Lecture 6 - Structure and Function of the Digestive System

hi everybody dr mike here in this video i'm going to introduce to you the digestive system so very basically the digestive system takes in food and breaks this food down into its micronutrients and then absorbs these nutrients into the bloodstream for it to be dispersed to the tissues of the body to be used for energy or as building blocks now whatever remains gets defecated and leaves the body and this is this is the major function of the digestive tract now when i say digestive tract i'm also referring to that of the alimentary canal and that's the primary component of the digestive system i think that's worth writing down is the elementary canal now the elementary canal is this hollow muscular tube that goes from the mouth and snakes its way all the way through down to the anus now the thing is this this elementary canal whilst a muscular tube also has other layers to it that allow for it to have many different functions depending on what aspect of the tube we're referring to now in addition to the elementary canal another primary component of the digestive system are the accessory digestive structures now accessory digestive structures are not components of the elementary canal but they are accessory components and they often have ducts or tubes that lead into the elementary canal so the first thing i want to do is go through the various aspects of the elementary canal and i'm going to do this in blue so first thing is the mouth the mouth is the first aspect of the elementary canal then we go down to the pharynx which is the back of the throat then we go to the esophagus then the stomach then the small intestines and then we move through to the large intestines now the large intestines right at the very end which is the final structure of the elementary canal is that of the anus now these in blue they're all aspects of the elementary canal now the accessory components which we're going to highlight here in red these accessory components include those of the oral cavity which includes the tongue which includes teeth and includes salivary glands of which there's many kinds it also includes that of the pancreas which is which sits around about here and the liver which sits round about here now underneath the liver we've got something called the gallbladder so we've also got the gallbladder now what i might do is just put a little asterisk here and then i'll put an asterisk here for gallbladder and these are all various aspects of the accessory structures now what i want to talk about is the function of the digestive system so the function of the digestive system let's begin with that of ingestion so number one ingestion taking food in so eating let's say intake which is eating the second function we need to talk about is that of secretion so the digestive system actually secretes substances and these substances are enzymes and mucus enzymes and mucus now these enzymes can be digestive enzymes for example things that break down proteins fats or carbohydrates and the mucus is obviously an extremely important structure because we're going to have substances moving through this elementary canal there's going to be friction in this environment and we don't want to damage the cells of that tissue so mucus is also very important another important function of the digestive system is that of mixing in actual fact mixing and propulsion so the foodstuffs that we take in we need to mix mix mix it up and we also need to push it through the tract this process of mixing and pushing is termed peristalsis number four another function of the digestive system is that of digestion so we can't forget that primary role of digestion now importantly you've got both mechanical and chemical digestion mechanical and chemical now what's the difference between the two mechanical is physical digestion that's actually part of this mixing and propulsion process that's where we physically tear things apart so our teeth for example and our tongue allowed to break things apart that's mechanical digestion our stomach can throw things around that's mechanical digestion chemical digestion involves these enzymes that are being released or secreted from the digestive tract and again they're molecular scissors that chop up big carbohydrates big triglycerides and big proteins into their smaller components of glucose galactose fructose for example of fatty acids and glycerol or other amino acids respectively that's number four number five is out of absorption so once we've broken these things down we need to absorb them and they're actually absorbed into the blood stream well most of them are absorbed into the bloodstream some like fats are absorbed into the lymphatic system and different substances are absorbed at different areas of the tract so for example alcohol can be absorbed at the stomach but not much else you'll find the small intestines will be one of the primary sites for absorption when it comes to nutrients but the large intestines are a really important site for vitamins and water and electrolyte absorption okay all right that's number five number six which is the final one is that of excretion so number one is intake last one is going to be excretion an excretion is defecation and what we are excreting from the body obviously at the anus is going to be indigestible products or substances that we no longer require and that's the final stage of the functional processes of the digestive system so what we've gone through here first of all is we've broken the digestive system into the elementary canal and the accessory structures we'll be talking more about this in detail in future videos and all the different functions of the digestive system hi everyone dr mike here in this video we're looking at the histology of the git which is the gastrointestinal tract now histology is the study of cells and tissues if i were to take a biopsy of your skin and then slice it up into very thin segments and look at it under the microscope that is histology and remember with the gut or gastrointestinal tract it's one big long tube that starts at the mouth and moves all the way down to the anus i've made a mistake in my lectures before in which i've stated today students we're going through math to anus unfortunately it's not a very good way to start a lecture but we are going through cheek to cheek and if we look at this continuous tube you'll find that from the esophagus it goes to the stomach to the small intestines to the large intestines sigmoidal colon rectum and anus and if you were to continue from your cheeks of your face and move into your oral cavity you could effectively move all the way down through and exit out at your other cheeks okay now remember that means that the inside of our git is continuous with the outside of our body and the outside of our body is lined with a certain type of cell called epithelia which means the inside of the git is also lined with epithelia but this epithelia changes in its structure depending on where along the git we're talking about because remember with epithelia its form or structure equals its function so if it's there for protection it's going to be many layers of squished epithelia which we call stratified squamous that's actually what our skin is covered with stratified squamous epithelia if it's there to allow for gases to move through it's a single layer which we call simple and squamous squished but there's not going to be any diffusion happening in the grt so you're not going to see any simple squamous but if you've got a simple layer but it's made up of columnar cells big long cells with big intracellular compartments it's going to be there for secreting substances and absorbing substances and you see this a lot throughout the tube of the git so if we have a look at the epithelia so remember with this big long tube going from the mouth to the anus you'll find that this big long tube is made up of around about seven different layers you can see these layers here the most internal layer being the hollow inside like i said is lined with epithelia all right the next layer that surrounds that all epithelia sits on connective tissue therefore the next layer is connective tissue and we term that the laminar propria and this connective tissue layer has blood vessels nerve fibers and lymphatics i'll talk about it again in a sec then the third layer is called the muscularis mucosa this is a muscle layer very thin muscle layer made up of two different types of layers one is circular muscle which means if you've got the hollow tube the muscle is arranged around that hollow tube which means if it constricts it narrows the hollow inside which we call the lumen so the lumens the hollow inside so the circular muscle narrows the hollow lumen and the second layer is longitudinal muscle and it goes along the length of the hollow tube which means when it contracts it shortens the tube together circular and longitudinal can help move things through these three layers together the epithelial lamina propria muscularis mucosa are all termed the mucosal layer of the grt the very first most internal layer of the git if we look at just epithelia to begin with and we start at the esophagus remember the esophagus is simply a pipe a conduit that allows for food stuff to go from the mouth to the stomach it doesn't absorb anything doesn't secrete anything doesn't let for anything else like that happen it's just there for movement and therefore the type of epithelia is going to be epithelially for protection which we know is stratified squamous epithelia when we get to the stomach it's pretty much the first site of digestion both chemical and mechanical digestion and the types of cells you'll find will be a simple layer so a single layer of columnar epithelia now this columnar epithelial layer can form these pits that we call gastric pits these gastric pits have a number of different types of cells you've got what's called mu mucous secreting neck cells so it secretes a mucus you've got parietal cells which secrete hydrochloric acid and g cells and other different types of cells that secrete a whole bunch of enzymes and chemicals that aid in the digestive process in the stomach now they don't have anything called goblet cells this is another type of mucus secreting cells but they're specific to the small and large intestines so when we move down to the small large intestines they are also simple columnar remember when you've got columnar cells they have very large intracellular compartments which means they have a lot of smooth endoplasmic reticulum rough endoplasmic reticulum golgi apparatus mitochondria ribosomes so they can produce a lot of things the types of things they're producing are enzymes and chemicals for secretion into that hollow inside but they're also there to absorb stuff and maybe change it around a little bit if it needs to so remember that so in the small intestines this is the first site predominantly of absorption of nutrients of minerals of vitamins of electrolytes of water all these things are being absorbed in the small intestines which means if it's absorption