12. Alimentary Tract (Part 2)

Question 1

Summarise the 9 regions of the abdomen and the lines they are formed by.

Answer 1

• Transpyloric plane -> Horizontal line located midway between the suprasternal notch and the upper border of the pubic symphysis, approximately at the level of the lower border of the L1 vertebral body.
• Transtubercular plane -> Horizontal line located midway between the transpyloric plane and the upper border of the pubic symphysis, corresponding to the level of the iliac tubercles and the L5 vertebral body.
• Mid-clavicular lines

Question 2

Draw the 4 quadrants of the abdomen.

Answer 2

These quadrants are created by a vertical line along the mid-line, passing from the xiphoid process to the pubic symphysis, and a horizontal line passing through the umbilicus.

Question 3

Summarise what pain in each of the four quadrants of the abdomen may indicate.

Answer 3

Question 4

What is the peritoneal cavity?

Answer 4

• A potential space found between the parietal and visceral layers of the peritoneum.
• The smooth layers of the peritoneum permit free movement between the abdominal viscera and abdominal walls.
• Think of the peritoneum as the abdominal/pelvic equivalent of the pleura of the lungs or the pericardium of the heart

Question 5

What are the two types of peritoneum?

Answer 5

• Parietal peritoneum -> Lines the internal surface of the abdominopelvic wall and underside of the diaphragm.
• Visceral peritoneum -> Covers the outer surface of many organs and suspends them from the abdominopelvic wall.

Question 6

What is mesentery?

Answer 6

• A double layer of visceral peritoneum that suspends intra-peritoneal organs from the posterior abdominal wall.
• Blood vessels and nerves run within the mesentery to supply the intra-peritoneal organs.

Question 7

Summarise the innervation to the parietal and visceral peritoneum.

Answer 7

Innervation of the parietal and visceral peritoneum follows the same pattern as the pleura:

• Parietal peritoneum -> Innervated by the somatic segmental nerves innervating the skin of the abdominal wall, so sensation, including pain, pressure and temperature, is well localised.
• Visceral peritoneum -> Shares the same autonomic innervation as the viscera it surrounds. Sensitive to stretch and chemical irritation only, which is poorly localised.

Question 8

What is the transverse mesocolon?

Answer 8

The mesentery that suspends the transverse colon from the posterior abdominal wall.

Question 9

What is the sigmoid mesocolon?

Answer 9

• The mesentery that suspends the sigmoid colon from the posterior abdominal wall.
• Located within the left iliac fossa.

Question 10

What is the meso-appendix?

Answer 10

A tiny piece of mesentery attaching the appendix to the posterior abdominal wall.

Question 11

What is the retroperitoneum?

Answer 11

The organs that sit behind the parietal peritoneum and are therefore not entirely encased by peritoneum are described as retroperitoneal.

Question 12

What are primary and secondarily retroperitoneal organs?

Answer 12

• Primary retroperitoneal organs are those that developed and subsequently remained within the retroperitoneum.
• Secondarily retroperitoneal organs are those that developed initially within the intra-peritoneal compartment before retracting back to the posterior abdominal wall and the retroperitoneum before birth.

Question 13

What are the retroperitoneal organs?

Answer 13

The mnemonic “SADPUCKER” can be used:

• S = Suprarenal (adrenal) glands
• P = Pancreas (except tail)
• K = Kidneys
• A = Aorta/IVC
• U = Ureters
• E = (o)Esophagus
• D = Duodenum (2nd and 3rd parts)
• C = Colon (ascending & descending)
• R = Rectum

Question 14

What are the secondarily retroperitoneal organs?

Answer 14

Ascending and descending colon

Question 15

What is the greater and lesser sac of the peritoneal cavity?

Answer 15

The peritoneal cavity can be divided into the greater and lesser peritoneal sacs:

• The greater sac comprises the majority of the peritoneal cavity.
• The lesser sac (also known as the omental bursa) is smaller and lies posterior to the stomach and lesser omentum.

Question 16

Draw the position of the greater and lesser sacs of the peritoneal cavity in the axial section?

Answer 16

Question 17

Describe the position of the lesser sac and how it connects to the greater sac.

Answer 17

• Located behind the stomach
• Opens into the greater sac via the epiploic foramen (foramen of Winslow)

Question 18

Answer 18

Question 19

What are the two main compartments of the greater sac of the peritoneal cavity?

Answer 19

• Supracolic compartment -> Located superior to the transverse mesocolon and contains the stomach, spleen and liver.
• Infracolic compartment -> Located inferior to the transverse mesocolon and contains the small bowel loops, ascending and descending colon.

Question 20

What is the epiploic foramen?

Answer 20

The foramen connecting the greater and lesser sacs of the peritoneal cavity. It is found posterior to the stomach.

Question 21

Answer 21

Question 22

What are the pieces of mesentery in the peritoneal cavity you need to know?

Answer 22

• Small bowel mesentery
• Meso-appendix
• Transverse mesocolon
• Sigmoid mesocolon

Question 23

What are the peritoneal pouches?

Answer 23

The reflection of the parietal peritoneum onto the superior surfaces of the pelvic organs (bladder, uterus), creates pouches either side of these organs in which fluid can collect.

In males:

• Recto-vesical pouch -> Between the posterior surface of the bladder and the anterior surface of the inferior of rectum.

