in a's so it is an enzyme it's just a bit of an old-fashioned name so what actually happens once we get into the lumen of the stomach is the pepsinogen is converted into pepsin so inactive pepsinogen is converted into active pepsin and this conversion process takes place under the influence of hydrochloric acid so the hydrochloric acid which is in the lumen of the stomach will convert the pepsinogen into pepsin and also any pepsin that's in the lumen of the stomach already will also convert pepsinogen into pepsin so it's activated once it's in the lumen of the stomach preventing water digestion and pepsin is a protein digesting enzyme ass of protease and it severs several types of peptide bonds and that means it breaks down proteins into peptide fragments so the proteins are broken down by the pepsin into peptide fragments because as you probably know there's about 20 amino acids in human proteins in human tissues and we need we need these amino acids from plants and animals that we use so that's one type of the Meanor I said that's another type that's another type just have to be imaginative on your shape so yeah that's another type and it may be an upside down on there that's another type that's another type so there's these different amino acids and these are held together by peptide bonds so the amino acids are held together by peptide bonds to form these long chains of peptides the polypeptides and these fold into proteins so what these are proteases do the proteolytic digesting enzymes are going to break these peptide bonds and pepsin will break several of these breaking these down into smaller changes sometimes described as an anti row peptide ace it acts on the bonds inside the inside the long chain of amino acid polypeptide units so it's starting this digestion over protein and it's doing so in the presence of hydrochloric acid so the pH in the stomach is going to be roundabout to which we've mentioned is good because that means it's a very hostile environment for bacteria which we don't want to be infecting the gastrointestinal tract if they do we could get food poisoning with vomiting and diarrhea and things like that now there's actually another enzyme produced in the stomach called gastric lipase and what this will do is it will break down short chain triglycerides so I'm sacked him on short chain triglycerides and is breaking those down into fatty acids and monoglycerides and the monoglyceride has remained as a glyceride unit whether one fatty acid attached to it so we went from diglycerides to monoglycerides and we'll see that that really the vast majority of this fat digestion is taking place in the duodenum under the influence of pancreatic lipase but this just does a it makes a small contribution to the process so here we have our diagon of the stomach from the physiology notes book we noticed the esophagus the cardiac sphincter the fundus the body the pylorus this area of the stomach and the duodenum and the pyloric sphincter because sometimes in children the pyloric sphincter can be too tight and we get pyloric stenosis gnosis stenosis means narrowing off and that means that the fruit can't get through into the duodenum and that can cause the stomach to contract vigorously lead into projectile projectile vomit and we refer these to our surgical colleagues are able to fix this usually food go down to the duodenum and from the physiology notes book this is a picture of the gastric pits is just a it's not sort of diagram really where we notice the air the gastric pits these will be the gastric glands down here producing the hydrochloric acid producing the pepsinogen which is converted to pepsin and of course all this will be protected by a layer of mucus protecting the top of the gastric mucosa here's a blow-up diagram of a gastric fitting again from the physiology nose book and it just reviews already sketched out that we've got the that parietal cells producing the hydrochloric acid the G cells which we haven't gone into in detail producing the endocrine columnar gastrin and the chief cells producing a pepsinogen or going into the lumen of the stomach where is the peptic juice so next we're going to go from the stomach down into the first part of the small intestine which of course is the duodenum and that takes us into the territory of the pancreas and the pancreatic juices so pancreatic juice is the juice produced by the pancreas and I think it's probably useful here just drop a little bit of a background anatomy before we look at the the details here so the duodenum is going to start here just after the pyloric sphincter and the duodenum actually curve around this way like this and he goes up and carries on his way to where joins on to the judging them so this would be the duodenum here first part of the small intestine now the pancreas is actually located in in this loop of the duodenum so the pancreas is actually kind of located here like this Pangos is this garnish shape and we know the pancreas is an organ with a head a body and a tail but the head is kind of nestled into this loop within the duodenum now the main pancreatic duct here and this is going to collect pancreatic secretions from the exocrine tissue in the pancreas and that's going to come down here and there's actually a duct goes into the duodenum about here like this and the main one carries on like this down there it was the main duct to that now this duct here there's a superior duct is called the accessory duct and that's taking a pancreatic juices into this more proximal part of the duodenum but the main one is going through here going into about 10 centimeters into the jury dhinam so it is still the first half of the duodenum really where the bulk of the pancreatic juices are going to be delivered into and throughout the pancreas tissue this clusters of EXO crying tissue clusters of EXO crying tissue occupying about 99% of the bulk of the pancreas and these are called ER asani the Athenee these clusters of EXO crying tissue and the cells in the the asagna called asana cells so the pancreatic juices are actually produced by these asana cells going in and down the pancreatic duct here but of course just above here we have another very significant organ just here here we have the liver this is where the liver is and tucked underneath the liver just here we have the gallbladder just there with its cystic duct and above that we have the common hepatic duct and leaf right and the left hepatic duct took Tim PR on the gallbladder and then the common bile common bile duct is going to go down here so the bile is