we need to increase the surface area of the small intestines to maximize the amount of things we absorb so what we have are these projections of the git in the small intestines that look like this projection up and down like this they look like fingertip-like projections and they're called villi only the small intestines have villi and they're there again to increase the surface area in actual fact the villi are just projections of the lamina propria they are not projections of the epithelia they're lamina proper you can see this underlying white area here is lamina propria projecting up again in the small intestines what you can see are these single or simple single layer columnar epithelia lining on top of that lamina propria but you can also see on top of the simple columnar epithelia these little look like more fingertip-like projections on the epithelia and they're called micro villa so the microvilli are extensions of the epithelia and the villi are extensions of the lamina propria very important increase the surface area allows for us to absorb all the things we need to absorb you've seen this green thing that i've drawn in here part of the lamina propria well that is going to be a lymphatic vessel and what you see is these lymphatic vessels move up the villi like this and they're called lacteals these lacteals are important because when the small intestines absorb fat which they often do fat unlike glucose fat unlike proteins get absorbed straight into the lymphatic system and then shuttle around the body via the lymphatics really important point if we compare the small intestines to the large intestines the major difference is there's no villi in the large intestines no villi there are microvilli that you can see here lining the simple columnar epithelia but that's basically it both small intestines and large intestines have glands and these glands have goblet cells that secrete large amounts of mucus as well now remember once we get down from the large intestines to the rectum the rectum from proximal to distal from most inside to most outside changes the type of epithelia it starts off as simple columnar like pretty much everywhere else and then it goes to simple cuboidal so the cells get a little bit smaller then it goes to stratified squamous many layers of squished cells so now we're looking at protection right and then once we get to the very end we're nearly at the other cheeks right and so we're going to have stratified squamous epithelia with keratin keratin is a protein that your epithelia produces to make cells strong and waterproof we have this in our skin which is no surprise because that's going to be like i said continuous with the very end of the rectum so this is a quick overview of the mucosa of the gastrointestinal tract hi everybody dr mike here let's continue our journey looking at the different layers of the gastrointestinal tract we call that histology of the gastrointestinal tract so in a previous video i said to you that the very first most internal layer of that big long tube that extends from the mouth all the way down to the anus is called the mucosal layer and the mucosal layer is made up of three separate layers it's got the epithelia which lines the inside this is a barrier that protects one environment from the next environment and i said the epithelia changes as we move from the mouth all the way down to the anus the next layer underneath that is the lamina propria which is loose connective tissue and contains blood vessels nerve fibers lymphatics and then the next layer is a very thin layer of smooth muscle two layers in fact one called the circular layer which goes around the hollow inside and a longitudinal layer which goes the length of the hollow inside and what that does is it changes the diameter of the micro environment helps push things through helps tails glands to release some enzymes and substances so they're the three layers of the mucosa now let's look at the next layer called the submucosa submucosa is also connective tissue just like the lamina propria it's loose connective tissue just like the lamina propria loose connective tissue means that the fibers embedded in the gels of this connective tissue which are collagen and elastic fibers they're loosely arranged which means like i've said previously this connective tissue can be pulled around it can be stretched it can be distorted and it then just pulls itself back to its normal position this is very important for the git as food stuffs move through it's going to distort the diameter of the hollow lumen now this loose connective tissue of the submucosa again like the lamina propria has blood vessels lymphatics and nerve fibers but something very important here are the nerve fibers the nerve fibers form a plexus now a plexus is like a braiding when somebody's hair is braided it's where these nerves form these plexuses all right so like multiple braidings and they're called either meissner's plexus or the submucosal plexus what do they do well these nerves what they do is they innervate the blood vessels so they can change the diameter of the blood vessels it also tells glands which are predominantly going to be extensions of the epithelia and lamina propria right tells them to secrete their enzymes or substances that they're producing and also tells the muscularis mucosa this circular and longitudinal layer to change its diameter as well so in order for the blood vessels the glands and the smooth muscle in the mucosal layer to do their job they need the meissner's plexus or the submucosal plexus that's present here in the submucosa these nerves actually come from another plexus called the myenteric plexus which is located between these two layers here these two layers are more smooth muscle they're the most important smooth muscle when it comes to mixing substances and pushing substances through the git between these two layers is the myenteric plexus and some of these nerve fibers penetrate through this layer to get to the submucosal layer to then innervate these areas here so this is the submucosal layer of the gastrointestinal tract hi everybody dr mike here we're now on to our third layer looking at the histology of the gastrointestinal tract what we've spoken about so far is if we look at the hollow inside of the tube that extends from our mouth to our anus we've got the first layer which is actually made up of three individual layers called the mucosal layer we have epithelia then connective tissue called laminopropria then a thin muscle layer called the muscularis mucosa the next layer is another connective tissue layer that contains blood vessels nerve fibers and lymphatics and that's called the submucosa and importantly it's got a certain nerve plexus present within there and this nerve plexus tells this smooth muscle and the glands of the epithelia to secrete their enzymes and change the diameter of that hollow inside and also tell the blood vessels to change their diameter as well in the mucosa but now we're going through this third layer and this third layer you can see is made up of two muscle layers both are called the muscularis externa together but what you'll find is the deepest layer is a circular smooth muscle layer so when you've got the hollow tube you're going to have a muscle layer that wraps around the hollow tube so when it contracts it narrows the inside of that tube that's called the circular muscle the next one is longitudinal muscle that goes the length of the hollow tube and when that contracts it shortens the tube so what that means is when it comes to gastrointestinal tract motility moving stuff from proximally to distally what do these two particular muscle groups do okay first if you look at the circular smooth muscle it narrows the lumen makes it larger narrows makes it larger that means it's really important in mixing the food it actually can segment the food by doing this it segments the food and mixes the food you'll also find that in areas where this circular smooth muscle is thickened it forms the sphincters and you're going to have sphincters at the lowest part of the esophagus which is the top of the stomach called the cardiac sphincter you're also going to find one at the bottom of the stomach going into the small intestines called the pyloric sphincter and you're also going to find two very important sphincters right at the very end of this entire tube the internal and external anal sphincter the longitudinal muscle well when it contracts it shortens the tube which means it helps push food along the movement of foodstuffs through the git is called peristalsis and that's important because of this longitudinal muscle layer now what tells this muscle to contract because muscle needs nerves to innervate it to tell it to contract well there's another plexus remember what i said plexus is plexus is just like a braiding of nerves there's another plexus of nerves here that sit between the circular and longitudinal muscles and they're called the myenteric plexus also known as the hour box plexus now this our back or myenteric plexus is really important because again it tells the circular smooth muscle to contract it tells the longitudinal muscle to contract now a couple of other important points when we look at the esophagus the most proximal one-third the top one third is skeletal muscle which means you consciously control it which means you consciously control the first third of your esophagus that's going to be swallowing then you've got the next third which is the middle third that's actually a mixture of skeletal muscle and smooth muscle and then the bottom third you'll find is just smooth muscle which means you do not control it so there's this reflex system which when you open up the esophagus when food goes into and it stretches it at the proximal end it triggers peristaltic waves to transmit down the esophagus and push the food stuff down okay another important point when it comes to the muscularis externa the circular and longitudinals when we get to the stomach we don't just have these two layers we've actually got three muscle layers an additional muscle layer called the oblique muscle layer and you can see i've got the stomach and i took some sections out so we've got the oblique muscle layer then we've got the circular muscle layer then we've got the longitudinal muscle layer why does the stomach have an additional muscle layer because the stomach doesn't just release enzymes to digest food it's not just a pit that sits there waiting for food to ferment inside that's not what happens the stomach is a dynamic organ it moves it shifts around what you'll find is because of these three muscle layers the stomach can jack knife in upon itself it can squeeze it can shift and jack knife and this is important for chemical and more specifically mechanical digestion so this is the muscularis externa layer this is the third layer of the gi layer of the grt hi everybody dr mike here we are now looking at our last layer the most external layer of the gastrointestinal tract when we're looking at the histology and that is called the serosal layer or adventitia layer so what we've