1.1.2 Gut and Peritoneal Cavity

Question 1

Peritoneum
- Peritoneal membrane is a single continuous membrane of __________ epithelium (mesothelium), lining the inner abdominal wall – the whole abdominal cavity has an inner lining
- The __________ is a potential space within the layer of peritoneum – components of the GI tract are suspended in peritoneal reflections (mesenteries)
o In reality, there is nothing in the peritoneal cavity proper apart from a small amount of fluid
- The abdominal cavity and pelvic cavity are continuous – referred to as the abdominopelvic cavity
o Most gut structures are at the abdominal part of the cavity, whereas in the pelvic part of the cavity contains pelvic viscera
o Inferior to the thoracic diaphragm is an extension of the abdominal cavity into the thoracic cage
o The lower part of the cavity extends into the pelvic cavity, surrounded by the pelvic bones

Answer 1

simple squamous; peritoneal cavity

Question 2

Digestive tract – the oesophagus runs from the mouth and pharynx through the thoracic cavity through the diaphragm to enter into the abdomen

• The abdominal part of the oesophagus enters the stomach, which then continues as the C-shaped gut tube known as the duodenum
• The duodenum then becomes jejunum and ileum
• The ileum ends in a large sac like known as the cecum, from where the ascending colon starts
• The ascending colon then becomes the transverse colon, descending colon and finally the ______, which ends as the rectum and the anal canal

Answer 2

sigmoid colon

Question 3

Development of the gut tube
- The gut tube is formed from the ________________
- By the 4th week of intrauterine life, the gut tube is enclosed within the intraembryonic coelomic cavity
- On the outer surface, the gut tube is covered by the parietal peritoneum and it is suspended from the mesogastrium (mesentery of the gut) – dorsal mesentery suspends it from the posterior abdominal wall
o Mesenteries – peritoneal folds attaching the viscera to the abdominal wall, acting as a conduit for the vessels, nerves and lymphatics that supply the viscera (mainly the intestines and colon)
o The visceral peritoneum covers the suspended organs and the parietal peritoneum lines the abdominal wall – in continuity through the mesenteries

Answer 3

endoderm and splanchnic mesoderm

Question 4

Divisions of the GI tract – foregut, midgut and hindgut
- Foregut – ___________ to the 2nd part of the duodenum at the entrance of the bile duct (major duodenal papilla)
- Midgut – 2nd part of duodenum to ____________
- Hindgut – distal ⅓ of the transverse colon to the rectum
- The entire gut tube is suspended from a dorsal mesentery
o In addition, the foregut has a ventral mesentery – encloses the liver and pancreas
o The ventral mesentery splits into the _____________ and the lesser omentum

Answer 4

distal ⅓ of the oesophagus; ⅔ along the transverse colon; falciform ligament

Question 5

Divisions of the peritoneal cavity – divided into the greater and lesser sac (omental bursae) in continuity with each other
- In the foregut region, the liver is in the ventral mesentery and initially, the dorsal mesentery holds the whole gut tube whereas the ventral mesentery is only in the ___________
- As development of the liver proceeds, the mesentery twists and turns – part of the peritoneal cavity is trapped behind the liver and stomach
o As the liver grows, it moves to the ______ while the dorsal mesentery and spleen move to the ___.
o The original right side of the upper peritoneal cavity is now _______ (lesser sac of the peritoneal cavity)
o In the upper part of the peritoneal cavity towards the diaphragm, there is the _______ of the peritoneal cavity
- The omental bursa (lesser sac) is in continuity with the greater sac of the peritoneal cavity

Answer 5

foregut region; right ; left; posterior; lesser sac

Question 6

Omenta – peritoneal folds that connect the stomach with other peritoneal organs

• Greater omentum – lower part of the foregut mesentery extending down as a double fold
  o Acts as an apron anterior to the gut structures like the intestines
• Lesser omentum – part of the ventral foregut mesentery lying between the liver and the lesser curvature of the stomach
  o Divided into the _________________ – important structures such as the portal vein, hepatic artery and bile duct run between the posterior abdominal wall and the liver within the lesser omentum near its free edge
  o Free edge – ventral mesentery ends at the start of the midgut

