8.1 - Anatomy: Overview of the Digestive Tract

Question 1

What does the digestive tract consist of? (8)

What are the accessory organs of digestion? (6)

Answer 1

Digestive tract: mouth, pharynx, oesophagus, stomach, small intestine, large intestine and rectum.

Accessory organs of digestion: teeth, tongue, salivary glands, liver, gallbladder and pancreas.

Question 2

• What does the oesophagus connect?
• Where does it originate and extend to?
• At what spinal level does it pass through the diaphragm? What hole?

Answer 2

Oesophagus

• Muscular tube that conveys food from pharynx to stomach.
• It originates at the inferior border of the cricoid cartilage (C6) and extends to the cardiac orifice of the stomach (T11).
• Passes through the diaphragm at T10 via oesophageal hiatus.
• ~25cm long

Question 3

What is the structure of the esophagus?

Answer 3

Question 4

What are the 4 physiological constrictions of the esophagus (anatomical relations)?

Answer 4

The anatomical relations of the oesophagus give rise to four physiological constrictions in its lumen – it is these areas where food/foreign objects are most likely to become impacted. They can be remembered using the acronym ‘ABCD‘:

• Arch of aorta
• Bronchus (left main stem)
• Cricoid cartilage
• Diaphragmatic hiatus

Question 5

What is the vasculature of the esophagus?

Answer 5

Cervical part: inferior thyroid artery.
Thoracic part: oesophageal branches of descending aorta.
Abdominal part: oesophageal branches of the left gastric artery and the inferior phrenic artery.

Thoracic

The thoracic part of the oesophagus receives its arterial supply from the branches of the thoracic aorta and the inferior thyroid artery (a branch of the thyrocervical trunk).

Venous drainage into the systemic circulation occurs via branches of the azygous veins and the inferior thyroid vein.

Abdominal

The abdominal oesophagus is supplied by the left gastric artery (a branch of the coeliac trunk) and left inferior phrenic artery. This part of the oesophagus has a mixed venous drainage via two routes:

• To the portal circulation via left gastric vein
• To the systemic circulation via the azygous vein.

Question 6

What is the innervation of the esophagus?

Answer 6

Esophagus - Innervation

The oesophagus is innervated by the oesophageal plexus, which is formed by a combination of the parasympathetic vagal trunks and sympathetic fibres from the cervical and thoracic sympathetic trunks.

Two different types of nerve fibre run in the vagal trunks. The upper oesophageal sphincter and upper striated muscle is supplied by fibres originating from the nucleus ambiguus. Fibres supplying the lower oesophageal sphincter and smooth muscle of the lower oesophagus arise from the dorsal motor nucleus.

Question 7

What is the lymphatic drainage of the esophagus?

Answer 7

Lymphatics

The lymphatic drainage of the oesophagus is divided into thirds:

• Superior third – deep cervical lymph nodes.
• Middle third – superior and posterior mediastinal nodes.
• Lower third – left gastric and celiac nodes.

Question 8

3 clinical significances of the esophagus?

Answer 8

1. Barrett’s oesophagus refers to the metaplasia (reversible change from one differentiated cell type to another) of lower oesophageal squamous epithelium to gastric columnar epithelium. It is usually caused by chronic acid exposure as a result of a malfunctioning lower oesophageal sphincter.
2. Esophageal varices - portal hypertension
3. Esophageal carcinoma

Question 9

What are the 4 parts/main anatomical divisions of the stomach?

What is the transpyloric plane? What level is it at?

Answer 9

1. Cardia – surrounds the superior opening of the stomach at the T11 level.
2. Fundus – the rounded, often gas filled portion superior to and left of the cardia.
3. Body – the large central portion inferior to the fundus.
4. Pylorus – This area connects the stomach to the duodenum. It is divided into the pyloric antrum, pyloric canal and pyloric sphincter. The pyloric sphincter demarcates the transpyloric plane at the level of L1.

Question 10

What are the greater and lesser curvatures of the stomach?

• Which arteries supply each curvature?
• Which ligament is the lesser curvature attached to?

Answer 10

• Greater curvature – forms the long, convex, lateral border of the stomach.
  
  • Arising at the cardiac notch, it arches backwards and passes inferiorly to the left.
  • It curves to the right as it continues medially to reach the pyloric antrum.
  • The short gastric arteries and the right and left gastro-omental arteries supply branches to the greater curvature.
• Lesser curvature – forms the shorter, concave, medial surface of the stomach.
  