gone through so far is the most internal layer being the mucosal layer then the submucosa then the muscularis externa and now this very final layer termed the serosa or adventitia now why do i say serosa or adventitia well a serosa or sarosa layer is a double membrane layer made up of epithelia one of these layers will be stuck to the organ and that's going to be called the visceral layer and then there's going to be another layer that's going to be most closest to the body cavity and it's going to be called the parietal layer in between those two epithelial layers is a fluid called a cirrus fluid that helps produce basically it's a lubricant and helps reduce friction between the organ and the surrounding structures now serosal membranes are going to be surrounding organs that sit within the cavity of the gastrointestinal area called the peritoneal cavity so serosa wraps around organs that sit within the peritoneum known as intraperitoneal these organs include the liver the stomach the spleen the very first part of the duodenum called the duodenal bulb or bulb of the duodenum the rest of the small intestines being the ilium and jejunum the transverse colon which i've drawn behind these structures but in actual fact the transverse column sits in front of all these structures and the sigmoidal colon so all of these areas that i've highlighted in blue is covered by serosa like i said double membrane epithelia produces serous fluid and it wraps organs that sit within the peritoneal cavity now adventitia is not epithelia it is connective tissue it's loose connective tissue and it wraps and binds organs that sit outside of the peritoneal cavity specifically sit behind the peritoneal cavity called retroperitoneal and what you can see is organs that sit retroperitoneal that are bound by adventitia include the pancreas most of the duodenum the cecum and the ascending colon the descending colon and they're all bound by adventitious connective tissue and it binds them to the walls of the abdominal cavity okay so basically is there to hold it into place so what's the difference between the serosalea or the adventitia layer both of which is the most external layer of the gastrointestinal tract serosa is epithelia double membrane serous membrane that produces serous fluid as a lubricant it binds organs that sit within the peritoneal cavity adventitia is loose connective tissue it grabs a hold of organs and anchors them to the walls of the body cavity and it's for organs that sit outside of the peritoneum known as retroperitoneal hi everybody dr mike here now let's look at the anatomy of swallowing so we're going to look at some of the muscles we're going to look at some of the nerves we're going to look at some of the activities of these muscles and nerves in order for us to get a nice delicious cheeseburger into our esophagus so in order to get that cheeseburger down there what you need to do is open your jaw put into your mouth close your jaw and do this on repeat opening closing of the jaw requires certain muscles now in actual fact there's three muscles that allow for us to close the jaw one muscle that allows for us to open the jaw now the three muscles that allow for us to close the jaw include the masseter so if you to tense your jaw right now you can feel the masseter right here then another muscle is the temporalis close the jaw again and then put your fingers on your temples you're now feeling the temporalis muscle and the last one is out of the medial pterygoid which is deep deeper to the masseter okay so these three muscles allow for closure of the jaw now in order for us to open the jaw we only need one muscle and that's the lateral pterygoid and what the lateral pterygoid does is takes the epicondyle of that of the mandible and basically loosens it out of that joint all right so these four muscles are involved with chewing now what nerve innervates these muscles well it's the trigeminal nerve and the trigeminal nerve is cranial nerve five so it's going to be coming out of the brain stem to innervate these nerves and its cranial nerve five now trigeminal nerve is both a sensory and a motor nerve in this case this is its motor nerve function but its sensory nerve function is that of sensation of the face so if you take your three fingers like this these are the three branches of the trigeminal nerve you have the optic the ophthalmic the maxillary and the mandibular okay so sensation from these particular areas via the trigeminal nerve all right but we know that in order to break food up it's not just opening and closing at the jaw we need to manipulate that food in our mouth via our tongue but first to keep the food in the mouth so it doesn't fall out we need to close those lips and we need to tense the muscles of the cheek okay so the buccanator muscles which are the muscles of the cheek and the orbicularis auras which are the muscles of the lips both need to close off now they do this because of the facial nerve so facial nerve facial nerve is going to be this motor nerve which and facial nervous cranial nerve seven and that's going to tighten those lips orbicularis oris and the cheeks need to be tightened as well the buccinator muscles and that is by cranial nerve seven all right now movement of the tongue the tongue needs to move the food around the mouth to deliver it to the teeth so that the teeth can obviously chew it up in order for the tongue to move there's multiple muscles associated with it talk about those in a second but the nerve that innervates these muscles predominantly is going to be the nerve called the hypoglossal nerve and this is cranial nerve 12. so cranial nerve 12 term the hypoglossal nerve i'll write it up here again is a cranial nerve that's coming out of the brain stem telling the tongue to move all right now if we want to talk about taste of the tongue well taste comes from the facial nerve which is the anterior two thirds the front two thirds of the tongue for taste is via the facial nerve the posterior one third of the tongue is via another nerve called the glossopharyngeal nerve and i'll talk about that one in a second so now what we've got is we've had a bit of food into the mouth the lips are tight the cheeks are tight the jaw is moving up and down and the tongue is manipulating that food so far we've done we've spoken about cranial nerves five seven and twelve doing these functions for us now what happens is we need to moisten that food so in order to moisten the food we need to tell the salivary glands to release saliva now you're going to have the parotid salivary glands par meaning near oated meaning ear so they're near the ear salivary glands you have the sublingual under the tongue submandibular alright so these three salivary glands release saliva now the parotid salivary glands they stimulate to release saliva via the glossopharyngeal nerve which i haven't spoken about yet so the glossopharyngeal nerve is cranial nerve nine let's write it over here glosso pharyngeal nerve which is cranial nerve nine that's going to tell the parotid salivary gland to start salivating the sublingual and submandibular salivary glands again via facial nerve cranial nerve seven now what we've got is a moistened bit of food that's broken up that we term a bolus b-o-l-u-s and now this bolus which is being manipulated around the mouth by the tongue what happens is the tongue will contract and as the tongue contracts it lifts up and back now the muscles that help this process are what we term the suprahyoid muscles now if you were to take me in this position you'll see here's my jaw like that there's the jaw there and you're going to have the adam's apple which is the laryngeal prominence which is laryngeal cartilage and then the windpipe which is these parts here and then the hyroid bone which is this floating bone that sits up here which you can't see but there's the hyoid bone from a lateral view there's the hyoid bone from an anterior view and you can see there's multiple muscles attached into the hyoid bone and up towards the tongue now these suprahyoid muscles when they contract they're going to lift as you can see they'll lift the hyoid which is attached to the larynx and trachea and lift the larynx and shakir up so that means as the tongue elevates it's going to lift the hyoid and lift the trachea up as well now if it lifts it up it's going to lift it up like this which means the whole airway here moves up and this lid called the epiglottis closes over that means that food when we go to swallow will not go into our airways hopefully now another thing is as this tongue elevates it's going to push this food bolus against the roof of the mouth now the roof of the mouth has the soft palate and the hard palate the hard palate has bone soft palate does not now there's nerves in this soft palate so when the food bolus hits this nerve this nerve is actually going to be the glossopharyngeal nerve cranial nerve 9 when it hits that nerve it sends a signal to the brain stem particularly the medulla which is our swallowing center and sends a signal back out now the signal that's coming back out is cranial nerve 10 which is called the vagus nerve and the vagus nerve tells the muscles of the soft palate to contract and move up and back like that closing off the nasal cavity so now what we've done through the use of the vagus nerve through the use of contraction of the suprahyoid muscles we've lifted the tongue up closed off the larynx and the airways we've lifted the soft palate up by the vagus nerve closing off the nasal pharynx and so now we've turned what used to be a combined compartment of air and food to just the compartment of food and so now that food bolus can move back due to pushing backwards of the tongue that food balance bolus will hit against the oropharynx again stimulate glossopharyngeal and vagal nerves so right here there's going to be 9 and 10 cranial nerve 9 and 10 it's going to send afferents to the brainstem efference back out predominantly the efferents are going to be that of cranial nerve 10 which is the vagus nerve and allow for us to swallow now as we move this airway up this way to close it off it actually stretches open the esophagus and allows for that food bolus to move in so as you can see it's quite complex couple of cranial nerves involved and muscles involved what are the cranial nerves involved with swallowing well we've got the trigeminal nerve we've got the facial nerve we've got the hypoglossal nerve we've got the glossopharyngeal nerve and we've got the vagus nerve as well so this is the anatomy of swallowing we know that digestion involves both chemical digestion which is the use of enzymes to cut like molecular scissors cut open these nutrients into small products and mechanical digestion which is the physical tearing apart of these macronutrients into micronutrients regardless the aim is to get these big macronutrients and those macronutrients are proteins fats and carbohydrates aim is to get these macronutrients down into their smallest components which are specifically proteins we want to get down into amino acids fats we want to break down into two particular components