okay we're going to talk about the digestive system and answer the questions what are the digestive system organs and what are their functions and what accessory digestive organs contribute to digestion and what's the vascular supply and innervation of the gi tract hello everyone my name is dr morton and i'm the noted anatomist so let's begin by talking about digestive organs and specifically start in the oral cavity and so the oral cavity has teeth and the teeth masticate which means it's the physical digestion or the physical breakdown of food and what does that mean well we have this mandible that allows us to chew so what happens is you get food and you put food in your mouth and you start chewing that piece of pizza keeps going breaking down and just becomes pizza but just smaller pieces of pizza that's physical digestion taking food and making it smaller pieces of the same food but no chemical bonds were broken now let's enter salivary glands in the oral cavity and that's where saliva moistens food and it forms a bolus and the salivary animal is let me start that again salivary amylase in saliva starts the chemical digestion of carbohydrates so there we have three glands submandibular salivary gland the parotid gland and the subligul salivary gland and these glands make saliva but the submandibular that makes the most by far like 75 to 80 percent of the saliva parotid makes maybe 20 fifteen to twenty percent and just two to three percent is that sublingual salivary gland and these glands are paired three on each side um so if you zoom in let's take a look there's saliva coming from these three areas and what the saliva does it takes these small pieces of food and it forms a ball and we call that ball a bolus and that's what you swallow down the pharynx into the esophagus but then also salivary amylase within saliva chemically starts digesting carbohydrates and you break chemical bonds so that's how polysaccharides become disaccharides or monosaccharides that is chemical digestion breaking chemical bonds and carbohydrates proteins or fats you make about a liter and a half of saliva every single day that's like four and a half cans of soda just give you an idea how much saliva you you me we all make next let's go to the esophagus the esophagus transports food from the oral cavity to the stomach and during that transportation no metabolic changes occur it's simply being transported so there's the esophagus now the esophagus is interesting in that it has three different architects of muscle in its wall depending on where we're at so proximally their skeletal muscle lines the esophagus from the pharynx down to the top of the esophagus that's what allows you to voluntarily swallow food distally the part of the esophagus that goes into the stomach that's all smooth muscle that's involuntary so you do not have any conscious control over it and somewhere between the proximal and distal part that skeletal and smooth muscle mix so you go from voluntary to involuntary as you swallow that bolus of food down so there's that orange circle represents a bolus of food and so swallowing voluntarily we see that peristalsis is this movement that takes over after you swallow so when you swallow just sit there and swallow your own spit you go um you voluntarily did that that skeletal muscle but then there's this process called called peristalsis that's involuntary that takes over and that's how we move the food all the way through the rest of the gi tract all the way down until you get down to defecate and now you've got skeletal muscle that allows you to defecate voluntarily again as whatever's left over comes out and so that's a nice transition to a little uh tangent um that we're going to top with the layers of the gi tract here's a cross section of the gi tract and there's four layers that we're going to go over the first mucosa second submucosa third muscularis externa and finally the serosa let's start with the mucosa there in pink the mucosa is lined with epithelium that's the part that's in the lining the lumen and deep to all basement membranes of epithelium is loose connective tissue we call that the lamina propria and the mucosa is there to protect or to help with absorption in secretion there's epithelium that's lining the lumen and there's the lamina propria that's where the capillaries are found for absorption let's take one of those capillaries and blow it up and there we've got the mucosa and the mucosa consists of two parts epithelium in the case in this one is simple calamity epithelium that we see in the stomach small intestine and large intestine the esophagus is stratified non-cratinized epithelium but most of the gut tube is simple columnar deep to that is the lamina propria and that's loose connective tissue and that loose connective tissue housed the systemic capillaries that absorbed carbohydrates and amino acids and the central lacteals the lymphatic capillaries that absorb fats so this motif is something we're going to see throughout the digestive system deep to the mucosa is the submucosa means sub like a submarine below and this consists of dense connective tissue with lots of vessels and nerves and there are some like some blood vessels these are the larger vessels the macroscopic vessels that feed the capillaries that go into the lamina propria the muscularis mucosa that i just outlined there is a thin layer of smooth muscle that is the fence between the mucosa and the submucosa next is the muscularis externa the muscularis externa consists of an inner circular