in this video I want to do an overview of the digestive system overview of the digestive system now the primary function of the digestive system is to acquire nutrients but while it's acquiring those nutrients the nutrients or foodstuff the bolus that's making its way from the oral cavity down the alimentary canal needs to be broken down and processed and that process begins in the mouth and as we saw in a prior video we have an oral vestibule in an oral cavity and that oral vestibule goes from the lips back to the teeth so if we basically hold these lips up away from the teeth we could look right down the oral cavity and down part of the elementary canal I'm just going to do a real rough drawing of this here so here I have my teeth or teeth essentially working backwards further and further they go the surfaces of those back molars back molars and we have this longitudinal line called the Palatine rafi that run down the roof of our mouth you may have looked in the back your mouth and seeing the hard palate back there before that's going to lead back to the soft palate and the uvula the soft palate in this region and the uvula now once you go back more posterior past what's called the palate of Glossop you'd think palate Oh tongue palate tongue arch you're also going to see a palate Oh pharyngeal arch that's between the palate and the Wawro Ference before we see that posterior wall way back there now that's where we'll find some mucus associated lymph tissue in these paired Palatine tonsils okay so we're looking down the throat back behind the roof of the mouth let me go ahead and continue and pull these lips down in the front as well continue by pulling these lips down in the front and before we get to the teeth we would get into the vestibule so long here we have all this gummy tissue all this gum tissue and down here we also have all this gum tissue and the right and left sides are going to be separated by something called an inferior labial frenum now we have a couple friendly ones one of the friendly ones are going to be here we also have a superior labial frenum labial referring to the lips but there's also a lingual frenulum okay this is kind of a hard part to draw the tongue basically folded up comes across like so and when we fold up that tongue on the underside of it we see a lingual frenulum so superior labial inferior level and lingual frenulum on the backside of that time now before I put in the teeth let me also add a sublingual fold with sublingual ducts or openings that will allow some of the glands to secrete saliva into the world cavity okay now let me add some teeth in here let's do some more liners back here and then we can come around and do a series of teeth up okay all right this is the oral cavity proper between the lips and the teeth is the oral vestibule all right we see the hard palate the soft palate Google I along with some Palatine tonsils on either side leading back to the very posterior wall of the world pharynx which is going to be way back in there the role of the mouth is to serve as an opening into the alimentary canal now technically we could also enter in to the alimentary canal through the paired nasal vestibule and sometimes people do when you put in a feeding tube or NG tube but the main role of the mouth that gives it an advantage over the nasal cavity which is designed for respiration is that we can get mastication or chewing and some mechanical digestion breaking down the food stuff and we also have things like salivary amylase that breaks down carbohydrate we have lingual lipase they can in the acidic environment of the stomach break down a little bit of lipid there's no proteases that break down protein in the world cavity and so though we have a little bit of chemical digestion it's mostly about acquiring the nutrients and turning them into a bolus now what's going to happen with that bolus is it's going to travel down the oropharynx down the hypo or laryngeal pharynx go posterior to the trachea and down the esophagus now as I go through the alimentary canal in a very cartoon fashion I want to divide this all up by maybe got is a four got mid gut and hind gut the foregut includes the oral vestibule oral cavity the oral pharynx the hypopharynx the esophagus and leading into this storage container that most people will recognize as the stomach and the stomach has a kardia this area right here let me do it in a different color the cardia the entranceway into the stomach the fundus this upper part a body a pyloric part before it goes through a true sphincter where there's actually thickening of muscle into the first part of the duodenum okay now the stomach's primary role is storage not digestion storage the duodenum primary job is digestion the esophagus basically got the food down to our abdominal cavity now we have a greater curvature of the stomach and we have a lesser curvature of the stomach also if we section this within the stomach are these deep folds and those are known has read a these deep folds these are the rugae so I would call this the rue de of the fundus the rugae of the body of the stomach of course this folds the rue de of the pyloric Antrim or the pyloric part before I get into the first part of the duodenum this is now the first part of the do one [Music] this is all for guys what I've drawn here is all four guys and I'm going to switch my colors for the next length it's important to understand the different regions of the digestive tract because if you understand that you'll also understand the blood supply here's my abdominal aorta coming through the respiratory diaphragm and it comes behind sorry not through but behind the respiratory diaphragm at the level of approximately t12 the esophagus comes through the respiratory diaphragm the actual sphincter of the respiratory diaphragm when the respiratory diaphragm moves down for respiration it actually pinches the Safa kiss here those muscle fibers pinched here at the cardiac okay there's debate over there if there's a cardiac sphincter or not the sphincter is actually formed by the respiratory diaphragm this prevents food intake Wow respirations occurring so the Safa gas passes through the respiratory diaphragm at the level of T 10 a little bit higher than where the aorta passes through now the inferior vena cava punches up through into the heart through the right leaflet of the diaphragm in the central tendon when the diaphragm contracts during respiration it actually pulls outward on that central tendon on this side whereas it constricts over on this side so that we never