Download THE PERITONEUM : MUSTAFA SAMHOURI 16/9/2015 MOHD ALLOH

#7
THE PERITONEUM
: MUSTAFA SAMHOURI
16/9/2015
MOHD ALLOH
1
In the last lecture we began talking about the abdominal cavity
starting with the first structure: the peritoneum.
The peritoneum:
Peritoneum (peri=around,
tonum=stretching) is a stretched sac
(containing fluid) that surrounds the
abdominal organs to reduce friction
among organs such as the stomach,
intestine, liver, colon and their
surroundings.
Note: The liver is a solid organ
(meaning that it doesn’t move), but
it’s very close to other movable
organs like the intestine, so it’s
covered by the peritoneum.
So the peritoneum is made up of two layers: the layer that covers
the internal surface of the abdominal wall is called the parietal
layer and the part of the sac which will cover the organs
themselves is called visceral layer. Between the 2 layers we will
have a cavity filled with fluid called the Peritoneal Cavity.
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The peritoneal cavity extends between the organs and is divided
into two parts: the main part of the cavity found among most of the
abdominal organs is called the Greater Sac (the brown space in
the sagittal section figure and the white space in the cross section)
and the small tiny space behind the stomach is called the Lesser
Sac (the blue space in the sagittal section and the light blue in the
cross section). The lesser sac is connected with the greater sac
through a small opening located between the liver and the stomach
called Epiploic
(Omental) Foramen aka
Foramen of Winslow
and it is considered a
passage between the
greater and lesser sacs.
Note: The peritoneum is
not like the pericardium
or pleura as they are
simple sacs surround one organ but the peritoneum covers more
than one organ.
Each organ that is covered entirely by two visceral layers (like the
stomach and liver, you can see how they are covered) is called an
intraperitoneal organ, while Retroperitoneal organs (behind
peritoneum) are covered from* one surface (like the kidneys, they
are covered only from their anterior surface).
So you have to distinguish between the peritoneal cavity and the
abdominal cavity. The peritoneal cavity is the cavity that’s covered
by the peritoneum which is filled with only fluid, but the
abdominal cavity is the cavity that is covered by the abdominal
wall and it contains the peritoneum and the abdominal organs.
3
Each area of peritoneum covering a specific organ has a
specific name:
Visceral layers covering the stomach = Omenta (plural);
Omentum (single).
There should be two omenta: one going from the lesser curvature
of the stomach towards the liver and the other going down from the
greater curvature of the stomach
towards the intestine.
So the stomach will be covered
by the visceral peritoneum that
will continue anteriorly to
become the parietal layer of the
anterior wall; while the other will
reflect posteriorly to the lesser
sac and continue with the parietal
layer of the posterior wall.
The two layers covering the stomach will cover other organs.
Those going down from the greater curvature of the stomach are
known as the Greater Omentum. However the one going up from
the lesser curvature toward the liver will be known as the Lesser
Omentum.
Visceral layers covering the small intestine = Mesentery.
Visceral layers covering the large intestine = Mesocolon.
Visceral layers Covering Solid Organs = Ligaments.
They are all continuations of one another.
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Remember that the peritoneum is one continuous sac covering
multiple organs and on each organ the layer has its own unique
name making it easier to study.
Note: all these structures that we talk about (omentum, mesentery
and mesocolon) are double layers of visceral layers, posterior and
anterior or superior and inferior depending on the location and
orientation of the organ.
Omentum:
The stomach is inverted making a G-shape like organ which is
made up of a greater curvature below and a lesser curvature above.
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The omentum that descends down from the greater curvature is
called the greater omentum and as it descends down it will cover
the small intestine then it will reflect sharply and ascend to the
transverse colon. There it will split and cover the transverse colon
anteriorly and posteriorly and this layer is called the transverse
mesocolon.
In addition to the transverse
mesocolon, another part
coming from the fundus will
head toward the diaphragm
(covering the stomach as
well) and it’s called the
Gastrophrenic Ligament.
