Digestive System, Mecahnical and chemical digestion, Absorption full lecture

so we know that the process of digestion is breaking down large complex food molecules into much simpler molecules which can then be absorbed into the lymphatic and into the blood system of the body to be transported to organs and tissues where the nutrients are required to facilitate physiological processes and digestion can be broken down into two components really a lot of people when we talk about digestion the immediately think of chemical digestion this is the action of the enzymes chemically breaking down large molecules into small molecules by facilitating these catabolic breaking down reactions but there's also another very important aspect of digestion that can be overlooked and that is mechanical digestion the process of mechanical digestion the physical breaking down so this is the chemical breaking bound this is the physical breaking down and as we will see both are essential for the digestive process now here we have the model of the digestive system that were used to the diagram of the digestive system that were used to and I think we'll just draw a little bit more on we'll start with the mouth up on top so this goes up to the pharynx at the back there then the mouth will come off the mouth will be here but the mouth then this of course will go on forming the the nasal cavities so this will really these will be the nasal cavities here this will be the oral cavity here so the lips will be at the front of the oral cavity just here and the tongue will be on the floor of the overall camera teachers there like that so we'll start off thinking about what's going on in the oral cavity first of all and the first thing we can think about is water and mucus softening food so water and mucus basically the the Paris pathetic branch of the autonomic nervous system is going to cause the production of saliva in the mouth this is a parasympathetic autonomic activity now the converse of this is sympathetic activity and very often sympathetic activity does the opposite of parasympathetic activity so if parasympathetic activity is going to moisten the mouth by causing the production of saliva from the saliva glands then sympathetic activity is going to do the opposite of that and I think we can all relate to this if you're anxious or afraid you get a dry mouth because the sympathetic activity is not going to cause the production of saliva and as you get increase in sympathetic activity you get a corresponding reduction in parasympathetic activity so you get a dry mouth when you're anxious the physiologically the parasympathetic nervous system is stimulating the production of saliva and survivor is actually comes from the saliva glands and it's stimulated by the seventh cranial nerve which is the facial nerve and the ninth cranial nerve which is the glossopharyngeal nerve these components of the autonomic nervous system and physiologically saliva is going to be produced on an ongoing basis and we actually produce about a liter to 1.5 liters of saliva per day and that keeps the mouth moist but it also runs down the esophagus and keeps the esophagus moist as well so the esophagus is also moistened by saliva important that the esophagus is kept moist and well lubricated so that food can pass down it and travel down it easily as the peristaltic waves of contraction carry food down the esophagus it's also worth mentioning that if someone is systemically dehydrated especially if it's as bad as hypovolemic if someone dehydrated or hypovolemic then the production of saliva will go down so it's always worth inspecting the mouth and if the mouth is dry that's the possible sign of dehydration and if the mouth is dry very dry that's a possible sign of hypovolemia so quite a useful clinical indicator looking at the level of moisture in the mouth and if you're wondering what the normal levels are the best thing to do of course is just compared to your own and see how moist the patient's mouth is compared to your own mouth so we have this water and mucus the mucus softening the food and then we have this process of mastication going on in the mouth mastication mastication just means chewing or not quite sure why we don't just say chewing but is it it's mastication I suppose there's a bit more to it than that because you've got the teeth coming together crushing food tearing food you've got the tongue regulating the activity of the food putting the food just between the teeth so can be appropriately chewed up you've got the muscles in the cheek again putting the food in just the right position so there's actually an awful lot of complex neurological control going on in this process of mastication and most of the time we get it right and of course it's absolutely infuriating and paper when you get it wrong because that's when you bite your tongue when it's not fully this could be very painful when the tongue gets in between the teeth but the fact that that happens very rarely indicates just how good that the level of neurological control is of this process of mastication and what will happen here is the food will be formed into a bolus of food like that ready to be swallowed a nice swallowing size for the food mixed up with saliva so this is going to contain the food it's going to be moistened by the water moistened and lubricated by the mucus from the saliva ready to be swallowed and the process of swallowing for some reason is called deglutition so a deglutition or deglutition is the process of swallowing this bolus of food so it can then pass down thee passed down the esophagus towards the stomach now the next anatomical area of interest when we're talking about this process of mechanical digestion is the stomach itself as a mod of mechanical digestion going on in the stomach because what we have in the stomach are these these mixing waves the stomach has mixing waves and the mixing waves are going to churn the food up in the stomach and that's going to form chime so chime is the next stage after the bolus goes into the stomach becomes chime because in the stomach what you get is rippling peristaltic movements every 15 to 25 seconds so there's these rippling movements in the wall of the stomach as the