Description

Large Intestine Overview

• Latin Name: Intestinum Crassum
• Extends from: End of Ileum to Anus
• Length: 1-1.65 meters
• Function:
  • Absorption of water and electrolytes

Parts of the Large Intestine:

• Caecum
• Appendix
• Ascending Colon
• Transverse Colon
• Descending Colon
• Sigmoid Colon
• Rectum

Caecum

• Topography: Right Inguinal Region
• Size: 6-8 cm long, 7-7.5 cm wide
• Ileal Orifice: Ostium Ileale
• Ileocecal Valve: Regulates flow between small and large intestine

Appendix Vermiformis

• Size: 2-4 cm long, 0.5-1 cm wide
• Orifice: Ostium Appendicis Vermiformis
• Positions of the Appendix:
  • Caudal Position (40-50%)
  • Medial Position (17-20%)
  • Lateral Position (17-20%)
  • Posterior Position (9-13%)
  • Anterior Position (rare)

Appendicitis

• Inflammation of the appendix
• May cause peritonitis
• McBurney’s Point: Common site of pain
• T10 Dermatome: Early stage pain felt at the umbilical region

Ascending Colon (Colon Ascendens)

• Length: 12-20 cm
• Topography: Right Lateral Region, Right Hypochondriac Region
• Syntopy:
  • Anteriorly: Anterior Abdominal Wall
  • Laterally: Lateral Abdominal Wall
  • Posteriorly: Right Kidney, Quadratus Lumborum, Transverse Abdominal Muscle

Transverse Colon (Colon Transversum)

• Length: 30-80 cm
• Topography:
  • Right Colic Flexure (Flexura Coli Dextra) – Right Hypochondriac Region
  • Umbilical Region
  • Left Colic Flexure (Flexura Coli Sinistra) – Left Hypochondriac Region
• Skeletopy: L2 – L1 (Left colic flexure is higher, held by the phrenocolic ligament)
• Syntopy: Transverse Mesocolon, Greater Omentum

Descending Colon (Colon Descendens)

• Length: 15-20 cm
• Topography: Left Lateral Region, Left Iliac Fossa
• Syntopy: Small Intestine, Left Kidney, Quadratus Lumborum, Abdominal Wall
• Ascending and Descending Colon: Mesoperitoneal Viscera (Partly covered by peritoneum)

Sigmoid Colon (Colon Sigmoideum)

• Length: 15-80 cm
• Extends from: Left Iliac Fossa to the Sacroiliac Joint
• Continues into: Rectum
• Held in place by: Root of the Mesentery (Radix Mesenterii)

Rectum

• Length: 15-20 cm
• Location: Anterior to Sacrum
• Key Structures:
  • Sacral Flexure (Flexura Sacralis)
  • Perineal Flexure (Flexura Perinealis)
  • Rectal Ampulla (Ampulla Recti)
  • Anal Canal (Canalis Analis)
  • Anus

Layers of the Large Intestinal Wall

Tunica Mucosa

• Simple Columnar Epithelium
• Goblet Cells
• Intestinal Crypts
• Lamina Propria
• Lamina Muscularis Mucosa
• Semilunar Folds of the Colon (Plicae Semilunares Coli)
• Solitary and Aggregated Lymph Nodules
• Transverse Folds in Rectum:
  • Superior Transverse Fold (Plica Transversalis Recti Superior)
  • Middle Transverse Fold (Plica Transversalis Recti Media)
  • Inferior Transverse Fold (Plica Transversalis Recti Inferior)
• Anal Structures:
  • Anal Columns (Columnae Anales)
  • Anal Sinuses (Sinus Anales)

Tela Submucosa

• Loose Connective Tissue and Blood Vessels
• Rectal Venous Plexuses (Hemorrhoidal Plexus) – Hemorrhoidal Zone

Tunica Muscularis

• Circular Muscle Fibers:
  • Internal Anal Sphincter
  • External Anal Sphincter
• Longitudinal Muscle Fibers:
  • Tenia Coli:
    • Tenia Libera (Free Tenia)
    • Tenia Omentalis (Omental Tenia)
    • Tenia Mesocolica (Mesocolic Tenia)
  • Haustra of Colon (Haustrae Coli)
  • Transverse Grooves (Sulci Transversi)