actually we want to break them down into glycerol and fatty acids and carbohydrates we're going to break down ultimately into glucose now the reason why the reason why we want to break proteins down into amino acids fats down into glycerol and fatty acids and carbohydrates down to glucose is because we want to use them in whatever way we think is best we can't absorb proteins fats and carbs from our small intestines into the bloodstream we can only absorb them when they're in these micronutrients forms plus the way i like to think about it is when it comes to carbohydrates we need glucose because glucose will ultimately be used to create atp which is the energy currency of the body allows us to survive fats we like to break down into glycerol and fatty acids because they play a very important role when it comes to forming membranes and general structure of the body proteins well well fats also can create atp as well proteins we want to break them into amino acids i like to think of this as though a protein is a house and you don't like the way that that house is you want to reuse the bricks that make the house to make a totally different house so you break the proteins up into their amino acid constituents and then you can take those amino acids and build whatever protein you want okay and proteins they play all the functional roles within the body now the question is how do we go from carbs to glucose fats to glycerol and fatty acids and proteins to amino acids well today i want to talk about how this happens through chemical digestion so this is using those molecular scissors to chop them up so we can get them down into their smaller units now the molecular scissors are enzymes and usually enzymes end in the suffix ase a's so you're going to find that the enzyme that breaks down comes to glucose is called amylase the enzyme that breaks fats down is called lipase and the enzyme that breaks proteins down is called protease now there's different subcategories of amylase lipases and proteases but we're just going to generally refer to them as amylase lipase and protease so where does this occur in the body so if we start at the mouth where digestion does occur so mouth choo choo choo we've got the esophagus which is through peristalsis pushing it down to the stomach which then starts to jack knife in upon itself release some enzymes push it to the small intestines and then to the large intestines where we go to the sigmoidal colon and the rectum and then the anus for excretion but when it comes to chemical digestion let's start at the mouth so you take a big bite of a burger and then as you chew that's mechanical digestion your salivary glands are going to release an enzyme called amylase therefore the mouth is the first site of chemical digestion and it's the first sign of chemical digestion for carbohydrates so mouth by releasing saliva now there's a little bit of lipase that's being released in this saliva but we're going to say at the moment it's negligible we just want to generally focus on where it's happening mouth saliva amylase then as we go into the esophagus there's no chemical digestion occurring at the esophagus it's simply a conduit between the mouth and the stomach as we get down into the stomach the stomach starts to release some enzymes and these enzymes are proteases so these enzymes are specific to break proteins to amino acids and the enzyme is called pepsin so the stomach is actually the first site of protein digestion now remember that pepsin isn't actually released as pepsin it's released as pepsinogen by these particular cells called chief cells there's a number of different cell types within our gastric pits now these chief cells release pepsinogen and if it ends in ogen it means it's stored in an active something needs to activate it now the thing that activates pepsinogen is hydrochloric acid and hydrochloric acid is released from another cell within the gastric pits of the stomach called parietal cells so chief cells release pepsinogen parietal cells release hydrochloric acid hydrochloric acid travels to the pepsinogen and chops it and activates it into pepsin and what does pepsin do well pepsin breaks some of these chemical bonds of proteins it's a protease now from the stomach we move to the small intestines now the small intestines is the first site of fat digestion and it's because of the pancreas the pancreas actually releases all three types of enzymes so what we can do is we can move through and we can say that the pancreas even though it's not the side of digestion the pancreas will release proteases into the small intestines the pancreas we'll release lipases into the small intestines and the pancreas will release amylase into the small intestines this is important because it tells you that by the time we get to the small intestines nearly everything is chemically digested digested except fats this is very important because as the fats move through it's heavily reliant upon the pancreas so if somebody has pancreatitis or some issue with their pancreas then what you'll find is potentially those fats won't be digested and you can get a fatty stool so that fat gets pushed all the way through now here are the major sites there's also some cells within the small intestines called brush border cells and they release some proteases and some amylases as well but not lipases you can see how important the pancreas is for fats to be digested now these lipases aren't going to be that successful unless the gallbladder squirts down a little bit of bile as well if you want to know more about bile and the gall bladder and the liver watch that particular video but this is just a very brief summary overview of chemical digestion in the gastrointestinal tract hi everyone dr mark here in this video we're going to talk about the esophagus and a little bit about gastroesophageal reflux now the esophagus is a conduit it's a pipe that sends food from the pharynx which is the back of the throat down to the stomach now the pipe's around about 25 centimeters long it's a very muscular tube and it's made up of two types of muscle it's made up of skeletal muscle which we can control consciously that's actually the upper third of this 25 centimeter tube is skeletal muscle and then the lower two thirds of this 25 centimeter tube is actually smooth muscle which we don't consciously control now in order for muscle to contract which it needs to for the esophagus it needs to be innervated by nerves and the most important nerve here is the vagus nerve controlling the esophagus to contract and relax in this wave-like motion termed peristalsis now you can break the esophagus up into three major parts the cervical the thoracic and the abdominal areas if we look at the cervical esophagus you'll find that it begins at around about the cricoid cartilage so what's the cricoid cartilage find your laryngeal prominence which is also termed your adam's apple both males and females have an adam's apple it's a secondary sexual characteristic that's exaggerated by testosterone but both males and females have it feel the laryngeal prominence then move down and you'll feel a squishy part and then go below that and you'll feel another bit of cartilage and that's the cricoid that is where your esophagus begins at the cervical area now if you were to correspond that to your vertebrae it's around about c6 all right now this cervical area you can see that this cervical esophagus is actually sitting behind a posterior to the aorta and the trachea as well so you can see it hidden in my picture here this is the esophagus behind the trick here here it's bifurcated into the bronchi and this is the aorta that's just come out of the left ventricle of the heart the heart's been taken away now you can see with the aorta that it moves to the left and it arches and it's called the aortic arch and then starts to descend down the thorax and then into the abdomen through the diaphragm which i'll talk about in a sec you can see the three main branches of the aorta you can see the brachiocephalic you can see the common carotid and you can see the left subclavian and as it moves down the aorta it then moves behind the esophagus and that's when we get to the thoracic esophagus thoracic esophagus is sitting in front of the aorta and by that time we've got the bifurcation of the trachea until it branches 23 odd times and it's turned from bronchi into bronchioles and then into everything it needs to turn into for the respiratory portion or the gas exchange area of the lungs now the thoracic esophagus as it moves down what you'll find is that now what we're talking about with the esophagus 25 centimeters long like i said the top third is comprised of skeletal muscle so that means you consciously control that swallowing portion or the movement of foodstuffs in the top third the bottom two thirds is smooth muscle which means you don't consciously control it so what you'll find is most of the thoracic esophagus and then as we move through the diaphragm now the diaphragm is going to be sitting under here at around about t at around about t10 t11 or around about the seventh rib area you're going to find that the esophagus moves through the diaphragm and turns into the abdominal esophagus now the abdominal esophagus is only around about 1.5 centimeters long and then it turns into the stomach first part called the cardiac area of the stomach a couple of things that means it must move through a hole in the in the stomach called the hiatal area and you can get something called a hiatal hernia so you can see here the esophagus going down there's the diaphragm what can happen sometimes is that the cardiac area of the stomach can for whatever particular reason fold upwards through this gap and bulge out and that's called a hiatus hernia this can actually result in reflux which i'll talk about shortly a couple of things is that you can also see that there are these ligaments either side or tendons either side of the esophagus that's moved through the diaphragm and the one they're both called the cross you've got the left and right cross and the right cross actually puts pressure on that esophagus and is one of the reasons why things do not or should not reflux up into the thoracic area of the esophagus from the abdominal region now you can also see that the aorta has actually now entered the diaphragm as well and you can see as the aorta goes through the thoracic area it then re-enters the diaphragm and now it's the abdominal aorta and you can see a very important branch of the abdominal aorta here called the celiac trunk i've spoken to you about blood supply to the stomach to the liver to the spleen to the first part of the small intestines all come from the celiac trunk here and you're going to have the hepatic artery you can have the splenic artery you're going to have the left gastric artery watch that video if you want to know more about blood supply to those areas so a couple other things remember that as we look at the tract of the git going from the mouth all the way down to the anus four major layers being the mucous layer the submucosal layer the muscularis externa and