Gut and peritoneal cavity

Question 1

What is meant by the abdominal wall

Answer 1

Abdominal wall – muscle and connective tissue deep to which lies the abdominal cavity.

Question 2

What is meant by the peritoneum

Answer 2

Peritoneum – continuous membrane lining the abdominal cavity consisting of mesothelial layer supported by a layer of connective tissue

Question 3

Describe the mesothelium

Answer 3

SINGLE continuous membrane of simple SQUAMOUS epithelium – MESOTHELIUM.

Question 4

What is meant by the peritoneal cavity

Answer 4

A potential space between the visceral and parietal peritoneum.
In life there is nothing in the peritoneal cavity proper apart from a small amount of fluid – it is potential space.
Intra-abdominal organs are suspended in peritoneal reflections called mesenteries.
The situation is analogous to the plural cavities in which the lungs are suspended.
Some organs are found outside the peritoneal cavity.

Question 5

What is the difference between the visceral and parietal peritoneum

Answer 5

Parietal peritoneum: lines the walls of the cavity
Visceral peritoneum: lines the viscera of the cavity
Connection: mesentery

Question 6

What is the purpose of the peritoneal fluid

Answer 6

Lubricates movement of the G.I organs

We can pump CO2 into it to push the organs apart to look at the structures of the abdomen.

Question 7

Which structures of the G.I tract are not protected by the thorax or pelvis

Answer 7

Ileum 
Jejunum 
Duodenum
Caecum and large intestine
Parts of the sigmoid colon

Question 8

When does the pharynx become the oesophagus

Answer 8

below the cricoid cartilage

Question 9

Outline the embryonic development of the gut tube

Answer 9

See diagram!
Connection between yolk sac and gut tube
Gut tube fuses with itself (in a circle)- connection to yolk sac lost
It is suspended from the posterior abdominal wall by a peritoneal fold – the dorsal mesentery
Gut tube lined by endoderm
Covered by somatic mesoderm
All enclosed by a surface ectoderm

Question 10

What does the gut originate from

Answer 10

The gut tube originates from the endoderm and splanchnic mesoderm

Question 11

What is meant by the mesenteries

Answer 11

Peritoneal folds attaching viscera to the abdominal wall.

Conduit for VESSELS, NERVES and LYMPHATICS supplying viscera.

Question 12

Describe the mesentery

Answer 12

Large fan shaped double-fold of peritoneum that connects the jejunum and ileum to the posterior abdominal wall
duodenojejunal junction is its superior attachment, just to the left of the upper lumbar part of the vertebral column.
Passes obliquely downward and to the right, ending at the ileocecal junction near the upper border of the right sacro-iliac joint
Fat between the two peritoneal layers contains the arteries, veins, nerves and lymphatics that supply the duodenum and ileum

Question 13

Describe the transverse mesocolon

Answer 13

Fold of peritoneum that connects the transverse colon to the posterior abdominal wall
Its two layers leave the posterior abdominal wall across the anterior surface of the head and body of the pancreas and pass outward to surface around the transverse colon
Anterior layer of the transverse mesocolon is adherent to the posterior layer of the greater omentum

Question 14

Describe the sigmoid mesocolon

Answer 14

Inverted, V-shaped peritoneal fold
Apex is near the division of the common iliac artery into its external and internal branches
Left limb of descending V along the medial border of the psoas major muscle
Right limb descends into pelvis to end at S3

Question 15

What is meant by intraperitoneal organs

Answer 15

lie within the cavity, surrounded by visceral peritoneum, and suspended by the mesentery (e.g. Small intestine)

Question 16

What is meant by retroperitoneal organs

Answer 16

RETROperitoneal – structures, e.g. kidneys and great vessels that lie between parietal peritoneum and abdominal wall.

Question 17

List the retroperitoneal organs

Answer 17

Kidneys & ureters
Suprarenal glands 
Aorta/Inferior vena cava
Nerves: lumbar plexus, sympathetic trunk
Oesophagus
Rectum
Duodenum (except the first part) *
Pancreas (tail is INTRAperitoneal) *
Colon (ascending and descending only)*

Question 18

Why are the duodenum, pancreas and colon described as secondary retroperitoneal structures

Answer 18

• These organs originally had a mesentery, then became secondarily retroperitoneal when the mesentery fused with the body wall

Question 19

Describe the foregut

Answer 19

FOREGUT – Distal 3rd of oesophagus to the 2nd part of the duodenum at the entrance of the bile duct (Major duodenal papilla).

Question 20

Describe the midgut

Answer 20

MIDGUT – 2nd part of the duodenum to two-thirds along transverse colon.
All of S.I is in midgut

Question 21

Describe the hindgut

Answer 21

HINDGUT – Distal third of transverse colon to the rectum.