and outer longitudinal layer of smooth muscle intercircular outer longitudinal that go in opposite direction contraction of the inner circular and outer longitudinal layer of smooth muscle is what causes segmentation the breaking down of the bolus into smaller chunks and peristalsis that movement of food through the gi tract notice between the inner circular and outer longitudinal layers is this nerve we call it it's a normal cell body we call that our box plexus or the myenteric plexus and then deep to the inner circular there's another one we call that meissner's plexus or the sub mucosal plexus because it's kind of in that kind of it is between the inner circular layer and the submucosa these are describing autonomic neurons that line the gi tract that help with its functioning so we call these gi gastrointentional intramural ganglia within the wall like an intramural sports team is a sports team within your own school extramural means you fight or not fight you know what i mean you play against a different school gi intramural ganglia are within the wall of this um but simply these are postganglionic parasympathetic neuronal cell bodies that's what they are that is the second neuron in the parasympathetic chain but we have another name for this is the enteric nervous system all these words are talking about the same thing the neuronal cell bodies that line the wall of the gut tube either in the submucosal plexus or myenteric plexus that help with its functioning all of these are derived from neural crest cells they're talking about the same thing yeah thanks anatomists so let's talk about peristalsis it's like getting toothpaste out of a toothpaste container so here's the toothpaste container we open the lid and we go like this squish and you notice that when you do that toothpaste comes out and then you push squish push squish push squish push squeezing and pushing that's where you get toothpaste out well peristalsis is like getting toothpaste out of a container here's a gi tract and the then you see that you squeeze that's called segmentation you break the bolus into a smaller pieces of bolus and then peristalsis is you move it like that so we see just like squeezing which is the inner circular layer and pushing which is the outer longitudinal layer that's how you get toothpaste out of a container and that's how you get a bolus of food or the chyme to move through the gi tract finally is the serosa which is a mesothelial lining it's another name is the visceral peritoneum it's the serous lining that makes serous fluid all right now here's an h e stain of the ilium we're going to zoom in on and we're going to focus on this area so the mucosa consists of epithelium and there's the lamina propria and the dotted line is the basement membrane okay the laminate appropriate houses the capillaries for absorption then there's the muscularis mucosa that i just drew on a smooth muscle that separates the mucosa from the submucosa which is primarily connective tissue blood vessels and nerves then we have the muscularis externa made a smooth muzzle of an inner circular and an outer longitudinal layer and then finally there's the serosa of mesothelium there are the layers of the gi tract let's talk about the stomach now like the stomach's topography is this between the esophagus and duodenum as you go from mouth to anus so there's the stomach between the esophagus and the duodenum but it's also superficial to our spleen pancreas and aorta where there's the stomach and it's superficial you know it's hard to tell from that picture of the spleen is deeper to the stomach and the pancreas lies deep to the stomach as does the abdominal aorta the function of the stomach well peristalsis moves the movements the peristaltic mu let me say that again peristaltic movements churn the gastric contents and it makes the bolus into chyme and so this would help facilitate the physical breakdown of food and the mixing of secretions from gastric glands turn this bolus into chyme so goblet cells of the epithelium lining the stomach make mucus that protects from the acidity that's derived from parietal cells and parietal cells produce hydrochloric acid with a ph of like one and a half to two also intrinsic factor which helps with the reabsorption of vitamin b12 by the small intestine and the chief cells secrete this pro-enzyme called pepsinogen that when mixes with hydrochloric acid becomes pipsin starts the chemical digestion of proteins so here are the different regions of the stomach okay and i've just drawn these on well there's the cardia because it's deep to the diaphragm which above that is the heart and the cardiac sphincter separates the esophagus from the stomach the fundus is the dome-shaped area at the top of the stomach that's where gas usually goes that's where the next belch is sitting there's the body of the stomach the big part in the middle and then the funneling part of the end is called the pylorus which gives rise to the pyloric sphincter which is a thickening of the inner circular layer of the muscularis externa that helps keep contents from the stomach and the small intestines separate then we have this very large curvature we call the greater curvature and a smaller one called the lesser curvature on top now the lesser momentum is some mesothelium that attaches to the lesser curvature and the greater momentum is peritoneum that attaches to the greater curvature we take a cross section through the stomach and there's gastric rugi that if i draw it looks like this and it allows to