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.
Welcome back to The Anatomy Lab everyone. Thanksgiving is upon us, so in today's video,
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...
[Intro]
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 here.
You can see the stomach down on the tray here - it's often referred to as this
J shaped organ - eh, kind of like a J - and you can see a curve here and a
curve there. The larger of the two curves is referred to as the Greater Curvature
of the stomach - great name - 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. So let me put the probes down here and you can kind of see
how the stomach would be divided into three sections here.
This first section here 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. If you take a look at Geoffrey here,
you could see that 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 over here, you can see again, here's the stomach there.
Now, here are the ribs that I’m tapping, so you can kind of see on that left side here and then
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 do. I mean, how many of them ever come and say
"Mommy, daddy, my tummy hurts". No they're never holding right here, they're always holding right
here, 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 - some of you let them go watch TV because you're more soft - he's a little
bit of a sucker so they go watch TV "to rest", and as soon as you turn your back, they're sitting
there "My parents are so gullible... Little did they know I was touching my small bowel".
What we hope would happen or at least one of my hopes, desires and dreams is that if I ever
have a little kid and they come up to me and they say "Daddy, my jejunum hurts", I’m like
"I’m not sure if you're telling me the truth or not, but I don't care, you can stay home from
school because you know your anatomy and that's the most important topic of all time", agreed?
All deception aside, it's good to know stomach left upper quadrant, small intestine occupies
more of the central abdomen there. Small intestines we'll save for a different video
because we've got to talk about the function of the stomach once food gets down in there.
Yes, 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 this
dissection here, what you can see here is the very bottom of the esophagus. Sometimes people nickname
it "the food tube". As we swallow the food., it 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 use another dissection here, 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 at the end of the video here.
But one of the things that's really awesome is if you look at the inside lining of the stomach here.
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 in our video when we talk
about stretching of the stomach. But I want to pretend we're going to zoom in and zoom in and
zoom in like the magic school bus and see what the tunica mucosa has to offer for us.
So if we were to look at this tunica 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; we're going to talk about
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 we can do a whole other video on. 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 show here.
So, if you imagine right here, 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 digestive quicker. Proteins 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 - just look at my body, 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 "Eh, maybe it's more like two to four liters". Okay, so here's two liters,
just these four bottles. If I get a little adventurous and go up to four liters,
that's what I’m talking about here. That would be a lot of food or stuff going into the stomach.
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 here. So I’m going to go into the -
what's left of the esophagus here. Now, you guys can see that 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 in to here as you can see it start to expand here.
I got to get some of the air bubbles out of the bottle here. Let's do some more.
There we go. See the stomach expanding and stretching here.
There's 500 milliliters right here. So, you can 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 and I’m a little nervous, I’m a little nervous.
Yeah... Stretching... I don't want the stomach to burst. And for those of you that are hoping
that it might burst for an epic YouTube video, I’m not going to do that because I really want
this stomach to stay intact. 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,
send that reflex signal back to the brain to kind of relax the smooth muscle to allow for
food to come in. Now again, on an average human that's about - when it relaxes,
volume of 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 again 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.
One is just again 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 or duodenum, however you like to pronounce it
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 besides appetite
suppression, that doesn't get released until food is entered into the duodenum or the duodenum.
So you could kind of think maybe that is contributing to the delay of feeling full
because if you remember earlier on in the video, 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.
Thanks for watching everyone. Hopefully you learned some new information about the stomach.
Like, subscribe, ring the bell... We now have our online store that people can go to and get
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about future videos, questions, comments - we love them and also have an awesome thanksgiving
and pack that thing full of two liters of food, maybe three - depends on how you feel.