Tunica Serosa

• Intraperitoneal Viscera
• Mesoperitoneal Viscera

Sources:

• Memorix Anatomy 2nd Edition
• Biorender
• University Notes and Lectures

Transcript

Introduction
0:03
What’s up. Meditay here, and in this video, we’re gonna go through the anatomy of the
0:07
Large Intestine. So in the last video, we went through the anatomy of the Small Intestine.
0:12
Now the step after the Small Intestine is the Large Intestine, as you see here. So in
0:18
this video, we’re first going to go through the different parts of the large intestine,
0:22
as well as the topography, basically where the different parts are located in relation
0:27
to the surrounding structures. Then we’ll go through the layers of the large intestinal wall.
Small Intestine Overview
0:32
So here, I’ve highlighted the large intestine or Intestinum Crassum in Latin.
0:37
Crassum means dense or thick. It starts at the end of the Ileum
0:42
and ends at the anus, so the whole colored part is the large intestine.
0:47
And so, if you’d stretch out the large intestine, you’d see that it would approximately be between
0:53
1-1,5 meters long. It’s not as long as the small intestine, and its functions differ
0:59
The primary function the large intestine has is the absorption of water and electrolytes,
1:05
and if, for instance, the bolus, or the content, passes through the large intestine too fast,
1:11
or the absorption of water in the large intestine is altered,
1:14
you’d get really watery feces that’ll be the case of diarrhea.
1:18
So now, the first parts of the large intestine are the
1:21
Cecum and the appendix closest to the Ilium of the small intestine. And then we have something called
1:27
The colon and the colon are divided into parts. We have the ascending colon, which goes up
1:33
There’s the transverse colon, going horizontally to the left,
1:36
Then there’s the descending colon. It goes down, then the
1:40
Sigmoid colon, which curves a little. And Lastly, we have
1:43
The rectum. So, now let’s look at each of these parts in detail, starting down here, at the
Caecum
1:49
Caecum and the appendix So, as always, I like to start with the topography
1:54
to have the orientation right. Let’s do the Holotopy first, which means the location of the
1:59
organ in relation to the body as a whole. So the caecum and the appendix lie in the right inguinal
2:06
region, as you see here, so any localized pain in that area, think of the appendix or the caecum.
2:13
Now let’s start with the anatomy of the caecum first. The caecum is about 6-8cm long
2:18
and about 7-7,5 cm wide, and so the caecum is the connection point between the small
2:26
and large intestine, right? So, if we change the angle a little bit, you’ll see a hole right here.
2:32
This hole Is called the Ileal Orifice, connecting the Ileum with the caecum so
2:37
that the small intestine can release its content into the large intestine to be processed further
2:42
and then secreted out. But here’s a cool thing with this hole is that it’s controlled by this
2:47
Valve the ileocecal valve, which is a sphincter muscle valve that separates the small and large
2:54
intestine. And its critical function is to stop the content inside the large intestine from going
3:00
back into the small intestine again. You don’t want the content here that goes into the large
3:04
intestine to go back into the small intestine again. You want it to go outside the right way.
3:09
So that’s the caecum. Now going over to the
Appendix
3:11
appendix. Or appendix vermiformis. Vermiformis means worm since the appendix has a worm shape.
3:18
That’s where the vermiformis in the appendix vermiformis comes from.
3:21
The appendix is about 2-4 cm long and about 0,5-1cm wide, so it’s very tiny.
3:29
The appendix connects to the caecum through an opening at the top here called the orifice of
3:35
the vermiform appendix. Now the appendix may be found in different positions,
3:40
and this is very important to keep in mind as you’re studying the appendix clinically, so
3:44
The normal one is The caudal position; as you see in this picture,
3:48
you’ll find it in the caudal position about 40-50% of the time. And in some other people
3:54
In 17-20%, you’ll find it in the medial position going into the promontory of the sacrum
4:00
And 17-20% again, you’ll find it in the lateral position towards the inguinal ligaments.
4:06
And then in some other people In 9-13%, you’ll find it going
4:10
posteriorly behind the caecum, and then really rarely you’ll find it going
4:15
Anteriorly in front of the caecum. Sometimes, and it happens pretty