muscular wall of the smooth muscular wall of the stomach contracts and that's going to macerate and mix the food muscle red means it makes it wet so it's going to be well mixed up there's saliva there as well but it's also going to be mixed up with gastric secretions in addition mixing the fruit with gastric secretions now these stomach mixing waves don't occur very much in the top of the stomach in the fundus so that's the fundus of the stomach at the top that's largely involved in storage so when you eat a large meal that will that will distend and they'll be storage your food in there waiting to go into the lower part of the stomach but other parts of the stomach we get these our stomach mixing waves producing this semi liquid chime now in the gastric pits in the lining of the stomach there's a special sort of cell called parietal cells and these parietal cells will produce hydrogen ions and chloride ions H+ and Cl minus and of course that gives rise to the formation of the main acid in the stomach HCl hydrochloric acid which is the main acid in the stomach now the hydrochloric acid is obviously a strong acid and that's good because it means that bacteria that come into the stomach can be partly killed by the very acidic medium that they're confronted with when they get into the stomach but the hydrochloric acid also unfolds proteins so proteins are often in a very large sometimes a globular arrangement like this highly folded like that which is good because they form physiological functions as proteins but the hydrochloric acid will help them to unfold and become a longer thinner strand and that's good because it means that the digestive enzymes can access them more easily the unfolding of the proteins is greatly increasing the surface area of the protein over which digestive enzymes can then take effect now I think the next one we'll mention in terms of mechanical digestion is boil so bile of course is produced in the liver it goes down the bile ducts after being stored in the gallbladder goes down the hepatic ducts common hepatic duct into the gallbladder down the common bile duct and into the duodenum and fats are actually emulsified by bile so ball does not digest fat in any way that it emulsifies it so what will happen is a large globule of fatty material will be emulsified down into many smaller globules massively increasing the surface area for the digestive enzymes that break down fat the lipase to access the surface of the the fat and this emulsification process means that it looks at a white creamy color so for example milk is white because it's an emulsion of fat and it's interesting to note that the liver actually produces 800 to a thousand mils of BI on the day now much less of that goes into the the duodenum because the bile is stored and concentrated in the gall bladder so if you think about where we're going with this digestive process we started with the with the mouth we went on to the stomach mentioned bile we're now in the small intestines in the in the small intestine called small because it has a more narrow lumen than the large intestine and we noticed that one of the thick processes going on here is called segmentation segmentation so what's happening in this process of segmentation well the small intestine is essentially a long tube so here we have a long tube like this and there's longitudinal muscles on the outside but there's also circular muscles and what happens in segmentation firstly is there's contraction of areas of circular muscle let's say there's a contraction here and there's a contraction there and these contractions are largely stimulated by distension so when the chime comes in then these segments will be formed by contraction of the circular muscles and this is controlled by the my enteric plexus so in the walls of the intestine there's a lot of neurological tissue called the my enteric plexus which is controlling this process and in the duodenum these contraction will happen about 12 times a minute in the ileum it's a bit slower maybe eight times a minute so initially we've got this contraction let's say the initial contractions of these three these three areas so this contraction of the circular muscle they're they're roughly the same time and I think you can now see that means we've got two segments hence the name segmentation that's the first stage now the second step is that the muscle fibers in the middle of each segment will also contract so we're going to get contraction of the muscles here and the muscles here so now we've got even more segments we've got further segmentation you could call these sub segments if you like then the third thing happens is the fibers that contracted in the first place that's that one there that one there and that one they're the first ones to contract they will relax so they're going to be relaxed so what this means is that we've got larger segments again and then this repeats this repeated process and what this actually means is that the material in the small bowel is essentially sloshing back and forward so we tend to think about peristalsis as being a process where we go progressively along there along there along there all the way through the intestine to the large intestine so we tend to get Mercer as a progressive process and that's true peristalsis is but this muscular segmentation happens before the peristaltic processes propel the material through the small bowel so the aim of segmentation is not to propel material from the stomach towards the large intestine but rather to mix it up and to churn it all together so it's localized mixing contractions and as that happens materials going to be absorbed from the small bowel into the blood supply into the lymphatics therefore as it's absorbed its volume is clearly going to be reduced so there's going to be a reduction in volume as it's washes back and forward and as it sloshes back and forward is going to be well mixed it's going to come in contact with all the right enzymes and of course the mixing is going to mean that it comes into contact with the walls of the small intestine which is where the absorption takes place from the segmentation process is helping the digestive process and it's helping the absorptive the absorption