  • The most inferior part of the lesser curvature, the angular notch, indicates the junction of the body and pyloric region.
  • The lesser curvature gives attachment to the hepatogastric ligament and is supplied by the left gastric artery and right gastric branch of the hepatic artery.

Question 11

What is the gastrohepatic ligament?

• What does it connect?
• Functions?
• Contents?
• What is the lower end continuous with?

Answer 11

Question 12

What are the 2 sphincters of the stomach?

• What marks the transition point between the esophagus & stomach?
  *

Answer 12

Inferior Oesophageal Sphincter

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 esophagusand 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.

Pyloric Sphincter

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 13

What is the vasculature of the stomach?

Answer 13

Stomach: right and left gastric arteries (anastomose along lesser curvature) and right and left gastro-omental arteries (anastomose along greater curvature).

Arterial Supply

• The arterial supply to the stomach comes from the celiac trunk and its branches. Anastomoses form along the lesser curvature by the right and left gastric arteries and along the greater curvature by the right and left gastro-omental arteries:
  
  • Right gastric – branch of the common hepatic artery, which arises from the coeliac trunk.
  • Left gastric – arises directly from the coeliac trunk.
  • Right gastro-omental – terminal branch of the gastroduodenal artery, which arises from the common hepatic artery.
  • Left gastro-omental – branch of the splenic artery, which arises from the coeliac trunk.

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 14

What is the parasympathetic & SNS innervation of the stomach?

Answer 14

• Parasympathetic nerve supply arises from the anterior and posterior vagal trunks, derived from the vagus nerve.
• Sympathetic nerve supply arises from the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. It also carries some pain transmitting fibres.

Question 15

Which omenta connect to the stomach?

Answer 15

Question 16

2 Clinical Significances of the stomach?

Answer 16

1. GORD
2. Hiatus Hernia - when a part of the stomach protrudes through the esophageal hiatus of the diaphragm into the chest

Question 17

Where does the small intestine run to and from?

Answer 17

It extends from the pylorus of the stomach to the ileocaecal junction

Question 18

What are the 3 parts of the small intestine?

• Which is the shortest?
• In which quadrants do jejunum and ileum mostly lie?

Answer 18

1. Duodenum

• First, shortest and widest part.
• Fixed
• C-shaped
• 4 parts

2. Jejunum - Mostly in upper left quadrant
3. Ileum - Mostly in right lower quadrant

Question 19

What are the 3 parts of the small intestine?

• Length of each?
• In which quadrants do jejunum and ileum mostly lie?
• Which are retroperitoneal?

Answer 19

1. Duodenum = Retroperitoneal = 25cm long

• First, shortest and widest part.
• Fixed
• C-shaped
• 4 parts

2. Jejunum - Mostly in upper left quadrant = 2.5metres
3. Ileum - Mostly in right lower quadrant = 3.5metres

Question 20

What are the 4 divisions of the duodenum?

• Which section is connected to the liver? How?
• Which section has the major duodenal papilla? What is that?
• At what point does the duodenum connect to the jejunum?

Answer 20

D1 – Superior (Spinal level L1)

The first section of the duodenum is known as ‘the cap’. It ascends upwards from the pylorus of the stomach, and is connected to the liver by the hepatoduodenal ligament. This area is most common site of duodenal ulceration.

D2 – Descending (L1-L3)

The descending portion curves inferiorly around the head of the pancreas. It lies posteriorly to the transverse colon, and anterior to the right kidney.

Internally, the descending duodenum is marked by the major duodenal papilla – the opening at which bile and pancreatic secretions to enter from the ampulla of Vater (hepatopancreatic ampulla).

D3 – Inferior (L3)

The inferior duodenum travels laterally to the left, crossing over the inferior vena cava and aorta. It is located inferiorly to the pancreas, and posteriorly to the superior mesenteric artery and vein.

D4 – Ascending (L3-L2)

After the duodenum crosses the aorta, it ascends and curves anteriorly to join the jejunum at a sharp turn known as the duodenojejunal flexure.

Question 21

What is the clinical significance of the duodenum?

2 complications of duodenal ulcer perforation? Which artery?

Answer 21

• most common site of duodenal ulceration = 1st segment
• H.pylori & NSAID overuse
• An ulcer in itself can be painful, but is not particularly troublesome and can be treated medically. However, if the ulcer progresses to create a complete perforation through the bowel wall, this is a surgical emergency, and usually warrants immediate repair. A perforation may be complicated by:
  
  • Inflammation of the peritoneum (peritonitis) – causing damage to the surrounding viscera, such as the liver, pancreas and gall bladder.
  • Erosion of the gastroduodenal artery – causing hemorrhage and potential hypovolaemia shock.