the serosal layer you can see those here mucus submucous here's the two muscle layers and then the peritoneum which is the serosa anchoring it to the body cavity in the esophagus the mucous layer has epithelia that's stratified squamous squished and many layers why it's there for protection when you swallow food it's going to graze and cut you don't want to damage the deeper layers perfect once you get to the stomach so this is the gastroesophageal junction gastro beans stomach esophageal being esophagus junction being the part in between and you can see that the epithelia in the stomach is simple columnar that's because these columnar cells produce mucus and bicarbonate which neutralizes the acid that's produced in the stomach that also means that if they're not present in the esophagus they can't neutralize acid so if acid refluxes up into the esophagus it can damage the walls here and can ultimately result in inflammation called esophagitis it can damage the cells change the way the cells are shaped and that's turned barrett's esophagitis these cells these stratified squamous cells can actually turn into what looks like simple columnar cells because it's thinking i need to protect myself i need to turn into simple columnar to produce mucus and so forth but in actual fact the change in cell type is a precursor or can be a precursor to cancer esophageal cancer alright now what we all have here at this gastroesophageal junction is a sphincter called the lower esophageal sphincter and you can see that with the muscle layer here the muscularis externa there's two major types the circular muscle which goes around the tube when that contracts it narrows the lumen and you've got longitudinal muscle which goes down the length when that contracts it shortens the tube together they allow for peristalsis move stuff through but here at the gastroesophageal junction the circular muscle is thickened and creates a sphincter a nice tight enclosed area so things cannot go back up through now things like spicy foods caffeine chocolate they can all relax that lower esophageal sphincter and what it can do is allow for gastric contents to spurt back up into the esophagus damaging the cells potentially resulting esophagitis barrett's esophagitis and also cancer ultimately if chronically exposed this may happen okay i think that's going to be enough when we look at the anatomy of the esophagus a little bit about gastroesophageal reflux hi everyone dr mike here in this video we're going to take a look at the anatomy of the stomach now the stomach is the widest portion of the gastrointestinal tract remember that's that big long tube that starts at the mouth and snakes its way all the way down to the anus now it's not just this pit or this storage unit for food the stomach is actually a dynamic active organ and what it does is it plays an important role for both mechanical digestion that's tearing food stuffs apart and chemical digestion which is utilizing molecular scissors that we term enzymes to break food apart all right now if we were to locate the stomach on my anatomy the very first part of the stomach is going to be what we term the cardiac orifice this is where the esophagus turns into the stomach so that means as the esophagus moves down the thoracic area through the diaphragm into the abdominal area it actually goes from being midline to a little bit left of the midline and it starts to curve away now as it curves away it starts to form that cardiac orifice of the stomach and in order to identify the cardiac orifice there's an easy way to do it get a ruler take your left incisor and measure 40 centimeters straight down take you to around about here and that's going to be where your cardiac orifice is that's this portion the very first part of the stomach now as you can see to the left of the cardiac orifice is the roof of the stomach that we term the fundus now the fundus has a number of different glands in there that i'll talk about in the future video but if you want to identify the fundus on your body it's going to sit at around about the fifth rib in actual fact it go mid clavicular find your clavicle go mid clavicle go all the way down until you below your nipple just below your nipple that's around about the fifth rib this is where your fundus is of your stomach okay now if you have stomach pain you don't actually feel in this area you feel in the epigastric area and that's got to do with embryological origins when you were developing in your mummy's tummy or womb it has to do with that all right so you've also got the body of the stomach which is the majority of it you've got the polaric area in the pyloric area has the polaric antrum then the polaric canal and then the very first part of the small intestines that we term the duodenum now the lateral boundaries of the stomach and medial boundaries include the lesser curvature and the greater curvature of the stomach as well and in addition to that you can see i've cut out some portions of the stomach here this is the musculature of the stomach remember if we look at the histology or the layers of tissue of the stomach you're going to find that the most internal is going to be the mucosal then there's going to be the submucosal then the muscle layer and then the serosal layer which anchors it to the body now the muscle layer throughout the entire git mouth to anus has two muscles circular muscles longitudinal muscles but the stomach has an additional one called an oblique muscle which is at an angle this oblique muscle in collaboration with the circular and longitudinal allows for the muscle the stomach to actually fold in upon itself and jack knife this plays a very important role in that mechanical digestion okay now if you look at the blood vessels that supply the stomach i've done a video on it but we know that around about here you're going to have the abdominal aorta with a branch called the celiac trunk and the celiac trunk has a couple of branches one of which is the left gastric artery which comes and gives oxygen and nutrients to the lowest part of the esophagus and the superior portion of the lesser curvature then you've got the splenic artery which branches off goes behind the stomach feeds the spleen also up to the fundus and the superior portion of the greater curvature then you're going to have a branch to go off to the liver because the liver sits across that side and it's called the hepatic artery and that has a branch the hepatic artery will feed the lesser curvature of the stomach and there's another branch that comes off and feeds the inferior portion of the greater curvature there's a lot of stuff there when it comes to nerves that innervate we look at the vagus nerve that's the 10th cranial nerve it's the wanderer it goes below the head and that goes to the stomach and when it innervates the stomach it tells the stomach to start moving the motility of the stomach start to release enzymes and mucus from the glands start to relax the pyloric sphincter to move food stuff through that is the vagus nerve that's parasympathetic innervation of the stomach what about sympathetic innervation of the stomach that's going to come from around about thoracic 5 to thoracic 8 via the splanchnic area the spike neck nerves and that's going to stop the stomach from doing those sort of digestive activities so this is a quick overview of the anatomy of the stomach hi everybody dr mike here now let's take a look at the histology of the stomach this is looking at some of the cells and tissues of the stomach and the chemicals hormones and enzymes that these cells and tissues release so firstly remember that with the stomach you've got the majority of the stomach being the body you've got the roof of the stomach being the fundus and then you've got the exit portion of the stomach that would turn the pyloric area now if we have a look if we're to cut the stomach open and look in it looks as though there's this honeycomb shape to it and that's because there's multiple gastric pits or glands present that look like this now in actual fact for every single square millimeter of the stomach inside the stomach you're going to find between 60 to 100 of these pits or glands now as you can see if we look at predominantly the fundus of the stomach it's mainly cells that produce mucus in these pits and glands but as we go through the body you're going to find that we've got what we term principal glands the principal glands look like this there's multiple cell types in these principal glands and what we're going to do is we're going to start deep within the gland and then go more superficial so deep what we find is that we have these sporadically placed neuroendocrine cells and there's multiple types of neuroendocrine cells neuroendocrine is basically telling you that they are like hormone producing cells okay and they produce things like gastrin somatostatin histamine serotonin ghrelin i'm going to talk about this in detail very shortly the other types of cells present at the base of these gastric pits include the chief cells now what the chief cells do is they produce pepsinogen now pepsinogen is an inactive enzyme so remember that if there's a word in biology that ends in ogen it means it's stored and inactive which means it needs to be activated pepsinogen is stored in an active it gets activated by hydrochloric acid these are produced by the parietal cells talk about that in a second now when pepsinogen is activated by hydrochloric acid it chops it up turns it to pepsin and what pepsin does is it is the molecular scissors that break up proteins so when we chemically digest proteins in the stomach it's because of pepsin now the other type of enzyme that's present here that breaks up one of our macro nutrients includes that of lipase but it's not the predominant site of fat digestion but some fat is digested in the stomach now if we go up towards the neck of these gastric pits you'll find the parietal cells now it is the parietal cells that produce hydrochloric acid in actual fact they pump out hydrogen ions that's just h and chloride ions that's the cl and they come together to form hydrochloric acid now it's that acid that denatures proteins so remember proteins are strings of amino acids that are folded in upon themselves in this quaternary or 3d sort of shape now what happens is acid opens it up makes this nice big long linear molecule so that pepsin can come along and chop it up nice and easily the analogy i use is it's very difficult to get a ball of wool and just chop it up with scissors it's easy to chop it up once you untangle it now it also releases the parietal cells intrinsic factor intrinsic factor is important for us in our small intestines to absorb vitamin b12 vitamin b12 is important to produce red blood cells so if you don't have enough intrinsic factor you don't absorb vitamin b12 you can become anemic that's not enough red blood cells and this results in tiredness lethargy things like that all right as we move up we're going again at the neck of these cells we've got mucous neck cells they produce mucus with a multitude of different enzymes within they only last around