In females:

• Vesicouterine pouch -> Between the posterior surface of the bladder and the anterior surface of the uterus, descending adjacent to the anterior fornix of the vagina.
• Rectouterine pouch -> Between the posterior surface of the uterus and the anterior surface of the rectum.

Question 24

Describe gas under the diaphragm.

Answer 24

• Gas contained within the peritoneal cavity is called pneumoperitoneum.
• This is often caused by serious problems within the abdomen, including perforated bowel (due to conditions such as peptic ulcer disease, bowel obstruction, ischaemia, diverticulitis).
• It may also be caused by gas injected into the abdomen during operations.
• The gas is clearly seen on erect chest X-rays, where it collects under the domes of the diaphragm. Here, the gas collects between the parietal peritoneum of the abdominal wall and the visceral peritoneum covering the surface of the liver

Question 25

What is the greater omentum? What are the important relations?

Answer 25

• A large, fatty fold of peritoneum that hangs from the greater curvature of the stomach to cover the anterior abdominal viscera like an apron.
• The greater omentum inserts into the transverse colon at its distal end.
• The greater omentum functions to isolate regions of infection and inflammation within the abdomen by wrapping around and sticking to affected areas.

Question 26

What is the lesser omentum? What are the important relations?

Answer 26

• A smaller fold of peritoneum that runs from the lesser curvature of the stomach to the inferior edge of the liver.
• The free edge of the lesser omentum contains the portal triad of vessels: proper hepatic artery, common bile duct and the hepatic portal vein.
• Also forms the anterior border of the epiploic foramen.

Question 27

What vessels does the lesser omentum contain?

Answer 27

The portal triad of vessels:

• Proper hepatic artery
• Common bile duct
• Hepatic portal vein

Question 28

Describe the passage of the oesophagus.

Answer 28

• In the neck, the oesophagus follows the curve of the vertebral column, between the trachea and the vertebral bodies.
• Passes within the posterior mediastinum (behind the heart), anterior to the descending aorta, to the diaphragm.
• Enters the abdomen through the oesophageal hiatus of the right crus of the diaphragm just to the left of the mid-line, at the level of T10.
• It then has a short course in the abdomen to the gastro-oesophageal sphincter

Question 29

Where does the oesophagus pass through the diaphragm?

Answer 29

• Right crus of the diaphragm just to the left of the mid-line.
• At the level of T10.

Question 30

What types of muscle make up the oesophagus?

Answer 30

• Upper 1/3rd -> Voluntary striated muscle
• Middle 1/3rd -> Mix of striated and smooth muscle
• Lower 1/3rd -> Smooth muscle

Question 31

What are the three constriction points in the oesophagus?

Answer 31

1. Upper oesophageal sphincter – a constriction at the oesophageal origin, formed by the cricopharyngeus muscle.
2. Thoracic constrictions – two constrictions caused by the crossing of the aortic arch and the left main bronchus across the anterior surface of the oesophagus.
3. Lower oesophageal sphincter (diaphragmatic constriction) – after a short 1.25cm abdominal course, the oesophagus terminates at the cardial orifice of the stomach. The musculature of the diaphragm and acute angle of the oesophagus immediately above this gastro-oesophageal junction creates a physiological sphincter that can prevent reflux of gastric contents into the oesophagus.

Question 32

Answer 32

Question 33

Describe the arterial supply to the oesophagus.

Answer 33

• Thoracic part -> Oesophageal arteries, arising from the thoracic aorta
• Abdominal part -> Left gastric and left inferior phrenic artery

Question 34

Describe the venous drainage of the oesophagus.

Answer 34

The inferior part of the oesophagus is drained by two venous systems:

• Portal circulation -> Via the left gastric vein to the hepatic portal vein.
• Systemic circulation -> Via the azygos vein to the superior vena cava.

These two connected venous systems create a porto-systemic anastomosis, which can become problematic in cases of portal hypertension.

Question 35

The lower oesophageal veins connect the … and … veins.

Answer 35

Azygos and gastric

(This is a portal-systemic anastomosis that can become problematic in cases of portal hypertension)

Question 36

Describe oesophageal varices.

Answer 36

• The presence of the porto-systemic anastomosis at the base of the oesophagus creates an intrinsic link between the pressures of the portal and systemic venous systems.
• In cases of portal hypertension, caused as a result of hepatic portal vein thrombosis and liver cirrhosis, the raised portal pressure is transferred into the systemic venous system, which cannot accommodate such increases in pressure.
• This causes the anastomotic venous system to distend and thin (oesophageal varices).
• These varices are prone to rupture, which can result in significant blood loss into the GI tract.
• Following rupture, the aim is to stop the bleeding through either endoscopic banding or injection of sclerotherapy to trigger venoconstriction.
• Once stabilised, the portal hypertension can be treated with the insertion of a transjugular intrahepatic porto-systemic shunt, relieving the pressure within the portal vein.

Question 37

What are the different parts of the stomach?

Answer 37

• Fundus
• Body
• Pyloric region -> Antrum, Canal, Sphincter

Question 38

Where is the transpyloric plane?

Answer 38

• Halfway between the jugular notch and the superior border of the pubic symphysis.
• This is approximately at the level of the L1 vertebral body.

