Today, we’re going to talk about the challenges we put our poor little stomachs through like how much food can these organs accommodate and once the food’s in there, what does the stomach do with it, also we need to talk about the deception that all children have given to us with their tummy aches for many many years, so we’ll address that as well as why does our stomach not eat itself alive with all the acid it produces that and more coming up. So let’s start with some of the stomach basics and the external anatomy of the stomach and how it sits in the human body, that is going to help us understand how the kids have been deceiving us for years so let’s take a look at the dissection, you will see the stomach down on the tray, it’s often referred to as this j shaped organ kind of like a j and you can see a curve and a curve there, the larger of the two curves is referred to as the greater curvature of the stomach, the smaller curve the lesser curvature of the stomach. The stomach can also be segmented into three regions which again will help us with location and future topics in this discussion. The first section is referred to as the fundus of the stomach, the central larger portion is referred to as the body of the stomach and the last portion, the pyloric region or the pylorus. Here now, there’s a really important sphincter in the pylorus region or the pyloric region and that’s right here called the pyloric sphincter, you can see that with the naked eye because the smooth muscle gets so robust there really strong sphincter that only allows a little bit of material to pass through at any given moment which we’ll talk about later but first we’ve got to talk about the location here, the stomach is located in the left upper quadrant of the abdomen, it would actually sit a little bit underneath the rib cage here, the left side of the rib cage and that would be about from here over the swooping of the stomach where the pyloric region or the pylorus would be more exposed outside of the rib cage, so this region right here so you have some of it under the rib cage, some of it’s swooping to the midline, if you take a look at the cadaver dissection, the stomach there now here are the ribs so you can kind of see on that left side that there’s the greater curvature of the stomach and it’s swooping towards the midline.
Now do you feel a little bit deceived by children, i mean how many of them ever come and say mommy, daddy, my tummy hurts, they’re never holding right here they’re always holding the wrong side and we fall for it, they’re lying to us, their stomach’s not hurting because it’s over here and all of us we feel bad for them so we let them stay home from school and when they go up into their room to rest whereas they were touching their small bowel. It’s good to know your anatomy and that’s the most important topic of all time agreed, all deception aside, it’s good to know the stomach, left upper quadrant, small intestine occupies more of the central abdomen. So let’s talk about the function of the stomach, once food gets down in there and also we’re going to talk about when we over stuff the stomach but let’s start with just regular old meals like regular sized meals, how the stomach will handle that, so if you go back to the dissection, what you can see is the very bottom of the esophagus, sometimes people nickname it the food tube, as we swallow the food goes down the esophagus down into the stomach, once it gets into the stomach we’re gonna have some of the cells stimulate the release of certain compounds or chemicals, now let’s see another dissection so just to compare this is about two-thirds of a stomach and it is a little bit larger in size especially the fundus, this is about where the esophagus would come into this stomach so you can definitely see the fundus is larger than the other stomach which again teaser, we’ll talk about stomach stretching in size later but one of the things that’s really awesome is if you look at the inside lining of the stomach, now this inside lining is referred to as the tunica mucosa, tunica just refers to a layer mucosa because it’s going to secrete some mucus, now these gastric folds are called gastric rugae, rugae just literally means folds, this will be important again later when we talk about stretching of the stomach.
Let’s see what the tunica mucosa has to offer us, so if we were to look at this tuna mucosa at the microscopic level, we would see some really important cell types that secrete certain substances, we’re going to talk about three cell types, they are chief cells, parietal cells and mucous cells, so the chief cells secrete two very important substances, one is pepsinogen, the other one is called gastric lipase, pepsinogen gets converted to pepsin by the acid in the stomach and then it helps break down peptide bonds which essentially we’re breaking down proteins here, the gastric lipase helps break down fats so we’ve got those secretions released by the chief cells but i also mentioned another cell type called parietal cells, those also secrete two very important substances, the parietal cells secrete intrinsic factor and the hydrochloric acid intrinsic factor is necessary to absorb vitamin b12, really important vitamin that can be a whole other topic. Hydrochloric acid has other functions, hydrochloric acid helps denature proteins so it’s again helping in aiding with helping and aiding with digestion, we can also see that it’s going to kill pathogens, bacteria and certain viruses don’t like a ph of 2 and it’ll just destroy those things so we kind of have to think about this other idea though, how does the hydrochloric acid not eat away our own stomach lining, that tunica mucosa that i mentioned ,well that was the third cell type, the mucous cells. Those mucous cells secrete mucus and it coats the whole lining of the stomach, so if we go to this whole area here, the whole inside lining of the stomach gets coated in mucus so you could kind of think the lining of the stomach coated with mucus with acid on top and that helps to stop the acid from eroding the stomach or causing problems, if you take any medications that lower the mucous production which ibuprofen and advil contribute to, you can make that mucus a little bit thinner and therefore the acid can irritate the stomach a little bit more, so now we can see that the stomach coats the food in substances like hydrochloric acid and enzymes which helps aid in the breakdown of the food but the stomach doesn’t stop there, it continues to mix the food which also aids in digestion, it often gets referred to as a muscular blunder so if you take a look at the dissection here again, imagine the wall of the stomach has smooth muscle in there and that smooth muscle is going to contract and mix the food in a certain way.