about one week before they're replaced and when we go up to the surface the most superficial cells are those are the surface mucous cells and they produce mucus as well different type of mucus to that of the mucous neck cells but they also produce more importantly bicarbonate now bicarbonate ions why is this important they mop up hydrogen ions which means hydrogen ions are an acid bicarbonate is a base they neutralize each other so you can see at the surface of your stomach you actually have bicarbonate that can neutralize the acid and protect your stomach so it does not digest itself so it's the surface mucous cells that are important and the bicarbonate for you not digesting your own stomach all right if we go down to the neuroendocrine cells it's important that we look at g cells g cells produce gastrin now what gastrin does is it stimulates gastric activity so what that means is gastrin stimulates the parietal cells to produce acid and start digesting things gastrin stimulates the ecl cells which are the enterochromafin-like cells to produce histamine histamine also stimulates the parietal cells to produce acid g cells that produce gastrin also stimulate ghrelin ghrelin is released from the pd1 type endocrine cells ghrelin is a hormone that travels to our brain and tells us we're hungry let's start eating and ghrelin also goes to the parietal cells to stimulate acid production now in addition to all this gastrin stimulates the d cells that produce something called somatostatin but what somatostat does is the opposite it inhibits histamine from telling the parietal cells so basically somatostatin inhibits the parietal cells from producing acid so it has an antagonistic effect now why is this important clinically because a lot of our d cells are located here at the pyloric area and when somebody has a helicobacter pylori bacterial infection it leads to inflammation in this pyloric area and inflammation can lead to death so the d cells die which means no somatostatin being produced which means no inhibition which means you start to over produce acid and this is one reason why people who have h pylori infection in their gut have increased acid production so i think that's a nice quick overview of stomach histology hi everyone dr mike here let's take a look at the anatomy of the duodenum so remember the duodenum is the very first part of the small intestines so it's firstly coming out of the stomach and then it goes to the second part of the small intestines called the jejunum so if we take a look what i've drawn up here is a couple of things firstly you can see the big aorta the largest vessel in the body running down behind that of the duodenum and also behind the pancreas which you see sits inside this c flexure of the duodenum now a couple of things the denim can be broken up into four parts the first part the second part the third part and the fourth part so we're going to discuss them in these four parts firstly i want to have a look at the vascular supply so what are the dedicated blood vessels that feed the duodenum oxygen and nutrients so it stays alive well firstly remember at the aorta we've got a trunk that branches off called the celiac trunk which has three branches of its own these branches include the left gastric artery which feeds the stomach lowest part of the esophagus couple of other things then you've got the splenic artery which goes and feeds the spleen here you've got the common hepatic artery that goes to the liver and gallbladder and part of the common hepatic artery we've got a branch called the gastroduodenal artery now the gastroduodenal artery goes behind the first part of the duodenum and branches into two parts these two parts are the superior pancreatic duodenal arteries now one of them is anterior so it sits in front of the pancreas the other one is inferior so it sits behind the head of the pancreas now the superior or i should say the anterior and posterior superior pancreatic duodenal ducts you can see that they give blood so oxygen and nutrients to the first and second portion of the duodenum now what feeds the second third and fourth portions well you can see down at a lower portion of the aorta you've got another branch that comes off now we can't see where it branches because it happens behind the pancreas but this branch is called the superior mesenteric artery and one of the branches of the superior mesenteric artery is the inferior pancreatic duodenal artery and again there's a posterior segment segment and there's an anterior segment now the anterior and posterior segments of the inferior pancreatic duodenal artery i know it's a mouthful they give oxygen and nutrients to the second part of the duodenum and the third part of the geranium so you see i've written it up here now the fourth part of the duodenum all right coming off this superior mesenteric branch of the aorta there is what's called the first jejunal artery and the first judging artery has branches right and this is a duodenal branch and this is what feeds the fourth segment of the duodenum now in actual fact this g first jejunum artery and its branches can actually anastamosize okay so this means it can come together with another artery right and it can actually come together with that of the superior mesenteric arteries and that means the fourth part of the duodenum can actually get two blood supplies one coming from the superior mesenteric one coming from the celiac trunk which means it very rarely becomes ischemic meaning if this part got blocked it doesn't matter it's going to get blood from up here if this part gets blocked it doesn't matter it's going to get blood from down here okay so the fourth fourth portion of the duodenum very rarely becomes ischemic so a lack of blood or oxygen to that area now if we again break it up in those four particular segments let's have a look the first segment which starts at the pyloroduodenal junction so pyloric remember the polaric sphincter this is the end of the stomach the pyloro duodenal junction that's right here this is where it begins now that portion is around about 2.5 centimeters the whole thing is about 5 centimeters so you could probably deduct around about 2.5 centimeters from that alright so again round about 5 2.5 to 5 centimeters long as it goes across it actually goes not just across but it goes up and it goes back so it actually goes up and to the back alright so remember that as it goes up into the back you can see it sits in front of the gastro-duodenal artery why is this important well some people remember coming from this part is going to be acid from the stomach acid from the stomach can perforate the small intestines if it perforates the first portion of the duodenum it can go through and actually perforate the gastroduodenal artery and this leads to significant hemorrhaging okay so that's an important clinical point another important point is that this part here right part one actually sits at the level of the first lumbar vertebrae all right so sits at the level of the first lumbar vertebrae as we get across we hit something called the superior duodenal flexure that's this bend here and from the superior duodenal flexor to the inferior duodenal flexor is our second part which is around about 10 centimeters long and this lies just a little bit to the right of the vertebral column in actual fact it goes from lumbar one lumbar 2 and lumba 3 vertebrae so that's basically the distance that the duodenum covers so it goes down down down now an important point of the second portion of the duodenum is that there's a little hole here called an ampulla now this ampulla is the hepatopancreatic ampulla ampulla also known as the ampulla of vata what's important about it well the bile duct so the the gallbladder is going to be sitting right here it's going to have its own duct the bile duct and the pancreas has a duct called the pancreatic duct those two come together here at the hepatopancreatic ampulla and they really release their substances into the second portion of the duodenum the gallbladder releases bile which emulsifies fats breaks it down and the pancreas releases a whole bunch of amylase lipase proteases and also bicarbonate other alkaline substances to break all that food stuff down now as we move down from the inferior hepata inferior duodenal flexure this is the first part of the third portion and it goes all the way across to the fourth portion which is just a little bit to the left of the aorta all right now this third portion is around about 10 centimeters long and actually sits in front of a couple of important structures for example it sits in front of the right ureter this is the tube that goes from the right kidney to the bladder sits in front of the right psoas muscle sits in front of the right garnadel vessels as well and then it gets to the fourth portion now the fourth portion is about 2.5 centimeters long so if you add all this up it's around about 25 centimeters which is about 12 inches which is about 12 finger tips wide which is what duodenal means 12 fingertips wide and we get to the fourth segment this turns into the jejunum okay and you can see the fourth segment sits to the left of the aorta so this is the anatomy of the duodenum now take a look at the pancreas now the pancreas is both an exocrine and an endocrine gland now what does that mean well endocrine means that it releases hormones into the bloodstream and exocrine means it releases chemicals into hollow tubes and hollow organs so let's first draw up the pancreas and then we'll talk about very quickly both of those two functions that the pancreas plays all right so first thing i want you to draw up is we're going to draw the stomach or at least the stomach and the pyloric sphincter leading into the duodenum and then we're going to exaggerate the duodenum which is the first part of the small intestines and within the c shape of the duodenum that's where we're going to place the pancreas now when we look at the pancreas the pancreas has a head a body and a tail okay so we've got the head the body and the tail and there's a number of ducts so ductile systems within the pancreas that lead into the duodenum so let's draw that up so these are just some branches of that ductile system and i'm just going to leave it there i'm not going to close it off yet because there's going to be another duct that comes in that's very important another thing i want to draw up i know that stomach is very small i'm also going to draw a very small liver because the liver is not the focus of today's lecture either but it will be of another lecture and we're going to draw two ducts that come off the liver like this and then we're going to have the gall bladder and then we're going to have another duct that comes in behind and this is going to be the duct that connects up with the duct of the pancreas all right a couple of other things that when we looked at these look at these ductal cells that come off these interloba and interlobular ductal cells if i was to just zoom in on this area right here for example we're going to find as an example here you're going to see that there's going to be groups of