W3: Oesophagus, stomach, bowels, vascular and innveration of alimentary

Question 1

Discuss oesophagus entering the diaphragm

Answer 1

The oesophagus 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.

Question 2

Discuss oesphagus musculature

Answer 2

The external longitudinal layer of muscle in the upper 1/3rd of the oesophagus is made up of voluntary striated muscle, whereas the lower 1/3rd is made up of involuntary smooth muscle. The middle 1/3rd is formed from a mix of striated and smooth muscle.

Question 3

Discuss constriction points within the oesophagus

Answer 3

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.

Physiological sphincter maintained by 4 main factors:

1. Oesophagus enters the stomach at an acute angle.
2. Walls of the intra-abdominal section of the oesophagus are compressed when there is a positive intra-abdominal pressure.
3. Prominent mucosal folds at the gastro-oesophageal junction aid in occluding the lumen.
4. Right crus of the diaphragm has a “pinch-cock” effect.

Question 4

Describe arterial supply of oesphagus

Answer 4

The thoracic part of the oesophagus is supplied by the oesophageal arteries, arising directly from the thoracic aorta. Also recieves branches from inferior thyroid artery (from thyrocervical trunk) - superior 1/3

The abdominal oesophagus is supplied by the left gastric and left inferior phrenic artery.

Question 5

Discuss venous drainage of the oesophagus

Answer 5

Thoracic part: venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein.

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

• The portal circulation: blood drains through the left gastric vein to the hepatic portal vein.
• The systemic circulation: blood drains through 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.

= lower oesophageal veins connect azygos and gastric veins

Question 6

Oesophageal Varices

Answer 6

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.

Present with haematemesis (vomiting of blood)

Question 7

Levels of oesophagus

Answer 7

It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11).

Question 8

Which level is the cap of the duodenum found?

Answer 8

Transpyloric plane (L1)

Question 9

Discuss structure of the stomach

Answer 9

• Cardia: surrounds the opening of the oesophagus into the stomach.
• Fundus: dilated, superior portion of the stomach lateral to the cardia, which is often filled with gas.
• Body: the large, central part of the stomach.
• Pylorus: the distal part of the stomach, leading to the duodenum. Subdivided into:
  
  • Antrum
  • Pyloric canal
  • Pyloric sphincter (controls entry of chyme into the duodenum)
• Greater curvature: the longer, convex border of the stomach passing from the cardiac notch to the inferior aspect of the pylorus. Acts as the site of origin of the greater omentum.
• Lesser curvature: the shorter, concave border of the stomach, passing from the oesophageal termination to the superior aspect of the pylorus. Acts as a site of origin of the lesser omentum.

Question 10

Structures at the transpyloric plane

Answer 10

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Question 11

Stomach innervation

Answer 11

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.

Question 12

What are the two stomach sphincters?

Answer 12

Inferior oesophageal and pyloric

Question 13

Discuss inferior oesophageal sphincter

Answer 13

The oesophagus passes through the diaphragm through the oesophageal hiatus at the level of T10. It descends a short distance to the inferior oesophageal sphincter at the T11 level which marks the transition point between the oesophagus and stomach (in contrast to the superior oesophageal sphincter, located in the pharynx). It allows food to pass through the cardiac orifice and into the stomach and is not under voluntary control.

Question 14

Discuss pyloric sphincter

Answer 14

The pyloric sphincter lies between the pylorus and the first part of the duodenum. It controls of the exit of chyme (food and gastric acid mixture) from the stomach.

In contrast to the inferior oesophageal sphincter, this is an anatomical sphincter. It contains smooth muscle, which constricts to limit the discharge of stomach contents through the orifice.

Emptying of the stomach occurs intermittently when intragastric pressure overcomes the resistance of the pylorus. The pylorus is normally contracted so that the orifice is small and food can stay in the stomach for a suitable period. Gastric peristalsis pushes the chyme through the pyloric canal into the duodenum for further digestion.

Question 15

How many layers do the omenta have?

Answer 15

The greater and lesser omenta are two structures that consist of peritoneum folded over itself (two layers of peritoneum – four membrane layers).

Question 16

Discuss greater omentum

Answer 16

Greater omentum – hangs down from the greater curvature of the stomach and folds back upon itself where it attaches to the transverse colon It contains many lymph nodes and may adhere to inflamed areas , therefore playing a key role in gastrointestinal immunity and minimising the spread of intraperitoneal infections.

