Digestive System | Summary

welcome to this video on the digestive system summary the purpose of this video is to go over all of the main organs accessory organs and key histology of the digestive system this would be a good review for a student that's preparing for something like the tea's test or just wanting to go over the whole thing at once or it would also be a nice intro for our student that is just beginning their study so I highlighted main organs in yellow and then I want to put a nice big box around that because when you go to look back at this page of your notes you'll want to have that one specifically jumping out at you and then here for the accessory organs I think I'm even gonna make a nice orange box like that and then we're going to add on here something that's I haven't written yet this column will be for the key histology so we're not gonna do super in-depth but I'll give you the overview of it to refresh your memory okay key histology will highlight this one in green put that black box around it all right and we are ready to go so I'm going to start with the main organs over here and you can see that we have a nice mouth with a nice red tone so the mouth is the first main organ of the digestive system and so let's go ahead and highlight that and what happens here is that the teeth and the tongue will and mix together with saliva and they form what's called a bolus let's go ahead and highlight that book or put a box around this word bolus and peak it like it literally means ball in Latin okay now this ball this bolus goes down the esophagus and it moves by peristalsis so let's add that word peristalsis right here peristalsis is the rhythmic muscular contraction of the digestive system to move food through and it starts here in the esophagus when the food gets to the bottom of the Figgis there is a sphincter muscle that means a circular muscle and it is will highlight that in orange and this is also called the le s or lower esophageal sphincter so L and the food has to go through here if this loosens up too much that's when you hear about gastric reflux and some stuff like that okay next up is the stomach I guess so the stomach consists of three parts grab a blue highlighter for the fundus a fundus is a part of a structure that sort of goes up above its original opening so the uterus also has a fundus and then grab a purple highlighter for the body of the stomach that's most of it put that in purple and then pylorus means gate and it will highlight it in green and it's that last portion of the stomach all of this region here and then use your green highlighter for another sphincter muscle this one is called the pyloric sphincter and the food is not allowed to leave the stomach until is uniformly mixed to form a uniform mixture called chyme so take your pink highlighter or sorry pink pen again and put a box around this word chyme because that's an important vocabulary word that refers to what we call this stuff after it's been all thoroughly mixed so the stomach has three layers of muscle that's more than for example the small intestine has I'm going to add a little light over here sorry it's got some shadows on you this morning and these so there's muscle cells that go up and down and then this direction and then obliquely as well and those work together to turn the food and the stomach to make it this uniform kind okay now there's special cells in the stomach called parietal cells maybe we can use an orange highlighter on this so the parietal they make hydrochloric acid and I put a little here in the bottom of the stomach here and that hydrochloric acid has two big roles one is it's going to just damage or inhibit pathogens from passing into your digestive system or down into your intestines and it's other cool role is it activates an enzyme called pepsin and chief cells are the name of another type of cell in the stomach that make this pepsin and then pepsin I'll add this to pepsin is and is going to begin the breakdown of protein in the stomach okay so then we come to the small intestine and the small intestine is actually quite long many feet long and it has these folds in it so it's long with folds and those folds are called villi and it's singular they're called villus and you'll learn later that even the cells themselves have more folds on them - and those are micro villi but let's use our pink pen again another vocabulary word here so these are the folds in the intestine and the purpose of these is to increase surface area I'm just going to put SI for surface area and then that's going to make digestion more efficient so the duodenum is the first part of the small intestine it's actually the shortest it literally means 12 fingers long and then the jejunum and the ileum are the next two now the bulk of the chemical digestion will occur in the duodenum so I'm going to say almost all chemical digestion is going to occur here so all the pancreatic enzymes are going to mix with the food and significant portion of the absorption even here all in that little foot and then the jejunum and the ileum clean up the rest and are going to finish absorbing the nutrients it's kind of like the 80/20 rule the duodenum does about 80% of the work and then the jejunum and ileum do the last little bit even though the duodenum is the smallest part of all so if you take your blue highlighter this is meant to be a little sketch of the duodenum right here so it can maybe put an arrow this is meant to be the duodenum and it receives and the pancreatic enzymes that will break down foods and it also receives bile from the liver or the gallbladder we'll talk about that too in a second and then later we're going to do a close-up of the histology that so this circle will refer to that we're looking at a little close-up so then the last segment of the large intestine is the large or sorry of the digestive system is the large intestine so if you grab your pink highlighter it starts with oops sorry we should have done yellow first like this so the large intestine starts with the appendix which is a little dead end pouch right here hanging off of the start of the large intestine and it is an immune organ so it has immune function that's something I talk about more in other videos like for