2. The gut and peritoneal cavity Flashcards by Georgia Leggett

What type of epithelium is the peritoneum?

Simple squamous epithelium: mesothelium

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Peritoneum

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

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What is contained in the peritoneal cavity?

Nothing
It is a potential space
There is only a small amount of fluid

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How does the peritoneum relate to viscera of the abdomen?

Intra-abdominal organs are suspended in peritoneal reflections (mesenteries)

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Which germ layers does the gut tube develop from?

Endoderm and splanchnic mesoderm

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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

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Mesenteries

peritoneal folds attaching viscera to the abdominal wall

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What do the peritoneal folds act as a conduit for?

Nerves
Blood vessels
Lymphatics

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Visceral and parietal peritoneum

VISCERAL: covering the suspended organs
PARIETAL: lines the abdominal wall.

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What is the difference between intraperitoneal and retroperitoneal?

Intraperitoneal: surrounded by peritoneum
Retroperitoneal: behind the peritoneum, not totally surrounded by peritoneum.

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State 3 viscera that are secondarily retroperitoneal.

Duodenum (except the 1st part)
Pancreas (tail is intraperitoneal)
Colon (ascending and descending only)

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State 5 viscera that were retroperitoneal from the start.

Kidneys
Great vessels
Adrenal glands
Oesophagus
Rectum

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What are secondary retroperitoneal organs?

Organs that originally had a mesentery, then became secondarily retroperitoneal when the mesentery fused with the body wall

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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

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What does the ventral mesentery split into?

Falciform ligament

Lesser omentum

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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

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What is the lesser omentum?

Fold of peritoneum between the liver and the lesser curvature of the stomach

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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.

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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.

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What vessels run within the lesser omentum near its free edge?

Hepatic portal vein
Hepatic artery
Bile duct

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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.

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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