going to be produced in the liver goes down the common hepatic duct stored and concentrated in the gallbladder then when required is going to go down the common bile duct and the common bile duct actually goes through the tissues of the pancreas and he joins up with the main pancreatic duct so this last part of the duct is common between the pancreatic duct and the common bile duct and this area where it's common is called the hip a toe pancreatic ampulla he Paco he Pato pancreatic ampulla in the old days was called the ampulla of Virata so here we just have bile here we just have pancreatic juices but here we have both before being released into the lumen of the duodenum now what is the other 1% of the pancreatic tissue made of we've said it's 99% the the a semi these clusters of EXO cry and tissue or the other 1% distributed about a million of them distributed all over the pancreas are the well known and loved pancreatic islets of langerhans and these of course produce the the alpha cells in the pancreatic islet of Lion produce glucagon the beta cells produce the insulin but today we're thinking about the exo Kriner asila products of the pancreas so let's think about what these products are these products are in the pancreatic in the pancreatic juice so these are going to be in the pancreatic juice and again quite large volumes of pancreatic juice are produced about 1200 to 1500 mils of pancreatic juice are produced every day and we didn't comment when we thought about mechanical digestion that these volumes are important because they give the fluid medium and the pancreatic juice will mix in the lumen with the intestinal juice the suckers enteric us to give us this watery environment but the pancreatic juice itself it contains water of course the enzymes which were going to look at in a minute and also contains a sodium bicarbonate and this is important because this gives us the alkaline medium the medium in the small bowel is alkaline until the the pH of the pancreatic juice is roundabout pH 8 so it's it's very much towards the alkaline side of the spectrum altering the pH of the environment of the small bowel now again because the pancreatic Asuna cells are producing digestive enzymes and as we'll see these are going to be proteases like pages and amylase errs we don't want these protein digesting enzymes to be activated in the pancreas itself because sometimes they are sometimes they are so if a gallstone for example gets stuck in here in the hip a toe pancreatic and Pula then can you see that means that the digestive juices from the pancreas can't get out and they can down back in the pancreas now we'll see that these are produced as pro enzymes inactive enzymes but if there's an obstruction then these enzymes can become activated and that can mean that the pancreas will start digesting itself this is a remarkably painful condition this is the pathophysiological basis of pancreatitis it said Auto digestion of the pancreas or people that drink a lot of alcohol the small ducts in the pancreas especially people are drinking alcohol over long time periods the small ducts get blocked up and again if the small ducts are blocked up the enzymes can't escape and we can get pancreatitis so very painful condition of self digesting of the pancreas so it's absolutely vital that the enzymes are produced as these pre-and enzymes or pro enzymes and one of the enzymes produced by the pancreas is a trypsinogen trypsinogen now this is a protease but it's a it's a pro enzyme it's produced in in inactive form trypsinogen now when it gets into the lumen of the small bowel so once they're in the lumen of the small bowel then of course we want this to start working must exactly what we want it to work so we don't want it to work in the gland but we do want it to work in this in the small bowel so we need to be activated once it gets into the lumen of the duodenum which is protected by a mucosa and the trypsinogen is actually activated into trypsin by entero kinase and inteiro kinase is what we call the brush border enzyme it's produced by the entero sites lining the lumen of the duodenum so the trypsinogen will come into contact with the brush border of the duodenum the brush border will contain entero kinase and that will activate it into the active protease trypsin so we're now activated trypsin in the movement of the duodenum now further active inactive enzymes produced are chymotrypsinogen and the trypsin once it's produced as well as digesting proteins on its own will activate the kymo trypsinogen and convert that into chymotrypsin so trypsinogen is first activated into trypsin by the enteric kinase then the chymotrypsinogen is activated into chymotrypsin by the trypsin and the trypsin will also activate these as well this is a this is pro carboxy peptidase another protein digesting enzyme it will digest that it will activate that rather into carboxy peptidase again trypsin will will do this and it's the same within the end of the protease that the pro last days will be activated into our last days and the elastase is going to digest elastic tissues in the food that is consumed so these enzymes here are all active proteases now you might wonder why we've got four different protein digesting enzymes well the answer is that these different enzymes will actually work on different peptide bonds so you remember in our proteins we have these different long chains of Minar us is different peptide bonds so different protease enzymes will break different peptide bonds between pairs of amino acids that's why we have these different variety or this variety of protein digesting enzymes now we also notice that the pancreas produces a pancreatic amylase and the amylase is going to break down carbohydrates into simpler sugars and the pancreatic amylase as well as breaking down starch which is sometimes caught well starches is vegetable starch it also breaks down glycogen the glycogen is this huge polysaccharide molecule of usually glucose units well it is glucose units but it comes to mammals so so starch comes from plants glycogen comes from animals in fact glycogen is sometimes called animal starch so that will break down those carbohydrates but there are some polysaccharides there are some carbohydrates that amylase will not digest so which which polysaccharide carbohydrates will pancreatic amylase not break down well the answer to that is cellulose containing polysaccharides and in fact anything that's not broken down by the gastrointestinal tract such as cellulose is a fiber dietary fiber so dietary fiber is not acted