The Gastrophrenic Ligament
will continue and reflect over
the diaphragm and become
the parietal peritoneum. We
classified it as a ligament because it goes to a solid organ and also
as a part of the greater omentum due the fact that it is a visceral
peritoneum descending from the greater curvature of the stomach.
So the flow of the visceral peritoneum from the greater curvature is
as follows:
1- Greater Curvature towards the Diaphragm which is called the
Gastrophrenic Ligament.
2- Then a part will cover the spleen which is called the
Gastrosplenic Ligament.
3- Then the inferior continuation towards the small Intestine which
will be called the Gastrocololic Ligament (the only one made
up of four layers)
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The lesser omentum mainly covers
the liver, however what’s unique
about the lesser omentum is that
not only it comes from the stomach
but also from the first 2cm of the
duodenum. So the first 2 cm of the
duodenum is intraperitoneal.
The first 2 cm of duodenum is intraperitoneal, but why?
The answer is during embryological development the duodenum is
actually intraperitoneal but because of the rotation of the stomach
90 degrees to the right, so the duodenum will slide between its
visceral layers and go to the right side. So as it slides from anterior
to posterior and loses its covering, it will become retroperitoneal
except the first 2 cm.
Note 1: the duodenum is called a secondary retroperitoneal organ
because, when it develops, it is initially covered by visceral
peritoneum and then it will leave it and become retroperitoneal.
Note 2: primary retroperitoneal organs (like the kidneys) develop
and stay behind the peritoneum..
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The free margin of the lesser omentum coming from the first 2
cm of the duodenum to the liver is called hepatodoudenal
ligament. So if we look at the lesser omentum, as it’s coming from
the stomach to the liver it’s called the lesser omentum. However if
it’s coming from the liver to the stomach it’s called a ligament. So
the lesser omentum is the part of the visceral peritoneum between
the stomach and liver.
The foramen of Winslow or the Epiploic Foramen (Omental
Foramen) is an important foramen that connects between the
lesser and greater sacs. The hepatoduodenal ligament will form an
anterior border of this opening.
The four borders of the Foramen of Winslow are :
Anterior
The portal triad which is at the free margin of the
lesser omentum, we call it the Hepatoduodenal
ligament.
posterior
Inferior vena cava. “refer to the cross section in
page #2”
superior
Liver (caudate lobe).
inferior
Duodenum.
What’s the meaning of the Internal Omental Herniation..!
Sometimes part of the intestine can be
looped from the greater sac and it enters
through the foramen of Winslow into the
lesser sac behind the stomach. In this case
it will be called an internal omental hernia.
( internal : inside the abdominal cavity)
( omental : passing through omental
foramen into the omental bursa “lesser
sac”)
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Treatment of Internal Omental Herniations:
Now we have to treat these conditions, but none of the boundaries
of the foramen of Winslow can be cut, so what’s the solution?
We can treat it by aspirating the gut content by inserting an
endoscope or a needle into this loop of intestine and aspirating the
content, so it will collapse and easily be pulled out. However,
sometimes the intestine will not come back even if it’s collapsed, it
will be stuck there, so in this case you have to interfere surgically.
You perform a surgical opening through the abdominal wall then
you enter through the descending part of the greater omentum
(gastrocolic part) by cutting through it, then you push the
herniated loop out of the lesser sac by inserting the index finger
through the anterior 2 layers of gastrocolic ligament of the greater
omentum.
# Mesentry:
it’s a double layer of visceral peritoneum covering the small
intestine (it connects the small intestine to
the posterior abdominal wall)
# Mesocolon:
it’s a double layer of visceral peritoneum
covering the large intestine (connects the
large intestine to the posterior abdominal
wall)
Note: The ascending and descending
colon are retroperitoneal structures.
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There are three regions of “Mesocolon” covering three parts of the
large intestine.
1) Transverse mesocolon covers the transverse colon.