increase the contents in the stomach to up to like one and a half liters to allow you to consume more food like at one of those all you can eat buffets now let's talk about small intestines so small intestines are about seven meters long but they don't get their name because they're short they get their name because the lumen is small the luminal diameter is small and this is where digestive processes are completed where nutrients are chemically digested and then they're absorbed the small intestine has three parts it has the duodenum they jejunum and the ilium let's start with the duodenum it's the first part of the small intestine it's distinguished by bruner's glands and it has four parts so there's the duodenum it has these bruner's glands and these asterisks show these glands that help produce the bicarbonate that's secreted into the lumen and then it has four parts the first part of the duodenum the superior part has what's called the duodenal cap or bulb there's the pylorus of the stomach in the pyloric sphincter and there's the first part of the duodenal bulb and in this barium swallow you can see the pylorus of the stomach pyloric sphincter and there's the duodenal cap or dewalt duodenal bulb duodenal or duodenal tomato tomato the first part is also smooth walled so there you can see the first part is smooth and the second part is not smooth wall because it has these circular folds smooth not smooth okay and then the first part is intraperitoneal where the rest of the gi tract is retroperitoneal so there is the hepatoduodenal ligament of the lesser momentum attaching to the first part of duodenum that's intraperitoneal where the rest of the duodenum parts two three and four are retroperitoneal now part two of the duodenum is called the descending part it starts as retroperitoneal it has circular folds and it has what's called the major duodenal papilla so there's the second part it's descending because the food descends vertically has a circular fold that you'll see characteristic for the entire small intestine for increasing surface area for absorption and that's also where the common bile duct and the pancreatic duct form wonder twin powers to make the major duodenal papilla and that's how you get bile and pancreatic enzymes into the second part of the duodenum at the end of the second part of the duodenum we have the beginning of the horizontal or third part that's the separation from the embryonic foregut from mid-gut more on that later the third part or transverse part of the duodenum is where the superior mesenteric artery and vein cross over the duodenum that's one of the clinical characteristic features traversed by the smv and sma in this picture you can see the parts of the duodenum and you'll see then the superior mesenteric vein and artery crossing over the third part of the duodenum and finally the fourth part or ascending part of the duodenum is where the duodenal regional junction occurs and where we go from retro back to intraperitoneal organs so there's the fourth part and there's the ligament to trites which is skeletal muscle coming off the diaphragmatic cura and that's what points to where the duodenum and j genome have the duodenal duodenogenic junction it's a surgical landmark that's often used it's also where we see there's the fourth part where the jejunum in ilium that's the duodenal jejunal junction retroperitoneal to intraperitoneal so there's our four parts of the duodenum now let's talk about the rest of the small intestines with the jejunum and the ilium the jejunum is located in the upper left quadrant and the ilium is in the lower right quadrant so here we have the small intestines the greater momentum is reflected upper left quadrant primarily that small intestine you see is the junum lower right quadrant that primarily is the ilium there we've got where they're basically located and the j-juna and ileum are considered intraperitoneal organs and they're tethered to the posterior abdominal wall by mesentery this is a sagittal section of the abdominal cavity and there was focusing on all those circles are showing cross-sections or in this case sagittal sections through the jejunum and ileum notice that mesentery anchors it to the back of the abdominal wall and these two-layer mesentery is where we find the vessels and nerves coursing to the gut tube now the jejunum is the second part of the small intestine as we've shown here and it has a lot of circular folds the fancy way of saying is the plique circularis lots of circular folds as you can see there so there's lots of lots of absorption of the nutrients from the food we're eating now the ilium is the third part of the small intestine there are fewer circular folds in the jejunum and so when we see the ilium ng genome lots of circular folds fewer circular folds they're there but just not as many here is an actual catavaric small intestine opened up where there's a genome look at the number of those circular folds in contrast to the ilium where they're there there's just fewer of them because a lot of the absorption has already occurred all right now the ilium also histologically has something called pyres patches which is dense lymphatic nodules in the lamina propria that you see all those purple dots are showing nuclei of lymphocytes lots of them and that's histologically how you distinguish the ilium from the jejunum and from the duodenum so histologically duodenum has bruner's glands helium has pyrus patches jejunum has neither and finally the ileum has the ileocecal valve because