hello everyone now we start studying the digestive system and I have divided this system into four different videos for this video these are our learning objectives the digestive system includes two major groups of organs we have the organs that make up the alimentary canal also called digestive tract and we have the accessory digestive organs the digestive system is basically a muscular tube that goes from mouth to anus and this is what we call alimentary canal or digestive tract and then associated with this canal but not in the canal per se we have the accessory digestive organs we should include teeth tongue salivary glands liver gallbladder and pancreas so in other words the accessory organs are organs that are nearby the elementary canal in help with digestion looking at this diagram we can see the muscular tube that goes from mouth to anus so if we follow it down we see that it starts with the oral cavity and at the level of the oral cavity we have the tongue teeth and salivary glands that produce saliva with the help of teeth and tongue the food is mixed with the saliva and then we do not have food anymore now it's called bolus then the bolus goes back towards the pharynx which is basically the back of the throat and the pharynx is involved with swallowing so the firm's helps you squeezing the bolus down toward the surface and then the esophagus which is another piece of the muscular tube goes down in our neck behind the trachea and then it crosses the diaphragm and eventually they suffer those drains the bolus into the stomach so as you can see the stomach is in the abdominal cavity and the stomach receives the bowls that just travel through there so folks in the stomach we have lots of acid in this acid is involved in the digestion of the bows when the bolus is mixed with the acid in the stomach it's not called bolus anymore then it's called time now what happens is that the stomach can contract and force the chyme into the duodenum which is the first part of the small intestine digestive juices such as the pancreatic juice produced by the pancreas and the bio produced by the liver and stored at the gall bladder they are delivered here at the duodenum so at the duodenum the first part of the small intestine is where we have most of the digestion happening the second part of the small intestine is called jejunum in at the jejunum we have most of the nutrients being absorbed after the jejunum we have the ileum which is the last portion of the Amoy intestine the ileum is what meets up with the first segment of the large intestine which is called Sikkim attention to the cecum we have the appendix and when the appendix gets inflamed the person has appendicitis so after the cecum we have the a sending column then the transverse column the descending column then the sigmoid column and finally the rectum and anus the large intestine is involved with dehydrating feces and storing feces until they are released and one last thing i'd like to point out look at this diagram is that as you can see the small intestine is not a smaller in length than the large intestine so the large intestine is called large because it is a has a wider diameter in the small intestine receives the name of small because it has a small diameter so the lumen of the small intestine is narrower than the lumen of the large intestine and that's what makes the small intestine small the large intestine large knots their length here we have a list of functions of the digestive system and in order to study digestive system we need to have the clear definition of these terms in our mind so ingestion is when you ingest food so is the action of taking food and putting food into the mouth then we have mechanical processing which is the action of mechanically crushing the food down into smaller pieces and mechanical processing happens in the mouth by domestication which is the same thing as chewing and it's mainly done by our teeth tongue and hard palate but it's important to notice that mechanical process can also happen in other parts of the digestive tract and we'll talk more about that later so when we have the muscular contraction leading to additional mechanical breakdown after we swallow we also have mechanical process as you can imagine the smaller the pieces of food we swallow them easier it will be for the chemical digestion to happen because we have a larger surface area for the digestive enzymes to work on so the digestion also referred as chemical processing is where we find the real magic happening and we have chemicals and enzymes working together to break down the swallowed food into smaller and smaller units until these small units are capable of being absorbed through the digestive epithelium so when we talk about the smallest unit of organic compounds we are talking about amino acids nucleic acids fatty acids and monosaccharides so we can summarize and say that the process of digestion consists of disassembling organic food into smaller fragments by breaking down carbohydrates lipids proteins and nucleic acids for absorption now in order for digestion to happen there is a lot of secretion happening and there is the secretion of enzymes acid emulsifier and let's all to aid in digestion then after we have there is Mallis 2 units possible these units they are absorbed and what that means is that they leave the lumen of our digestive tract and they cross the digestive epithelia and they go into our bloodstream or into our lymphatic system in the case of fat and if you recall when I covered the circulatory system I said that the veins of our digestive organs converge into one big vein that we call hepatic portal vein and the hepatic portal vein goes straight into the liver and then the liver does its job and we'll talk more about that later now Compact ation is the dehydration of undigested material so it makes the undigested material more compact hence the name compact ation and these leads to the formation of species that are defecated is created out of the body through the anus so I said that the digestive tract is