4:19
often in patients. Unfortunately, Inflammation of the appendix may happen,
4:24
and that is called appendicitis. It’s a very common cause of acute severe abdominal pain.
4:29
If the appendix is not removed or treated, it can become necrotic and rupture, resulting in
4:35
peritonitis (Inflammation of the peritoneum). I’ll talk more about the peritoneum in a separate
4:40
video, but if it ruptures, all the bacteria from the appendix will get into the peritoneal space,
4:47
which is all the blue area here in this picture. And In a pretty severe case of appendicitis,
4:52
the abdomen is usually tender at McBurney’s point, which is on the right lower side, as you see here,
4:58
but what’s interesting here. Many miss this throughout their clinical practice.
5:02
An early appendicitis Is usually felt centrally within the abdomen. And that is because the
5:08
sensory fibers from the appendix go through the sympathetic nerve fibers and enter the spinal cord
5:14
at T10, which corresponds to the umbilical dermatome, as you see here.
5:18
So pointing where it hurts is a hard thing unless the infection is severe. In that case, we gotta
5:25
have to diagnose it further. That was a little taste into clinics as you’re studying anatomy.
5:29
So that was all for the anatomy of the caecum and the appendix.
Ascending Colon
5:33
Now let’s do the ascending colon. The ascending colon is called Colon Ascendents in Latin because
5:38
it ascends as you see here. It stretches between 12-20 cm long and reaches up to the inferior
5:46
surface of the liver. And if we Look at the topography of the
5:49
ascending colon. We’ll start with the Holotopy again. Holotopy is the location of
5:54
the ascending colon in relation to the body. You’ll see that a significant part of the
6:00
ascending colon lies in the right lateral region, but at the region where it bends, also called the
6:06
right colic flexure, that one will be in the right hypochondriac region. Now, if we turn this picture
6:12
to the side, just like this. We can look at the syntopia, meaning its position to other organs.
6:18
So, anteriorly you’ll find the anterior abdominal wall,
6:21
Laterally, the lateral abdominal wall but posteriorly, You’ll find the quadratus
6:26
lumborum muscle as well as the right kidney behind it, but there’s actually one more
6:31
muscle you’ll find behind the ascending colon, and that’s if we add the transverse
6:35
Abdominal muscle, you’ll find this muscle originating from the backside of your body,
6:40
so you’ll find this muscle as well when you look at the different structures
6:43
behind the ascending colon. So that is the Ascending colon. Next, we have the transverse
Transverse Colon
6:49
colon. And if we go back to this picture again, The transverse colon is here, and the length
6:54
of it varies a lot. It can reach about 30-80 cm long, which means that the transverse
7:01
colon is the largest part of the large intestine. Now let’s get into the topography of it. Adding
7:07
the lines, you’ll see that the transverse colon starts from the right hypochondriac region with
7:11
the Right Colic Flexure. Remember we talked about this one. And then the transverse colon
7:16
curves a little downwards to end up in the umbilical region, to then go upwards again
7:22
and end up at the left hypochondriac region where there’s another curvature
7:26
Called the Left Colic Flexure. And what’s interesting with these two flexures
7:30
is that you’ll find the left flexure A little bit higher than the right flexure,
7:34
if we look at its position in relation to the vertebrae, you’ll see the right flexure lies
7:40
at the region of the 2nd lumbar vertebra,
7:42
while the left flexure you’ll find it at the level of the 1st lumbar vertebrae, so the left one is
7:47
slightly higher. The reason why the left flexure is higher has to do with the fact that there’s a
7:53
ligament holding the left flexure of the colon and pulling it higher than the right flexure.
7:58
So let’s visualize that by adding a perfectly drawn diaphragm, you’ll find the Left Colic
8:04
Flexure connected with the diaphragm through this ligament right here, the Phrenocolic Ligament.
8:09
And if you remember the word phrenic, phrenic is everything that has something to do with
8:12
the diaphragm. That’s why it gets the name phrenocolic ligament. It holds the left flexure up
8:19
and connects it with the diaphragm. Now the Transverse Colon is fixated in place,
8:23
very similar to the small intestines, and it’s important to mention it here because
8:28
