in this video we're going to look at the responses to the stomach filling uh specifically emphasizing motility and contraction keep in mind that paristtoalsis does happen in the stomach it is slightly modified the stomach has this incredible capacity to stretch to accommodate incoming food now previously we had sort of mentioned how when you smell food the anticipation of food can result in triggers like hydrochloric acid secretion likewise the anticipation of food will facilitate the stretching of regions of the stomach like the body and the fundus and the stomach has this incredible capacity to stretch uh recall that in the absence of food the stomach sort of shrinks where it holds about maybe 50 mls but upon filling it can fill up to four lers of food that is over a gallon of food so overall when there's low amounts of food in the stomach the pressure is going to be fairly constant it's not until you have about one and a half liters of food that pressure starts to rise and the change in pressure is going to cause the sort of a reflex mediated relaxation to occur also the stretching of the stomach is coordinated to the swallowing reflex uh in the brain stem uh and this is sort of a Yes and so then the third the third point I want to make is gastric accommodation and what this refers to is the stomach has this capacity that despite it being stretched uh it's not going to increase tension in the smooth muscle it's not going to contract more forcibly so uh we refer to this as plasticity so again we mentioned the parastoaltic uh type of motility that occurs uh and this moves material from the body into the um pyloric antrum and there's sort of a base rate of contraction that is set here so we have these groups of cells called entic pacemaker cells some textbooks will refer to these as interstatial cells of cahal uh but these cells are all sort of interconnected via gap junctions so any electrical stimulus that happens is going to almost instantaneously spread to neighboring cells and so this is going to involve uh the rhythm of contraction but it does not impact the force of contraction there are other factors that play into instigating the force of contraction so distension or stretch is one so the the higher the stretch the more force of contraction after a certain point you know when you have a certain amount of food in the stomach uh and then the hormone gastrin which we earlier talked about in its properties to produce or increase the production of hydrochloric acid that's also going to initiate a stronger force of contraction so when we get to the antrum of the stomach about 30 mls or or more closer to like the pyloric canal you have about 30 mls of material there so 30 mls of kime and what happens with this rhythmic contraction it will cause the partial relaxation of the pyloric sphincter and 3 mls of material is going to be squirted into the uh dadnum the relaxation then causes the partial closure of this pyloric sphincter the remaining 27 mls of the 30 actually gets propelled back into the antrum so we refer to this as retropulsion so it sort of facilitates the grinding and mechanical breakdown of material so when the material the kim enters the dadum you have stretch receptors in the dadum as well as various chemical signals now we mentioned that early on you have the stimulatory effects but our emphasis here is going to be on the inhibitory effects that the dadum plays on stomach activity so those dadinal cells specifically the dadinal intereroendocrine cells in response to these signals they're going to release those interogens that we mentioned before serritin choleiccystokinine and vasoactive intestinal peptide and these are antagonist to gastrin not just for hydrochloric acid production but also for contractile force so they're going to lower the force of contraction and the rate that the stomach is dumping content in the dadum because we want to avoid overdumping we need to effectively neutralize the kind that is in the deadnum to properly digest that material to properly activate the enzymes in the small intestine the high acidic kime cannot be dumped into the small intestine in large volume that's why we're doing 3 ml sort of spurts so the content of the kim through chemo receptors is also going to be detected if it's very carbohydraterich uh the stomach contractions are going to be sort of uh much more elevated and you're moving material through into the dadum so you're not retaining that material in the stomach for very long usually the stomach can uh empty its uh contents within about 4 hours if however fatty kimeim is detected the progression of material through the dadum as well as the dumping of content out of the stomach is going to take significantly longer it can be over 6 hours and that sort of uh the reasoning behind that is lipids are much more difficult to both break down and to absorb than carbohydrates so again all of this is going to be controlled and information is being sent to the central nervous system promoting parasympathetic responses because that antagonizes sort of gastrin and contraction so lastly let's talk about emmesis or vomiting so vomiting can be caused by two main effects either extreme stretching which leads to the dumping syndrome that we mentioned before or there might be some intestinal irritants like bacterial toxins too much alcohol really spicy foods so chemicals uh are going to be detected via those chemo receptors uh and that information is going to go to the part of the brain stem known as the imic center and that can trigger this response that can lead to a number of effects for example the rising of the soft pallet so the uh vomitus doesn't go up through your nose um and then sort of the opening of the cardiac sphincter so that material can leave the stomach uh but there's an issue if we have excessive vomiting because of the pH environment of the stomach juices if there's excessive vomiting that means in order for us to reform stomach acid the acidic stomach acid we have to draw some of those hydrogen ions from circulation and so this is going to cause pH imbalance or alkalossis in the blood