Question 17

Discuss lesser omentum

Answer 17

Lesser omentum– continuous with peritoneal layers of the stomach and duodenum, this smaller peritoneal fold arises at the lesser curvature and ascend to attach to the liver. The main function of the lesser omentum is to attach the stomach and duodenum to the liver.

Question 18

Discuss stomach arterial supply

Answer 18

1. Right gastric: arises from the common hepatic artery, passing along the lesser curvature to supply the stomach from its superior aspect.
2. Left gastric: arises directly from the coeliac trunk, passing along the lesser curvature to supply the stomach from its superior aspect.
3. Right gastro-omental: arises from the gastroduodenal artery, itself a branch of the common hepaticartery. Supplies the stomach from its inferior aspect by passing along the greater curvature.
4. Left gastro-omental: the largest branch of the splenic artery. Supplies the stomach from its inferior aspect by passing along the greater curvature.
5. Short gastric arteries: small branches of the splenic artery, distributed along the greater curvature ofthe stomach.

Question 19

Discuss venous drainage of the stomach

Answer 19

The veins of the stomach run parallel to the arteries. The right and left gastric veins drain into the hepatic portal vein. The short gastric vein, left and right gastro-omental veins ultimately drain into the superior mesenteric vein.

Question 20

Innervation of the stomach

Answer 20

Parasympathetic innervation to the stomach, which stimulates motility and gastric secretion, 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 21

Hiatus hernia

Answer 21

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

Question 22

Pyloric stenosis

Answer 22

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 23

Discuss divisions of the duodenum

Answer 23

The duodenum is the most proximal part of the small intestine and is divided into four parts:

• 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 turn-ing 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 24

What does the duodenum curve around during its course?

Answer 24

Head of the pancreas

Question 25

Duodenal Ulcers

Answer 25

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 26

Duodenum, Pancreas and Gallbladder communicaiton

Answer 26

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 prox- imal 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 27

Discuss jejunum and ileum

Answer 27

The jejunum and ileum form the remainder of the small intestine. The jejunum is approximately 3 metres in length and is mostly concerned with absorption of food digested by pancreatic enzymes within the duodenum. The ileum, which is between 2-4 metres in length, functions predominantly to absorb remaining products of digestion, as well as bile salts and vitamin B12. The ileum terminates at the ileocaecal valve, where the large intestine begins. Both the jejunum and ileum are suspended from the posterior abdominal wall by small bowel mesentery, which contains the nerves and blood vessels supplying the bowel.

Question 28

Discuss large intenstine

Answer 28

The large intestine is formed from the caecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon and rectum, extending between the ileocaecal valve and the anal canal.

1. Caecum – a dilated proximal part of the large bowel found in the right iliac fossa, varying in position de- pending on distension.
2. (Vermiform) Appendix – a thin projection of large bowel arising from the wall of the caecum and typ- ically found at McBurney’s point, 2/3rds of the distance from the umbilicus to the anterior superior iliac spine. The appendix is connected to the mesentery of the ileum via the meso-appendix.
3. Ascending colon – passes vertically through the right lumbar region, terminating at the hepatic flexure.
4. Transverse colon – crosses the abdomen at the boundary between the umbilical and epigastric regions, terminating at the splenic flexure. Unlike the ascending and descending colons, the transverse colon is intra-peritoneal, suspended from the posterior abdominal wall by the transverse mesocolon.
5. Descending colon – passes vertically through the left lumbar region, terminating at the level of the iliac crest.
6. Sigmoid colon – highly variable in length, forming a loop of large bowel within the left iliac fossa in which faeces can be stored until defaecation. The sigmoid colon is an intra-peritoneal structure, suspended from the pelvic wall by the sigmoid mesocolon.
7. Rectum – follows the curved roof of the pelvis formed by the sacrum and coccyx. Usually only contains faeces immediately prior to defaecation. Distally, the rectum widens to form the rectal ampulla, which is highly distensible. Transverse folds (or valves) of mucosa form along the length of the rectum, which function to support the weight of accumulating faecal matter. The rectum terminates at the anorectal junction, situated around 5cm from the anus.

Question 29

Where is McBurneys point?

Answer 29

2/3rds of the distance from the umbilicus to the anterior superior iliac spine

Question 30

What are taeniae coli?