process as well so that's this process of segmentation and then when that process of segmentation is finished and there's been a lot of absorption then there's migrating motility complex complexes of muscular contraction and these will also be contractions but they occur much more sequentially in waves than some of this paper so we imagine that this is one length of the small intestine here they'll be contraction there that's contraction there and what's like what that's going to do when the area contracts you can probably see that that's going to push material along now material will be pushed back to some extent as well but that will be stopped from going back into the stomach by the pyloric sphincter which will be closed off so the material is going to be pushed along a bit and then if we imagine the same length of bowel a short time later that bits going through a relaxed and this bit will over that this bit of the wall will have contracted like that so that means that the bolus which was there that's been moved along is now was there has been moved along now it's been moved along a bit and it's going to be going to be there and and then this muscle is going to relax and the next part of the muscle is going to contract so we go further along slightly boss my Scalia but never mind you getting the idea and that part that bar is going to contract so the bolus is pushed further along pushed further along like this so we get this wave of muscular contraction just like any para starting process really pushing the material further along the lumen of the small intestine as we go along and that's what we call although the the migrating motility complex this wave of contraction going down the small intestine pushing material from the stomach towards the colon and for such a wave of contraction to go all the way along this more than I'm from the base of the stomach to the terminal Illium that's going to take about 90 to 120 minutes and altogether the chine remains in the intestine for about three to five hours before it's absorbed or pushed through to the colon so that was the migrating motility complex now we notice that there is a intestinal juice intestinal juice and the intestinal juice is produced imagine this as a length of the small bowel here so the intestinal juice is going to be produced by the lining of the small intestine it's produced by the lining of the small intestine and it's produced mostly in the lining walls of the first parts of the small intestine the duodenum and the jejunum and about one to two liters of this fluid are produced today so there's quite a lot of it being produced one to two liters a day of being secreted into the lumen of the small intestine and this is very important because it makes everything in here fluid because it's got to be fluid to mix with the digestive enzymes it's got to be fluid to come into contact with the wall of the small intestine to facilitate absorption so this if you'd like it's kind of a it's a diluting so the intestinal juice is diluting the contents of the small intestine now of course there's already pancreatic juice in here so that's going to further dilute the pancreatic juice and as we thought that did I say what 1 to 2 liters of this are produced every day a lot of its reabsorbed the partners not reabsorbed will go to the colon and probably be reabsorbed nearly all of it reabsorbed in the colon if not before and it's a clear yellowish fluid it contains water and mute now some people think that this juice contains digestive enzymes it doesn't but of course it does mix with the pancreatic juice that does contain digestive enzymes so when it's produced from the wall of the small intestine it won't could you it won't contain digestive enzymes but when it's all mixed up with the pancreatic secretions then yes there will be digestive enzymes in the fluid within the lumen of the gastrointestinal tract although it doesn't come from this intestinal juice produced by the wall of the small intestine this just contains it but mostly water and mucus and it's quite alkaline the pH here is about erm well we know the small intestine is generally an alkaline environment so it's about seven point six is the pH of this intestinal juice and in the old days this juice used to have a great name it was called the circus in taraknath the sucker sent Erika's but these days we call it Lea the intestinal juice so combining with the pancreatic juice to produce this liquid medium for mixing for coming into contact for absorption so we see that there's quite a few aspects of mechanical digestion all these aspects of digestion we've talked about aren't chemical we haven't chemically broken down the food yet they're all physical processes so we've had water and mucus softening the food about the process of mastication without the stomach mixing waves mixing up chime we've had the hydrochloric acid unfolding the proteins that bile emulsify the fats the segmentation sloshing back and forward in the small intestine the progressive peristaltic migrating motility complex of muscle or complexes of muscular contraction and finally this inter Steindl juice all aspects of mechanical digestion so of course in the next video we want to go on and think about the processes of chemical digestion 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 aids 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 protti 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 as 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 - parotid glands - submandibular glands and - 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 glance IRA put the the sort of side of the head here round 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 tongue is in there and lingual means to do with the tongue so the sibling was the library 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 are in 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 with 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 kind of 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 sick well I 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 wonder that 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 the 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 is another