a muscular tube that goes from mouth to anus and here we have a look at the histology of this tube and we can identify forming layers the mucosa the submucosa the muscular layer in this serosa now in many segments of the digestive tract we find these circular folds which are also called like a circulars and the point of having these folds is to increase the surface area and we'll talk more about this later ok so here we have the lumen of the organ and surrounding the lumen of the organ we have the mucosa within the mucosa layer we find the mucosal epi Stadium in limine appropriate depending on where we are in the digestive tract so depending on the organ the mucosa epithelium of the mucosal layer will consist of simple epithelium or stratified squamous epithelium for example in areas with lots of abrasion like the oral cavity pharynx and esophagus we'll have known keratinized stratified squamous epithelium now on the stomach is more in large intestine where lots of secretion and absorption happens we do not need several layers of squamous cells then we just have simple columnar epithelium but I will mention that as we travel along our digestive tract underneath the mucosa epithelium we have the lamina propria lumen appropriate if you recall is a little bit of connective tissue which is actually areolar connective tissue and in these areolar connective tissue we find sensory nerve endings lymphatic vessels and blood vessels that can nourish the avascular epithelium right above it now if you pay attention here you see that just below the lamina propria we find a really thin layer of smooth muscle and that receives the name of muscularis mucosae contraction of muscle fibers in these muscularis mucosae change the shape of the lumen and moves the plaque a circular is around now underneath the mucosa we have the submucosa the submucosa is a layer of irregularly arranged dense fibrous connective tissue so if you recall dense irregular connective tissue is made up of a very disorganized array of collagen so this makes it extremely stretchy and very difficult to tear and when you're thinking about digestive organs which have to do lots of stretching and shaping this makes sense right in the submucosa we find blood vessels lymphatic vessels and nerves these nerves in the submucosa forma network and this network of nerves are called submucosal neural plexus these plexus innervates the mucosa and they contain sensory neurons as well as parasympathetic and sympathetic nerve fibres now as you can see here we have this pulp with structures and these are glands and we find these glands in the mucosa and in the submucosa as well and the secretion produced by these glands are transported through ducts in direction to the epithelial surface that surrounds the lumen underneath the submucosa we have another layer called muscularis externa i also named the muscular layer like you see here the muscular layer is usually made of 2 a smooth muscle layers that run in different directions and you can see them running in different directions in this diagram we have the circular muscle layer and the longitudinal muscle layer when the circular muscle layer contracts the diameter of the lumen decreases and when they longitudinal layer contracts that shortens the length in that specific area so we can conclude that the contraction of these Chuy's muth muscle layers mechanically process they ingest food and also move it along the tract now at specific locations of our digestive tract we have a thickened layer of the circular smooth muscle and since you know that when the circular is moved muscle contracts it decreases the diameter of the lumen the areas of our digestive tract where we have thickened circular muscle layer is where we will find is factors between the circular and along you know muscle layers we find the my enteric neural plexus now look at this I just mentioned to neuro plexus the submucosal neuro plexus and the my enteric neural axis based on their location you can conclude what they would be involved with the submucosal neural axis isn't the submucosal layer and there is where we find glands right so the submucosal neuro plexus will be involved with the control of secretions of the digestive tract on the other hand the my enteric neural plexus is between two muscle layers so we can expect that these plexus will be involved with contraction of these two muscle layers right now deep to the muscular layer we have either the serosa that we see here or the adventitia layer this serosa is also called visceral peritoneum the serosa is a serous membrane that surrounds the outside of a digestive organ however not all digestive organs have a serosa in the organs that are not surrounded by a serous membrane we do not call it serosa layer on the very outside instead we call it adventitia lee and the advantage layer is basically a dense network of collagen fibers that is very thick and that anchors the organs today structures nearby so out of all the just abstract organs just the pharynx the esophagus and the rectum do not have a serosa instead the pharynx the esophagus and the rectum have the advantage layer which anchors them to the nearby structures now I just said that the serosa layer is the same thing as the visceral peritoneum so when we say serosa we could use that interchangeably with the zero peritoneum because both refer to the same layer the visceral peritoneum is the serum membrane that covers the outside of the digestive organs if you recall when we talked about the lungs we had a double wall serous membrane called pleura membrane and it was composed of the visceral pleura layer in the parietal pleura layer between the visceral and the parietal pleura layers we had the pleural cavity filled with pleural fluid when we talked about the heart we had another double walled serous membrane called serous pericardium in the serous pericardium was formed by a visceral layer and a parietal pericardium layer and between the visceral and the parietal layers of the pericardium we had the pericardial cavity that was filled