there's the ilium there's the cecum so what do you call the valve between them the ileocecal valve that represents the termination the end of the road for small intestines which leads us now to the large intestines or the colon what are some of the features of large intestines well they're about one and a half meters long so they get their name because the luminal diameter is large compared to the small intestine even though they're far shorter the large intestines absorb water and salts and also vitamins that are produced by the intestinal bacteria flora and the colon basically compacts and then eliminates feces the large intestine is then further characterized by teeny e coli hostra and epiploic appendages let's go through each one of those so the tini e coli are thickening of outer longitudinal layer of the muscularis externa and there are three separate longitudinal bands anterior posterior and lateral and they run the entire length of the colon and so we see there we can see the anterior and posterior and then the anterior again we just don't see the lateral very good and um a little tightening of the teeny e coli form these hostra and the hofstra are small pouches in the colon that give it a segmented appearance very characteristic of the colon or large intestine and finally the epiploc appendages which are small outpouchings of fat filled serosa covering the outside of the colon like that all right so now let's talk about the cecum it's located in the low lower right quadrant of the abdomen it's a blind ended sac it's the start of the large intestines and coming off the cecum is the vermiform appendix right there it's attached to the cecum and it has an unknown function for the most part though more literature showing that it might have very important intestinal flora inside and it's variable length and position but the surface anatomy to locate the appendix is called mcburney's point you find the asis anterior superior iliac spine find the umbilicus and from the right side i should say the asis you draw an imaginary line and a third of the way up is mcberney's point if you push on that that's where the origin of the appendix is off the cecum the ascending colon arises from the cecum courses vertically to the liver it's on the right side of the abdomen and it ends at the right colic or hepatic flexure the transverse colon is an intraperitoneal organ it's the superior part of the abdomen and it courses from the right colic flexor all the way to the left colic lecture did you hear that that's my dog hold on um and the transverse colon is anchored to the posterior abdominal wall by the transverse muscle colon so something that happens in the transverse colon is there's a transition from the embryonic mid gut to hindgut so there's our transverse colon somewhere we usually say two thirds along the way the mid gut becomes the hind gut now why do we care about that well that's going to become important when we start talking about vascular supply and innervation okay all right now the descending colon is on the left side of the abdomen it courses from the left colic or splenic flexure down to the sigmoid colon and the sigmoid colon then is on the left side of the pelvis it's an intraperitoneal organ anchored to the pelvic wall through the sigmoid mesocolon and then finally the rectum is the terminal straight portion of the gi tract rectum or rectus means straight like rectus abdominus or erector spinae the rectum is a retroperitoneal organ so here in my one little illustration there's the rectum and there's protoperitoneum and notice that the rectum is behind it like that okay now the anus is the exit of the gi tract and there's the anus and so the anus has skeletal muscle for the external anal sphincter that's what allows you to defecate when you want to the internal anal sphincter is smooth muscle that's involuntary and as more feces backs up behind the anus into the rectum the more pressure is on the internal anal sphincter the more it becomes relaxed and the more you feel like oh i gotta make it to the toilet and that's where the external anal sphincter comes into play to help you until you're ready to sit down let's talk about the accessory digestive organs okay and start with the liver now the liver is located in the upper right quadrant of the abdomen and it produces bile now bile is what we say emulsifies fat takes big fat droplets and breaks them think of cracking a rock into tiny pieces it's still a rock they're just smaller pieces and that enables to reduce so that digestive enzymes can better break the chemical bonds in these smaller droplets of fat but the liver has a ton of other functions like it helps with cholesterol metabolism it takes part in the urea cycle produces proteins like albumin it produces clotting factor it helps to detoxify blood and so forth the liver has the following lobes right left lobe quadrate and caudate here's a visceral inferior view of the liver there's the falsiform ligament and the gallbladder and there's the portal triad more on that later and that's the groove for the inferior vena cava to the right of the gallbladder is the right lobe to the left of the false form ligament is the left lobe between the gallbladder and false form ligament is the quadrate lobe and between the inferior vena cava and the left lobe is the caudate lobe there are the four anatomic lobes of the liver now the portal triad consists of the proper hepatic artery the portal vein and common bile duct so there and we'll view in a little bit closer there is