Question 39

What structures are found in the transpyloric plane?

Answer 39

• Pylorus
• Root of transverse mesocolon
• Duodenum (D1)
• Gallbladder fundus
• Duodeno-jejunal flexure
• Hila of kidneys
• Hepatic and splenic flexures of colon
• 9th costal cartilage
• Neck of pancreas
• Origin of the SMA
• Termination of the spinal cord

Question 40

Describe the innervation of the stomach.

Answer 40

• The stomach’s embryonic origin as a foregut structure means it is supplied by branches of the coeliac trunk and innervated by the coeliac plexus of nerves.
• Parasympathetic innervation to the stomach is supplied by the anterior and posterior vagal trunks of the vagus nerve.
• The sympathetic supply is supplied by the coeliac plexus, which receives input from T6-T9 nerve roots via the greater splanchnic nerve.

Question 41

Describe the arterial supply to the stomach.

Answer 41

• Right gastric artery -> From the common hepatic artery.
• Left gastric artery -> From the coeliac trunk.
• Right gastro-omental artery -> From the gastroduodenal artery, itself a branch of the common hepatic artery.
• Left gastro-omental artery -> The largest branch of the splenic artery.
• Short gastric arteries -> Small branches of the splenic artery.

Question 42

Describe the venous drainage of the stomach.

Answer 42

Via veins running in parallel with the arteries, which ultimately converge on the hepatic portal vein.

Question 43

At what level is the cardia of the stomach typically found?

Answer 43

T11

Question 44

What are the relations of the greater and lesser omentum to the stomach?

Answer 44

• Greater omentum:
  
  • Connects the greater curvature of the stomach with the transverse colon
• Lesser omentum:
  
  • Connects the lesser curvature of the stomach to the porta hepatus and ductus venosus of the liver
  • The free edge of the lesser omentum contains within it the common bile duct, hepatic artery and hepatic portal vein, forming the portal triad.

Question 45

What is a hiatus hernia?

Answer 45

• Hiatus hernias occur when the viscera of the abdomen pushes into the thoracic cavity through the oesophageal hiatus of the diaphragm.
• This most commonly occurs in older patients, due to progressive weakening of the hiatus.
• Hernias may also result from congenital abnormalities of the diaphragm.
• Hiatus hernias are usually asymptomatic, but can cause chest pain, bloating and difficulty swallowing.
• Treatment is usually focused on relieving symptoms, but in severe cases, the defect may be surgically repaired.

Question 46

What is pyloric stenosis?

Answer 46

• A relatively common condition seen in neonates where the circular muscle surrounding the outflow tract of the stomach (pyloric sphincter) becomes thickened.
• This results in obstruction of the outflow tract and forceful contractions of the stomach, which attempts to force ingested food through the stenosed orifice.
• Classically, newborns experience non-bloody projectile vomiting after most feeds, leading to poor weight gain, lethargy and malnutrition.
• Pyloric stenosis can be surgically treated with a Ramstedt’s procedure, in which the muscle is divided to open the outlet.

Question 47

What are the different parts of the duodenum?

Answer 47

• D1 (superior part): 5cm proximal part, arising from the pylorus of the stomach, passing laterally to the right, before curving sharply inferiorly.
• D2 (descending part): passes from D1 to the inferior border of the L3 vertebral body, before turning sharply medially. The major duodenum papilla, into which the contents of the ampulla of Vater drains through (bile and pancreatic enzymes, via the common bile duct and pancreatic duct), is found in the wall of D2. The major duodenal papilla is surrounded by a muscular sphincter of Oddi, which controls the entry of these fluids into the duodenum.
• D3 (horizontal part): passes transversely to the left, crossing the mid-line.
• D4 (ascending part): passes superiorly until reaching the inferior edge of the pancreas. At this point, it curves and then terminates at the duodeno-jejunal flexure. This flexure is surrounded by a peritoneal fold called the ligament of Treitz.

Question 48

Which side of the abdomen does the duodenum curve out to?

Answer 48

Right side

Question 49

Between what vertebral levels is the duodenum?

Answer 49

L1 and L3

Question 50

What demarcates the boundary between the foregut and the midgut?

Answer 50

The entry of the biliary and pancreatic ducts into the duodenum.

Question 51

Where in the duodenum do the biliary and pancreatic ducts enter?

Answer 51

2nd (descending) part

Question 52

What demarcates the point where the dudodenum becomes the jejunum?

Answer 52

• The ligament of Treitz (which joins the duodenum to the diaphragm).
• This is at the duodeno-jejunal flexure.

Question 53

Describe the blood supply to the duodenum.

Answer 53

• First part -> Coeliac artery
• Second part -> Superior mesenteric artery

Question 54

Draw the relations of the duodenum.

Answer 54

Question 55

What is the sphincter of Oddi?

Answer 55

The smooth muscle that surrounds the end portion of the common bile duct and pancreatic duct. This muscle relaxes during a meal to allow bile and pancreatic juice to flow into the intestine.

Question 56

What is the duodenal papilla?

Answer 56

• The point where the junction of the pancreatic duct and the bile duct enter the duodenum.
• Marks the transition between foregut and midgut regions of the GI tract.

Question 57

Describe duodenal ulcers.

