Here we go — okay!
Let's make sure we're good here...
I don't know why I'm making that noise, but that's okay...
Welcome to the lab everyone! Today is the day that I'm gonna measure
real human small intestines with this.
For those of you who've never watched one of our videos —
we are an anatomy lab so we have access to such things.
But why do this? Well I typically teach my students that the human
small intestine is about 20 to 21 feet long, but I've never measured it.
So we're going to measure not just one, we're going to measure three different small intestines,
one of which is outside the body so we'll have fun uncoiling that.
The other two are in the individual body so we're going to have to get a little creative
measuring those.
We want to compare the three and also compare it
to that 20-foot figure that we always mentioned and see how they match up,
and even compare it to these outlandish figures that you may have heard of that sometimes people
will say the human intestinal tract can be up to 15 times longer than the actual body!
So a six foot tall person could have 90 feet of intestine?
I think we'd need a different one of these if that were the case!
So we'll try to debunk that, as well as talk about why we have the length that we have,
and even compare to carnivores, herbivores, and see what their lengths are.
Which do you think is going to be the longest? Carnivores? Omnivores? Herbivores? Let's find out!
So let's start with small intestine number one.
This reminds me of back in the day when I was a wee little anatomy student,
and I went to the digestive system lab and my teacher rummaged through a bag and pulled out
a digestive tract and then plopped it down on the tray and said to us, "fix it".
Now what did my teacher mean by, "fix it"? Well the teacher was trying to illustrate
a really important point after he plopped down the digestive tract here, but there was this idea
that he wanted us to understand that the digestive tract is one long tube from the mouth to the anus.
If you guys have heard of the first part of the tube after you go from the mouth to the throat,
you go to the structure called the esophagus.
You can see the bottom part of this esophagus right here.
Then we just expand and we call it the stomach,
and as the stomach narrows — as you can see right here — then we get to the small intestine.
Now the majority of all this coiling is the small intestine so the name isn't because of its length,
the name is because of the diameter, which is about one inch on average.
This is what we're going to measure today to see if it holds up to the 20 foot — you know,
claim — and you can see me just pulling it out
here and we're going to uncoil this and measure it across the table.
Let's just mention real briefly here the last part of the tube is the large
intestine. You can definitely see a change in diameter from here to here,
and the large intestine kind of sits like this: goes up, across, down, and then squiggles out.
So, we might as well kind of orient it like that.
Put the stomach about where it would be in the left upper quadrant and then all of this
wonderful gut tubey — you know that's a technical term... gut tubey-ness — right in the center.
Real quick before we measure — the small intestine here is primarily absorbing nutrients,
except for the very beginning part of it which is called the duodenum or the duodenum,
and that's about 10 inches on average so we're like — yeah, about from here to here is where
we'd have some digestion taking place, and then the rest of it's all about absorbing nutrients.
That'll come back when we have a little bit of a discussion on the lengths in a second, but
to the measuring table!
I don't think this is going to be 20 feet! Well let's measure it and — where is it...
and yes I touched my shirt...
So let's go ahead and measure this — now that I've found the tape measure that I put on my belt — and
we'll see what it comes out to. Let me use this tray as a little anchor point here, and yes — we
may be a few centimeters millimeters off but we're going for a general idea here. There we go.
Oh! It fell off...
Yeah, here we go.
Okay! Let's make sure we're good here!
I don't know why I'm making that noise, but that's okay...
Okay! Huh... we're good here — pyloris down to the cecum... Wow! So here is the junction of the
large intestine and the small intestine, here. That's where we hit 10 feet...
We're at 10.7 — in between 10.7 and 10.8. Ten feet, seven and a half inches??
Hmmm... I'm slightly disappointed... I have a couple ideas
on why this could be shorter, however we need to measure the other ones first. But before we go to
small intestine number two, I just do want to mention this — 10 feet is actually what they say
the small intestine is in a living person. Because there's tone in the smooth muscle and when that
tone is there — or present — or that smooth muscle is contracting, that shortens the tube. But when a
person passes away, and therefore in a cadaver, all that smooth muscle relaxes and that's where
they get the 20 to 21 feet — at least what we think — and we're going to compare these other two
first before we draw all of our final conclusions. So let's go measure small intestine number two!
So now we're to small intestine number two, and as you can see this is going to be a little bit
of a different measuring process because the intestines are still in the cavity here, but
I've got my snazzy pink twine that we're gonna take along every little inch of this thing,
pin it to the beginning — I did have to change my snazzy pink glove so it wouldn't clash and so
you could see better — but let's pin this at the beginning and take it down the small intestine.
Some of you may be wondering what this yellowy tissue is — this is called mesentery. It helps
hold the intestine to the body wall and also has tons of blood vessels penetrating through
it so we can absorb as many nutrients as possible from this long small intestine.
Okay! We are to the end
of the small intestine where we can see here's the last part of the tube here.
There's the beginning of the large intestine, and we're going to just snip the string here...
and then — whoops! Then we'll measure! So let's gather up this string,
measure the third small intestine, and then compare all three at the same time.