2) Sigmoid mesocolon covers sigmoid colon.
3) Mesoappendix covers appendix.
THE PERITONEUM
https://www.youtube.com/watch?v=4WgEzsH1lQ0
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The doctor drew a midsagittal section for the abdominal cavity in
the lecture and discussed the peritoneum and the surrounding
structures. Up above you can find a link to an 8 minute video for
this specific section from the doctor’s lecture.
Drawn here is a midsagittal section with a lateral view of the
abdominal cavity, you can see part of the stomach, above and
anterior to the stomach you can see part of the liver, below the
stomach is the transverse colon, behind the stomach you can see
part of the pancreas and you can see some loops of the small
intestine.
Now where is the spleen? The spleen is located on the left side of
the abdominal cavity and here we’re looking at the structures in the
midline so we can’t see the spleen.
As we know the abdominal cavity is composed of peritoneum
surrounding many organs, so how would the peritoneum come and
cover around all these organs? First the doctor put the lesser
omentum (hepatogastric ligament “part of the lesser
omentum”) which is two layers of visceral peritoneum located
between the stomach and the liver, this
two layers will go and cover around the
liver, once visceral peritoneum reflects on
the diaphragm “the roof of the abdominal
cavity” it becomes parietal peritoneum, so
there’s a small area in the superior surface
of the liver which is devoid of peritoneum
this is called the Bare (naked) area of
the liver and if you look at this area you
will find it rough because it’s not covered by the glistening
membrane.
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Now what would the lesser omentum do when it reaches the
stomach? It has to cover as a visceral layer all the way around the
stomach and it will leave the stomach from the greater curvature
descending all the way down to
cover the whole abdominal
intestines and forming an
“apron”, suddenly it will abruptly
ascend again until it reaches the
transverse mesocolon, so by
looking at the gastrocolic part of
the greater omentum you will
see 4 visceral layers, two
descending layers and two
ascending layers, once it reaches
the transverse colon it will split to cover it, then the visceral layers
will go and attach the transverse colon with the posterior
abdominal wall, so this part is the transverse mesocolon.
Once these visceral layers reach the posterior abdominal wall they
will split, one will go up and the other will go down so now we call
this the parietal peritoneum, the parietal layer which will go up will
go and move anterior to the pancreas, so you see the pancreas is
not covered by the peritoneum, there’s no other layer behind it, so
the pancreas is retroperitoneal, as the parietal peritoneum ascends
up it will go to join the other
parietal layer so the complete sac
is closed now, this is called the
lesser sac behind the stomach.
The lesser sac has two expansions,
a superior expansion and an
inferior one, so it’s not actually
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behind the stomach; only the main part of the sac is just behind the
stomach. The inferior expansion between the 4 layers of the
greater omentum which is called inferior recess is very
important during inflammation and has a role in the accumulation
of fluid and pus inside the peritoneum. The other potential space is
the superior expansion which goes up behind the liver and is called
the superior recess of the lesser sac.
What about the other part of the peritoneum? As this parietal layer
descends down, it will go anteriorly and cover around the small
intestine, so this is now the mesentery. Another layer will go with
it and cover around other loops of intestine. All of these together
are called the mesenteries of the small intestine, then they will
reflect in the lower abdominal wall (in the pelvis usually) to
become parietal peritoneum and they will go along the inferior and
anterior wall of the abdominal cavity and join with the other
parietal layer forming the greater sac.
Now how can we connect between the greater & lesser sac..! By
moving more to the right with this sagittal section we will see a
small opening which is the foramen of Winslow, this foramen
connects between the greater sac & the lesser sac.
- As a Quick review :
Lesser omentum greater omentum transverse mesocolon
parietal peritoneum mesentry parietal peritoneum  viscera
around the liver.
Remember that it’s only one sac which continues with itself,
but it has different names in different regions.