Answer 57

• Peptic ulcers are erosions of the mucosa of the GI tract, typically found within the stomach (gastric ulcers) or proximal duodenum (duodenal ulcers).
• The vast majority of ulcers are caused by extended NSAID use (e.g. ibuprofen) or Helicobacter pylori infection.
• Duodenal ulcers typically cause consistent burning epigastric pain, which is relieved by eating food.
• Perforation of duodenal ulcers may cause catastrophic bleeding into the GI tract, due to erosion into the gastroduodenal artery which is close by.
• To reduce the risk of progression of duodenal ulcers, patients are prescribed acid suppression medication, antibiotics for H. pylori infection and NSAIDs stopped.

Question 58

What organs is the pancreas closely related to and why is this important?

Answer 58

• The communication between the pancreas, gallbladder and duodenum is clinically important.
• One of the most common causes of pancreatitis is the presence of gallstones within the distal biliary tree, just proximal to the duodenal papilla, blocking the common outflow.
• This results in a backlog of pancreatic juice into the parenchyma of the pancreas, causing auto-digestion, pancreatitis and ultimately tissue necrosis.
• Similarly, a procedure known as ERCP, used to remove gallstones impacted within the common bile duct via the duodenal papilla, can cause pancreatitis by releasing fragments of gallstones into the pancreatic ducts, which can trigger irritation and inflammation.

Question 59

What are the parts of the small intestine apart from the duodenum?

Answer 59

• Jejunum
• Ileum

Question 60

Compare the jejunum and ileum.

Answer 60

• Jejunum:
  
  • Located in the left upper quadrant of the abdomen.
  • Typically red in colour (darker than ileum).
  • 2-4cm in diameter.
  • Thick walled.
  • Highly vascularised in comparison to ileum.
• Ileum:
  
  • Located in the lower right quadrant of the abdomen.
  • Typically pink in colour (lighter than jejunum).
  • 2-3cm in diameter.
  • Thin walled.

Question 61

Compare the structure and length of the jejunum and ileum?

Answer 61

• Jejunum
  
  • 2.5m
  • Numerous mucosal folds
  • Few Peyer’s patches (gut associated lymphoid tissue)
• Ileum
  
  • 3.5m
  • Smaller, less mucosal folds
  • Large number of Peyer’s patches

Question 62

What are taenia coli, haustra and epiploic appendices?

Answer 62

• Taenia coli -> Longitudinal strips of smooth muscle on the outer surface of the large intestine. The taenia coli allow segments of the colon to contract independently.
• Haustra -> The small pouches caused by sacculation, which give the colon its segmented appearance.
• Epiploic appendices -> Peritoneum-lined protrusions of subserosal fat that arise from the surface of the large bowel.

Question 63

Describe where the small bowel mesentry attaches.

Answer 63

Root of the mesentery:

• 15 cm.
• Lies obliquely across the posterior abdominal wall.
• Forms a line from the left of the vertebra L2 to the right sacroiliac joint.

Question 64

What are the main parts of the large intestine?

Answer 64

• Caecum
• Appendiz
• Ascending colon
• Transverse colon
• Descending colon
• Sigmoid colon
• Rectum

Question 65

Label this large intestine.

Answer 65

Question 66

Describe the appearance of longitudinal muscle in the large intestine.

Answer 66

It is condensed into thin stripes called taeniae coli.

Question 67

What are the puffy parts of the large intestine called?

Answer 67

Haustra

Question 68

On which side of the body is the ascending colon?

Answer 68

Right

Question 69

What prevents reflux from the caecum to the ileum?

Answer 69

Ileocaecal valve

Question 70

Describe the position of the appendix of the large intestine.

Answer 70

It is at the start of the caecum, although the direction it points in is variable.

Question 71

What is appendicitis and what are the symptoms? [IMPORTANT]

Answer 71

• It is inflammation of the appendix of the large intestine, usually due to infection
• Symptoms:
  
  • Initial pain around the bellybutton due to the appendix being innervated by the T10 nerve root
  • Pain later at McBurney’s point

Question 72

What are the main flexures of the large intestine that you need to know?

Answer 72

• Hepatic flexure
• Splenic flexure

Question 73

Which parts of the large intestine are retroperitoneal and which are intraperitoneal?

Answer 73

• Caecum -> Intraperitoneal
• Ascending colon -> Secondary retroperitoneal
• Transverse colon -> Intraperitoneal
• Descending colon -> Secondary retroperitoneal
• Sigmoid colon -> Intraperitoneal
• Rectum -> Superior 2/3rd retroperitoneal

Question 74

What are the folds in the rectum called? Describe them.

Answer 74

They are called the ‘valves of Houston’:

• 2 are on the left
• 1 is on the right

Question 75

At what vertebral level does the rectum begin?

Answer 75

S3

Question 76

Where is the anorectal junction?

Answer 76

It is at the point when the rectum pierces the pelvic floor muscles.

Question 77

What is the rectal ampulla?

Answer 77

A dilated portion of the rectum.

Question 78

Describe colon cancer.

Answer 78

• Colorectal cancer accounts for 15% of cancer related deaths in the Western World.
• More than 50% of cases occur within the rectum and sigmoid colon, usually after transformation of a benign polyp.
• Depending on where the tumour occurs, patients may experience a change in bowel habits, bleeding and abdominal pain from obstruction.
• Treatment options include surgical excision and chemotherapy

Question 79

Compare the small and large intestine.