cells around what looks like an open area at the ends of these interlobular ducts so this is the pancreatic duct pancreatic duct and this is going to be an interloba and this is going to be an interlobular duct okay and then at the end of this interlobular duct there's going to be a group of cells around what looks like an open cavity now these groups of cells here are called asini for pleural acini or they are assanis cells asanas or asani's pleural we're going to talk about exactly what those cells do very shortly now a couple of other things what i want to do is now name or label what these all these tubes are called okay so first thing is if we start up here at the liver we've got the left and right hepatic duct so we've got the left the paddock duct and we've got the right hepatic duct that's those two there and they come together to form the common hepatic duct common hepatic duct then you've got the gallbladder right there and then the duct of the gallbladder is called the cystic duct that's the cystic duct and then when the cystic duct comes together with the common hepatic duct that's going to be the bile duct now you can see that the bile duct comes together with the pancreatic duct there's so many ducts involved here pancreatic duct and bile duct come together and they come together at what's called the ampulla of veda the ampulla of vapor let's highlight that ampulla of vata and then here we have a sphincter in which this bile duct and pancreatic duct which come together will empty their contents into the duodenum and this is called the sphincter of od sphincter of od okay now we've set the scene we can talk about exactly what happens when the stomach decides to squeeze the contents that kind that's within the stomach through the pyloric sphincter which is remaining relatively tight remember the stomach has these muscular contractions it's got three muscular layers instead of just the longitudinal and the circular it's also got an oblique layer which allows the stomach to start pushing climb through and it squirts this chyme sorry can draw that up very well it squirts this climb through the pyloric sphincter into the duodenum okay so now we've got foodstuffs moving through the duodenum now this food stuff's going to be proteins fats carbohydrates okay now remember this is important in the mouth you have amylase that's secreted by the parotid gland so the protein gland secretes amylase which breaks carbohydrates down to sugars so now we've broken down one of the three proteins fats or carbs carbs once we get down to the stomach the stomach has hydrochloric acid that denatures proteins that just unfolds them but also has these proteases right and there's proteases that are molecular scissors that cut up proteins so now we've digested chemically digested proteins what haven't we digested yet fats so this is a very important very important point when it comes to the duodenum and the pancreas is that it plays a very big role in fat digestion i haven't told you the specifics yet but without the pancreas sixty percent of the fats that you digest in your foodstuffs would not get absorbed all right and we'll get back to that point so we've got proteins fats and carbs broken some of which are broken down but predominantly there's a lot of fat coming through here now as this food stuff's moved through i'm just going to rub off the sphincter of od here so i can highlight some important points as this foodstuffs continue to move through it ends up stimulating some cells in the duodenum and these cells are called enteroendocrine cells so these are enteroendocrine cells i'll write it down here entero endocrine cells now entero is referring to the grt that's easy endocrine is referring to the endocrine system which means it releases hormones into the bloodstream and what hormones does it release well these enteroendocrine cells release secretin and cholecystokinin so secretin and cholecystokinin secretin and c c k for cholecystokinin now this is important what stimulated their release what stimulated their release was foodstuffs moving through and acid moving through let's first start with cck what does cholesterol do once it's released into the surrounding bloodstream well first thing it does is it will go to these or one of the things it does i should say it will go to these individual asana cells and stimulate them to release the products that they create now what products do they create asana cells produce something called pancreatic juices let's write that down asana cells produce pancreatic juices and the pancreatic juices what we call pancreatic juices are proteases amylase and lipase protease amylase lipase breakdowns proteins fats carbs they cumulatively are the pancreatic juices now an important point is that the proteases for example are inactive in the astana cells and are still inactive when they're released from the astana cells now what stimulated them to release i told you it was the cck so cck stimulated acid cells to release these pancreatic juices into these interlobular and into loboductal cells and then into the pancreatic duct where it will finally be released into the duodenum but they are inactive and they're inactive because there's an inactivator within these pancreatic juices that keep them inactive once they get to the duodenum there are certain chemicals called enterokinases so what i've drawn up here are entero kinase and these enterokinase activate the inactive proteases okay so these inactive proteases for example is trypsinogen if it ends in ogen it's inactive usually stored and needs to be activated so trypsinogen once it's activated chop off the og en it becomes trypsin and the great thing is once these enterokinases activate the proteases what happens then is that one activated protease will then be able to activate the rest of the proteases and will be able to activate any other pancreatic juices that need to be activated and therefore they can start doing their job here the reason why they're inactive in the pancreas is for obvious reasons so they don't digest the pancreas itself very important now for certain diseases such as pancreatitis there's a couple of different causes of pancreatitis the two major causes of pancreatitis are going to be alcohol abuse and also gallstones gallstones blocking the pancreatic duct here coming from the gall bladder gall bladder is going to be filled with bile and bile emulsifies fat so it's like a detergent breaks fats apart but there's a one of the major components of bile is cholesterol and if you have too much cholesterol it starts to solidify or crystallize and form stones and some of these stones can block this duct if this happens all the pancreatic juices that are released tend to back up and if they stay there for too long or they become um in quantity too much they can start to activate themselves and start to digest the pancreas which isn't a good thing okay so what what's happened foods come in stimulated secretin and cholecystokinin cck so far it's been released into the bloodstream it's activated the acid cells to release pancreatic juices which are the inactive proteases amylases lipases they travel down the pancreatic duct into the duodenum where they're activated by enterokinases and now can start chopping up foodstuffs but the fats that have come through remember it's fine for proteins it's fine for carbs because they've already partially digested from the product gland in the mouth and from the stomach but fats we know that when you cook with fats cook with oils they form these big globules we need to break those globules down into more manageable pieces it's hard to get the molecular scissors to chop them up because they're too large so we need to break them up into smaller tiny globules which are called globules called mycells or missiles and what they what produces these well that's the bile in the gall bladder which means cck also travels to the gall bladder and stimulates the gallbladder to contract releasing the bile that it has stored which it has also received from the liver so this bile then travels down through the bile duct and again with the pancreatic juices will move into the duodenum the bile just like detergent emulsifies the fats breaks it up into manageable pieces and now the lipases can chop it up again without a gallbladder for example for from a cholecystectomy that's removing the gallbladder you have reduced capacity to break down fats and digest them so you may have to change your diet a little bit reduce the amount of fats potentially okay now what we haven't spoken about is the secretin what does the secretin do well the secretin specifically is stimulated from the acid that's been pushed through the duodenum cck was predominantly stimulated by food secretin by the acid and what secretin does is it again it's a hormone so it travels to the bloodstream but it doesn't go to the acinat cells it goes to a cell type that's sitting across the ducts here these are ductal cells also known as intercalated ductal cells i'll write it down here ductile cells and what do the ductal cells release the ductal cells release bicarbonate bicarbonate and bicarbonate is hco3 negative and what bicarbonate does is it buffers hydrogen ions it is a mop that absorbs hydrogen ions so this is important because i told you that the stimulus for secretin was this acid coming through and we know that acid is simply just an abundance of hydrogen ions releases secretin secretin stimulates these intercalated ductal cells they release bicarbonate into the pancreatic ducts they travel through into the duodenum and neutralize the acid this is wonderful because unlike the stomach remember the stomach has mucous membranes in here and produces its own bicarbonate to protect itself that's why the stomach doesn't digest itself the duodenum does not have such protective mechanisms so the pancreas is relied upon in order to release this bicarbonate for protection all right what's the last thing well actually another thing i'd like to say is that in addition to secreting cck stimulating intercalated ductal cells and asana cells acetylcholine does this as well now acetylcholine i'll write it down here acetylcholine and i didn't highlight that the secretin here but acetylcholine as well an acetylcholine is a neurotransmitter especially the most pronounced neurotransmitter for the parasympathetic nervous system which is the nervous system that innervates the git to tell it to start secreting substances because it's the rest and digest part of the autonomic nervous system so the enteric nervous system all right which is comprised predominantly the vagus nerve the parasympathetic nervous system will release acetylcholine and help stimulate this process as well hi everybody dr mike here let's look at the rest of the small intestines we've spoken about the duodenum the first 25 centimeters let's now talk about the rest of this big big six meter long tube it's broken up into two parts that of the jejunum and the ilium now if i take this big six meter long tube what you'll find is at the very first segment that's where the duodenum was found again 25 centimeters and