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Ligaments
One of the important ligaments in
the liver is the Falciform
Ligament which connects the
liver with the anterior abdominal
wall. The falciform ligament is an
expansion of the bare area
anteriorly with the sac as it
reflects toward the diaphragm. So
it’s basically two layers of
visceral peritoneum reflected
onto the anterior abdominal wall
to provide a passage for the
umbilical vein during embryonic
or fetal life.
Note that the umbilical vein is
the major part of the umbilical
cord which passes through the
fetus to go and attach to the
portal vain in the liver. So that’s
why to reach the liver you don’t
need peritoneum, that’s why the
peritoneum reflects to allow the
passage between the two visceral
layers to get into the liver. After
birth, the umbilical vain will be
obliterated so we call it the round ligament (ligamentum teres).
Hepatoduodenal ligament is the free edge of the lesser omentum
which contains portal triad.”Refer to page #6 for a clearer picture”
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Nerve supply
Peritoneal sensation depends on the part of peritoneum which is
affected. If it’s visceral the nerve supply will be autonomic by the
same organ the peritoneum is covering (omentum receive the
autonomic nerve supply from the stomach), however since the
parietal peritoneum is covering the abdominal wall it will receive
Somatic nerve supply (responsible for general sensation; mainly
pain).
Now if the pain was from the parietal peritoneum, it will be exactly
from the same region you feel pain in, however if the pain was
from the visceral peritoneum you will not feel it in the same
region. Since the visceral layer is affected, the pain sensation will
be referred from the same supplying organ from which the
autonomic nerve supply is coming from.
Parietal peritoneum
Visceral peritoneum
(sensation)
1) T7 – T12.
autonomic nerve supply
2) L1(iliohypogastric&ilioinguinal). (only for stretch)
3) Obturator nerve (in the pelvis)
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Epigastric area pain is a referred pain for
the stomach mainly (Foregut), umbilical
region pain is a referred pain for the small
intestine, cecum and appendix (Midgut),
hypogastric region pain which is the area
below the umbilicus is a referred pain for
the large intestine (hindgut), and then the
pubic symphysis pain by L1 (ilioinguinal
nerve) is a referred pain for the urinary
bladder.
So the pain here is referred, but the pain in the parietal layer is
direct because it’s supplied by somatic nerves from the abdominal
wall.
Appendicitis, when it starts the pain of the appendix will be in the
periumbilical region,as it becomes swollen and starts to hit the
parietal peritoneum, the pain will start to move from the
periumbilical region down into the lower right quadrant (lower
right inguinal region).
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Organs relation to peritoneum
-
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Intraperitoneal organs
Stomach.
Appendix : it has its own
mesentery called
mesoappendix.
Transeverse colon.
Sigmoid.
Liver : except 3 region
one of them is the bare
area.
Spleen.
Retroperitoneal organs
- Duodenum : “secondary
retroperitoneum” except
the first 2cm remain
covered with the
hepatoduodenal ligament.
- Jegunum.
- Ileum.
- Cecum : “secondary
retroperitoneal” covered
with peritoneum but it will
leave the mesentery as we
move from the appendix to
the cecum so it’s partially
covered with peritoneum.
- Acsending colon
“secondary”.
- Descending colon
“secondary”.
- Rectum: within the pelvis.
The upper part is covered
anteriorly &lateraly
, the middle part is covered
anteriorly.
And the lower part(no
covering, subperitoneal).
- Pancreas : except for the
tail which is
intraperitoneal.
- Kidney “primary”.
A useful mnemonic to help in recalling which abdominal viscera are
intraperitoneal or retroperitoneal :-
Another mnemonic going along with SAD PUCKER is 112 212111, this
correlating to which ones are Primarily (1) or Secondary (2)
Retroperitoneal. Alternatively, PADD (Pancreas, Ascending
colon, Descending colon, Duodenum) can be used to remember which
structures are secondarily retroperitoneal.