Answer 79

Question 80

Answer 80

Question 81

Describe a digital rectal examination.

Answer 81

• A DRE is a commonly performed examination in the hospital, used to screen for a variety of lower GI pathologies.
• When performing the examination, doctors assess the size and shape of the prostate in men, palpate for masses within the anal canal and assess anal sphincter tone.

Question 82

What is the anal canal?

Answer 82

The anal canal connects the rectum to the anus, passing downwards and posteriorly.

Question 83

What is the pubo-rectal sling?

Answer 83

The puborectal sling (part of the levator ani muscle group) surrounding the recto-anal junction kinks the anal canal forward, which functions as a sphincter.

Question 84

Compare the muscles and innervation of the two anal sphincters.

Answer 84

Internal anal sphincter:

• Smooth muscle
• Autonomic control

External anal sphincter:

• Striated muscle
• Pudendal nerve (s2-S4) control

Question 85

What are the anal cushions?

Answer 85

Submucosal tissue which assists the continence mechanism.

Question 86

What are anal columns?

Answer 86

6 to 10 longitudinal mucosal folds in the anal canal.

Question 87

What are anal valves?

Answer 87

Small valve-like folds at the lower ends of the anal sinuses in the rectum. They join the anal columns.

Question 88

What is the pectinate line?

Answer 88

Indicates the junction of the superior part of the anal canal (visceral: derived from the embryonic hindgut), and the inferior part (somatic: derived from the embryonic proctodeum).

Question 89

What is the perineal body?

Answer 89

• A fibro-muscular structure located in the midline of the perineum.
• Its exact location is the midline of the perineum at the junction of the anus and urogenital triangle in both females and males

Question 90

What is the ischiorectal fossa?

Answer 90

The fat-filled wedge-shaped space located lateral to the anal canal.

Question 91

Where is the boundary between the midgut and hindgut?

Answer 91

2/3rd of the way along the transverse colon

Question 92

What are the three major arteries supplying the GI tract?

Answer 92

• Coeliac
• Superior mesenteric
• Inferior mesenteric

Question 93

What organs does the coeliac artery supply?

Answer 93

Foregut derivatives:

• Liver
• Stomach
• Proximal duodenum
• Abdominal oesophagus
• Spleen
• Pancreas

Question 94

What are the branches of the coeliac artery you need to know? Summarise what they supply.

Answer 94

• Common hepatic -> Liver, duodenum, and pancreas.
• Left and right gastric (right from common hepatic) -> Lesser curvature of stomach
• Left and right gastroepiploic arteries (left from splenic, right from common hepatic) -> Greater curvature of stomach

Also worth knowing the splenic artery, since it gives rise to the short gastric arteries and left gastroepiploic artery.

Question 95

What organs does the superior mesenteric artery supply?

Answer 95

Midgut derivatives:

• Distal duodenum
• Small intestine
• Ascending and transverse colon (proximal 2/3rds)
• Head of pancreas
• Caecum and appendix

Question 96

What are the branches of the superior mesenteric artery you need to know? Summarise what they supply.

Answer 96

• Jejunal & ileal arcades -> Anastamoses supplying the ileum and jejunum
• Ileocolic artery -> Distal ileum, ceacum, appendix and proximal ascending colon.
• Appendicular artery -> Appendix
• Right colic -> Ascending colon
• Middle colic -> Transverse colon

Question 97

What organs does the inferior mesenteric artery supply?

Answer 97

Hindgut derivatives:

• Descending colon
• Rectum
• Sigmoid colon
• Distal 1/3rd transverse colon

Question 98

What are the branches of the inferior mesenteric artery you need to know? Summarise what they supply.

Answer 98

• Left colic artery -> Descending colon
• Sigmoid artery -> Lower part of the descending colon, the iliac colon, and the sigmoid colon
• Superior rectal artery -> Rectum (all mucosa)

Question 99

Describe the blood supply to the rectum and anal canal.

Answer 99

• Superior rectal artery (from inferior mesenteric) -> Supplies whole of the rectal mucosa and upper part of the anal canal, up to the dentate line
• Middle rectal artery (from internal iliac) -> Supplies the muscle layers of the rectum
• Inferior rectal artery (from internal pudendal) -> Supplies inferior parts of the rectum and anal canal

Question 100

What is important to remember about the superior rectal artery?

Answer 100

• It arises from the inferior mesenteric artery.
• It supplies all the rectal mucosa.

Question 101

What is important to remember about the superior rectal artery?

Answer 101

• It arises from the internal iliac artery.
• It supplies the muscle wall of the rectum.

Question 102

What is important to remember about the inferior rectal artery?

Answer 102

• It arises from the pudendal artery
• It supplies the anal canal

Question 103

Describe the anastamoses of the alimentary tract arteries.

Answer 103

• Anastomoses of the terminal branches of the superior mesenteric artery and inferior mesenteric artery form a continuous arterial arcade along the inner border of the large intestine, known as the marginal artery (of Drummond).
• Straight vessels, known as the vasa recta, pass from this artery to the colon itself within the mesentery.
• This anastomosis is critical to allow continued perfusion of territories supplied by the SMA or IMA should one of the arteries become occluded.