microbiology and stuff but it believed it's believed that it holds like a reservoir of good bacteria to help reap all innate your repopulate your colon after a diarrheal infection okay then we go ascending the colon and so let's put that one with our orange highlighter so we ascend and then we're going to go across so transverse I'll use a green for that and you can you this is the direction then the stool is moving along or the forming feces and all along here the water is being reabsorbed back into your bloodstream and if that didn't happen then that's what diarrhea is is if the large intestine isn't able to reabsorb that water and then people can get really dehydrate so then the sigmoid colon oops I forgot to highlight that this is the descending this is the descending colon and then the sigmoid colon is shaped like an S that's how it gets its name this is the sigmoid colon and it kind of forms an S shape like that and then the very last section I'll highlight in pink and that's the rectum that word in Latin literally means straight and so it's a straight last part of the colon so then so we can say that it reabsorbs water so that we don't get diarrhea and we don't get dehydrated and it's also covered with normal flora and that normal flora has so many different functions we're really just kind of scratching the tip of that iceberg at this point that it's going to be important in regulating your metabolism and your weight and your mood how your brain is functioning your appetite and that's in making some vitamins for you as well as helping to prevent diseases by pathogens so lots and lots of functions there okay let's move on to the accessory organs and the accessory organs include the and we'll highlight these in orange accessory organs they include the salivary glands the liver the gallbladder and the pancreas so these are the organs that don't actually touch the food but they have to be secreting their products in order to help digestion occur so you have three pairs of salivary glands parotid that literally means by the ear so this one's up by your ear and then there's the sublingual sub means beneath linguae means the tongue so this one's under your tongue oh if you've ever seen people Gleek they are actually somehow able to squirt saliva out from these and then the submandibular pair that is under the mandible so you have these three pairs of salivary glands and like we'd already talked about before the saliva mixes the food up into what's called a bolus that can then be swallowed I also owe saliva also contains lysozyme that helps to prevent pathogens from entering into your digestive system okay then the liver has over 200 functions it quite possibly is my favorite organ so it's really hard for me to not talk about it a lot in here but the purpose of this video is to give you a fairly concise summary so I'm going to restrain myself it makes bile that's a huge role in its digestive function and bile emulsifies fats what that means is it breaks it into droplets and it also modifies glucose it can store it to glycogen and then the other direction too so it can store lots of extra carbohydrate as glycogen or it can break it down into the simple glucose and then put that back into the blood so it's important in regulating your blood sugar the gallbladder stores and concentrates bile and so when you eat a meal with fat then smooth the muscle around the gallbladder squeezes it out into this bile duct here so let's use green bile is green so can put a little highlighter here this would be duct coming from the liver and then going into the duodenum so you could use your black pen to show okay look the bile is coming in through the bile duct and then that emulsifies and that means break it into small drops then the pancreas makes the digestive enzymes all the ones that you need and then those digestive enzymes come in through what's known as the pancreatic duct into the duodenum so see all this excitement that's happening here in the duodenum to chemically digest and absorb the nutrients so I'm going to list the the enzymes here because it's pretty common that you would be asked what these are these main enzymes so the digestive enzymes that come from the pancreas can be in three broad categories the first is the ones that break down carbs and amylase is the name that comes up the most for this so amylase breaks starch into simple sugars and actually specifically into executive just said glucose let's take a blue pen and put box around that oh you know what we should also put a pink box around is probably this word file and maybe we should highlight that in green we made the bile duct cream okay and then the second enzyme is a group of enzymes that I'm just gonna call proteases so this is sort of a catch-all phrase for a variety of enzymes they can break down protein and you might remember that we mentioned pepsin already so that one's in the stomach but the rest of them come from the pancreas these are enzymes break protein into amino acids and then a third probably my favorite personal favorite is lipase and lipase breaks fats or lipids down into fatty acids okay and then take a blue pen put a box around lipase all right good now let's go to this right here put the Circle C key histology column so now we're going to do a close-up of that okay so now if you were to take see that black line that's the the wall of the intestine now I'm going to show you close-up of the parts of that that's column three over here basically we've got four layers so and we're going to highlight all of these in green so layer number one is called the mucosa and all it contains are mostly is the simple columnar epithelial cells and sometimes you might get asked that so simple columnar epithelium and then there also are goblet cells in these mucus layers and they make mucus and remember I told you that there are these little wrinkles on these cells these are referred to as micro villi micro villi are the wrinkles on these cells and then in it since that's kind of another keyword let's put a pink box around that okay then the next layer is the submucosa and the submucosa consists of three main things first of all notice all of these white blood cells so there this area is full of white blood cells so that they are