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GIT in the Abdomen:
Gastrointestinal tract in the abdominal cavity consists of 4 parts :
1- Esophagus (abdominal part)
2- Stomach
3- Small intestine
4- Large intestine
Note : Dr.Allouh said this topic is
included in the lab only.
1-
Abdominal esophagus
It’s very small intraperitoneal tube
(1.25 cm) that starts from the
esophageal opening (at T10) and ends at cardiac orifices (at T11).
2-
Stomach
It’s an intraperitoneal organ, which is divided into 4 regions :
1- Cardia: surrounds the esophageal
opening.
2- Fundus : the most superior part
of the stomach (dome shape).
3- Body: central part, the largest
part of stomach.
4- Pylorus (gate guard) : consists of
antrum and canal, guarding the
gate into the duodenum.
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Curves of the Stomach (2 curves):
1- Greater curvature: on the left side of stomach.
2- Lesser curvature: on the right side of stomach.
Openings of the stomach (2 openings):
1- Cardiac orifice (cardioesophageal junction) :
It’s the upper opening that is between the esophagus and
stomach, it’s a physiological sphincter.
2- Pyloric sphincter :
It’s the lower opening that is between the stomach and
duodenum, it’s an anatomical and physiological sphincter.
Note:
Sphincter: a cylindrical muscle that normally maintains
constriction of a natural body passage or orifice which relaxes as
required by normal physiological functioning.
Anatomical sphincter: has a localized and often circular muscular
thickening to facilitate its action as a sphincter. So there is a
function with an anatomical structure, so the sphincter is built in.
(a ring of muscle that contracts to close an opening) .
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Physiological sphincter: A sphincter that is not recognizable at an
autopsy because its resting arrangement cannot be distinguished
from adjacent tissue. Functional sphincters do not have this
localized muscular thickening, however, they can achieve their
action through muscle contractions around (extrinsic) the structure.
So there is no built in sphincter (no structure).
So in this case (Cardiac orifice) its function is coming from the
right crus of diaphragm.
 If we say anatomical sphincter we mean a structure and
function, while if we say a sphincter is a physiologic
sphincter we mean that it has a function without an intrinsic
structure. So it’s redundant to say a sphincter is anatomic and
physiologic sphincter.(anatomic is enough)
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Layers of the stomach:
The layers that make the wall of the stomach are: (arranged from
inside to outside)
1- Mucosa
2- Submucosa
3- Muscularis The external layer
is longitudinal, the middle
layer is circular, and the
internal layer is oblique.
4- Serosa (visceral peritoneum)
Why does the stomach need 3 layers of muscles?
 Because the stomach is an expansible organ, so it needs to
accommodate distension and collapsing. Therefore, the third
layer provides added protection from tearing.
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3- Small intestine
Composed of 3 parts :
A) Duodenum ( C shaped due to
the presence of head of pancreas
so it will be bended )
B) Jejunum
C) Ileum
Note: remember that the pancreas and the duodenum (except the
first 2 cm over the omental attachment) are retroperitoneal organs,
while the jejunum and ileum are intraperitoneal organs.
A) Duodenum (4 parts):
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Parts of Duodenum :
 Superior (first) part :
at the level of L1 next to the pylorus – it has a horizontal
direction.
 Descending (second) part:
right to L2 and L3. It has an opening of the pancreatic and
bile ducts. The bile duct descends behind the first part of the
duodenum and penetrates the head of the pancreas and fuses
with the main
pancreatic duct
(Wirsung duct) and
form a large duct
called Ampulla of
Vater (referring to
German anatomist
his name is
Abraham vater)
aka
Hepatopancreatic
Ampulla which
opens in the second part of the duodenum and makes a small
elevation called the major duodenal papilla. There is
another elevation called minor duodenal papilla that is
made by accessory pancreatic duct (duct of Santorini –
Italian anatomist).
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So the ampulla of Vater opens into the major duodenal
papilla, and duct of santorini opens into minor duodenal
papilla.