Question 104

Describe the venous drainage of the GI tract.

Answer 104

• Venous drainage of the GI tract first passes through the portal venous system before reaching the systemic circulation, in order for products of digestion to be processed within the liver.
• In general, blood from foregut structures drain to the hepatic portal vein through the splenic vein.
• Midgut derivatives are drained by the superior mesenteric vein, which joins the splenic vein behind the neck of the pancreas to form the hepatic portal vein.
• Hindgut structures drain via the inferior mesenteric vein, which usually joins the splenic vein before the formation of the hepatic portal vein.

Question 105

Describe the venous drainage of the rectum.

Answer 105

• Superior rectal vein -> Drains into the hepatic portal system
• Middle and inferior rectal veins -> Drain directly to the systemic circulation.

Anastomoses, known as the rectal venous plexus, form between the systemic and portal systems around the rectum.

Question 106

Name the main sites of portal-systemic anastomosis in the GI tract.

Answer 106

• Rectum
• Oesophagus
• Paraumbilical region
• Retroperitoneum

Question 107

Summarise the lymphatic drainage of the GI tract.

Answer 107

Drains to the pre-aortic lymph nodes (note that this is not para aortic like for the ovaries, etc.):

• Foregut derivatives -> Drained by the coeliac nodes
• Midgut derivatives -> Drained by the superior mesenteric nodes
• Hindgut derivatives -> Drained by the inferior mesenteric nodes

Question 108

Describe haemorrhoids.

Answer 108

• Haemorrhoids are highly vascular submucosal cushions which may swell, become itchy and bleed in response to hard stools and raised luminal pressures.
• The term “haemorrhoids” may be used to describe both normal, physiological anal cushions and pathological, engorged structures.
• External haemorrhoids are found below the dentate line, whilst internal haemorrhoids lie above the dentate line.
• Depending on the degree of bleeding and protrusion of the haemorrhoids, they may be surgically removed or endoscopically banded to reduce the risk of further bleeding.

Question 109

Where may colorectal (bowel) cancer spread to?

Answer 109

• First to the liver
• Prior to distal spread, metastatic disease is often found in the local lymph nodes surrounding the bowel.
• Other common sites of metastasis include peritoneum and vertebrae.

Question 110

Summarise the parasympathetic, sympathetic and somatic innervation of the GI tract, including ganglia.

Answer 110

Parasympathetic:

• Vagus nerve -> To foregut and midgut
• Pelvic splanchnic nerves -> To hindgut

Sympathetic:

• Coeliac ganglia (thoracic splanchnic sympathetic nerves) -> To foregut
• Superior mesenteric ganglia (thoracic splanchnic sympathetic nerves) -> To midgut
• Inferior mesenteric ganglia (pelvic sympathetic nerves) -> To hindgut

Somatic:

• Pudendal nerve -> To anal canal and external anal sphincter

Question 111

Where are the parasympathetic ganglia of the GI tract found?

Answer 111

Within the walls of the GI tract, close to their terminal organs.

Question 112

Describe the enteric nervous system.

Answer 112

• Myenteric plexus
  
  • Located between the inner circular and outer longitudinal muscle layers of the GI tract
  • Responsible for peristalsis
• Submucous plexus
  
  • Located within the submucosa
  • Responsible for glandular secretion and electrolyte transport across the mucosa

Question 113

When does pain from the GI tract become more localised?

Answer 113

• Visceral afferent fibres travel with the autonomic fibres to diffusely terminate within the spinal cord.
• As such, sensation within the GI tract is poorly localised until the parietal peritoneum becomes involved.
• When the parietal peritoneum becomes involved, due to its innervation by the somatic nervous system, sensation becomes well-localised.

Question 114

Describe the general distribution of referred pain from the GI tract.

Answer 114

In general, visceral sensory information is referred to the epigastric region for foregut structures, the umbilical region for midgut structures and the hypogastric region for hindgut structures.

Question 115

Describe the afferent and efferent components of the vomiting reflex.

Answer 115

Afferent:

• Fear
• Pain
• Gastric irritation

Efferent (sympathetic, lower intercostal, phrenic and vagus nerves):

• Deep breath taken to avoid aspiration of vomit
• Increased salivation to reduce damage to teeth caused by stomach acid (parasympathetic innervation)
• Glottis closed, soft palate elevated and larynx raised, opening the upper oesophageal sphincter and closing off the nasopharynx.
• Sharp contraction of the diaphragm inferiorly to create negative pressure within thorax, causing the oesophagus and lower oesophageal sphincter to open.
• Abdominal wall muscle contraction to raise intra-abdominal pressure and expel stomach contents into the oesophagus and ultimately into the external environment.

Question 116

Summarise the named nerves involved in the defecation reflex you need to know.

Answer 116

• Afferent: Pelvic plexus, Spinal cord centre
• Efferent: Sympathetic, Pudendal

Question 117

Describe the afferent and efferent components of the defecation reflex.

Answer 117

This reflex is triggered on mass movement of faeces towards the rectum, initiated by high intensity contractions of the colon.