it differs from the rest of the large intestines. So let’s make that vertical cut and look at
8:32
a sagittal view of the abdominal cavity; you’ll see this, right?
8:37
So the transverse colon is right here, and just for orientation sake,
8:40
you’ll find the stomach and the liver up here and the small intestine down here.
8:45
Now the transverse colon is fixated, it’s attached to the posterior abdominal wall
8:50
through the transverse Mesocolon. I’m not gonna go into too much detail about the peritoneum yet,
8:55
since that’s for another video. But the peritoneum is a fatty layer that protects and fixates the
9:01
organs in place within the abdominal cavity. And there’s something called the Greater Omentum,
9:07
which goes down from the stomach, curves, and then completely wraps around the transverse colon, to
9:13
then form the transverse Mesocolon, which anchors the transverse colon to the posterior abdominal
9:18
wall. And don’t confuse it with the root of the mesentery, which anchors the small intestine
9:23
to the posterior abdominal wall. Don’t worry too much if this went too fast for you. You’ll
9:28
see this again as you study the peritoneum. Now, If we look at the transverse colon anteriorly
9:33
again, And look at the syntopy of the transverse colon, meaning its position to other organs.
9:38
You’ll see that superiorly you’ll find the liver, the stomach, and the spleen.
9:43
And then, inferiorly, you’ll find the rest of the small intestine.
9:47
Posteriorly you’ll find the pancreas, as well as the descending part of the duodenum
Descending Colon
9:52
So that is the general structures of the transverse colon and the topography as well.
9:56
Now let’s do the descending colon. So let’s go back to this picture again.
10:01
The descending colon is right here, and it’s about 15-20 cm long.
10:06
You’ll find it in the left lateral region lying in the Left Iliac Fossa. The lower part of the
10:11
descending colon lies in the Left Iliac Fossa. And it connects with the sigmoid colon. And so
10:16
let’s look at the descending colon at a different angle so we can look at its
10:20
relation to other organs. Anteriorly and laterally,
10:24
we have the abdominal wall And then medially, you’ll find the small intestine
10:29
And posteriorly, you’ll have the same structures as the ascending colon. You’ll find the kidney,
10:34
the left one this time, and the quadratus lumborum.
10:37
Another thing you need to know about the ascending and the descending colon is that a huge part of
10:42
the large intestine is entirely surrounded by the peritoneum except the descending and the ascending
10:49
colon. And I’ll try to visualize that for you So, if we make a transverse cut and look at
10:54
it from this view, you’ll see this picture right here. We call the ascending and the
10:59
descending colon the mesoperitoneal viscera, and they’re mesoperitoneal because they’re
11:05
partly covered by the peritoneum as you see here. It’s only covered by the peritoneum from 3 sides.
11:12
In contrast to things like the transverse colon and the rest of the small intestine,
11:16
which are entirely surrounded by the peritoneum, they’re what we call intraperitoneal viscera.
11:22
I’ll talk about these in-depth when I talk about the peritoneum, but now, keep that in
11:27
mind that the ascending and descending colon are only partly covered by the peritoneum. So
11:32
That is the descending colon. Now going over to the sigmoid colon
Sigmoid Colon
11:36
So let’s change the picture again. The sigmoid colon is
11:39
Right here. It can be anywhere between 15-80cm, so it varies as you see, might be long or short.
11:47
In some people, the sigmoid colon can even get to 1 meter,
11:51
so keep that in mind it can be short or long. So, a huge part of the sigmoid colon lies in the
11:58
Left iliac fossa. It goes downwards, and then at the level of the sacroiliac Joint,
12:04
it bends backward and then continues to then become the rectum. Now let’s make a
12:08
vertical section again and look at a sagittal section of the abdominal cavity. Remember,
12:13
we already went through all f these structures, but the Sigmoid colon, which is down here.
12:18
You’ll find it also being fixated to the posterior abdominal wall through the root of the mesentery.
12:25
So that is the sigmoid colon Next, we have the rectum. And so let’s
Rectum
12:29
start by looking at it anteriorly. Right here. It’s about
12:32
15-20cm long and has kind of an S shape. It has some curvatures.
12:39
So superiorly it’s connected With the sigmoid colon and looking at
12:43