At this part the fusion of the
forgut and midgut happens
and this is very important
regarding the blood supply:
@ foregut : blood supply by
celiac artery
@ Midgut : blood supply by
superior mesenteric atrtery
 Horizontal or transverse (third) part:
Also called the inferior part, is anterior to the inferior vena
cava at the level of L3.
 Ascending (fourth) part :
It is at the left side of L3 (at level
of L2 from wiki). Ligament of
Treitz (suspensory ligament of the
duodenum) which is a connective
tissue and smooth muscle that will
hold the duodenum up in this area
>>> so it can go interiorly at the
flexure
(bending)
called
duodenojejunal
junction to
become the jejunum.
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B) Jejunum
Jejunum (Latin word which means empty) is an intraperitoneal
part. Jejunum length is 1m (from duodenojejunal flexure to the
ileum) found in the upper left half.
C) Ileum
Ileum: (Greek word which means
twisted). The Ileum’s length is 2m
(it ends at the Ileocecal junctionvalve) found in the lower right
half.
How to distinguish between the jejunum and ileum?
1- The lumen of jejunum is wider than the ileum’s (as we
descend downward the lumen will become narrower).
2- More numerous and larger Plicae
Circulares in the Jejunum than the
Ileum. (pilcae circulars are circular
folds in the small intestine that
increase the surface area >>> more
number of cells >>> increase the
absorption)
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3- Mesentric artery will descend into the intestine and form
arcades (small arches). These arcades are less in the jejunum
and more in the ileum (they start to grow more and more when
we go from jejunum to ileum.
4- Fat deposition increases in lower parts. (Therefore, more fat
is deposited in the ileum than in the jejunum)
Note: fats located near the root of arteries (don’t enter the the
intestine but surround it).
5- Payer’s patches are found only in the ileum. (in lamina
propria and submucosa)
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Characteristic
Position
Diameter
Wall
Circular Folds
Vascularity
Vasa Recta
Color
Lymphatic
Follicles
Fat in
mesentery
Jejunum
Upper left half
Greater
Thicker
Larger, numerous and large
villi
Greater
Long
Deeper red
Solitary
Less
4-Large intestine
Composed of 6 parts :
 Cecum and Appendix
 Ascending colon
(retroperitneal )
 Transverse colon
(intraperitoneal)
 Descending colon
(retroperitoneal)
 Sigmoid colon
(intraperitoneal)
 Rectum (in pelvic cavity)
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Ileum
Lower right half
less
thin
Fewer, smaller and
fewer villi
less
short
Paler pink
Aggregated
(prayers patch)
more
Distinguishing features between the small and large intestines:
Note: if the small intestine is enlarged (there is food inside the
lumen) it may reach the size of an empty large intestine.
3 main features:
1- Haustra (saccules) :
They are saculations or pouches
of the colon formed by taeniae
coli.
2- Taeniae coli :
They are three longitudinal bands of muscle that extend from
the base of the appendix (so the appendix is not sacculated) over
the cecum, ascending colon, transverse colon, descending colon,
sigmoid colon reaching the rectum.
In histology of the large intestine we have a lining of mucosa,
submucosa (site of vasculature), muscularis (which has inner
circular and outer longitudinal layers of muscle fibers) and
serosa.
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The longitudinal layer of the muscularis externa of the large
intestine will gather up in three bundles instead of being
distributed all over the organ. They are taenia omentialis, taenia
mesoconica and taenia libera.
So actually taenia coli are three bundles of muscles that
represent the longitudinal muscle layer. Their arrangement in
three bundles makes them stronger.
3- Epiploic (omental) appendices:
They are fatty tags attached to the outer wall of the colon.
4- Right (hepatic) and left (splenic) flexures (flexure = curve)
‫شكر خاص ألخوي عبد القادر دمحم وأخوي عمران نصيرات و شباب ما وراء‬
.‫ير هذا التفريغ النور‬
َ ‫الكواليس الذين بدونهم لم‬
.‫أخوكم مصطفى السمهوري‬
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