Answer 6

hepatogastric ligament and the hepatoduodenal ligament

Question 7

Epiploic foramen – communication between the greater and lesser sac
o Bounded anteriorly by the free border of the lesser omentum – hepatoduodenal ligament containing the ___________________
o In the Pringle manoeuvre, a large atraumatic haemostat is used to clamp the hepatoduodenal ligament (free border of the lesser omentum), interrupting the flow of blood through the hepatic artery and the portal vein and thus helping to control bleeding from the liver

Answer 7

common bile duct, hepatic artery and hepatic portal vein

Question 8

Compartments of the peritoneal cavity
- Both the lesser sac and greater sacs are capillary thin spaces – when fluid or any gas fills the spaces, the cavity will enlarge

• The greater sac can be divided into 2 major compartments, supracolic compartment and infracolic compartment – separated by the ____________
  o Mesentery of the small intestine further separates the infracolic compartment into right and left infracolic compartments
  o On either side of the ascending colon and descending colon, there is a _________ (depression in that area of the body wall) – canal for drainage of fluid, a pathway for any fluid in the supracolic compartment to flow downwards towards the pelvic area
  o In a vertically standing patient, if there is a collection of fluid underneath the diaphragm, the fluid can flow down the paracolic gutter towards the pelvic cavity

Answer 8

mesentery of the transverse colon; paracolic gutter

Question 9

Fluid movement – normally, there is about 50ml of peritoneal fluid, but this quantity can increase in diseased states
o Usually, peritoneal fluid moves upwards towards the inferior side of the diaphragm – absorbed by the vessels in the diaphragmatic wall to return to the venous circulation
o In a liver abscess, pus from the liver abscess tends to pass downwards along the ________ – most of the inflammatory exudates move towards the pelvis in a person who is sitting up

Answer 9

paracolic gutters

Question 10

Organisation of the GI tract – the GI tract is a long tube but it not uniform or smooth throughout the length, undergoing several modifications (e.g. in the stomach, large intestines and colon)
- The enteric nervous system of the gut (intrinsic) is made of the ____________ plexus at the muscularis layer and ____________ in the mucosa – coordinates gut function

Answer 10

myenteric (Auerbach’s); submucosal (Meissner’s) plexus

Question 11

Abdominal oesophagus – pierces the diaphragm at the level of T10, the muscular part of the diaphragm at the ________ and contributes to the ____________ (prevents gastro-oesophageal reflux), then entering the stomach

Answer 11

right crus; lower oesophageal sphincter

Question 12

Stomach – large muscular sac to hold food

• Fundus – at the top, lies below the diaphragm
• Body – joins the oesophagus at the _____ of the stomach, then narrows down into the pyloric antrum which then leads into the pyloric canal
• At the distal end of the pyloric canal, there is a _________ which controls the passage of food from the stomach into the duodenum
• There are 2 curvatures of the stomach, a greater curvature on the right side and a lesser curvature on the left side

Answer 12

cardia; pyloric sphincter

Question 13

Duodenum (a retroperitoneal structure except for beginning and end) – C-shaped tube with 4 parts, joining the stomach and the jejunum, lying between the gastroduodenal junction and duodenojejunal junction

• 10 inches long (1st part is 2’’, 2nd and 3rd parts are 3’’ and 4th part is 2’’)

Superior (L1):

• Part of the 1st part (superior part) is ________
• ___________ – where most of the duodenal ulcers occur
• Passes anteriorly to the bile duct, ________, portal vein and inferior vena cava

Descending (L2-L3)
- Contains the entrance for the common bile duct (major duodenal papilla) as well as the minor duodenal papilla where the __________ enters

Inferior (L3)
- Crosses the inferior vena cava, _________ passes anterior to it

Ascending (L3-L2)
- Terminates at the duodenojejunal flexure.