it from a slightly different perspective, this is a posterior lateral perspective.
12:47
You’ll see that up here it lies Right Infront of the sacrum.
12:51
And so, Let’s now make a vertical cut of only the rectum to focus on its curvatures
12:56
So the first curvature is the Sacral Flexure because it lies in front of the sacrum.
13:01
But then we have another flexure called The Perineal Flexure. The perineum is the
13:06
region between the external genitalia and the anus. So this is called the Perineal flexure
13:13
because it lies in this space in the perineal space. And so in the upper part of the rectum
13:19
in front of the sacral bone, we call this place The Rectal Ampulla and the Rectal Ampulla is about
13:25
10-14 cm long and 7-7,5 cm wide, and what’s interesting with
13:31
the Rectal Ampulla is that if this space would be Full. You’ll have the feeling that
13:35
you’d wanna go to the toilet. And then, the lower part of the rectum is called the anal canal.
13:40
The anal canal is about 2,5-3 cm long and 2,5 cm wide, and it’s also the last step in the
13:47
The digestive system before the content goes out through the anus.
13:51
So that was the general structure of the large intestine.
Layers of Large Intestinal Wall
13:54
The next thing we gonna talk about is the Layers of the Large Intestinal Wall. So, now,
14:00
if we take a small section of the large intestine and look at a histological picture, you’ll notice
14:05
the same general layers just like the rest of the gastrointestinal tract. There’s the
14:09
Tunica mucosa And then beneath that, we have tela submucosa
14:13
Then the tunica muscularis and then the outer layer is the
14:16
Tunica serosa. So it doesn’t really differ from the rest of the tubes in the digestive system,
14:22
But it has some characteristics that are special for the large intestine,
14:25
and we’re gonna highlight these differences as we go through the layers. So let’s focus on the
14:30
Tunica mucosa first the Inner layer. The mucosa of
14:33
the colon is lined by a simple columnar epithelium with a thin brush border. And if we take a small
14:40
section of the mucosa and zoom in. You’ll see that we have a large number of goblet cells
14:46
secreting mucus for lubrication. Note that there are no plicae or villi, which remember were on the
14:53
small intestine. Instead, there are those straight intestinal crypts called crypts of Lieberkuhn,
15:00
which are just tubular glands secreting mucus. And between the crypts, there is Lamina Propria,
15:06
with Many cell types, including plasma cells, lymphocytes, and macrophages can
15:11
be seen here in the lamina propria. Then there are Lamina Muscularis at the bottom. Typical
15:16
Mucosa structures. Now there are no plicae in the large intestine, but instead, there are
15:22
other folds called the Semilunar Folds. They’re well developed in the colon, but there is some
15:28
slight lack of them in the caecum, and they’re entirely absent in the appendix and the rectum.
15:33
Now the Tunica Mucosa of the Large Intestine has those solitary lymph
15:38
nodules within the lamina propria, just like the small intestine. But in the appendix,
15:43
You’ll find these lymph nodes being aggregated together, forming what
15:47
is called the Aggregated Lymph Nodules. And Therefore, because they’re aggregated together,
15:52
we sometimes call the appendix vermiformis for the Abdominal Tonsille. And so, another
15:57
structure that the mucus membrane forms are, You know, at the rectum, remember the Rectal
16:02
Ampulla is here. The mucus membrane below the Rectal ampulla forms these
16:08
Transverse fold called the Transverse Folds of Rectum. So we have the Superior Transverse Fold,
16:14
the Middle transverse fold, and an inferior transverse fold
16:18
And down here, the mucus membrane forms these columns called Anal Columns at the anal canal,
16:24
and between them, the mucus membrane forms Anal Sinuses between each column. So that is the tunica
16:31
Mucosa. And next, we have the Tela submucosa. So, if we take a small section
16:36
of the tela submucosa, we’ll see that it contains blood vessels. Here on the right, you see a Vein,
16:42
and to the left, here is an artery since arteries are thicker than veins. Arteries are thicker due
16:47
to their layers. You’ll find nerves here in the tela submucosa and a lot of connective tissue.
16:52
and it’s basically the same along the large intestine except at the anal canal
16:57
So remember, the anal canal is here, right? And on either side of it, we have something called
17:03