at the end that's where you'd find the first part of the large intestines called the cecum but in between that's where the jejunum and ilium lie the first two fifths of this big long six meter tube is the jejunum and the last three fifths is that of the ilium which means the ilium is obviously the longest portion of the small intestines the jejunum is 2.4 meters long and the ilium is 3.6 meters long now if we were to take a look at the hollow inside of these tubes so the lumen of these two tubes there are some similarities and there are some differences remember all the way through the git you're going to have those same four layers from internal to external you're going to have the mucosa and the submucosa then the muscularis externa and then you're going to have the serosa or adventitia now you can see here that the serosa and adventitia is term mesentery here this is what is holding these hollow tubes this big long six meter tube to the dorsal body cavity and that's termed mesentery all right now as we have a look you can see the longitudinal layer and the circular layer of the muscularis for both then you can see the mucosa and submucosal layer here and you can see that you've got all these multiple folds that we term villi and both the jejunum and the ilium have villi however the villi are more pronounced in the jejunum you find that from the duodenum to the jejunum you have very pronounced villi that we term plique circularis and then as we continue to move through the small intestines they begin to diminish by the time we get to large intestines you'll find they're basically absent another thing that you'll find is within this submucosa you have these areas of dense lymphoid tissue so they're there for immune function called pyres patches and you'll see the pies patches basically only in the ilium you don't really find them in the jejunum and you don't really find them in the duodenum either again they're there for an immune roll now if we have a look at basically the histology the cells the tissues and you have a look at the folds so here you can see you've got the villi but you've also got some glands or crypts now these crypts are called crypts of liberkun and there's multiple different cell types within them i'll talk about that in a sec but the two most pronounced cell types within the small intestines so that's all of this jejunimonium is that of the absorptive enterocytes so this is the most common cell type of the small intestines now these absorptive enterocytes they are simple so one layer columnar long and they have microvilli on the ends of them microvilli are like small villi their fingertip like projections every single absorptive enterocyte has about 3 000 microvilli on them and again they're there to help increase the absorptive capacity the second most common type of cell is out of the goblet cell and they produce mucus okay so goblet cells play a really important role in lubricating that area and protecting it from mechanical damage and also from protecting it from invading pathogens as well now you can also see that as we move down now i'll talk about the glands and crypts in a second but as we move down into the submucosa where we have the blood vessels the nerve fibers and the lymphatics that i've drawn the lymphatics in here now the small intestines have lymph vessels these blunt ended lymph vessels that go up into these villi and this is important because when these absorptive villi absorb remember they're going to be absorbing the micronutrients that have now been broken down from the macronutrients proteins fats carbs right so carbs are going to be broken down into glucose fructose so forth protein is going to be broken down into amino acids and fats are going to be broken down into glycerol and fatty acids now these triglycerides these fats glycerol fatty acids they actually get absorbed here at the lymphatics right the rest get absorbed into the blood vessels but the fat gets absorbed into the lymphatics that's very important now as we go into these glands or crypts of libicun there's a couple of different cell types one you've got enterocytes now these enterocytes aren't the absorptive kind they secrete ions and these ions can be sodium potassium magnesium chloride calcium but they also secrete alkaline fluid this alkaline fluid is really important to stop any acid that's coming through potentially from the stomach from breaking down the intestines now you've also got mucus cells these mucous cells are actually very similar to the goblet cells so they play a very important role to protect us from microbial invaders and panetta cells now these palette cells are also very important they also play an antimicrobial role so they release lysozymes for example tumor necrosis factor all these types of very important chemicals that help kill off any bacteria or invading pathogens that should not be there and the last one is those are the neuroendocrine cells i've spoken about in the stomach they release chemicals which can also be hormones and they play very important roles in the body in this case the neuroendocrine cells of the small intestines can release gastrin which promotes digestion in the stomach cck which is cholecystokinin it stimulates the gallbladder to contract and push bile into the small intestines and secretin which stimulates the pancreas to release various enzymes and ions and fluids and all these types of things so this is a quick run through of the jejunum and ilium hi everyone dr mike here in this video we're going to take a look at the large intestines the large intestines is only around about 1.5 meters long and you'll find that the small intestines lead to the large intestines so they're not longer than the small intestines but they are wider now i've drawn up an image here highlighting the large intestines as you can see and the large intestines are made up of the cecum the appendix the ascending colon the transverse colon the descending colon the sigmoidal colon the rectum and then the anus now what you'll find is something we've spoken about before we've spoken about the liver sitting in this upper right quadrant here then you can see we've got the duodenum remember that's the first part of the small intestines this c-shaped duodenum you can see that here's the first portion and the second portion and the third portion and then the fourth portion is here which means the rest of the small intestines the ilium and the jejunum or jejunum and ilium will be sitting right here in this window so you can see the large intestines frame the small intestines now it goes from the duodenum to the jejunum and then the ilium and this is where the ilium finishes at the ileocecal valve so it goes from ilium to cecum now the cecum is this blind ended pouch a couple of centimeters long and wide and it's quite small for humans but for other animals like rats or even cows the cecum is quite large and the reason why is because the cecum evolutionarily is there for us to be able to help digest indigestible foodstuffs often indigestible carbohydrates being grasses for example and what you'll find is if you open up the stomach of a cow or even a rat you'll find the cecum is huge because it's storing all these different macromolecules and trying to digest it how's it digesting it well it's utilizing enzymes but also utilizing the bacteria that's present in the vermiform appendix which is the little worm and the little worm is around about the size of the finger maybe a little bit smaller and what you'll find is we think that it is one of those vestigial organs meaning we can chop it off get rid of it it's not a problem that's true but it doesn't mean it doesn't play a role the role that the appendix plays is that of repopulating the gut when we've lost our gut flora so this may mean due to some sort of gastrointestinal upset you may have had significant bouts of diarrhea or even had significant amounts of antibiotics this may have killed off your gut flora the vermiform appendix plays an important role in squirting out more bacteria to help repopulate your gut so that's quite important so it goes from the cecum then to the ascending colon now what you'll find is that the ascending colon sitting behind here is going to be our right kidney then we've got the transverse colon and then behind here is going to be the left kidney and then we've got the descending colon to the rectum and then it's got sigmoid colon rectum and then anus now you can see that the cecum is sitting at the right iliac crest and or at least the iliac fossa so that's going to be part of that hip bone right and then you can see the sigmoid colon sits in the left iliac fossa now if we look at the appendix how can you identify the appendix we know it sits somewhere in this bottom right area how do we identify it there's something called mcburney's point now mcburney's point is you take the anterior superior iliac spine so this is this part here and take your umbilicus which is your belly button and you go two thirds of the way in between so around about there and that is going to be where your appendix sits and again that's called mcburney's point all right if we have a look superiorly you can see you've got the pancreas and you can see the tail of the pancreas sits within the spleen we've got the liver up here and you've got the abdominal aorta where it's branching and then you've got the vena cava as well all right let's go and have a look at the tube the large intestines as a hollow tube its function is predominantly there for absorption of water and production of fecal material and pushing along that fecal material you can see a couple of things first thing is that there's these what look like pouches that are formed along the large intestines they're called horstra and they're circulations circulations is because big long tube this big long tube has three longitudinal muscle groups called tennier collate running the length of them and this tene collar the longitudinal muscle is actually shorter than the length of the tube which means it forms these circulations or bunching up called horse drum what's the function of these horses well they help push material through under peristalsis again the tennie e coli what that does is produce the horse dra and help produce peristalsis you can see that you've got these what look like fat deposits called epiploic appendices and they are basically peritoneum filled up with fat why are they there we don't actually know we know they can become inflamed and the symptoms are very similar to that of appendicitis so what we've got is basically a quick summary of the anatomy of the large intestines and also what's going on at the tube of the large intestines

Channel: Dr Matt & Dr Mike

Views: 16,399

Rating: 4.9577465 out of 5

Keywords: digestive, system, gastrointestinal, tract, gastro, gut, intestines, small, large, colon, rectum, liver, pancreas, function, physiology, anatomy, lecture, nclex, nursing, medicine, university, swallowing, carbohydrate, protein, fat, carbs, metabolism, vitamins, minerals, digestion

Id: hndHaLSoYiM

Length: 95min 27sec (5727 seconds)

Published: Wed Aug 05 2020