small sugar units molto is actually a two sugar unit is also breaks it down to some three sugar units and when the saliva is swallowed with the food bolus this can actually carry on working for about an hour especially 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 got 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 that 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 to a diglyceride which contains two but it's starting off this process but the majority of fatty digestion is carried out and the pancreas as we'll 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 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 mucus 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 mucus 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 acids 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 lungs and the product of these cells is a pepsinogen and these cells have drawn in blue I 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 if there's a hole in the mucosa then 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 um you're the main group of cells in the gastric pits are called G cells and they produce an endocrine organ 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 glands 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 OTO digestion and pepsin is a protein digesting enzyme is a 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 amino 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 held together by peptide bonds that form these long chains of peptides that polypeptides and these fold into proteins so what these are protease is 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 of 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 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 with a 1 fatty acid attached to it so we went from diglycerides to monoglycerides and we'll see 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 makes a small contribution to the process so here we have our diagon of the stomach from the physiology nose 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 this 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 earth the gastric pits these will be the gastric glands down here producing the hydrochloric acid the juicing the pepsinogen which is converted to pepsin and of course all this will be protected by the layer of mucus protecting the top of the gastric mucosa here's a blow-up diagram of a gastric Britton again from the physiology nose book and it just reviews what we've 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 column on 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 dod i'm actually curved around this way like this he goes up and carries on his way to where it 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 pancreas is this kind of 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 bid the main one carries on like this down there was the main duct to that now this duct here this 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 duodenum 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 exocrine tissue occupying about 99 percent of the bulk of the pancreas and these are called air asani the Athenee these clusters of EXO crying tissue and the cells in the the asagna called Asuna cells so the pancreatic juices are actually juice 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 this cystic duct and above that we have the common hepatic duct and leaf right and the left hepatic duct tucked in behind the gallbladder and then the common bile common bile duct is going to go down here so the bar 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 hepatic pancreatic ampulla in the old days it was called the ampulla of Virata so here we just have boil 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 serve Ahana and these of course produce the the alpha cells in the pancreatic islet of Lion produced 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 you thee the pH of the pancreatic juice is roundabout pH 8 so 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 our lasers 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 ampulla 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's an 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 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 we're in the lumen of the small bowel then of course we want this to start working masses actually when we wanted 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 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 trips it 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 primer last days will be activated into our last days and the alas days 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 mean our 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 called 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 non water soluble fiber are very important for health and for the health of the gastrointestinal tract but the reason that there are 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 or continue the breakdown of fats now most fats when they're when they're consumed they contain a 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 it 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 illustration 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 dinner breaking up the triglycerides into glycerol monomer monoglyceride and monoglycerides and 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 an 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 micro villi I clearly discern with a electron microscope the 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 entero 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 the mucosa and 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 brush border 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 the 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 all we have in 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 fragments they need to be absorbed via active sport 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 in terror sites so these are the internal sites here and here they're converted into balls called 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 intera size and go into there into the middle but as far as