Relations of the duodenum are clinically important as aneurysms can compress the duodenum and peptic ulcers can erode into the walls of vessels

Answer 13

intraperitoneal; Duodenal cap; gastroduodenal artery

accessory pancreatic duct

superior mesenteric artery

Question 14

Jejunum and ileum – forms the rest of the small intestines
- The jejunum is in the _________ and the ileum is in the right lower quadrant and right suprapubic region
- Approximate length is 20 feet, with the first ⅖ being the jejunum and the other ⅗ being the ileum – entirely intraperitoneal (have a mesentery on their own)
- Difficult to distinguish the jejunum from the ileum by diameter alone but there are other features, particularly the arterial arcades and the vasa recta
- Morphology of the mesentery of the jejunum and ileum – fan shaped with a long free edge and a short root
o The mucosa in both the jejunum and ileum have circular folds in the inner folds called the ________________
o In the distal part of the jejunum towards the ileum, the folds decrease in number and become far apart
o In the terminal ileum, there are not many folds but there is a large number of lymphoid tissues – Peyer’s patches
- The division between the jejunum and ileum is not clear as the changes are very gradual, but there are very definite differences at the extreme ends of the jejunum and ileum

Answer 14

left upper quadrant; plicae circulares

Question 15

Jejunum vs Ileum

• Proximal 2/5 vs distal 2/5
• wide bored and thick walled visceral structure vs smaller diameter with thinner walls
• ____ arranged plicae circulaires and less plicae circulaires in the inside of the tube
• less prominent arterial arcades vs prominent arterial arcades
• ____ vasa recta vs shorter vasa recta

Answer 15

closely; longer

Question 16

Large intestine – extends from the ileum to the anal canal
- Starts from the cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum before finally ending in the anal canal - Cecum has an appendage – appendix
- From the cecum, the ascending colon originates and runs upwards and to the right of the liver
o It takes a sharp bend (right colic flexure) to continue as the transverse colon, which runs across the abdominal cavity, running near to the spleen and forms the left colic flexure (splenic flexure)

• The muscular wall in the large intestine is modified – long bands of muscle known as the ______, part of the longitudinal muscle in the muscularis externa
  o 3 bands of taenia coli – free (anterior), mesocolic (medial) and ________ (superior) that end up over the cecum, joining at the appendix (important to locate the appendix during surgery)
  o Along the large intestine, there are also large sacculations – haustra, outpushings of the intestinal wall
  o _____________ – fatty tags on the outside of the large intestine (along the colon but not the
  rectum)
• Ileocecal valve – at the junction between the ileum and cecum, allowing passage of food from the ileum to the large intestine
  o A physiological sphincter (not a true anatomical sphincter) but is not effective
• The appendix has its own mesentery and blood vessels (important to identify the ___________ for surgical removal)

Answer 16

taenia coli; omental; Appendices epiploicae; mesoappendix

Question 17

Coeliac trunk (or axis) – supplies the entire foregut (lower oesophagus, stomach and upper duodenum) and its derivatives (liver and part of pancreas).

• The spleen , though not part of the alimentary system (GI tract), shares its blood supply from the coeliac trunk
• There are 3 main branches of the coeliac trunk – ___________________ and __________(which further divides into the gastroduodenal artery and hepatic artery proper)
• The lesser sac of the stomach is supplied by the left and right gastric arteries and the greater curvature is supplied by the right and left gastro-omental artery
• Structures behind the liver and stomach – part of the retroperitoneum
  o These structures include the duodenum, pancreas, right kidney and great vessels
  o All the blood vessels are _______, including the coeliac trunk and superior mesenteric artery

Answer 17

left gastric artery, splenic artery; common hepatic artery ; retroperitoneal

Question 18

Superior mesenteric artery – supplies the small intestines and a major part of the large intestines
- Middle colic artery – supplies the transverse colon
- Right colic artery – supplies the ascending colon
- Ileocolic artery – supplies the cecum and ________, and part of the ileum
- Jejunal artery – supplies the proximal part of the jejunum
- Ileal arteries – supplies the ileum
o These branches usually anastomose extensively with each other