Afferent:

• Pelvic splanchnic nerves from rectum (S2-S4) -> Detects sufficient distension of the rectum

Efferent:

• Contraction of the sigmoid colon and rectum
• Relaxation of the internal anal sphincter (triggered by parasympathetic fibres of pelvic splanchnic nerves)
• Contraction of the external anal sphincter (triggered by inferior rectal nerve, branch of the pudendal nerve)

This combination of events triggers an urge to defaecate, which is permitted on voluntary relaxation of the external anal sphincter. Expulsion is aided by the Valsalva manoeuvre, which raises the intra-abdominal pressure.

Question 118

Summarise the named nerves involved in the vomiting reflex you need to know.

Answer 118

• Afferent: None named
• Efferent: Sympathetic, lower intercostal, phrenic, vagus

Question 119

Draw the surface anatomy of the liver, gall bladder, pancreas and liver.

Answer 119

Question 120

At what height is the liver found?

Answer 120

The right lobe of the liver is found deep to the 7-11th ribs, whilst the left lobe occupies the epigastric and left hypochondriac regions.

Question 121

Describe the lobes of the liver.

Answer 121

Anteriorly you can see only 2 lobes:

• Right lobe
• Left lobe

Inferiorly, you can see 2 more lobes:

• Caudate (more posterior)
• Quadrate (more anterior)

Question 122

Draw an anterior view of the liver.

Answer 122

Question 123

Draw an inferior view of the liver.

Answer 123

Note: The anterior side is at the bottom of this diagram.

Question 124

Which side of the liver is flatter?

Answer 124

Posterior

Question 125

What is the porta hepatis and what is found there?

Answer 125

• A deep fissure seen at the inferior side of the liver
• The portal triad (hepatic artery proper, hepatic portal vein and common hepatic duct) enter and leave the liver parenchyma here

Question 126

What separates the right and left lobes of the liver?

Answer 126

Falciform ligament

Question 127

What separates the lobes of the liver on the inferior side?

Answer 127

Porta hepatis -> It is sort of in the middle of all of the lobes.

Question 128

What vessels run through the porta hepatis?

Answer 128

• Hepatic portal vein
• Hepatic artery
• Common hepatic duct

Question 129

Describe the hepatic vasculature.

Answer 129

Blood supply:

• Hepatic artery and hepatic portal vein enter via the porta hepatis in the inferior liver
• They bifurcate into left and right branches and supply the liver (75% from hepatic portal vein, 25% from hepatic artery)

Blood drainage:

• Hepatic veins drain the liver and drain into the IVC at the superior end of the liver

Question 130

Describe the functional segments of the liver.

Answer 130

• It can be divided into functional left and right lobes by drawing a line through the midline of the gallbladder and the inferior vena cava.
• This division results in the caudate and quadrate lobes being a part of the functional left lobe.
• The functional right lobe of the liver processes blood coming from the head of the pancreas, the pylorus and antrum of the stomach, and the midgut via the superior mesenteric vein.

Question 131

Describe the position of the gall bladder.

Answer 131

• It is within the gall bladder fossa, on the inferior surface of the liver between the quadrate and right lobes.
• The fundus of the gall bladder is found posterior to the anterior end of the right 9th costal cartilage.

Question 132

What is the function of the gall bladder?

Answer 132

To store and ultra-concentrate bile prior to its release during meals.

Question 133

Describe liver cirrhosis.

Answer 133

Cirrhosis is the end-stage of liver fibrosis, which results in disorganised parenchymal architecture and impairment of liver function. Cirrhosis may be caused by chronic alcoholism or chronic hepatitis B/C infection. Biliary injury such as bile duct obstruction, primary biliary cirrhosis and primary sclerosing cholangitis may also result in liver cirrhosis. Symptoms are typically non-specific, and may include weight loss, fatigue and anorexia. With declining liver function, patients may become jaundiced and have ascites. Cirrhosis is considered irreversible and requires liver transplantation for a cure.

Question 134

What can portal hypertension be caused by and what can it lead to?

Answer 134

• Portal hypertension is the most common, serious complication of liver cirrhosis
• It may cause GI bleeding through oesophageal/rectal varices at the sites of porto-systemic anastomoses, ascites, pulmonary hy- pertension and kidney injury.
• Portal hypertension may cause the re-canalisation of the obliterated paraum- bilical veins within the ligamentum teres and abdominal wall, resulting in the appearance of caput medusae around the umbilicus.

Question 135

What are the ligaments of the liver essentially?

Answer 135

They are peritoneal attachments.

Question 136

Name the peritoneal attachments of the liver you need to know.

Answer 136

• Falciform ligament -> Remnant of the ventral mesentery of the foetus. Attaches the anterior surface of the liver to the anterior abdominal wall, dividing the liver into the left and right lobes. Its free edge contains the ligamentum teres (round ligament), a remnant of the umbilical vein.
• Triangular ligaments:
  
  • Left triangular ligament -> Attaches the posterior part of the superior surface of the left lobe of the liver to the diaphragm.
  • Right triangular ligament -> Passes from the posterior part of the bare area on the right side to the diaphragm.
• Coronary ligament -> Attaches the superior surface of the liver to the inferior surface of the diaphragm.
• Lesser omentum -> Passes from the lesser curvature of the stomach to the inferior surface of the liver. The portal triad is found within the free edge of the lesser omentum.

Question 137

What is the ligamentum teres and where is it found?

Answer 137

• It is a remnant of the umbilical vein.
• It is found at the free edge of the falciform ligament.