I know there's no final fatty digestion takes place as it goes through the entire slice 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 now in this video we want to be thinking about the process of absorption and the point of anatomy of particular interest for this purpose is the small intestine so here's the overall diagram of the gastrointestinal tract and the small intestine is going to stretch from the pyloric sphincter at the end of the stomach all the way through to the ileocecal valve where the ileum joins on to the or joins into the cecum now as we see from this diagram the small intestines in three components we have the duodenum the jejunum and we have finally the ileum as the distal part so the duodenum is pox the judge gnam is in the middle part medial and the ilium is distal pass of the small intestine and it's called small because it's more narrow as we see the lumen is more narrow than in the large intestine now the length of the small intestine there is a fair bit between individuals studies have shown is between three and eight point five meters in length with the average being round about five meters in length now you may well see longer figures than this quoted in the textbooks and that's because the textbooks are based on old data which is taken from post-mortem studies but the five meter average is the length of the small intestine as measured during surgical procedures when the patient is alive because of the death the smooth muscle in the small intestine will relax and the small intestine becomes longer if we measure it on the bench they're not probability your small intestine is about about five meters in length now what we want to do now is look at these structures here the small intestine the circular folds the villi and the micro villi because as this Anatomy that gives the small intestine a remarkably large internal surface area the surface area between the mucosa and the submucosa of the small intestine in the lumen of the small intestine through which absorption takes place this very large surface area is facilitated by this particularly interesting arrangement of anatomical on histological structures so first of all let's think about the small intestine so here's a length of the small intestine just here and it's got a muscular wall we could draw a muscular wall in there so there's the muscular wall at the small intestine right and inside as we know there's a mucosa and under the mucosa there is a submucosa now the submucosa is arranged in folds like this so it's folded on the inside these folds that project into the lumen of the small intestine I think if you look at those ready you can see that we have a much larger surface area exposed between the lumen and the submucosa here so this is the submucosa this black line is actually the mucosa this is the surface mucous membrane of the small intestine and we see that these circular folds are greatly increasing the surface area this would be the this would be the submucosa just here in this area here that we could just cover that in to clarify it so this area here is the submucosa and the submucosa are so important because it contains the blood vessels which are going to collect the absorbed nutrients and the venous branches are going to go to the liver by the hepatic portal vein the lymphatic branches are going to go to the lymphatic system to be drained back into the blood separately so that we have the submucosa so what we've drawn here are the circular folds these are circular folds so that's one circuit evolved that's another circular fault they're so large circular folds of mucosa projecting to the lumen of the small intestine this is the lumen in the middle here the gap down the middle now these are not present in action of the the first part of the duodenum and they disappear in the distal ileum but the rest of the small intestine has these circular folds and they're visible macroscopically they're up to eight millimeters deep and one large fold actually alternates with a with a smaller fold so it's a fairly precise arrangement of these circular folds and we can actually look at this enough to mean in something some more detail so let's say that's imagine these are the circular folds here these are the circular folds a little bit large at this time perfect so they're the circular folds in the lumen of the small intestine now as you probably know and as we mentioned the walls of the small intestine are lined with a muscle so just here just here there's going to be a layer of circular muscle so this muscle is circular in nature the muscle fibers running around about the diameter of the gastrointestinal tract then on the outside of those there's a layer of longitudinal muscle fibers that run along to to Denali of course we need both circular and longitudinal to facilitate the process of peristalsis and then finally on the outside here there's a layer reverse and Roza the outside tissue of the gastrointestinal tract and at the level of the small intestine that is going to consist of the the visceral peritoneum the V small peritoneal membrane and this fairly large area here this submucosa that's going to contain many blood vessels it's going to contain going to contain lymphatics they're going to be lymphatic vessels here as well there's going to be lymphatic vessels draining for where you into larger lymphatic vessels in this in this submucosal layer so we've seen we've got the small intestine and the circular folds but the next layer of complexity is the villi so what what are these villi well if you've got good eyes the villi are just visible to the human eye and the villi are present on the circular folds like this so these would be the villi not drawn to scale here you are smaller than this the feline would be in this position here so these will be villi lining the circular folds so the actual mucous membrane itself is isn't folded in these villi goes up only goes down with the villi and as we've said these villi are just visible to the human eye and the villi are actually highly vascular projections of the mucosal surface and they cover the entire surface of the intestinal mucosa the small intestine is completely lined with these villi and what they do is we can see that