Now the fancy pants phrase for the digestive system moving food downstream is called peristalsis and the stomach kind of does it with this propulsion and retropropulsion type of wave action that we’re going to talk about so if you imagine right, that here’s the beginning of the stomach where we come in here and then there’s the end going to the small bowel, the stomach tends to propel the food this direction and remember we had a really tight pyloric sphincter here and that pyloric sphincter is so tight that it typically only lets about three milliliters through, that’s not very much so really only small substances, so anything that gets pushed this direction and isn’t small enough gets pushed back and so you get this wave of back and forth with the stomach until any substance that gets pushed this direction, if it’s small enough it’ll sneak through, if it’s not, it gets pushed back for further mixing and further breakdown, one question we often get from students is how long does that wave back and forth happen in the stomach, well it depends a little bit, one it depends on how much food you ate which again we’re going to talk about in a second here and two the type of food, carbohydrates tend to be broken down the quickest so if you have a carbohydrate-rich meal, it will be digest quicker, proteins are kind of next in line and then fats the slowest so carbs, proteins and fats and the majority of the time we eat a mixture of all those but it kind of leans one towards the other depending on the type of foods you’re eating so it can be anywhere from two to four hours before you empty the stomach.
With this process of peristalsis or those waves of contractions going through the stomach, so finally we can talk about how much food we can pack into the stomach during thanksgiving dinner or during whatever food binge we want to go on, yes need to mention we changed locations in the lab, i had to set up a little experiment that we’re going to conduct with this cadaver stomach in just one second, however i want to mention if you were to do some research on how much you could pack into the stomach, you’d get a wide range of data, there’s some literature that will say the stomach can hold up to six liters, that would be all of this these are all 500 milliliters, so two of these bottles would be one liter, all of this going like how am i gonna get that in there, that’s pretty remarkable to think about six liters but then you look at some other research and they’re saying maybe it’s more like two to four liters, okay, now if you look at medical physiology books, a lot of them will actually mention the stomach in its relaxed state could get about 0.8 to 1.5 liters of food in there, so if we compared that to the bottles, here’s just one liter and you know 1.5 liters would be three of those bottles again that still seems like a lot, i don’t think i could even get two of these into this stomach right here but we’re gonna try because i have two bottles each with about 500 milliliters in it and we’re going to try to actually put this in the cadaver stomach here, okay so let’s start with the first 500 milliliters, i’m going to go into the what’s left of the esophagus here and now i’ve put like this black band over here, this is the pyloric sphincter again, now we’ll let a little fluid through, so i wanted to clinch that down so we could actually get a better idea of how much fluid will stay in the stomach, now as i push the fluid in here, there’s a couple of things that would happen in a living body as food was pushed in like i’ve pushed some of this water in here, the stomach would sense that through some of the sensory neurons and it would send this reflex arc back through the vagus nerve to the brain and the brain would quickly send a signal back down to the smooth muscle of the stomach to actually tell it to relax a little bit so that the stomach can accommodate some more food, as i’m pushing more and more and more interiors you will see it start to expand here, i got to get some of the air bubbles out of the bottle, let’s do some more there, we will see the stomach expanding and stretching, there’s 500 milliliters right here so you see the stomach stretched here kind of cool, can we get more in there i don’t know, but we’re going to try so here’s the next 500 milliliters but let’s just look at this here, we’ve kind of distended the stomach here, this is only about 600 milliliters that we got into the stomach here, now again let’s talk about the limitations of this little experiment here, one is we didn’t get that reflex that would normally happen in the human body for when food initially came in and send that reflex signal back to the brain to kind of relax, the smooth muscle to allow food to come in now again on an average human, that’s about when it relaxes volume about 0.8 to 1.5 liters before you really start to push on the walls and start to stretch the stomach which is the next topic we have to address here. What if you’re one of those people that constantly eats past capacity? let’s say in that figure of 1.5 liters, let’s say you eat 2 liters of food, multiple meals a day for weeks on end, could that change the capacity of your stomach and the answer is yes, we know the stomach is one of the most distensible organs in the digestive tract and if you constantly put pressure on those walls, it’ll distend more and essentially what people refer to as stretch and therefore you can have a greater food capacity, so then what does that do to appetite and appetite suppression or that feeling of being full. Let’s talk about kind of the normal idea here, normally there’s a structure in the brain called the hypothalamus, the hypothalamus regulates appetite and it gets a lot of information from different sources, this area of the stomach or the nerves in the wall of the stomach that sends information about stretch and distension that sends a signal up to the brain that says okay that’s enough, i don’t need to eat anymore but then there’s also hormones that get released when food enters into the stomach and specifically the next part, the small intestine or the structure called the duodenum, there’s some hormones released one in particular called cholecystechnin or cholecystokinin and that hormone gets involved in a lot of different things, one of which is appetite suppression, now some people talk about okay so i’ve heard if you eat really really quickly, it takes a minute for your brain to kind of catch up and tell you you’re full, there’s some truth to that but it’s variable from person to person, one way you can kind of think about, it is a signal that can get sent relatively fast to the brain is in the wall of the stomach, just nerve impulses going right back to the brain but if we’re talking about that release of cholecystokinin which does other things just besides appetite suppression that doesn’t get released until food is entered into the duodenum so you could kind of think maybe that is contributing to the delay of feeling full because if you remember, we talked about food only being able to pass through the pyloric sphincter in about three milliliters so it takes a little bit of time for the food to make it into the duodenum and that might be some of the explanation for the delay in some people feeling full when they’re just scarfing down food as fast as they can.
So putting the finishing touches on this discussion, yes we can stretch our stomach temporarily with a couple of food binges like thanksgiving dinner, big parties with friends, so you know occasionally here and there have at it, the stomach’s going to go back to its regular size with the smooth muscle contractions. Our chronic eating or overeating past capacity will stretch that stomach out, it can also influence this whole idea of like when will i feel full, well if the stomach’s larger and you get that stretch of the wall later in the feeding, meaning it takes more volume to stretch the stomach, you’re going to be able to eat more without feeling that sensation of being full so being able to eat more without feeling full. Is that such a bad thing i guess that depends on what your goals are.