on by any of the digestive enzymes and that means chemically it goes out as it came in and of course we know that water soluble fiber and none water soluble fiber are very important for health and for the health of the gastrointestinal tract but the reason that their fibers is because they're not acted on by by digestive enzymes such as amylase pancreatic lipase of course is going to start breaking down will continue the breakdown of fats now most fats when they're when they're consumed they contain a glycerol unit and they contain a three fatty acids because their triglycerides so this would be the glycerol unit and these will be the these will be the fatty acid units in the triglyceride so the pancreatic lipase is going to break down these triglyceride fats he breaks them down into monoglycerides which is a glycerol with one fatty acid left and the other two fatty acids are going to be liberated so we end up with a monoglycerides and fatty acids and the fatty acids can be long-chain or or short chain fatty acids could carry on illustrating this graphically we're going to end up with a monoglycerides and three three fatty acid units three fatty acid chains long chain or short chain so that's what the pancreatic lipase is going to do breaking up the triglycerides into glycerol monomer mono glycerol and a homologous horizon fatty acids now in the food we eat the food we eat of course is going to contain ribonucleic acid RNA in the cells and also deoxyribonucleic acid DNA in the nuclei and we notice that the pancreas produces specific enzymes for those so there's a ribonuclease and a deoxyribonucleoside on RNA and DNA now most of the products of digestion are going to be absorbed through the judge enum and through the ileum and we've looked before this very large at least 250 square meters of internal surface area through which absorption takes place but as well as just absorption there's going to be a final stage of digestion and this occurs in what we call the air the brush border and the brush border enzymes now what's happening here is the cells actually lining the mucosa as we've noticed are these columnar cells column shaped cells like this we noted on previous videos they have very tight junctions that interact with each interlace with each other so we've got these entero sites and on the surface of the intera sites we have these micro villi and we have noticed that the microvilli I clearly discern with a electron microscope but prior to that this looked with light microscopes this just looked like a brush border because of all the little hairs in it so great perfusion of these microvilli from the surface of the inteiro sites and here are the food products of digestion in the lumen of the small intestine and of course they need to be absorbed through these cells into the submucosa whether the rest of mucosa and the submucosa where they blood and lymphatics are in the villi for example now the phospholipid bilayer membranes on the surface of these contain digestive enzymes different digestive enzymes different digestive enzymes so that means when the products of digestion are absorbed they've got to go through this membrane and this membrane contains these enzymes and as they go through this brush border membrane the digestive process is going to be completed so these are what we mean by the brush border enzymes literally in the phospholipid bilayers of these Bush border micro villi and what happens here is this an enzyme so we can see there's a sucrase lactase maltese amino peptide a's dipeptide a's these are the enzymes or the main enzymes in the brush border and what are they doing well the sucrase in the roof boredom is finishing off the digestion of the disaccharide sucrose sucrose converting it into the monosaccharides glucose and fructose the lactase is digesting the lactose which is the milk sugar from milk and it's digesting that into the monosaccharides glucose and the monosaccharide galactose maltese is taking the products of starch digestion maltose which is a disaccharide there's also some oats some three sugar units here as well but the maltose is a disaccharide and that's being converted into a molecule of glucose and a molecule of glucose and then these last two are proteases protein digesting enzymes so there's amino peptide a's which cleaves amino acids at the end of the end of the peptide and then the final one dipeptide a's splits dipeptide days as the name suggests when there's two amino acids still linked together by a peptide bond it splits that final peptide bond to give single amino acid units so all we've got going in here by the time we get through this brush border membrane past these when the products of digestion have run this gauntlet of brush border enzymes membrane bound enzymes or we have it here is single amino acids and single monosaccharide sugar units and there's also active processes of absorption facilitating the absorption of these things and fatty acids and monoglycerides now the fatty acids and monoglycerides they can actually that can actually diffuse into these cells just by simple diffusion because they're fatty in the membrane is fatty so these just go into the cells the amino acids in the monosaccharides that the sugars and the protein fragrance they need to be absorbed by active transport but the fatty material can just a few straight into the cell so what we get is the fatty acids in the monoglycerides they go into these inteiro sites so these are the internal sites here and here they're converted into balls called a chylomicrons which then go on and go into the lymphatics because they're too big to go into the the blood capillaries so the chylomicrons are produced in the intere Esaias and go into the into the lymph but as far as I know there's no final fatty digestion takes place as it goes through the intera sites as there certainly is for the for the carbohydrates and the products of carbohydrates in the products of protein digestion so we started off with large insoluble molecules and what we have is we have simple sugars monosaccharide units single amino acids going into the blood and we have chylomicrons containing fatty acids and monoglycerides going into the lymphatics for removal to the circulatory system the digestive process is completed even as the final products are being absorbed by these fascinating cells the entero sites

Channel: Dr. John Campbell

Views: 10,060

Rating: 4.8987341 out of 5

Keywords: digestive system, enzymes, digestive enzymes

Id: Ft07M2pn9J0

Length: 43min 34sec (2614 seconds)

Published: Wed Jul 24 2019