The rectal venous plexus or sometimes called the hemorrhoidal plexus consists
17:08
of a high concentration of veins. These veins form an elevation on either side of the anal canal
17:16
called the hemorrhoidal zone, which is normal. If the hemorrhoid Plexi become enlarged,
17:21
they can get pushed out, as you see here. They can either protrude externally or internally
17:27
and cause symptoms like sudden perianal pain and perianal mass if they’re external hemorrhoids.
17:33
There are various risk factors for developing this, from increased intraabdominal pressure
17:38
or pregnancy or obesity to even heavy weightlifting. They often resolve by themselves,
17:43
though, and only cause symptoms for a few hours to days to some weeks, depending on the severity.
17:52
Next, we have the tunica muscularis right Here consisting of
17:55
Two parts, the inner layer being the circular muscle fibers and the outer layer
18:01
being the longitudinal muscle fibers. But the longitudinal muscle layer does not continue
18:06
over the whole surface of the large intestine. *new slide* There are some bands located on the
18:11
surface of the large intestine that is formed by the longitudinal muscle fibers being bundled
18:16
together. And they’re called Tenia Coli. We have 3 of them with different names. We have the Tenia
18:22
Libera, Tenia Omentalis, and Tenia Mesocolica. The Tenia Libera is highlighted here in Red.
18:29
It’s placed anteriorly in the caecum, ascending, descending, and sigmoid colon
18:34
but is placed inferiorly in the transverse colon. Libera means Free or not restrained. Meaning this
18:42
Tenia is not bound to any structure on the peritoneum like the other two are. I’ll show
18:47
you this on my other video about the peritoneum so that this video doesn’t get too long. But The
18:52
Next Is tenia omentalis here in green. The tenia omentalis is bound
18:57
to the greater omentum on the transverse colon and is therefore named after that.
19:03
On the other side, on the backside. You’ll find the tenia mesocolica in blue. It’s called
19:08
the mesocolic Tenia because that’s where the Transverse Mesocolon is attached to,
19:13
binding the transverse colon on the posterior side to the posterior abdominal wall.
19:18
Now, these muscular bands, the Tenia, are shorter than the intestine itself because of that. They
19:25
pull the large intestine closer, forming these sacculations you see on the surface called Haustra
19:31
Coli which are these bumps you see grossly, And between each bump, you’ll find some grooves called
19:38
the lateral grooves, which correspond to the Semilunar Folds, remember those from earlier?
19:44
So, one groove here is gonna be one Semilunar Fold. So that was the longitudinal layer.
19:51
Now the Circular layer will form so-called sphincters, and the sphincters it forms serve
19:56
one of the most important functions in the body. And this sphincter lies
20:01
At the anal canal. It forms the internal anal sphincter, which is involuntary,
20:06
and it also forms the External anal sphincter,
20:09
which is voluntary. So that is mainly the muscle layer. Now
20:13
Lastly, we have the tunica serosa found Right here. Now, remember I said that the
20:18
peritoneum grabs the intestine and surrounds them and fixates them to form this serious
20:23
slippery surface called tunica serosa? Here you see a picture again that kinda
20:28
Visualizes that. This is a transverse cut of the abdominal cavity
20:32
The intraperitoneal viscera are the ones that are completely surrounded by the peritoneum.
20:39
So completely surrounded by this tunica serosa. And these include the caecum,
20:44
the appendix, the transverse colon, the sigmoid colon, and the rectum. And then you have
20:48
The mesoperitoneal viscera which is only partly covered by the peritoneum,
20:53
as you see here only by three sides. So, these have the tunica serosa on only three sides.
21:00
And on the last side, that are not covered. It is covered by Tunica Adventitia or tunica fibrosa,
21:06
which is a fibrous layer. Now the Mesoperitoneal Viscera include the ascending and the descending
21:12
colon and also the middle part of the rectum. So that was everything I had for the large intestine.
21:18
I really hope this video helped you understand the complete anatomy of the Large Intestine.
21:22
The next videos are going to be about the rest of the accessory structures, which are the
21:26
Liver The gall bladder
21:27
And the Pancreas. If you found this video helpful.
21:30
Please put a like, share, comment. Whatever you find convenient to you. See you next time