Gut and peritoneal cavity Flashcards
What is meant by the abdominal wall
Abdominal wall – muscle and connective tissue deep to which lies the abdominal cavity.
What is meant by the peritoneum
Peritoneum – continuous membrane lining the abdominal cavity consisting of mesothelial layer supported by a layer of connective tissue
Describe the mesothelium
SINGLE continuous membrane of simple SQUAMOUS epithelium – MESOTHELIUM.
What is meant by the peritoneal cavity
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.
What is the difference between the visceral and parietal peritoneum
Parietal peritoneum: lines the walls of the cavity
Visceral peritoneum: lines the viscera of the cavity
Connection: mesentery
What is the purpose of the peritoneal fluid
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.
Which structures of the G.I tract are not protected by the thorax or pelvis
Ileum Jejunum Duodenum Caecum and large intestine Parts of the sigmoid colon
When does the pharynx become the oesophagus
below the cricoid cartilage
Outline the embryonic development of the gut tube
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
What does the gut originate from
The gut tube originates from the endoderm and splanchnic mesoderm
What is meant by the mesenteries
Peritoneal folds attaching viscera to the abdominal wall.
Conduit for VESSELS, NERVES and LYMPHATICS supplying viscera.
Describe the mesentery
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
Describe the transverse mesocolon
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
Describe the sigmoid mesocolon
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
What is meant by intraperitoneal organs
lie within the cavity, surrounded by visceral peritoneum, and suspended by the mesentery (e.g. Small intestine)
What is meant by retroperitoneal organs
RETROperitoneal – structures, e.g. kidneys and great vessels that lie between parietal peritoneum and abdominal wall.
List the retroperitoneal organs
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)*
Why are the duodenum, pancreas and colon described as secondary retroperitoneal structures
- These organs originally had a mesentery, then became secondarily retroperitoneal when the mesentery fused with the body wall
Describe the foregut
FOREGUT – Distal 3rd of oesophagus to the 2nd part of the duodenum at the entrance of the bile duct (Major duodenal papilla).
Describe the midgut
MIDGUT – 2nd part of the duodenum to two-thirds along transverse colon.
All of S.I is in midgut
Describe the hindgut
HINDGUT – Distal third of transverse colon to the rectum.
What does each division of the G.I tract have
Each part of the GI tract has its own arterial supply, coeliac trunk, superior mesenteric artery and hindgut.
Describe the dorsal mesentery
The ENTIRE gut tube is suspended from a DORSAL mesentery
Describe the ventral mesentery
In addition, the FOREGUT has a VENTRAL mesentery
What does the ventral mesentery split into
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
Describe the embryogenesis of the omental bursa (lesser sac)
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
Describe the omental bursa
Smaller division of the peritoneal cavity
posterior to the stomach and liver and is continuous with the greater sac through the epiploic foramen
What do the omenta consist of and what are they derived from
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.
Describe the lesser omentum
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
Describe the hepatoduodenal ligament of the omental bursa
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.
Why is this free edge present
This free edge is present because the ventral mesentery ends at the start of the midgut.
Describe the greater sac
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.
What are the relations of the greater sac
present anteriorly to the lesser omentum and inferior to the superior mesenteric artery - hence surrounding the intestines
What are the relations of the lesser sac
Lesser sac: present posteriorly to the lesser omentum and superior to the superior mesenteric artery
Becomes enclosed by the greater omentum
Describe the greater omentum
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.
What can accumulate on the greater omentum
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.
Describe the peritoneal compartments
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
Describe the movement of peritoneal fluid
peritoneal fluid produced in peritoneal cavity and generally moves superiorly to diaphragm for reabsorption (uses paracolic gutters and subphrenic spaces)
Describe the movement of exudate
inflammatory exudate tends to move inferiorly to pelvis, using the subphrenic spaces, paracolic gutters and the infracolic compartments
Can something pass from the right to left paracolic gutter
No
Due to falciform ligament attaching the liver to the diaphragm.
Describe the consequences of these compartments for the spread of cancers
Cancers can get into peritoneal fluid and move superiorly with it to metastasize