Question 22

Where does the ileum start?

Answer 22

The jejunum begins at the duodenojejunal flexure. There is no clear external demarcation between the jejunum and ileum – although the two parts are macroscopically different. The ileum ends at the ileocaecal junction.

Question 23

What are differences between the jejunum and ileum?

Answer 23

Jejunum

• Located in upper left quadrant
• Thick intestinal wall
• Longer vasa recta (straight arteries)
• Less arcades (arterial loops)
• Red in colour

Ileum

• Located in lower right quadrant
• Thin intestinal
• Shorter vasa recta
• More arcades
• pink in colour

Question 24

What is the arterial supply of the duodenum?

• Proximal to major duodenal papilla?
• Distal to major duodenal papilla?
• What is the significance of this transition?

Answer 24

• Proximal to the major duodenal papilla – supplied by the gastroduodenal artery (branch of the common hepatic artery from the coeliac trunk).
• Distal to the major duodenal papilla – supplied by the inferior pancreaticoduodenal artery (branch of superior mesenteric artery).

This transition is important – it marks the change from the embryological foregut to midgut. The veins of the duodenum follow the major arteries and drain into the hepatic portal vein.

Question 25

What is the arterial supply to the jejunum & ileum?

Answer 25

The arterial supply to the jejunoileum is from the **superior mesenteric artery**. The superior mesenteric artery arises from the aorta at the level of the L1 vertebrae, immediately inferior to the **coeliac trunk**. It moves in between layers of mesentery, splitting into approximately 20 branches. These branches anastomose to form loops, called **arcades**. From the arcades, long and straight arteries arise, called **vasa recta**. The venous drainage is via the **superior mesenteric vein**. It unites with the splenic vein at the neck of the pancreas to form the hepatic portal vein.

Question 26

What is the ileocaecal valve and its clinical significance?

Answer 26

Question 27

What is the colon? * Where does it extend to and from? * Function? * 4 components?

Answer 27

The **colon** (large intestine) is the distal part of the gastrointestinal tract, extending from the cecum to the anal canal. It receives digested food from the small intestine, from which it absorbs water and electrolytes to form **faeces**. Anatomically, the colon can be divided into **four parts** – ascending, transverse, descending and sigmoid. These sections form an arch, which encircles the small intestine.

Question 28

What are the 4 divisions of the colon (large intestines)? * When does the ascending colon become the transverse colon? * When does the transverse colon become the transverse colon? * Where is the colon attached to the diaphragm and how? * Which parts of the colon are retroperitoneal/intraperitoneal? Which mesentery? * Which quadrant is the sigmoid colon located in? * Where does the sigmoid extend to and from?

Answer 28

**Ascending Colon** * The colon begins as the **ascending colon**, a retroperitoneal structure which ascends superiorly from the cecum. * When it meets the right lobe of the liver, it turns 90 degrees to move horizontally. This turn is known as the **right colic flexure** (or hepatic flexure), and marks the start of the transverse colon. **Transverse Colon** * The **transverse colon** extends from the right colic flexure to the spleen, where it turns another 90 degrees to point inferiorly. This turn is known as the **left colic flexure (or splenic flexure**). Here, the colon is attached to the diaphragm by the phrenicocolic ligament. * The transverse colon is the least fixed part of the colon, and is variable in position (it can dip into the pelvis in tall, thin individuals). Unlike the ascending and descending colon, the transverse colon is intraperitoneal and is enclosed by the **transverse mesocolon**. **Descending Colon** * After the left colic flexure, the colon moves inferiorly towards the pelvis – and is called the **descending colon**. It is retroperitoneal in the majority of individuals, but is located anteriorly to the left kidney, passing over its lateral border. * When the colon begins to turn medially, it becomes the **sigmoid colon**. **Sigmoid Colon** * The 40cm long sigmoid colon is located in the **left lower quadrant** of the abdomen, extending from the left iliac fossa to the level of the S3 vertebra. This journey gives the sigmoid colon its characteristic “S” shape. * The sigmoid colon is attached to the posterior pelvic wall by a mesentery – the **sigmoid** **mesocolon**. The long length of the mesentery permits this part of the colon to be particularly mobile.

Question 29

What are the Paracolic gutters? Clinical significance?

