Hello all I'm Glenn Fox
and in this video
I'll discuss the large intestine my objectives for this video are for you to understand the relative location gross anatomy and
neurovascular of the large intestine
The large intestine is going to connect the small intestine specifically the ileum of the small intestine
with the
anal canal
it has
ascending and descending
Parts as well as a
rectum which are
retroperitoneal meaning they are behind the peritoneum and
It's going to sit in
the right and left
lower quadrants of the abdominal pelvic cavity in terms of its functions
The large intestine is vital to the absorption of water of
the gut tube it hosts the microbiome and
It's integral to the elimination of solid and sometimes
Fluid wastes from the gastrointestinal tube in terms of its gross anatomy
the large intestine consists of
the cecum and
It's attached appendix
The a sending colon
The transverse colon
The descending colon the sigmoid colon and
The rectum
Between the a sending and transverse colon
We have what's known as the right colic flexure oftentimes referred to as the hepatic flexure
for its association to the liver and
Then connecting the transverse with the descending colon
We have the left colic flexure. Sometimes referred to as the splenic flexure
Due to its association with spleen now the large intestine
Has a very characteristic look to it. There are these
Haustra or sacculations as you can see here these
segmentations of
the large intestine
these segmentations are formed because the outer layer of
the muscularis
that is the muscular wall of the gut tube and the large intestine is
condensed into three bands and
We refer to these bands as the tineae
coli and
So we have an omental
Tinea coli the omental tinea. Coli oftentimes will give rise to these omental appendages of
Fat these are places where the peritoneum
encircles visceral fat of the colon
There is also a mesocholic
tinea coli that mesocholic
tenia coli is
associated with the mesentery of the large intestine and
Then there's also the free
tanea, coli that
free
tinea coli
Isn't associated with anything and therefore it is free
Anyhow the tinea coli when they contract
They're going to pull the wall of the large intestine into these
sacculations or these
characteristic haustra and in between
We have these
invaginations of the wall of the colon known as the semilunar folds
Supplying the large intestine with blood are
two arteries the superior mesenteric artery and the inferior mesenteric artery or the SMA and
the IMA
The superior mesenteric artery is a more proximal branch
Of the abdominal aorta then is the inferior
mesenteric artery and
that superior mesenteric artery is
Going to send out
colic
Branches to supply the large intestine
So for instance, here's the SMA descending and we can see there is an ileocolic
artery
which descends down and
then there is a right colic artery and
a middle colic artery
Now what's important to note is that these colic arteries don't supply the wall of the large intestine
Directly, but rather they feed into something called the marginal artery and that
Marginal artery is then going to supply through cascades
The wall of the large intestine
directly
But as they say in the infomercials but wait there's more
there's also the
inferior
mesenteric artery the inferior mesenteric artery supplies to left colic
artery, which is heading out towards the
descending colon and this is going to feed into
The marginal artery that marginal artery is the same one up here
which is supplying the transverse ascending colons as well as the cecum and other parts of the
ileum with blood and so this marginal artery
represents an anastomosis
or a communication of blood between the SMA in the IMA
that inferior mesenteric artery also has
Typically several sigmoid branches these sigmoid branches will oftentimes
go into cascades themselves and they can sometimes be associated with the
marginal artery but aren't typically associated with the marginal artery and
then the terminal branch of the inferior enteric artery is
going to be the
superior rectal artery which supplies the rectum with blood
The venous return
from the large intestine is
Going to follow the same pattern of arteries, which supplied it
so for instance, there are colic veins these colic veins are going to feed into either the
Superior mesenteric vein which you can see here or the inferior mesenteric vein
what's interesting to note is that the inferior mesenteric vein typically drains into
the splenic vein and
Thus the hepatic portal vein is
born
from the splenic vein
Meeting up with the superior mesenteric vein. That's the typical pattern of return
the superior rectal vein
is going to find its origin in the rectal venous plexus and
this rectal venous plexus can sometimes
form anastomosis with branches from the inferior rectal vein
Keeping in mind that the superior rectal vein is
Portal meaning it feeds into the hepatic portal system
Whereas the inferior rectal vein is cable meaning that it eventually feeds into the inferior. Vena cava
Now if there's any issue with the liver that's going to hamper the return of blood flow via the portal vein
Then these portal caval and anastomosis can form and we can see
varices or dilations of these veins so these rectal varices
might be indicative of
liver failure
By means of portal hypertension, which is an increase of pressure in the hepatic portal vein
The large intestine is going to be
Innervated very similarly to the remainder of the gut tube
now the sympathetics
that are
Feeding into the enteric nervous system
are going to be from the
Superior mesenteric and aortic plexuses as well as the inferior mesenteric
plexus
These fibers are ultimately sourced from the Greater and Lesser
thoracic splanchnic
nerves
And
There are also lumbar
splanchnic nerves coming from
L1 and
L2 as well as L3 and L4
The story of the parasympathetics is a little more complicated
recall that the gut tube can roughly be divided into four gut midgut and hindgut and
the division between the mid gut and the hind gut is
2/3 of the way along the transverse colon
Some people will roughly put that division at the splenic flexure
So the foregut and mid gut are going to be predominantly supplied by the posterior vagal trunk
So that's the cranial part of the cranial sacral outflow. That is
Parasympathetics the hindgut is going to come from
pelvic splanchnic nerves
pelvic splanchnic nerves take their origin in
the ventral primary ram eye of
sacral nerves 2 3 & 4
These nerves are going to
these
preganglionic parasympathetic fibers
are going to travel through the inferior hypogastric plexus and
Then ascend out of the pelvis into the abdominal cavity where they innervate
The hindgut
Thank you for your time. And if you're in need of any further information, or
Visuals for the large intestine, please. Visit the blue link website