And again — finally to the end, oh look! There's the cute little appendix right there! But we're
not doing that right now, we are to the end and we've got a measure for anatomical awesomeness!
So we are finally all set up and we've got three strings representing
three different small intestines. We've got the original small
intestine — the real one — out on the table still for your viewing pleasure.
We've got the tape measure so we can check out the lengths and see how they compare to each other.
So let's do this!
So let's start with the first string here, and — spoiler alert — the first string
is small intestine number one, and we already knew that small intestine number one was about
10 feet seven and a half inches, and we could see that right there on the tape measure.
That was pretty short, and a little bit surprising actually.
If we go to the second string here, this was actually from the third intestine
that I measured, but I put it right here because it was second in length.
If we continue going down
we can see right about here on the tape measure, it measures about 13 feet two and a half inches.
Still not knocking on that door of 20 feet yet.
If we move down to the third string, this was small intestine number two.
This gets to about 17 feet eight inches.
So there's some variation between these three small intestines,
or small bowels, and we didn't quite get to 20 feet. So what does this all mean?
So first let's talk about some of the limitations here. Yes, this wasn't a
perfect measuring technique. It wasn't to the exact 16th of an inch or the exact millimeter,
but we got a pretty good idea that there's some variation between these intestinal tracts.
Also you have to take into consideration — if the body that you're measuring the
small intestine from has been embalmed versus a body that has not been embalmed.
You see, embalming fluid tends to have a little bit of a stiffening characteristic.
I'm not saying that's going to shrink the intestine by multiple feet, but for example with
the intestine that was about close to 18 feet, you might get closer to that 19 foot range in a body
that was not embalmed, as again, it wouldn't have that stiffening characteristic of the tissues.
So is it inaccurate to say that the small intestine can be over 20 feet long?
No, it's not.
There are plenty of reputable sources out there
that have measured small bowels and have got over 20 feet with their measurements.
It just so happens that in this lab,
we have all embalmed bodies, and the longest one only got to close to 18 feet — and that's okay.
What I think is probably more important that we say is there's a range,
as you can see from these differences that we found in our small intestines here.
An accurate range might be saying 4 to 7 meters or essentially 12 to 20 - 23 feet.
What I think is fascinating about all this, is the variation in length from person to person.
We're even going to compare to other animals in a second,
but when we talk about this length the small intestine is all about absorption.
That's why it's so long. We haven't even talked about the inside of the tube,
but this whole thing here that we've strung out over the table is all about length.
It's still longer than any other structure in the digestive tract, regardless if yours is 13
feet or 19 or 21 feet. It's all about absorbing as much of those nutrients as you possibly could.
Back to this whole idea of variation — have you ever felt like you've had different digestive
issues or different abilities to digest food compared to like a friend or a family member?
You see, I always tell students, "we're the same, but we're not."
Meaning we all have a biceps. We all have a small intestine,
but how that absorbs the nutrients it tends to absorb... what you're better
or more suited at eating, or absorbing and digesting, varies from person to person.
This is one of those variables that plays into that.
So let's illustrate this a little bit further with some of the
different ends of the spectrum here when it comes to digestion, meaning one end of
the spectrum would be say like, a cow — a full-fledged herbivore just eats plants.
Whereas the other end of the spectrum would be, say like a cat — a full-fledged carnivore.
When you compare the length of their intestinal tract, you see huge variations. You see,
the carnivores like cats have the smallest or shortest in length of the small intestine,
whereas the cows have the longest length.
I just went over a research study where they measured the small bowel of calves — like,
kind of sad, baby calves — they ranged from 55 to 80 feet in length.
So why is that? Why so long? Well plant material is actually harder to digest
or at least takes more time, and needs more transit time through a longer bowel
to digest things like cellulose and plant material that's harder to break down.
So cows for example are more suited for that.
Whereas if you're a little cat pouncing and eating critters — meat essentially,
the bowel is actually a little bit more simple and it's not as hard to digest the meat, per se,
and you can do that with a shorter small intestine.
There are some other cool things that play into that like carnivores tend
to have a pretty acidic stomach, but we'll get into that in another video.
So where does that leave the omnivore? That puts the omnivore right in the
middle of the two extremes of the plants and meat eaters, essentially.
That's where we fall into this omnivore diet,
where our digestive tract falls somewhere in between, as well as the other omnivores.
Where we can break down some meats and break down some plants and digest and absorb those materials.
That probably contributes to some of the
success that humans have through this evolutionary process.
Again that's super fascinating to think about, that even among humans some of us
are probably better at digesting meats, where others are probably better at digesting plant
products and kind of this variation of in between, based on gut length.
Again like I mentioned, you guys, that's just one variable of digestion and absorption.
We did not get to talk about this stuff right in here yet...
Cliffhanger!! Yes — I'm sorry we'll be going over what's inside the small
intestine in a future video, but hopefully you guys learned some awesome stuff about the length
of the small intestine and how that influences digestion among humans, and even other animals.
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Until the next video, think about all those wonderful Oreo cookies or whatever you love to
eat, just pushing through that four to seven meters of your small intestine — goodbye!