the proper hepatic artery that comes off the common hepatic artery a branch off the celiac trunk and then there's the portal vein which is basically the portal vein the union of the splenic and superior mesenteric vein this is what's draining all blood from the gi tract and then the common bile duct there that's what's delivering bile from the liver and gallbladder into the second part of the duodenum so the right and left hepatic duct feed into the common hepatic duct and they join the cystic duct to make the common bile duct and that's what we see there all right so there's our liver there's the gallbladder there's the stomach and there's the duodenum between that we're going to draw on the lesser omentum coming off the lesser curvature of the stomach which consists of two parts because anatomists name everything the hepatoduodenal ligament hepato for liver to the duodenum is the free edge of the lesser momentum and then the hepatogastric ligament is the rest and we talk about this because inside the hepatoduodenal ligament of the lesser momentum is the portal triad okay but this i wanted to show an h e stain of a microscopic section high power of the liver because all those cells you see around the side are hepatocytes but look here in the middle is a portal triad right there there's a hepatic duct hepatic artery and portal vein so what we see microscopically is the same relationship that you see grossly i think that's really cool all right now the mesenteries of the liver so we zoom in there is the visceral peritoneum that lines the liver parietal peritoneum that lines the wall and they reflect upon each other but notice there's this space right there where there is no mesentery we call it the bare areas and bare naked bare area there's no mesentery and that is now where when you have high pressure from ascites where fluid can push through that area from the abdominal serous fluid into pleural to become pleural fluid or in fluid in the pleural space i should say and there's the bare area of the liver and often these illustrations that you'll see there's also this falsiform ligament right here this ventral mesentery coming from the liver to the anterior abdominal wall and that falsifying ligament has at the bottom the ligamentum teres that's housing the umbili the obliterated umbilical vein and there we have it often what you'll see in the liver okay now let's talk about the gallbladder which is on the visceral surface of the liver with and it stores and concentrates bile so here we have the gallbladder and there's the cystic duct and the common bile duct and there's the main pancreatic duct and they form together the major duodenal papilla now that's in the second part of the duodenum now i want to see what happens like in the liver biles produce and so what happens is bile moves down these ducts to get down to go into the liver let me say again to get into the duodenum but that opening is not always patent that major duodenal papilla has a sphincter of odi that it keeps it closed at times and unless cholecystokinin is secreted that will remain that opening will remain closed so bile backs up and goes into the cystic duct where the gallbladder stores and then concentrates that bile let's talk about the pancreas and so the pancreas is located deep to the stomach there's the stomach there's the duodenum and there i've just highlighted the pancreas and there if we cut the stomach you see that the pancreas is retroperitoneal so we see these two lines of the peritone of the parietal peritoneum and between them there's the pancreas but the pancreas is behind the parietal peritoneum except for the tail that tail it touches the spleen that little bit it's like your toes sticking out the end of your bed sheets that's they consider intraperitoneal but the bulk of the pancreas is retroperitoneal and it's about 15 centimeters long to give you that and i i just include that because i remember when i first learned that just the system i had in my mind the pancreas is like the length of my index finger and it's pretty hefty now the pancreas has both exocrine and endocrine glands exercising glands or any exercising glands secretes their product to an epithelial surface so in this case the pancreas secretes digestive enzymes into the epithelial line duodenum and all those yellow circles represent asner glands and they produce digestive enzymes that go in the main pancreatic duct of warsong which then goes into the duodenum that second part so johann wurssong was he's a german anatomist that was dissecting in an anatomy lab in padua england and in 1642 he discovered this duct in the pancreas and he's like ta-da i'm going to name this and so we did name it and instead of publishing in journals he decided he's going to put him on copper plates instead so all these copper plates have this investigation the next year this other anatomy student jokomo cambiere discovers the same duck and he starts writing about it and someone says no no actually johan wersang already did it and through very hard feelings jokomo got so angry that one night when johan was going to home dr wursung was shot in the back by djokomo and killed over this structure so djokovic went to jail dr wersang died the structure was continued in his name and five years later dr wilson's graduate student said actually i'm the one who discovered it but i think there was enough death and violence and so he just let it go dr warsang is what it's named after now um those digestive enzymes in the duodenum from the pancreas is what i