the surface area has already increased with the circular folds while the villi they increase the surface area even more and in fact the villi alone increased the surface area by x 7 so the surface area is 7 times greater because of the presence of these villi on the circular folds and there's about 10 to 40 of these villi per millimeter per square millimeter so if we take a square millimeter surface area 10 240 villi there when I said these were visible to the to the AIA the probably not visible to mine if you've got young feet eyes I'm sure you could probably just see them but that they are quite small and and close together so 10 to 40 per cubic millimeter and height wise they're about naught point five to one millimeter in height so the scale here is if that's a good sized villi there that line from there to there will be one millimeter so next we can look at a villa in Venice in more detail Warner Villa said will villi so here we see the the villas here this one there like that so what we've drawn there in larger magnification is want one of those so what was of zoomed in to that level now so we've zoomed in from the circular folds to the villi on the circular folds now as you get to warm that water fitness now between individual villi there's actually an indented area like this intestinal crypts there like that then they'll be another another villus there like that it'll be another way to style clip there no no the fullest so that's the kind of arrangement that we see in there in the villi now in the center of each villus we'll go into other lymphatics it's called a lacteal so there's a central lacteal in the center of each lewis and the smaller than fatty vessels are going to drain into that and then these are going to connect to larger lymphatic vessels further down in the submucosa with the lymph eventually draining away into the larger lymphatic vessels and this is important because the fat soluble materials are absorbed into the lymphatic system not into the blood vascular system and then we're going to have blood vessels here so there's going to be arterial vessels small branches going off here like this there's going to be an arterial vessel going on say this side of the the villi and that's going to send out blood vessels across the individual villus like this that's going to go into our venous vessels which are going to drain again into where as would expect into larger into larger venous vessels so we have the lymphatic supply we have the blood supply going in going in like this we have the venous blood draining out and we have the blind ended lymphatic capillaries collecting lymphatic fluid and fast soluble material now this of course is the lumen of the small intestine here so what does soluble products of digestion are going to go into the blood supply the monosaccharides and the amino acids for example going to go into the blood supply and we can see that they're all going to be drained all these nutrients are going to be drilling via this vessel here one of the venous vessels and that's going all these vessels are going to join them they're going to form the hepatic portal vein and they're going to take this blood directly to the liver the fat soluble material is going to be absorbed into the lymphatic laughs teal and again that's going to drain away into progressively larger lymphatic vessels so we've got the in folding of the circular folds the in folding of the villi and we've seen the unfolding of the villi here but there's another particularly fascinating area of it folding as well because the surface of each villus is itself lined with numerous micro villi so the surface area this is also greatly enhanced with these microvilli so we see all these layers of infolding so the surface area of villus is directly enhanced by the presence of the micro villi on its surface now just before we're going to look at these micro villi in more detail let's just use this diagram from the physiology notes books to physiology notes summarize where we're at so first of all we noted that the intestine itself had circular folds then we noticed that this is all one circular fold here a small one circular fold we noticed that that was lined with the villi then we looked at the individual villi and we now notice the individual villi are themselves covered with smaller micro villi and these micro villi are generated by the intera sites and the intera sites are the most common form of cell lining of the lists so each villus of course is going to be lined with er this is a diagram out of that of your life each one is going to be lined with individual cells like this again not drawn to scale but we're going to be lined with individual cells like this each with their own nucleus of course lining the villi forming the mucous membrane so there's actually a single layer of epithelial cells covering the intestinal villi and the most common sort of cell lining the villi are the entero sites but there's also other cells for example there's a goblet cells to produce mucus and actually just before we go on I think I'll just tell you that that in these inter spinal crypts we have these intestinal crypts here so these intestinal crypts now the stem cells to produce the goblet cells and to produce the the intera sites are actually in these crypts intestinal crypts what used to be called the crypts of lubricant in the old days and these are the germ cells these are our mitotically dividing because it's fairly well known that the gastrointestinal tract is replacing its surface very frequently and these individual antara sites actually only live for about five days they're quite short and live cells that's why in clinical practice when we give patients chemotherapy they often have quite severe gastrointestinal side effects because that's inhibiting the mitotic activity and preventing this replenishment so what actually happens is the cells will divide down here and they'll move up onto this mucosa lining the the villi but as they get older they they actually physically move up here like this so so a cell down here is going to be maybe 1224 hours old but a set up here is going to be say four days old and then eventually the cells get to the top here up there and at that stage