The Peritoneum

We introduced to you the concept of serous membranes in the introduction and we

told you that the serous membranes are made of mesothelium ,they take the shape of

closed sacs; we don't tear them and put organs inside,no!organs are invaginate these

membranes and this lead to the arrangement of having two-layered membrane: one visceral

and one parietal. So far we studied the Pleural membrane which is a serous membrane ,the

Pericardial membrane which is also a serous a fibroserous and now we'll talk of another

serous membrane in the abdomen we call it the "PERITONEUM".

So serous membranes have different names in different locations. In the abdomen

we have a serous membrane called peritoneum ; abdominal viscera that invaginate this

membrane and this leads to having paretial and visceral..The paretial which lines internal

abdominal wall ;visceral which lines the abdominal organs around most not all;in between of

this two layers ,because our viscera in the Abdomen ,due to the contraction, is somewhat

motile;so to avoid friction we have the peritoneal cavity that has fluid inside to decrease the

friction.

*

*The Peritoneal Cavity DOES NOT contain any organs.

When I say ,or describe an organ to be INTRAPERTITONEAL ,I don't mean that it is inside the

peritoneal cavity ,I mean it's surrounded by the peritoneal membrane.

Picture of slide 3 is a cross section through the abdomen ,this is the peritoneum and organs

invaginate this membrane;the liver ,for example, it's surrounded by peritoneum ,the same

thing for the stomach and the spleen.You notice ,that some organs ,the kidney for example,

are not surrounded by the peritoneum,so we can't say that they are intraperitoneal ,instead

we describe them as being "RETROPERITONEAL".

Also notice that the infolding of the peritoneal membrane to surround organs lead to having

two large sacs within the peritoneal cavity;one we call it the GREATER SAC and the other we

call it the LESSER SAC;they are just parts of the peritoneal cavity.

We have just introduced the idea of intraperitoneal and retroperitoneal.

Intraperitoneal is covered by peritoneum , like stomach ,spleen ,jejunum and ileum which

are part of the small intestine.

Retroperitoneal is either posterior to the peritoneal cavity like kidney or only partially

covered with visceral peritoneum,like for example pancreas, ascending and descending

colons.Colon means large intestine ;made of ascending, transverse ,descending and sigmoid

that ends with rectum.

So we start talking about the peritoneal cavity,we will talk about the greater and lesser sacs.

As the name implies, the greater sac is the main part of the peritoneal cavity. Are the two

sacs separated? No they are collected, because they belong to the same space;But the area

of connection there Is a constriction and that's why it look like a foramen. The area of

connection between the two sacs we call it "EPIPLOIC FORAMEN" or the "OPENING OF

WISNLOW".Where is lesser sac located?It's located behind the stomach ,the greater sac is

more anterior.

In picture in slide 3,or the picture above, there's a small arrow…lateral to the

kidney,superior to the vena cava..the arrow indicates the position of the Opening of

winslow". The foramen has boundaries, in anatomy when we say a structures we want to

know its boundaries: (the picture here

laterally the liver has been

removed,the red arrow is the position

of the foramen ):

Anteriorly is bounded by

portal triad consisting of the portal

vein ,hepatic artery and bile duct. They are not seen because they are embedded into this

ligament, the hepatodoudenal ligament.

Posteriorly this foramen is bounded by inferior vena cava;

superiorly by the liver in specific the caudate lobe of the liver that had been removed.

inferiorly by the duodenum .

Peritoneum has special names at specific locations,sometimes we say omentum,omenta

plural; sometimes we call it mesentry & mesocolon and sometimes we use the term

ligaments and when we say ligament, ligaments within the peritoneal contest ,we are not

talking about fibrous or dense fibrous connecting tissue ,we are talking about duplication of

the peritoneal membrane ;instead of having one layer,and by one layer I mean visceral and

paretial ,we are having double layers.

So let’s specify when we use each term:

Omentum ,broad sheet of peritoneum ,double layered ,two visceral and two paretial,this is

what’s meant by double layer ;omentum connects organs with each others. To be specific it

connects the stomach to the transverse colon or the stomach to the liver.

Omenta has three parts :Greater omentum,lesser omentum and gastrosplenic omentum.

Let’s talk about the first part of omentum ,the GREATER OMENTUM.

1. The greater omentum ( the yellowish one ,pic in slide 10) is a layered omentum

connecting the stomach to the transverse colon .

*How is this connection made?The stomach has left and right border; the left border we call

it great curvature, from this great curvature ,the sheath of omentum descends like and

apron ,it extends anterior to the small intestine and then fold back to be attached to the

transverse colon, to the anterior aspect of the transverse colon.

2. Since we have great we must have lesser,THE LESSER OMENTUM; where’s it

located?it’s located ..here we have the great curvature of the stomach,which is the

left border,and we do have the lesser curvature that’s shorter and concave,while the

other was convex; so the connection between the lesser curvature and liver is by the

lesser omentum.Behind the lesser omentum ,there is the lesser sac. As you can

notice that the lesser omentum has a free border,we can call it the right

border ,that’s not attached and here is the hepatoduodenal ligament containing the

portal triad.

We introduced the idea of omentum,now we'll talk about MESENTRY.

MESENTRY ,is a double layer of peritoneum ,here it connects organs with the posterior

abdominal wall; a good example is the mesentry of the small intestine,is triangularly shaped

that sustains the small intestine and connect it to the posterior abdominal wall .The same

structure(mesentry) when it's related to the large intestine or any part of it ,we call it

MESOCOLON; so for the transverse colon we call it TRANSVERSE MESOCOLON and the same

thing for the sigmoid and mesoappendix. What about the ascending and descending colons?