able to capture any let's say there was a pathogen in your gut and it was able to get through that Bethulia lining then the these mast cells or other kinds of white blood cells would fight back and then there's a lot of connective tissue sort of holding everything together in the submucosa so I'm using these blue lying or sorry purple lines to represent connective tissue and then you've got lots of blood vessels so we'll highlight this blood vessel capillary in pink and then use your orange highlighter to draw or color the lymphatic vessels so these don't carry blood they carry extra fluid away and as you'll see soon they also carry the fats from your meal then below that is the smooth muscle layers or are the smooth muscle layers and there are three or sorry two of these in the most parts of the intestine you might recall I said the stomach has three layers it also has an oblique layer but most of the intestine just has like a circular layers and then a longitudinal layer and these little red circles represent like muscle fibers kind of coming out at you and then these ones are the ones that are wrapped around and though they forgot both because we have two layers there and then the last layer in green green highlighter is the peritoneum so you have the peritoneum is the serosa that surrounds your intestine and then the pleura is the serosa that surrounds your lungs and the pericardium is the serosa that surrounds your heart so these are specialized epithelial cells that make suros serous fluid sorry I mean serious fluid okay so now let's go back to the top of this picture and I want to show you what happens during nutrient absorption so take your orange highlighter and this is meant to represent like a lipid and it would be broken down into its individual fatty acids and the enzyme that does that we mentioned already is lipase and these fatty acids are so critically important that they are able to be absorbed through the intestine and then directly into the lymphatic system they don't have to go into the blood yet they go directly in and their curate as it's called chylomicrons but I don't think you need to know that right now so anyway they've got these fatty acids in the lymphatic vessel and then they go straight to the vena cava and they dump into the heart so fats travel through lymph vessels loops lymph vessels to the heart and the reason oh gosh sorry you can't see any of that okay so let me go back again so the fats travel through the lymphatic vessels to the heart and then I wrote fats travel through lymph vessels to the heart when I'm in class people are like I can't see I can't see and then I know to move it sorry about that so the reason that that's so important is because the heart relies almost exclusively on fatty acids to make its energy so it's very important that any fat in the meal the heart gets first dibs on it because of the importance of keeping the heart pumping and because it can't use glucose to make ATP so it has to get those fatty acids okay now this amino acids and the glucose have a different story if we go back up here so this would represent a car but like a starch breaking down into glucose or maybe a protein breaking down into amino acids and I'm gonna use my blue highlighter for that and then these nutrients get to be absorbed into the bloodstream because they need to be processed by the liver before they can get free rein so there they don't get as free much freedom to go as the fats do they have to be more carefully monitored so they only use a blue pen for this so the nutrient absorption then these ones go into the blood vessels and from there let's go ahead and put them in here they have to go straight to the liver through the hepatic portal vein and what that will then do is the liver will say okay there was a lot of glucose in this meal and there's no way we can let all of that go straight out into the bloodstream so I need to store some as glycogen because otherwise we're going to damage you know the body with high blood glucose and then it will take first dibs on the amino acids and then let those go to organs as needed so see the important role of the liver then and to help helping keep blood sugar steady all right thank you for your good attention and sorry about that one part you couldn't see I'll do a quick recap right here at the end so the digestive system summary you've got main organs accessory organs and then most students are expected to know some key histology the main organs are the mouth esophagus stomach small intestine and large intestine the accessory organs are the salivary glands the liver the gallbladder and the pancreas the pancreas makes virtually all of the important enzymes that are needed to break down your foods amylase proteases and lipase those enzymes go through the pancreatic duct which I can write on here the bile made by the liver enters the duodenum through the bile duct and all this comes together here in the duodenum for chemical digestion and nutrient absorption up here the simple columnar epithelium is the mucosa then the submucosa includes white blood cells mostly mast cells and those are going to release histamine and if something foreign is encountered and the purple represents a connective tissue to hold the tissue together this is a blood vessel the orange one is a lymph vessel and these are found in the submucosa then there are at least two layers of smooth muscle and then the peritoneum which is making serous fluid to prevent friction when the intestines move or to reduce it when the intestines move nutrients that are absorbed into the blood vessels include glucose simple sugars and amino acids they go through the hepatic portal vein straight to the liver for processing fats on the other hand goes go into the lymphatic vessels they get to bypass the liver and they go straight to the heart to provide fuel for this very important organ okay I'll see you in the next video

Channel: susannaheinze

Views: 172,670

Rating: 4.9106588 out of 5

Keywords: digestive system, main digestive organs, accessory digestive organs, intestine histology, liver, pancreas, digestive enzymes, stomach, small intestine, large intestine, duodenum

Id: DvLaQ53Tn1k

Length: 25min 35sec (1535 seconds)

Published: Mon Apr 15 2019