the cells commit suicide this process of apoptosis and they just flake off into the lumen so this this layer is constantly being replaced this flow of cells from the base up to the apex of the villi constantly renewing the mucosa of the lumen of the small intestine quite amazing generation of cells migration of cells and then when they've done their job they just know they've done the job in the committe apoptosis and that's the replaced by younger selves but interesting to note when you're looking if you look at a villa Sun to the microscope they're the younger self they're they're the older cells and put the top but as we say only about five days lifespan for these in Tarot sites and goblet cells so an ongoing process of mitosis from stem cells migrations nothing off the lining of your small intestine is always - you'll now now these antara sites are particularly amazing cells so let's look at one in in in more detail so we've said there's a single layer of epithelium covers the intestine intestinal villi covers the villi and these are Montera sites and goblet cells from a common stem cell ancestor in the intestinal crypts now the intera sites they're basically column shaped cells nothing unusual about that they're columnar cells they each have their own nucleus of course and they sit on a basement membrane as you would expect and these in terror sites are so important because these are the these are the absorptive cells is where absorption takes place from the lumen into the submucosa where the blood vessels click the absorbed nutrients there are actually relatively big cells of about 20 micrometers in height but the fascinating thing about them is the surface of these as we've said is folded into micro villi like this so this is the entire site through the micro villi on the surface so just to go back to our previous diagram when we drew the micro villi here on the surface of Avila's these microvilli are actually projections of these inter asides here so the micro villi are actually coming from here like this mostly projections of the intera slice and here we're seeing in in greater magnification now amazingly there's up to 3,000 up to 3,000 micro villi per cell so two two and a half three thousand of these microvilli on the surface of each antara site is an amazing level of complexity now we've said these cells are about 20 micrometers tall but the the micro villi themselves they're only about what 1 micrometer that's one thousandth of a millimeter in height like that and this arrangement of micro villi is form what is called the brush border the brush border now the brush border is a term which was developed during the days of light microscopes so when you looked at this with several hundred times magnification you could see it was like a bit like the surface of a brush you could see it was so many villi there like that look looks a bit like a brush so the cord a brush border this ill-defined border so this is the brush border now of course now we live in the days of electron microscopes we can see these in in exquisite detail so we now know that the brush border is composed of two to three thousand individual micro villi on the surface of each antara site such as the advantage of looking through the electron microscope now if we look at one of these micro villi now in in greater magnification so so that's a micro villi there and of course this is the surface of a cell so the surface of cells are made up of phospholipid bilayers so this is the phospholipid bilayer here we've now blown up one of these micro villi and the thing about phospholipid bilayers is that there are proteinaceous inclusions that can float on this phospholipid bilayer so floating in this phospholipid bilayer attached to the bilayer there are various proteins floating [Music] this is called the fluid mosaic model of the of the cell membrane this is like the fluid and proteins can float in this membrane this phospholipid membrane lining the surface of the microvilli in other words lining the surface of the intera side so again what this means is here is inside the cell because that's the blow-up of say here and here outside this is the lumen of the small intestine with the products of digestion here and this is so important because we know we're talking about observe absorption we have this large surface area but this is also where the final phase of digestion occurs via the action of these membranes or these membrane bound proteins and some of these membrane bound protein proteins are digestive enzymes and as nutrients pass through this membrane here they're going to be acted on by these digestive enzymes completing the digestive process so these enzymes for example will degrade disaccharides and oligo proteins small proteins disaccharides will be degraded into monosaccharides the single sugar units all ego proteins short proteins very short chains of amino acids will be degraded into individual amino acids so even though in the movement here there can be disaccharides and small chains of amino acids once we actually get into the cell thanks to these digestive enzyme proteins situated in the plasma membrane and the surface of the micro villi what we get here inside is only amino acids single amino acids and only single sugars they the monosaccharides sugars so just to contextualize this against this diagram the enzymes here are actually located around here in the surface membrane of the microvilli these final star jested enzymes so integral membrane bound proteins complete the process of digestion at the brush border which we now know to be an arrangement of micro villi and if we think about the antenna size they're even more amazing than this most books draw in Terris eyes like like I've drawn it here so most books when they're telling you about these and terror sites will draw them like this they'll have a I'll have a nice straight line there that lovely micro tree right there I'll have the next one next door like this and they'll rightly point out that the junction between two cells is a time two Junction it's a time Junction and these tight junctions here are important to prevent non selective diffusion so the cell is choosing what's going in bits and bobs can't nip in through there