Answer 29

The right and left ***paracolic gutters/recesses*** are peritoneal recesses on the posterior abdominal wall lying alongside the ascending and descending colon. These structures are clinically important, as they allow material that has been released from inflamed or **infected** abdominal organs to accumulate elsewhere in the abdomen.

Question 30

What are 4 characteristic features of the colon? Where do these features stop?

Answer 30

1. **Omental appendices** – small pouches of peritoneum, filled with fat attached to the surface of the large intestine. 2. **Teniae Coli** - Running longitudinally along the surface of the large bowel are three strips of muscle, known as the teniae coli. They are called the mesocolic, free and omental coli. 3. The teniae coli contract to shorten the wall of the bowel, producing sacculations known as **haustra.** 4. The large intestine has a much **wider diameter** compared to the small intestine. These features cease at the **rectosigmoid junction**, where the smooth muscle of the teniae coli broaden to form a complete layer within the rectum.

Question 31

What is the embryological origin of the colon? How does this correlate to their arterial supply?

Answer 31

Ascending colon and proximal 2/3 of the transverse colon – derived from the **midgut**. Distal 1/3 of the transverse colon, descending colon and sigmoid colon – derived from the **hindgut**. Midgut-derived structures = superior mesenteric artery Hindgut-derived structures = inferior mesenteric artery.

Question 32

What is the arterial supply to the 4 segments of the colon?

Answer 32

_The ascending colon_ receives arterial supply from two branches of the SMA**;** 1) ileocolic & 2) right colic arteries. The ileocolic artery gives rise to colic, anterior cecal and posterior cecal branches – all of which supply the ascending colon. _The transverse colon_ is derived from both the midgut and hindgut, and so it is supplied by branches of the superior mesenteric artery and inferior mesenteric artery: * **Right colic artery** (from the superior mesenteric artery) * **Middle colic artery** (from the superior mesenteric artery) * **Left colic artery** (from the inferior mesenteric artery) _The descending colon_ is supplied by a single branch of the IMA ; the **left colic artery**. _The sigmoid colon_ receives arterial supply via the sigmoid arteries (branches of the inferior mesenteric artery).

Question 33

What is the Marginal Artery of Drummond? Clinical significance?

Answer 33

Question 34

Venous drainage of colon?

Answer 34

* **Ascending colon** – SMV * **Transverse colon** – SMV * **Descending colon** – IMV * **Sigmoid colon** – IMV

Question 35

What is the innervation of the colon?

Answer 35

**Innervation** The innervation to the colon is dependent on embryological origin: * **Midgut-derived** structures (ascending colon and proximal 2/3 of the transverse colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the superior mesenteric plexus. * **Hindgut-derived** structures (distal 1/3 of the transverse colon, descending colon and sigmoid colon) receive their sympathetic, parasympathetic and sensory supply via nerves from the inferior mesenteric plexus: * Parasympathetic innervation via the pelvic splanchnic nerves * Sympathetic innervation via the lumbar splanchnic nerves.

Question 36

Lymphatic drainage of GIT? * Esophagus - 3 parts * Stomach * Small intestine * Large intestine

Answer 36

**Oesophagus**: * Cervical part: drain into the paratracheal lymph nodes and inferior deep cervical lymph nodes. * Thoracic part: posterior mediastinal lymph nodes. * Abdominal part: left gastric lymph nodes. **Stomach**: gastric lymphatic vessels. **Small intestine**: lacteals and mesenteric lymph nodes. **Large intestine**: right, middle and intermediat colic lymph nodes.

Question 37

GIT nerve supply?

Answer 37

Question 38

Parotid salivary gland? * Location? * Nerve supply? * Sympathetic? * PSNS? * 3 structures that lie within?

Answer 38

_Parotid salivary gland_ * **Location**: inferior to the acoustic meatus between the SCM and ramus of the mandible. * **Nerve supply:** * Sympathetic innervation from the plexus around the external carotid artery. * Parasympathetic innervation from glossopharyngeal nerve. * **Structures lying within gland**: 1. External carotid artery 2. Retromandibular vein 3. Facial nerve & branches

Question 39

Submandibular & Sublingual salivary glands? Locations & Nerve Supply for each.

Answer 39

Question 40

Which GIT organs are found in which abdo regions?

Answer 40

Question 41

What is McBurneys point?

Answer 41

Appendicitis is a fairly common inflammation of the appendix, often caused by bacterial infection. Initially, diffuse pain is felt in the periumbilical region. As the appendix becomes more inflamed and irritates the parietal peritoneum, the pain becomes well localized to the right lower quadrant ( Mc Burney’s point)