Do we have ascending mesocolon?no! Because these parts are retroperitoneal.

Slide 14 is a saggital view,you can see the transverse colon, transverse mesocolon,the

mesentry of small intestine and you can see how is attached to posterior abdominal

wall.These mesentries specifically and peritoneum in general are important ,because the

neurovascular supply of the abdomen in embedded in this membrane; so most of the nerves

and arteries in the abdomen ,not all,you can't see them unless you dissect the peritoneal

membrane.

Now LIGAMENTS,that are not made of dense fibrous tissue but are made by peritoneal

tissue .We have the FALCIFORM LIGAMENT (the one having the zig zag arrow),you can see it

on the anterior wall of the liver ,it connects the liver to the Diaphragm and to the anterior

abdominal wall .It ends by fusing with the LIGAMENTUM OF TERES(the straight arrows),a

remnant of your fetal life, the umbilical vein that was connecting the placenta to the fetus

remains in the adult life as a rudimentary ligament that wind up in the falciform

ligament .Another example we have on the peritoneal tissue is HEPATODOUDENAL

LIGAMENT ,as I just told you

about,lies in the free border of the lesser omentum ,so it connects

the liver to the anterior 2 cm of the duodenum .

We have talked about the peritoneum ,now let's talk about organs in the abdominal

wall.The main portion of the abdomen is occupied by the gastrointestinal tract (GIT),which is

made by esophagus ,stomach,small intestine and large intestine ,of course we have other

parts but they are irrelevant to the abdomen,example the larynx ,the pharynx ,the mouth

and the rectum .

THE ESOPHAGUS: The esophagus is a muscular tube ,it connects the pharynx to the

stomach ;it enters the abdomen through the esophageal opening ,an opening of the right

crus of the diaphragm at the level of T10; the hole length of the esophagus is about 25

cm;only less than 2 cm enters the abdomen and terminates at the cardiac orifice ,the

superior orifice of the stomach at level of T11.

THE STOMACH: is one of the intraperitoneal organs. We have four regions within the

stomach :

-the superior part,just around the orifice we call it the

CARDIAC.

- a domed shaped area we called it the FUNDUS .

-the major portion we call it the BODY.

Outer L??

Middle ??

inner ??

???

-the pyloric region,the last part ,made of two subdivisions :

1- Antrum

2- Pylorus , a tubular portion of the stomach and it ends by having an anatomical

sphincter at the junction between the stomach and the duodenum ,called PYLORIC

SPHINCTER. Do we have a sphincter between the esophagus and the stomach?We don't

have an anatomical sphincter ,if I dissect that region I won't find a structure of the

sphincter,but there is a physiological mechanism that acts as a sphincter ,just before the last

peristaltic wave reach the stomach ,the circular muscle ,which are everywhere in the

stomach will relax .

-anatomical and physiological sphincter :the pyloric sphincter

-physiological :the cardiac sphincter.

Anatomical sphincter :if I dissect that region I'll have a thickening of the circular muscle at

this area.

If we look at the outline of the stomach(the picture above helps a lot), we can see two

curvatures ,one is convex and longer,and the other is concave and shorter.The left one is the

greater curvature and the other is the lesser curvature; you can see that the lesser

curvatures terminates in the area called "INCISURA ANGULARIS ",a notch in the outer

surface of the stomach.

The shape of the stomach looks like a "J",it's J-shaped ,in tall and thin people, and it's more

transversely arranged in short ,obese people. But in all ways we assume that the stomach is

J-shaped.

The muscular wall of the stomach is made of three layers:

An outer layer which has longitudinal fibers.

The middle one which has circular fibers.

The inner one that has oblique fibers.

The mechanical digestion occur in stomach,by the action of those muscles, absorption of

food in the stomach is not that much, just few drugs are absorbed in the stomach, much of

the absorption occur in the intestine.

So we start talking about the small intestine: we have three parts in the small intestine:

Duodenum

Jejunum

Ileum

The small intestine is the longest part of the alimentary tract, the GIT ;in cadaver the small

intestine's length is around 9 m but of course in living individuals is shorter, because of the

muscle tone , minimal contraction of the muscle fibers, this tone decreases the length of

small intestine in living individuals.

THE DOUDENUM:

It's retroperitoneal except where it's attached with the hepatodoudenal ligament.

It's composed of four parts :

The superior first part,the junction between the pylorus and the duodenum (the area of

pyloric sphincter) ,and it's horizontal and matches the L1.

The second part is descending,it's slightly right to the lumbar vertebra 2 and 3.It surrounds

the head of the pancreas and receives bile secretions from the

liver and Gallbladder ;and also receives secretion from the

pancreas.

Ducts:are tubes that convey secretions from an organ to another.

The pancreatic duct and the bile duct from the liver ,they merge together and form one duct

and empty in the descending duodenum ,or the second part of duodenum, and that opening

through which the pancreatic and bile duct empty in the descending part is called "Major

papilla"or "the Ampulla of Vater",because of the anatomist who described this duct.

The pictures shows this clearly…the green duct is the pancreatic duct which merge with the

bile duct and empty in the duodenum in the Ampulla of Vater.

If we look inside the doudenum we will see a

Protrusion that correspond to the duct ,we call it the major

doudenum papilla ,a structure that we see in the lumen of the doudenum not in the outer

surface.

By: Sara Ibdiwi