2. The gut and peritoneal cavity Flashcards
What type of epithelium is the peritoneum?
Simple squamous epithelium: mesothelium
Peritoneum
continuous membrane lining the abdominal cavity consisting of mesothelial layer supported by a layer of connective tissue
What is contained in the peritoneal cavity?
Nothing
It is a potential space
There is only a small amount of fluid
How does the peritoneum relate to viscera of the abdomen?
Intra-abdominal organs are suspended in peritoneal reflections (mesenteries)
Which germ layers does the gut tube develop from?
Endoderm and splanchnic mesoderm
Which mesenteries suspend the different parts of the gut tube?
Entire gut tube is suspended by dorsal mesentery
Foregut is ALSO suspended by ventral mesentery
Mesenteries
peritoneal folds attaching viscera to the abdominal wall
What do the peritoneal folds act as a conduit for?
Nerves
Blood vessels
Lymphatics
Visceral and parietal peritoneum
VISCERAL: covering the suspended organs
PARIETAL: lines the abdominal wall.
What is the difference between intraperitoneal and retroperitoneal?
Intraperitoneal: surrounded by peritoneum
Retroperitoneal: behind the peritoneum, not totally surrounded by peritoneum.
State 3 viscera that are secondarily retroperitoneal.
Duodenum (except the 1st part)
Pancreas (tail is intraperitoneal)
Colon (ascending and descending only)
State 5 viscera that were retroperitoneal from the start.
Kidneys Great vessels Adrenal glands Oesophagus Rectum
What are secondary retroperitoneal organs?
Organs that originally had a mesentery, then became secondarily retroperitoneal when the mesentery fused with the body wall
What are the 3 divisions of the gut tube and what defines their borders?
Foregut: distal 1/3 of the oesophagus to just inferior of major duodenal papilla (2nd part of duodenum: at the entrance of the bile duct)
Midgut: 2nd part of the duodenum to 2/3 along the transverse colon
Hindgut: Distal 1/3 of transverse colon to the rectum
What does the ventral mesentery split into?
Falciform ligament
Lesser omentum
How is the lesser sac (omental bursa) formed?
Liver moves right
Stomach and spleen move left with the dorsal mesentery thus cutting off a space behind the stomach= the lesser sac
What is the lesser omentum?
Fold of peritoneum between the liver and the lesser curvature of the stomach
What is the greater omentum?
Lower part of the dorsal foregut mesentery extends down form the greater curvature of the stomach as the greater omentum.
Lies like an apron in front of the intestines.
Why does the lesser omentum have a lower free border and what opening does that form?
Because it is formed by the ventral foregut mesentery, which ends at the start of the midgut.
Opening to the omental bursa is called the epiploic foramen.
What vessels run within the lesser omentum near its free edge?
Hepatic portal vein
Hepatic artery
Bile duct
Describe how the abdomen is divided into different compartments.
Transverse mesocolon divides the abdomen into supracolic and infracolic compartments. Infracolic compartment is further divided by the mesentery of the small intestine (from the duodeno-jejunal flexure to the ileo-caecal valve) - dividing the infracolic compartment into right and left infracolic compartments.
There are also gutters running along the lateral sides of the ascending and descending colon called the right and left paracolic gutter.
What is the transverse colon suspended by?
Transverse mesocolon
What is the anterior layer of the transverse mesocolon adherent to?
Posterior layer of the greater omentum
Describe the how the direction of movement of peritoneal fluid differs from that of inflammatory exudate.
Peritoneal fluid moves towards the diaphragm
Inflammatory exudate moves towards the pelvis
State the layers of the gut tube.
Mucosa Submucosa Muscularis Serosa/adventitia Mesentary
Which layers have nerve plexuses and what are they called?
Submucosa: Meissner’s plexus
Muscularis (myenteric): Auerbach’s plexus
At which vertebral position does the oesophagus penetrate the diaphragm and through which crus?
T10
Through the right crus
What contributes to the lower oesophageal sphincter and why is this beneficial?
Diaphragm
Prevents gastro-oesophageal reflux
What are the 5 different parts of the stomach?