with pericardial fluid now we are talking about the digestive organs and we have the visceral peritoneum layer directly surrounding the digestive organs and guess what you have we will have the parietal peritoneum layer which will be lining the inner surfaces of our abdominal wall in between the visceral and the parietal peritoneum layers we have the peritoneum cavity that's filled with a watery fluid that lubricates the peritoneum surfaces so the importance of this peritoneum lining is that it will produce a continuous watery fluid that lubricates the surfaces we produce approximately seven liters of fluid each day so the peritoneum the serous membrane formed by the visceral and parietal peritoneum layers is enclosed within the abdomen the peritoneum encloses surrounds most of our abdominal organs in all organs that are located within the peritoneum are said to be intraperitoneal organs and this includes our stomach jejunum ileum is pling transverse colon and liver so these organs have the peritoneum surrounding them completely and are called intraperitoneal organs but not organs we have in our abdomen are surrounded by the peritoneum and these organs that are not we think the peritoneal cavity are said to be retroperitoneal when we say the word retro it means that it's something that is sort of in the past right it's behind so retroperitoneal organs are behind the peritoneum so they are not surrounded by the peritoneum and examples of retroperitoneal wardens includes our kidneys ureters and abdominal aorta during our embryonic development the pancreas in the last two thirds of the duodenum is start within the peritoneum but then they are pushed out of the peritoneum and with that they become retroperitoneal but because this organs is start as intraperitoneal and then they become retroperitoneal these organs are considered secondarily retroperitoneal now you can see in this diagram these areas where basically two peritoneal membranes fused to each other forming these folds of peritoneum this folds of peritoneum are called mesentery and they are responsible for anchoring each digestive organ to the place where they should be so looking at this diagram we can see that our organs are suspended in the abdominal cavity in what keeps our organs hanging the right position our six mesentery that we see here so if you look over here at the transverse column you can see that the transverse colon is basically suspended in the abdominal cavity and what holds the transverse column in place for you to not to fall down in the abdominal cavity is the transverse mental column which is a mesentery you can also see the false form ligament which is a mesentery that holds our liver to the diaphragm then we can see the lesser omentum which attaches the liver to the stomach the greater omentum which attaches the stomach to the trans skolem and we can also see in this diagram the mesentery proper which holds our ismo intestine in place and we see the sigmoid meso column which holds our large intestine in place especially at the level of this sigmoid column here you can see a different view of the lesser and greater omentum and the greater omentum literally hangs like an apron over the intestines and it contains a thick layer of adipose tissue that serves as energy reserve for our body as well as provides padding protection and insulation against heat loss across the interior abdominal wall now the digestive system has a series of movements that help to push food throughout the muscular table and also these movements help mixing the food within the tract so we have an even digestion of all we ate there are two types of muscle contractions and they're called peristalsis and segmentation peristalsis is a forward squeezing wave motion that will move the bolus which is the partially digested food is swallowed throughout the digestive tract peristalsis happens because we have the circular muscle fibers contracting in one specific area and then we have the longitudinal muscle contraction afterwards then like we see here this works as this pinching that will push the bow lose the mass of swallowed food forward so if you think that you have to paint first and then the forward movement happens it makes sense that the circular muscle layer that causes the pinching is on the inside and the longitudinal meso layer is on the outside like you see in this diagram we have the circular muscle layer on the inside and the longitudinal Musso layer on the outside and you can imagine there is houses like when you are squeezing toothpaste out of the tube you paint first and then you force the toothpaste out of the tube so peristalsis is the forward movement of whatever is swallowed through our digestive tract as you can see here from mouth to anus now we can have reverse peristalsis and reverse peristalsis happens in conditions like vomiting if we need to get contents from our stomach up and then back out of our mouth then peristalsis has to go the other way around and of course this just happens under certain conditions for the most part peristalsis goes in a forward direction which would be from mouth towards anus we also have another motion called segmentation and segmentation is a turning fragmenting motion that keeps mixing the bolus with the digestive materials until it turns into a big soup segmentation does not move the bolus in a particular direction when we think of segmentation movement we need to think intestines because segmentation is the movement we find in our intestines especially small intestine and it's the movement that keeps mixing what we ate with the digestive enzymes in no particular direction and it allows time for digestive enzymes to do their job to work on the food we ate basically because we have several contraction rings forming at the same time the chyme which is the bolus plus the acid we have in our stomach it doesn't move in any particular direction and keeps mixing with the digestive enzymes and this is all for the first video about the digestive system please let me know if you have any questions bye