want to talk about next these digestive enzymes that i've now schematically shown as scissors what they do is you've got pancreatic proteases and what these enzymes do is they take proteins and break the chemical bonds between individual amino acids and that's how we chemically digest proteins into their individual amino acids that's one of the ways the pancreas does this it also does it through pancreatic amylase which then breaks the chemical bonds between these different monosaccharides and disaccharides in these long-chained poly polysaccharides and that's how we get glucose and then finally the pancreatic lipase that takes and breaks the bonds between these fatty acids and glycerol in the duodenum and so that is one of the ways that the pancreas helps with digestion is making those digestive enzymes now the pancreas also contains endocrine glands and now in contrast endocrine glands secrete their products into the bloodstream which then circulates them the pancreas secretes insulin and glucagon and we have these things that have drawn orange circles they're called pancreatic eyelids of langerhans and that is what's producing the hormones insulin and glucagon and so insulin will take macromolecules like sugar glucose and put them into the cells glucagon will take macromolecules like glycogen and break them down and dump glucose into the bloodstream so the pancreas has exercise digestive glands enzymes and endocrine for insulin and glucagon all right let's talk about the spleen now spleen actually is located in the upper left quadrant like that it's technically it's not technically it is not a digestive organ but it has the same blood supply because it forms in the dorsal mesogastrium so i look i mentioned here because it has the same blood supply it's about the size of a fist and it stores blood and phagocytizes foreign blood particles and it produces pmns and it's other big functions that remove senescent and defective red blood cells all right let's now talk about the vascular supply and innervation of gi organs and begin by talking about this embryonic foregut midgut hindgut here's a schematic of the development of the gut tube in yellow and so there is what's called the superior mesenteric artery and this gut tube that's forming from mouth to anus has this part in the middle of your abdomen where the superior mesenteric artery has this part of the gut tube that wraps that it herniates out and so embryologists said why don't we call this the middle gut the mid gut so the part before it's the foregut and the part after it's called the hindgut so forget organs include stomach to the first couple parts of the duodenum and all the accessory digestive glands the gut is the second the third and fourth part of the duodenum all the way to the transverse colon and the hindguts transverse colon to the rectum knowing this is helpful now why do we care about learning four gut mid gut hindgut because if you know those it's very easy or i should say straightforward to learn the arterial supply so the celiac trunk supplies all four gut organs here we have the celiac trunk coming off the abdomen abdominal aorta so there's the stomach and there's the duodenum and the pancreas and the liver and gallbladder and the spleen all those organs they're supplied by the celiac trunk through those branches okay now the superior mesenteric artery supplies all mid-gut organs there's the sma so there's jejunum and there's the ilium and there's the cecum and appendix and there's the ascending and transverse colon all of those organs are supplied by the sma through those branches and finally oh part of me there is an anastomotic connection between the foregut and mid-gut so here we've got the celiac trunk and there is its branches called the superior pancreaticoduodenal arteries and there's the superior mesenteric artery with the inferior pancreaticoduodenal arteries so between these pink radical duodenal arteries we have an anastomotic connection between the foregut and mid-gut arterial supply now the ima supplies all hindgut organs so there's the ima and so there's the transverse colon descending and sigmoid colon in the rectum all of those are supplied by branches off the ima now there's an astomatic connection between the midgut and hindgut okay and so there in red i show this thing it's called the marginal artery of drummond and as we can see there kind of parallels the picture frame of the colon and so the superior mesenteric artery has this middle colic artery and the inferior mesenteric artery has this left colic and then watch we've got this very cool anastomotic connection through the marginal artery of drummond and finally lymphatics now lymph from the gi tract drains to lymph nodes arising from the organs arterial supply so there we have celiac lymph nodes so where is that lymph coming from all the four good organs there's the superior mesenteric nodes where is the lymph coming from all the mid-gut organs there are inferior mesenteric nodes where is that lymph coming from all the hindgut organs now the venous drainage of the gi tract to do that to talk about that we need to discuss the hepatic portal system the paddock portal system mirrors the arterial branches for the most part so for the foregut you have the celiac trunk supplies it and the gastric gastro mental spinach veins drain forget the mid gut supplied by the sma it gets drained by the smv hein guts supplied by the ima it's drained by the imv so we see that the aorta supplies the four gut mid gut hindgut and then the portal vein