impinge on the inferior vena cava so here's all the muscle fibers of that skeletal muscle of the diaphragm but it doesn't mess with that area this passes through at the level of t8 so we can see we're getting deeper and deeper whoops t8 if I went straight back from here I'd be at thoracic vertebrae 8 a little bit lower thoracic vertebrae 10 would be straight back here the Rasik vertebrae 12 would be straight back behind here this is easily remembered if you remember I ate 10 eggs at 12 or at noon the IVC passes through it t8 IVC at 8 esophagus eggs go down the esophagus at 10 and the diaphragm the sorry the aorta passes behind the respiratory diaphragm at t12 okay now the first vessels off the aorta are gonna be the inferior annex but shortly thereafter off the anterior aspect we have that celiac trunk and the celiac trunk gives that left gastric can you imagine it giving that left that gastric it kind of surrounds that stomach it also gives the common hepatic and the splenic artery so I'm drawing a little vascular tree here okay that goes out to the small a little lymphatic organ if it's hilum there's that spleen okay the common hepatic gives the hepatic artery proper and it also gives a gastro duodenum that will all ultimately feed that upper part of the duodenum and even a right gastric eventually that comes back around my point is the entire foregut if you know where it ends after that first part of the duodenum you know the blood vessels that feed it it's all fed by the celiac trunk for the most part okay it's all fed by that celiac trunk not the parts above the respiratory diaphragm but the parts below it and that will be a theme as we move through here so let's keep going I'm gonna switch colors let me go ahead and do a orange and I'm going to add in here the descending part of the duodenum or what we call the second part of the duodenum and the transverse part what we call the third part of the duodenum and the ascending part what we call the fourth part of the duo now after the first part we actually punched through the peritoneum of the domina cavity and we're not in the abdominal cavity anymore we're actually behind it but here at the fourth part of the ascending part we're going to punch back in to the abdominal cavity to form the jejunum and the jejunum folds over and over wrapped in here so tightly but at some point it's going to become the ileum the ileum and the only way to tell really where that transition happens is to look at the actual tissue within the tube and the food makes its way along until we come all the way back to dump into but it's okay through an ileocecal valve a true sphincter here the ileocecal valve into the cecum of the large intestine actually let me stick with orange because we're still in mid gut the mid guy the cecum has the little vermiform appendix off of it the way that the ilium have and the jejunum have that mucus associated limp tissue throughout okay but the cecum is going to lead to the large intestine and we have the ascending part and then over here by the liver we have the hepatic flexure that comes across now this is actually going to be just inferior to the stomach that I'm going to draw it down here the transverse colon now third two-thirds of the way down the transverse colon we're actually out of the mid gut so I'm gonna pick up with hindgut here the hindgut now even though I used Brown in the stomach I didn't think of what color I just grabbed but I'm gonna do the entire hindgut in brown but not the root day three gay are part of four guys okay a couple things this all became intro parrots meal but then at the a signing : it goes retro again it punches through that abdominal wall and it's actually behind the abdominal wall but then the transverse colon punches back through at the hepatic flexure or the right flexure of the colon as it comes across two-thirds of the way across it switches behind up and the colon continues across and then it descends at the splenic flexure or the left kolak flexure because the spleen would be right up in here and it descends down the descending colon is also retroperitoneal or behind the peritoneum but then we punch back through as the curling sigmoid colon that leads to the rectum and the rectum leads to the anal canal in the enos the end of the alimentary canal now there's a couple structures I didn't mention that I'll add in for the colon there's a tendon essentially on either side they wrap up and as this kind of folds over itself a little bit it cuts back through across this is the tane coli it's a band of tissue that kind of follows the colon and it's actually on either side of this tube so here's 1080 coli the tendon of the colon there's also things called epiploic appendages now hanging from the bottom of the stomach we actually have a skirt called the greater omentum and this skirt covers all these organs when students first open up a cadavers belly they're like this isn't what I was expecting I was expecting to see the organs and they can try to cut through to find those organs or they can just pick up the bottom of the greater omentum and fold it up and actually lay it on the cadavers chest or up here onto the stomach and underneath now you see all those organs like the spleen we got to dig back for the spleen but you see those intestines and the colon the other organs nothing up above them I don't know that's above okay the greater omentum is this complex folding that fuses it's essentially peritoneum kind of like the way the epicardium folds back on itself to form the parietal pericardium or the visceral pleura of the lung folds back on itself to form the parietal pleura we have that complex folding in the abdominal cavity as well so that we end up with mesothelioma on the outside of organs so that they can slip against one another and at points this mesentery forms folds that hey that's what the greater omentum is and it's a good place for blood vessels to travel through and nerves to travel through in order to get from point A to point B okay there's little adhesions of that mesentery tissue filled with adipose maybe a little bit of nervous and they're called epiploic appendages they're like little what pretty giant black droplets kind of hanging on these intestines they're called epiploic appendages epiploic appendages so we have the 10 a coli that below it appendages the left and right Kolak flexures the splenic flexure in the hepatic flexure the sigmoid colon the descending colon the a semicolon both of which are retroperitoneal the transverse colon which is intraperitoneal