Answer 18

appendix

Question 19

Venous drainage of the gut – different from the arterial supply as most of the venous blood from the gut initially enters the liver before entering the systemic circulation through the inferior vena cava
- Hence, the venous blood channels through the portal vein – enters the liver, carrying all the venous blood from the GI tract
o Posterior to the superior duodenum and________, running in the free edge of the lesser omentum
- The inferior mesenteric vein drains into the _____ and forms a larger channel
o The _____________ joins the splenic vein to form the portal vein which goes into the liver
o Liver processes the nutrients and blood is then collected back into the hepatic vein which then drains into the inferior vena cava

Answer 19

pylorus of stomach; splenic vein; superior mesenteric vein

Question 20

Portal-systemic anastomoses – portal veins anastomose with the adjacent systemic veins to form the portal-systemic anastomoses at 4 areas in the abdominal cavity

• _________ (portal) anastomoses with the oesophageal vein (branch of the azygous vein)
• Superior rectal vein (portal) anastomoses with the inferior rectal vein (branch of __________)
• _____________ (portal) anastomoses with epigastric veins (systemic)
• Colic veins (portal) anastomoses with ______________ (systemic)
• Liver or portal obstruction (increased portal venous pressure) causes these veins to dilate widely, leading to severe venous haemorrhage from the oesophagus or rectum if ruptured

Answer 20

Left gastric vein; inferior pudendal veins; paraumbilical vein; posterior abdominal wall veins

Question 21

Lymphatic drainage of the gut – follows the arterial supply
- Lymph nodes are grouped around the abdominal aorta
- Distal part of the large intestine and rectum drains through the lymphatic channels, travelling along the inferior mesenteric vein into __________________
- Small intestines and part of large intestine drain into ______________________
- At the opening of the coeliac trunk – coeliac nodes
- All the lymph nodes are connected to each other and the lymph channels drain the lymph upwards towards the cisterna chyli – elongated lymphatic sac located in front of the L1 and L2 vertebral bodies
o From the cisterna chyli, the thoracic duct arises, travelling through the diaphragm to enter the thoracic cavity to drain into the ___________

Answer 21

inferior mesenteric lymph nodes; superior mesenteric lymph nodes; subclavian veins

Question 22

Innervation of the gut – the abdominal viscera are supplied by autonomic nervous system (both parasympathetic and sympathetic), with sensory fibres more important than pain sensations

Parasympathetic

• regulate the reflex gut function (peristalsis)
• main nerve fibres from the vagus nerve (CN X) and ___________

Sympathetic

• Mediate pain
• Main nerve fibres from the thoracic splanchnic nerves (T5-T12) and _____________ in the sympathetic chain

Answer 22

pelvic splanchnic nerve (S2-4); lumbar splanchnic nerves (L1-L2)

Question 23

Innervation of the gut – the abdominal viscera are supplied by autonomic nervous system (both parasympathetic and sympathetic), with sensory fibres more important than pain sensations

Parasympathetic

• regulate the reflex gut function (peristalsis)
• main nerve fibres from the vagus nerve (CN X) and ___________

Sympathetic

• Mediate pain
• Main nerve fibres from the thoracic splanchnic nerves (T5-T12) and _____________ in the sympathetic chain

Splanchnic nerves – autonomic nerves are routed via plexuses (network of nerves) along the abdominal aorta and its branches, before the nerve fibres reach the respective viscera
o Thoracic splanchnic nerves (sympathetic) – greater (T5 to T9), less (T10 to T11) and least splanchnic nerve (T12)
o Lumbar splanchnic nerves (sympathetic) – L1 and L2
o Pelvic splanchnic nerves (mixed parasympathetic and sympathetic) – S2 and S4
§ Parasympathetic fibres directly go to visceral organs in the pelvis

• Autonomic control – sensory nerve fibres are most important in the innervation of the gut, running with the sympathetic (T1 to L2) fibres and mediate pain
  o Any pathology in the gut will be perceived through
  the sensory fibres travelling in the sympathetic
  pathway
  o Sensory fibres running with the parasympathetic system (sacral or vagal) are involved in the reflex
  regulation of the gut function

Answer 23

pelvic splanchnic nerve (S2-4); lumbar splanchnic nerves (L1-L2)