Question 22

What does each division of the G.I tract have

Answer 22

Each part of the GI tract has its own arterial supply, coeliac trunk, superior mesenteric artery and hindgut.

Question 23

Describe the dorsal mesentery

Answer 23

The ENTIRE gut tube is suspended from a DORSAL mesentery

Question 24

Describe the ventral mesentery

Answer 24

In addition, the FOREGUT has a VENTRAL mesentery

Question 25

What does the ventral mesentery split into

Answer 25

The foregut also has a ventral mesentery containing the liver, which splits it into the falciform ligament and the lesser omentum
Due to growth of the liver

Question 26

Describe the embryogenesis of the omental bursa (lesser sac)

Answer 26

gut tube originates from the endoderm and splanchnic mesoderm and is suspended from the posterior abdominal wall by a peritoneal fold (dorsal mesentery); liver, stomach and spleen originally midline, but liver moves right, and spleen to the left, so the original “right” half of the peritoneal cavity becomes posterior - the lesser sac of the cavity

Question 27

Describe the omental bursa

Answer 27

Smaller division of the peritoneal cavity

posterior to the stomach and liver and is continuous with the greater sac through the epiploic foramen

Question 28

What do the omenta consist of and what are they derived from

Answer 28

The omenta consist of two layers of peritoneum, which pass from the stomach to the first part of the duodenum to other viscera

Greater- The lower part of the dorsal foregut mesentery extends down as a double fold called the greater omentum (= apron) anterior to the intestine.

Lesser- The lesser omentum is part of the ventral foregut mesentery.

Question 29

Describe the lesser omentum

Answer 29

Lesser Omentum: extends from lesser curvature of the stomach/duodenum to the inferior surface of the liver, divided into the:
Medial hepatogastric ligament: connecting the stomach and liver
Lateral hepatoduodenal ligament: connects the duodenum and the liver (free edge contains the hepatic artery, bile duct and portal vein)
Two-layered and continuous with peritoneal coverings of the posterior and anterior stomach and first part of duodenum

Question 30

Describe the hepatoduodenal ligament of the omental bursa

Answer 30

Ends laterally as a free margin and serves as the anterior border of the omental foramen
Enclosed in this free edge are the hepatic artery, the bile duct and the portal vein (also lymphs)
Additionally, the right and left gastric vessels are between the layers of the lesser omentum near the lesser curvature of the stomach.

Question 31

Why is this free edge present

Answer 31

This free edge is present because the ventral mesentery ends at the start of the midgut.

Question 32

Describe the greater sac

Answer 32

Accounts for most of the space in the peritoneal cavity
Begins superiorly at the diaphragm and continuing inferiorly into the pelvic cavity
It is entered once the parietal peritoneum has been penetrated.

Question 33

What are the relations of the greater sac

Answer 33

present anteriorly to the lesser omentum and inferior to the superior mesenteric artery - hence surrounding the intestines

Question 34

What are the relations of the lesser sac

Answer 34

Lesser sac: present posteriorly to the lesser omentum and superior to the superior mesenteric artery
Becomes enclosed by the greater omentum

Question 35

Describe the greater omentum

Answer 35

large apron-like structure that attaches to greater curvature of stomach and first part of duodenum to drape inferiorly over the transverse colon and jejunum/ileum

it turns posteriorly and ascends to associate with, and become adherent to, the peritoneum of the superior surface of the transverse colon and the anterior layer of the transverse mesocolon before arriving at the posterior abdominal wall.

Question 36

What can accumulate on the greater omentum

Answer 36

As a thin continuous membrane- fat can accumulate and may become substantial
Two arteries and accompanying veins (right and left gastro-omental vessels) between the double layered peritoneal apron just inferior to the greater curvature of the stomach.

Question 37

Describe the peritoneal compartments

Answer 37

Paracolic gutters: run laterally to the colon
Infracolic compartments: inferior to the mesentery of the transverse colon (right/left divided by mesentery of small intestine - right = superior, left = inferior)
Supracolic compartment: above the mesentery of the transverse colon

Question 38

Describe the movement of peritoneal fluid

Answer 38

peritoneal fluid produced in peritoneal cavity and generally moves superiorly to diaphragm for reabsorption (uses paracolic gutters and subphrenic spaces)

Question 39

Describe the movement of exudate

Answer 39

inflammatory exudate tends to move inferiorly to pelvis, using the subphrenic spaces, paracolic gutters and the infracolic compartments

Question 40

Can something pass from the right to left paracolic gutter

Answer 40

No

Due to falciform ligament attaching the liver to the diaphragm.

Question 41

Describe the consequences of these compartments for the spread of cancers

Answer 41

Cancers can get into peritoneal fluid and move superiorly with it to metastasize