you can actually cut open the abdominal cavity and touch that organ but with these you cannot you would have to remove a layer of peritoneum and then reach back and touch them the kidneys are also back there retroperitoneal and i'd like to shade in everything in gray in this picture that's retroperitoneal so kidneys are actually kind of way way back in here along with their ureters so this isn't exactly right if it is close enough the urinary bladder is actually in the pelvic cavity down there in the true pelvis okay our retroperitoneal organs [Music] retroperitoneal organs are going to be the second third and there's a little debate over this it depends on the person fourth part of the duodenum that duo duo 12-inches duodenum of the first part of the small intestine responsible for most digestion so here is retroperitoneal but then we punch back in to the abdominal cavity as the jejunum which does a lot of absorption the ileum which resorbs bile acids and does a lot of absorption the cecum through the ileocecal valve but then were retroperitoneal as the a son naeun : but then were intraperitoneal as the transverse colon and then we go retro again punch back through back behind as the decent knee as the descending colon then the rectum after we come back in as the sigmoid colon the rectum is all going to be retroperitoneal now this is the alimentary canal the superior mesenteric artery which is the next vessel off the anterior aspect is going to feed the entire mid gut the blood vessels of this are going to feed the entire mid gut including that transverse colon at least the first two-thirds of it this happens two-thirds of the way two-thirds of the way down and then we have one third that's right that's fine guys okay so I'm going to add in a line like I did here delineating for gut from mid gut I can add in a line delaney anything hindgut from mid gut right there okay now hindgut is going to be supplied by the inferior mesenteric artery the next one off that anterior aspect and it gets that last bit of the transverse colon the descending colon the rectum okay supplies all of the hindgut this is the splanchnic circulation they call this the splanchnic blood supply okay and it supplies for gut mid gut and hindgut you should know where those divisions occur okay let me run through and label some of these structures now that I have it drawn I have the esophagus that drains into the cardia the fundus the bolus is churned by the stomach and that churning forms acidic chyme by the time it reaches the pyloric part and that acidic chyme that dike that churned up food is going to enter once the rest of the digestive system is ready for it it can leave the storage of the stomach to enter into the first part of the duodenum for the majority of digestion now there's a lot of mechanical digestion that happens here a little bit of chemical digestion with the lingual lipase the gastric lipase the pepsin but the majority of digestion is actually going to occur a chemical digestion is going to occur in the duodenum that first 12 inches of the small intestine we have the pyloric sphincter now with the stomach we also have a greater and lesser curvature a lesser curvature we have the first part of the duodenum where most digestion occurs we even have openings for the bile and the pancreas the major duodenum papilla and the minor duodenal papilla that are going to drain from the pancreas and the gall bladder these accessory glands into the second part of the duodenum okay I'll cover these in a later video well these organs actually individually at a later time including the liver okay let's continue on with the path here second part of the duodenum descending transverse a sending the the jejunum the ileum all this intestine in front here and then that ileocecal valve the way that I always remember which comes first jejunum irrilium as I remember the ileocecal valve so the ileum must be in front here and the jejunum must be in front of here jejunum difficult to tell where they divide from the external surface we would have to look at the epithelium on the inside the cecum the vermiform appendix and X there's two piece we have epiploic appendages we have the a sending : the hepatic flexure because the livers over on this side the hepatic flexure or the right hepatic flexure or just the right Kolak flexure the transverse colon so this is going to be a sending transverse we're dead messy now and decent oh boy can I draw this upside down d send Dean Coleman this is the splenic or the left colon flexure it's a left Kolak lecture where this one has the right Kolak flexion we have these 10 a coli this tendon of the colon running its length tin sorry tinny a you can look up the spelling of this coli the sigmoid colon the rectum leading to the Venus this is this long tube the transmits foodstuffs out is waste and in the mean time it acquires the nutrients and dumps it into the bloodstream now there's some accessory organs of digestion that I'll also talk about that includes the liver which would sit kind of underneath this respiratory diaphragm massive organ here and overlays that gallbladder we also have the pancreas now I want to mention the head the body and the tail of the pancreas which actually ends up over by the spleen okay the spleen isn't one of our organs of digestion so I'm going to leave it off with the main pancreatic duct the accessory and the main both open into that second part of the duodenum as the major and minor duodenal papilla this is all this fun Star Wars Anatomy the ampulla of Vater sphincter of Oddi okay the kidneys are also retroperitoneal as is the pancreas the majority of the pancreas and the kiddies you want to know what organs are in that abdominal cavity and you want to know which ones are actually behind it that would be retroperitoneal all the others are intraperitoneal that I've drawn there okay tons of structures there we're gonna elaborate on some of these organs further the splanchnic circulation that the hindgut highlighted here in brown is also applied by the inferior mesenteric the mid gut all highlighted in orange is supplied by the superior mesenteric and then the foregut is all supplied by the red or indicated by the red and supplied by the celiac trunk okay I think that I'll stop there now for an overview of the digestive system we just ran through all the parts [Music] here we can see the hindgut the mid gut and the foregut there in red and here we see that splanchnic circulation coming off of the anterior aspect of the a-word before it splits into the common iliac s--