Cardia Fundus Body Pyloric antrum Pyloric canal
What prevents food entering the duodenum?
Pyloric sphincter at distal end of pyloric canal
Ring of smooth muscle
What are the 4 parts of the duodenum?
Superior
Descending
Inferior
Ascending
Describe the superior part of the duodenum
Duodenal cap
Most duodenal ulcers occur here
Describe the descending part of the duodenum
Contains minor and major duodenal pappillae
Where accessory pancreatic duct and bile duct enter respectively
Describe the inferior and ascending parts of the duodenum
Inferior: Crosses IVC and has SMA anterior to it
Ascending: Terminates at duadenaojejunal flexure
Describe 5 characteristics of the jejunum (With respect to ileum)
Jejunum is proximal 2/5 In upper left quadrant of abdomen Has: Larger diameter Longer vasa recta Less prominent arterial arcades
Describe 5 characteristics of the ileum (With respect to jenjenum)
Ileum is distal 3/5 In lower right quadrant of abdomen Has: Smaller diameter Shorter VASA RECTA Prominent ARTERIAL ARCADES
Describe 3 ways in which the colon differs from the small intestines.
Colon has taenia coli (ribbons of longitudinal muscle)
Colon has fatty tags (appendices epiploicae)
Colon has a segmental/pocketed walls
What are the 3 main arteries supplying the gut and what do each of them supply?
Coeliac Trunk: foregut (pancreas, liver, spleen)
Superior Mesenteric Artery: midgut
Inferior Mesenteric Artery: hindgut
What does the coeliac trunk divide into?
Common Hepatic Artery
Left Gastric Artery
Splenic Artery
What are the branches of the superior mesenteric artery?
Jejunal Arteries Ileal Arteries Iliocolic Artery Right Colic Artery Middle Colic Artery
What are the branches of the inferior mesenteric artery?
Left Colic Artery
Sigmoid Arteries
Superior Rectal Artery
Describe the venous drainage of the gut.
Venous drainage does NOT follow the arterial supply.
All the venous blood from the gut drains through the liver.
Inferior mesenteric vein joins the splenic vein and the splenic vein then joins the superior mesenteric vein to form the hepatic portal vein.
Superior mesenteric vein joins the splenic vein behind the 1st part of the duodenum.
Where do you find portal-systemic anastamosis?
Oesophagus, rectum, umbilicus
Oesophagus: between oesophageal vein and left gastric vein
Umbilicus: between umbilical vein and epigastric veins
Rectum: between superior rectal vein and inferior rectal vein
There is a 4th anastomosis between the colic veins and posterior abdominal wall veins
What is the clinical significance of the portal-systemic anastamoses?
Liver or portal obstruction causes these veins to dilate widely, possibly leading to severe oesophageal or rectal haemorrhage.
Describe the lymphatic drainage of the gut.
Coeliac lymph nodes
Superior mesenteric lymph nodes
Inferior mesenteric lymph nodes.
All drain into the cisterna chyli and then through the thoracic duct.
Which vertebral level is the cisterna chyli positioned at?
In front of the vertebral body of L1 and L2
What are the main parasympathetic sensory nerves of the gut?
Vagus Nerve
Pelvic Splanchnic Nerves (S2-S4)
What are the main sympathetic sensory nerves of the gut?
Thoracic Splanchnic Nerves (T5-T12)
Lumbar Splanchnic Nerves (L1+L2)
What are the roles of the parasympathetic sensory and sympathetic sensory nerves of the gut?
Parasympathetic Sensory: involved in regulate reflex gut function
Sympathetic Sensory: mediate pain
What is the nervous supply to abdominal viscera?
Autonomic
What are the 3 divisions of the thoracic splanchnic nerves?
Greater Thoracic Splanchnic: T5-T9
Lesser: T10-T11
Least: T12
Why are the sensory fibres the most important clinically?
They are involved in mediating pain sensation.
Parasympathetic efferents to the gut
increase peristalsis
relax sphincters
increase secretion
Sympathetic efferents to the gut
decrease peristalsis
constrict sphincters
decrease blood flow and secretions
