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Raja Narayan 创建




other than the brain I'd say your intestinal tract your digestive system is one of the smartest organs in the body why is that well the digestive tract has its own nervous system it's got its own brain in fact we call it the enteric nervous system the enteric nervous system because the GI tract is able to act on its own without having to send neuronal information or signals to the brain or the spinal cord to regulate its action for example if we're in the presence of a really awesome meal something that's good enough for any hero and a half shell and we consume this meal and it goes through our mouth of the esophagus and it lands in our stomach right here and we've got our food right there what we initiate from this thanks to our enteric nervous system is called the gastrocolic reflex the gastrocolic reflex that involves the stomach the gastro part of this reflex as well as the colon because what happens is that the presence of food in your stomach as signal one tells the colon here it's time to make way for food that's coming down so your colon well actually as a response take food that's in here and push it further south and it does so to make room for the food that we're eating that's the reason why after you eat you feel like going to the bathroom it's not because the food you just ingested is about to come out it's because food that you ate awhile back has come to the end of its journey thanks to the gastrocolic reflex so neuronal control is one mechanism our GI tract uses to control what we do when food is present the other component will focus on down here is hormonal control now hormones as you might recall our substances that are released by tissues in our body that then go through blood vessels like this guy right here to go to some car Oregon our target tissue to cause an effect so I'm gonna talk about a couple of hormones here that regulate our GI tract when food is present so the first hormone we're gonna talk about is called gastrin now gastrin is a hormone that's released when we notice that there's food in our stomach gastrin is released out of the stomach to go to our bloodstream and then come back out actually to the stomach to stimulate the secretion of digestive juices so recall that when we have food in our stomach food in our stomach is going to cause gastrin to be released from mucosal cells the gastrin will then go on to cause secretion of a couple of things one you're going to get stomach acid or hydrochloric acid to be released from parietal cells in the stomach you're going to get pepsinogen to be released from chief cells in the stomach and remember this is the inactive form of pepsin that must be cleaved to become active to digest protein the other thing that gastrin does is that it increases stomach motility remember that one of the functions of the stomach is to churn food that's present it's not just to release acid and pepsinogen that's gonna digest food it also physically breaks down the food so we result in something that's called chyme and I'll write that right there chyme is what the stomach sends to the duodenum now gastrin release into our bloodstream is not unopposed it's checked when the stomach acid reaches a pH of 3 when this occurs then we're going to have a decrease in gastrin release so low pH decreases our gastrin release so I'm gonna say red is inhibition green is the go-ahead or the greenlight so remember the next part of our digestive process involves delivering time to our small intestine and we'll specify the first part of our small intestine and remember that's called the duodenum so chyme that's delivered to our do deena now this is going to cause the release of two other hormones the first hormone I'm going to talk about is called secretin so secretin and I've sort of started the color scheme here but once we have chyme delivered to our duodenum secretin is released into the bloodstream and it goes to places so first it's going to go down to the pancreas that I could have drawn up here on your GI tracts it's about right there in the duodenum but I'm just gonna write it out over here so secretin in the pancreas is going to cause the release of bicarbonate rich solution so this bicarbonate rich solution is going to involve our pancreatic enzymes but the most important part that we want to focus on here is the bicarbonate and why is that well the whole stimulus for secretin release was the acidic chyme that was delivered to our duodenum so of course we'd want to release a base like bicarbonate to neutralize that acid the other place secretin is gonna go from our bloodstream is actually right back up into the stomach this is going to cause an inhibition of stomach motility and acid release and pepsinogen release the kind of things we saw happen with gastrin the other hormone that's going to be released because we have time in our duodenum the acidic chyme in our duodenum is called Coley sista Kynan and as you remember this is a hormone that's related to our gall bladder and just like secreting our cholecystokinin is released from our intestinal mucosa so I can draw it coming from say here into our bloodstream and it's gonna go to places as well one it's going to go to the pancreas to stimulate the release of our pancreatic enzymes so release our pancreatic I'll just write Pank here the pancreatic enzymes and this will help in our digestive process one of the enzymes that is released from the pancreas that I'll explain in a minute it'll help clarify things is i pace remember lipase is used to break down lipids right so that's what the Li P stands for we're breaking down lipids the other thing cholecystokinin is going to do is go through the bloodstream and arrive at our gallbladder it's gonna go to our gallbladder and at our gallbladder cholecystokinin is going to cause the gallbladder to contract so contract our gallbladder and what do you think happens when the gallbladder contracts what's the main function of our gallbladder well if you remember the gallbladder is holding bile that was produced in the liver so when you squeeze the gallbladder you're gonna pump bile out of the gallbladder into the cystic duct and down and out through the common bile duct into the duodenum and that's gonna help emulsify fat and lastly the other thing that cholecystokinin does is that it comes back here and decreases our stomach motility we want to slow down the release of our chyme from the stomach because we need some time to process what we already have in here now it's a plain ol time that causes our cholecystokinin and our secretin to be released into the bloodstream or is it something more specific in the kind well let me ask you why do you think cholecystokinin was released if we had to point to a specific nutrient that was in the chyme that requires then our gallbladder to contract and release bile and have our pancreas release an enzyme like lipase what kind of nutrient do you think I'm suggesting here or macro molecule and all if you said fat you're absolutely right it's the fat in our chyme that specifically causes cholecystokinin to be released okay so what about our secretin well again this is up to you think about what's happening because of the secretin the main thing here is that we're having bicarbonate be released and so bicarbonates a base and we talked about how that's important for neutralizing our acidic chyme so it's not really a macro molecule that causes secretin to be released it's hydrochloric acid it's the acidity of our stomach acid that's now delivered to our duodenum that causes the need for our bicarbonate rich solution from the pancreas so great I think we have a good idea of how our GI hormones are helping us so far at least in our intestinal tract now I know that I gave a little shout out to the pancreas here and we separate least talked about how insulin is released when we have an increase in glucose levels in our blood stream to help us store that glucose for later use and then the opposite occurs when we have a decrease or low levels of glucose and we cause glucagon to be released to increase the amount of glucose than in our blood together these hormones work in a very beautiful manner to make sure that we have the correct hormone to respond to the right stimulus so we can get food that just arrived in our stomach processed all the way to the very end thanks to our hormones and as we mentioned earlier as well thanks to our enteric nervous system