drains the gut tube so the foregut through the gastric gastro mental and splenic veins and they all drain into the paddock portal vein so there's the foregut with the stomach and spleen though there's other organs i'm just going to focus on those two you have the splenic vein and there's the portal vein and you see all those veins that are draining the stomach and the spleen all end up going to the portal vein which drains into the liver the superior mesenteric vein receives blood from the mid gut so the superior mesenteric vein goes to the portal vein and into the liver so there's the mid gut with the jejunum and ilium and the cecum ascending and transverse colon and there's the superior mesenteric vein collecting blood from all the mediated organs into the portal vein into the liver and finally the inferior mesenteric vein receives blood from the hindgut and the imv goes to the splenic which goes to the hepatic portal vein which goes to the liver so there's our hindgut with their descending colon sigmoid colon and rectum and there's the inferior mesenteric vein going into the splenic vein going into the portal vein into the liver now let's conclude with the innervation of the gut tube autonomic innervation can either be sympathetic or parasympathetic so sympathetic innervation will reduce peristalsis or decrease it and decrease secretions but increase think your tone you're basically slowing down digestion or in contrast parasympathetic innervation will increase peristalsis and increase secretions but reduce fincure tone basically increasing digestion so remember parasympathetics are rest and digest so let's talk about the way that the autonomics will help so here we have in this illustration the foregut i'm just showing the stomach but it's basically all four good organs the sympathetic innervation comes from the greater splanchnic nerve which comes from the lateral horn gray matter of t5 to t9 courses through the sympathetic trunk without synapsing and then continues as the greater splanknick nerve to synapse in the celiac ganglion and then postganglionic sympathetic neurons wrap around like christmas lights in a christmas tree branch arteries from the celiac trunk that then supply sympathetics to the foregut organs now parasympathetic innervation will come from the vagus nerve that's arising from the medulla course through the celiac ganglia without synapsing hug along the same arteries and then synapse with postganglionic parasympathetics in the wall of the foregut that's the intramural ganglia arbox and meissner's plexuses there okay now the mid-gut organs these are going to be supplied by the lesser splancnix so coming from the lateral horn of t10 and t11 of course through the sympathetic trunk without synapsing the lesser splanchnic nerve will then synapse in the superior mesenteric ganglion postganglionic sympathetics follow the arteries to synapse in the wall of all the mid-gut organs slowing down digestion whereas the vagus nerve for parasympathetics courses through the superior mesenteric ganglia wraps around the arteries of the sma to supply mid-gut organs finally we have the hindgut organs which are going to be like transverse descending in sigmoid colon and rectum those preganglionic sympathetics arise in the lateral horn of l1 and l2 course through the sympathetic trunk without synapsing and these lumbar splancil synapse in the inferior mesenteric ganglia and then follow the arteries out to the hindgut or through the superior hypogastric plexus and the inferior hypogastric plexus course out to hindgut organs and innervate them parasympathetics arise from the s234 spinal cord levels in the lateral horn and then they course to the hindgut via these pelvic splanchnic nerves okay from s234 and then coursing in the hypogastric and inferior hypogastric plexuses supplies the hindgut organs so there we have it so the gi tract in a nutshell we have the oral cavity which is where teeth are that masticate and physically digest the food where the salivary gland secretes saliva with salivary amylase that moistens the food and forms a bolus that bolus then moves down the esophagus through peristalsis into the stomach which has goblet cells that make mucus parietal cells that make hydrochloric acid an intrinsic factor in chief cells that make pepsinogen which then that food stuff the chyme goes into the duodenum this is the location of biliary action and the enzymatic chemical digestion from the pancreas so the liver filters the blood but also produces bile where it's stored in the gallbladder and concentrated and that's where the bile emulsifies fat the pancreas produces and secretes digestive enzymes into the duodenum so the liver the gallbladder and the pancreas all dump their products into the duodenum which is the location of biliary action and enzymatic chemical digestion the rest of the small intestine duodenum j-genomic ileum is where the absorption of nutrients take place so we have amino acids and carbohydrates that go into the systemic capillaries and fats that go into the central lacteals the large intestine cecum the colon and rectum this is where the absorption of water and salts take place and so salts water and fat soluble vitamins and then the rectum and anus and we're out so if we then take a look at the gut tube and know the foregut mid-gut hindgut in the individual organs that make up those regions it's easier to understand the arterial supply the venous drainage and the innervation and that my friends is the digestive system in a nutshell [Music] you