Answer 30

three separate longitudinal ribbons (taeniae meaning ribbon in Latin) of smooth muscle on the outside of the ascending, transverse, descending and sigmoid colons.

Question 31

Discuss haustrations

Answer 31

Haustra are saccules in the colon that give it its segmented appearance. Haustral contraction is activated by the presence of chyme and serves to move food slowly to the next haustra, along with mixing the chyme to help with water absorption

Question 32

Discuss appendices epiploicae

Answer 32

Pouches of visceral peritoneum, containing fat, projecting from the surface of the colon

Question 33

Discuss valvulae conniventes

Answer 33

Also known as plicae circulares - mucosal folds in the small intestine which gives characteristic appearence on radiographs

Question 34

Compare small and large intestine

Answer 34

Question 35

Appendicitis

Answer 35

Acute appendicitis is the most common cause of acute abdominal pain requiring surgery. Appendicitis is thought to be caused by an obstruction of the appendiceal lumen, leading to bacterial overgrowth and inflammation. Due to the visceral peritoneum being irritated first, appendicitis first presents as vague periumbilical pain. Over time, once the parietal peritoneum becomes involved, pain becomes localised to the right iliac fossa, at McBurney’s point. Appendicitis, once confirmed, is treated with an appendicectomy.

Question 36

Colon Cancer

Answer 36

Colorectal cancer accounts for 15% of cancer related deaths in the Western World. More than 50% of cas- es 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 37

Digital Rectal Examination (DRE)

Answer 37

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 38

Blood supply of small intestine

Answer 38

Proximal part - coeliac trunk - gastroduodenal artery - superior pancreatoduodenal artery

Distal part - inferior pancreatoduodenal from the superior mesenteric

Question 39

Ampulla of rectum

Answer 39

The final segment of the rectum, the ampulla, relaxes to accumulate and temporarily store faeces until defecation occurs. It is continuous with the anal canal; which passes through the pelvic floor to end as the anus.

Valves support the weight of faecal matter

Within the rectum there are threetransverse folds (2 left and 1 right).

Question 40

Where is the rectosigmoid junction?

Answer 40

S3

Question 41

Discuss anal sphincters

Answer 41

The anal canal is surrounded by internal and external anal sphincters, which play a crucial role in the maintenance of faecal continence:

• Internal anal sphincter – surrounds the upper 2/3 of the anal canal. It is formed from a thickening of the involuntary circular smooth muscle in the bowel wall.
• External anal sphincter – voluntary muscle that surrounds the lower 2/3 of the anal canal (and so overlaps with the internal sphincter). It blends superiorly with the puborectalis muscle of the pelvic floor.

At the junction of the rectum and the anal canal, there is a muscular ring – known as the anorectal ring. It is formed by the fusion of the internal anal sphincter, external anal sphincter and puborectalis muscle, and is palpable on digital rectal examination.

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

Question 42

Discuss anal cushions

Answer 42

Small projec- tions of submucosa of the anal canal form the anal cushions, which aid continence to fluid and gas.

Question 43

What is the pectinate line?

Answer 43

he pectinate line, found between the middle and lower third of the anal canal, marks the junction between the hindgut and the ectoderm-derived procto- deum. The line is formed by the anal valves (transverse folds of mucosa) found at the inferior ends of the anal columns.

Question 44

Discuss internal cellular structure of the anus (long)

Answer 44

The superior aspect of the anal canal has the same epithelial lining as the rectum (columnar epithelium). However, in the anal canal, the mucosa is organised into longitudinal folds, known as anal columns. These are joined at their inferior ends by anal valves. Above the anal valves are small pouches which are referred to as anal sinuses – these contain glands that secrete mucus.

The anal valves collectively form an irregular circle – known as the pectinate line (or dentate line). This line divides the anal canal into upper and lower parts, which differ in both structure and neurovascular supply. This is a result of their different embryological origins:

Above the pectinate line – derived from the embryonic hindgut.

Below the pectinate line – derived from the ectoderm of the proctodeum.

Inferior to the pectinate line, the anal canal is lined by non-keratinised stratified squamous epithelium (known as the anal pecten). It is a pale and smooth surface, which transitions at the level of the intersphincteric groove to true skin (keratinised stratified squamous).

Question 45

Levator ani muscle

Answer 45

collection of 3 muscles

The function of the entire levator ani muscle is crucial, in that it stabilizes the abdominal and pelvic organs. It literally stops your organs from falling straight out of your pelvis and abdomen!