Question 138

Within what structure does the portal triad pass?

Answer 138

Lesser omentum

Question 139

What is the clinical relevance of the ligamentum teres?

Answer 139

• The ligamentum teres is a remnant of the umbilical vein.
• Portal hypertension may cause the recanalisation of the obliterated veins within the ligamentum teres, resulting in the appearance of caput medusae around the umbilicus.

Question 140

What is the bare area of the liver?

Answer 140

It is part of the right lobe, between the anterior and posterior folds of the coronary ligament.

Question 141

Describe liver metastases.

Answer 141

• The most common form of liver tumour are metastatic deposits from primary tumours located elsewhere.
• 50% of all metastatic lesions within the liver are derived from GI tract malignancies.
• Other common primary tumours metastasising via the blood to the liver include the breast, lung, kidney and ovaries.
• The liver is a common site of metastatic disease due to its extensive, dual blood supply and relatively porous sinusoids, allowing the transport of malignant cells into the liver parenchyma

Question 142

Describe the structure of the biliary tree.

Answer 142

• The right and left hepatic ducts unite to form the common hepatic duct
• After 6-8cm, the cystic duct from the gall bladder joins to the common hepatic duct to form the common bile duct
• The main pancreatic duct drains into the common bile duct as it reaches the level of the descending duodenum to form the Ampulla of Vater, which ultimately drains into the descending duodenum through the major duodenal papilla.
• Drainage is controlled by the Sphincter of Oddi.

Question 143

Is it the common hepatic duct or common bile duct that runs via the lesser omentum? And which runs in the porta hepatis?

Answer 143

• Both run in the lesser omentum -> First the common hepatic duct does. Then it becomes the common bile duct and continues running in the lesser omentum.
• Only the common hepatic duct runs in the porta hepatis

Question 144

What is the function of the cystic duct?

Answer 144

Allows bile to move in and out of the gall bladder by communicating with the common hepatic duct.

Question 145

What is Calot’s triangle? What does it demarcate?

Answer 145

• A triangle formed by the cystic duct, common hepatic duct and inferior edge of the liver creates
• It demarcates the location of the cystic artery and Lund’s node, the sentinel lymph node of the gallbladder.

Question 146

What does the cystic artery supply and what does it arise from?

Answer 146

• Supplies the gall bladder
• Arises from the right hepatic artery

Question 147

Describe the innervation of the gall bladder.

Answer 147

• Coeliac plexus -> Gives sympathetic and visceral afferent fibres
• Vagus nerve -> Gives parasympathetic fibres

Question 148

Where may pain from the gall bladder be referred to?

Answer 148

• If the gallbladder becomes infected, as in cholecystitis, involvement of the parietal peritoneum results in well-localised, sharp pain within the right upper quadrant
• This may be referred, via the phrenic nerve, to the C4 dermatome, due to diaphragmatic peritoneal irritation.

Question 149

Describe the different locations in which gall stones can form and what the consequences of this are.

Answer 149

• Biliary colic:
  
  • Gallstones within the cystic duct
  • Pain in the right upper quadrant for 1-2 hours after meal
• Cholecystitis:
  
  • Obstruction of the biliary tree, usually in cystic duct
  • Pain may be constant and there is often signs of inflammation, such as fever and raised white cell counts. Pain in the right upper quadrant, radiating laterally beneath the right breast to the back.
• Choledocholithiasis:
  
  • Gallstones within the common bile duct
  • Prevents bile from draining into the duodenum, resulting in a backlog of bile into the liver and ultimately jaundice.
  • Patients may also complain of pale stools and dark urine.
• Ascending cholangitis:
  
  • Similar to choledocholithiasis, but with the presence of fevers and right upper quadrant pain.

Question 150

Summarise the structure of the pancreas.

Answer 150

• Head -> Sits anterior to the inferior vena cava
• Uncinate process -> Separated from the pancreatic neck by the superior mesenteric artery and vein.
• Neck -> Sits anterior to the origin of the hepatic portal vein.
• Body -> Passes anterior to the abdominal aorta.
• Tail -> Passes within the splenorenal ligament to reach the splenic hilum.

Question 151

What are the endocrine and exocrine products of the pancreas and where do they drain?

Answer 151

• The exocrine products of the pancreas, including trypsinogen, chymotrypsinogen, carboxypeptidase, lipase and amylase, are drained from the parenchyma of the pancreas into the duodenum via the main pancreatic duct, which runs along the length of the pancreas.
• The endocrine units of the pancreas are the islet of Langerhans, which produce insulin, glucagon and somatostatin. These products drain directly into the bloodstream

Question 152

Describe the blood supply of the pancreas.

Answer 152

• Head of pancreas:
  
  • Superior pancreatico-duodenal arteries, from the gastroduodenal (from common hepatic, from coeliac artery)
  • Inferior pancreatico-duodenal arteries, from superior mesenteric artery
• Remaining pancreas:
  
  • Large splenic artery (from coeliac artery)

Note how the blood supply is split between the coeliac and superior mesenteric arteries.

Question 153

Describe innervation of the pancreas.

Answer 153

• Sympathetic fibres from the coeliac plexus -> Control blood flow
• Vagus nerve -> Stimulates pancreatic enzyme and insulin release