inadvertently like that and this is absolutely true but of course I'm having said this the gut lining in young children up to the age of a few months of age certainly say up to six months of age the mining can actually absorb ready formed proteins so for the first few months of life proteins larger proteins can actually get through this membrane somehow and they can get into the blood so for example if we feed a child cow's milk that's going to contain bovine albumin so one of the proteins in cow's milk is bovine argument and that means in a childhood we feed a child cow's milk we can actually get cow proteins actually in the child's circulatory system whereas if as adults we drink milk or eat cheese that's all going to be broken down into its individual components before it's absorbed the children can actually absorb it as whole proteins and this is why we don't want to give young children cow's milk but probably for the first year of life guidelines might vary but certainly for the first few months certainly for the first six months of life and I would pop this thing up to a year of life a year of age to be on the safe side because we don't want these proteins getting into the blood because these proteins of course are not human proteins they're cow proteins and that means that these will act as a as an anti jet these will be an antigen an antigen of course will cause the formation of an antibody which is an immune protein so we'll end up with immune boating's to cow protein and one of the reasons that that may well matter is that in the beta cells of the iris of Manahan it seems that there are probably proteins which are a similar shape to to cow protein this isn't completely understood but if we have a betta cell here this is a beef to sell and on the surface of the beetus and of course the fetus that produces insulin this is absolutely vital production of insulin is B to self which produces insulin it seems that these antibodies can mistake proteins on the surface of the beta cell for cow proteins and that means that these antibodies to the bovine albumin can actually attack and the vita cells and can potentially kill the Muny logically destroy the beta cells if we immunity logically destroyed the beta cells then that patient and fortunately is going to get time one diabetes mellitus so this is this is theorized it does make perfect sense and practically we certainly don't want to be given cow's milk to to your children because this membrane is not as x as it is in later childhood and in adults but then getting away from this digression I said that most textbooks draw this as a time junction and it's true but they tend to draw it straight like that this even more complicated so what you actually have if your imagine that's the air there they're the villi they're micro villi on top of a taro site and they're the microvilli on top of the intera site next door they're like that now the membranes between these two cells are actually in folded like this so the membranes are actually it folded you see that's giving you a much tighter Junction it's just amazing isn't it now that one will go off and form this cell again in folded Junction next to the next antara side and this membrane here will fall back for this entire site get the forwarding Junction so we see that the membranes are even tighter than most textbooks draw because they're in folded and as well as that there's pro tenacious desmosomes connecting them together like this making it really tight Junction so in adults and all the children certainly after the age of a year these junctions are going to be tight and things can't nip in they can't leap in unexpectedly because of these tight junctions everything's got to go through here and therefore be digested and regulated they're also going to go through the cell there I did to thee into the submucosa so we've got the the micro villi of interesting physiology about those micro of your life related to pathophysiology we've got the villi themselves with the micro villi on the surface we've got the circular folds with the villi on the surface and then we've got the five meters length of the small intestine itself and it's estimated that this gives an internal surface area over which absorption can take place of 250 square meters quite amazing I mean that the lungs are probably about a hundred square meters an internal surface area inside the alveoli but inside the gastrointestinal tract we have this 250 square metres have internal surface area so again just to clarify this final stage that's going on what's going on here this is the diagram from that physiologist again looking just maybe uses a bit of that if a summary so what we have here what I've actually drawn here is three int arrow sites that in actual fact each of these processes would take place through each antara side and the key thing here is this surface membrane over the entire site here where all this clever digestive and absorptive physiology goes on the external membrane of the individual terrified thrown into these folds actually brewery broken down as they go through the membrane here into the individual amino acids disaccharides such as molto's again will be broken down by enzymes in the surface membrane here into monosaccharides and fatty acids and glycerol well that's another clever thing these cells to do that they package fatty acids and glycerol in the intera sites into the the chylomicrons these small fat balls that go off into the lymphatic system and then into the blood so as I've said that this process is going on in a single cell so I mean our acids will go through one cell sugars will go through one cell and fatty acid well as well but I've just drawn us three separate cells just to just to clarify that process the final stage of digestion in the brush border so the brush border is from there to there that is the brush border which we now know love these these microvilli

Channel: Dr. John Campbell

Views: 40,109

Rating: 4.9067359 out of 5

Keywords: physiology, nursing, NCLEX, health, disease, biology, medicine, nurse education, medical education, pathophysiology, campbell, human biology, human body

Id: D3JR_EJsW4A

Length: 99min 25sec (5965 seconds)

Published: Tue Aug 27 2019