The gut and its derivatives

Question 1

What is the arterial, venous and lymphatic drainage of the oesophagus?

Answer 1

Arterial: Oesophageal arteries (from the thoracic aorta, bronchial arteries, gastric artery)

Venous: azygos vein, hemiazygos vein and oesophageal branches to the left gastric vein in the abdomen

Lymphatic: posterior mediastinal and left gastric nodes.

Question 2

What is the innervation of the oesophagus?

Answer 2

Thoracic part:
-Oesophageal plexus, which receives parasympathetic supply from the vagus nerve and sympathetic innervation from the cervical sympathetic trunk

Abdominal part:
-Parasympathetic innervation: arises from the
thoracic oesophagal nervous plexus, while its sympathetic component originates from the fifth to twelfth thoracic spinal nerves T5-T12

Afferent:
Travel via vagus nerves. Can sense osmo-, chemo-, thermo-, and mechanical stimulus

Oesophagus can feel temperature and mechanical pressure but not pain

Question 3

What are the layers of the stomach?

Answer 3

Layers:

1. Mucosa: innermost layer, releases stomach acid
2. Submucosa: second layer, contains nerve endings and blood vessels
3. Muscles
4. Serosa: inner lining of GI tube

Stomach muscle has 3 layers: circular, longitudinal and oblique

Question 4

What is the internal anatomy of the stomach?

Answer 4

Gastric folds or gastric rugae: ridges of mucosal and submucosal layers, that allow the stomach to expand

Sphincter: a ring of smooth muscle that can relax to allow the passage of some contents

Cardiac sphincter: prevents the acidic contents  of the stomach from moving upward into
the oesophagus (acid reflux)

Pyloric sphincter: separates the stomach from the small intestine

When sphincters contract = they prevent the movement
When sphincters relax = they allow movement

Question 5

What is a hiatal hernia?

Answer 5

Stomach protruding through oesophageal hiatus (T10) into the thorax

Question 6

What are the functions of the different parts of the small intestines?

Answer 6

Duodenum: shortest. is where preparation for absorption through villi begin. Has Brunner’s glands that produce alkaline mucus. Secondarily retroperitoneal

Jejunum: specialized for the absorption of nutrients. Intraperitoneal.

Ileum: absorbs vitamin B12, bile salts, and remaining products of digestion.
Intraperitoneal

Question 7

What are the different parts of the duodenum?

Answer 7

Superior, descending, horizontal, ascending

Question 8

What is the blood supply to the gut?

Answer 8

Coeliac Trunk (T12) - supplies foregut
Superior Mesenteric artery (L1) - supplies midgut
Inferior Mesenteric artery (L3) - supplies hindgut

Question 9

What is the blood supply to the stomach?

Answer 9

Coeliac trunk forms the right and left gastric artery and the splenic artery.
The splenic artery zigzags the stomach and goes to the spleen.
The common hepatic artery forms the gastroduodenal artery. This forms the right gastro-omental artery.
The splenic artery forms the left gastro-omental artery.
The left and right gastro-omental arteries anastomose

The supply to the stomach:

• Right and left Gastro-omental arteries
• Right and left Gastric arteries

Question 10

What are the branches of the coeliac trunk?

Answer 10

Coeliac trunk forms:

1. Gastric arteries
2. Splenic artery –> left gastroomental artery
3. Commo hepatic artery –> hepatic artery proper and gastroduodenal artery

The gastroduodenal artery forms the right gastroomental artery

Question 11

What are the branches of the superior mesenteric artery?

Answer 11

1. Jejunal and ileal arteries
2. Ileocolic artery
3. Right colic artery
4. Middle colic artery

Question 12

What does the superior mesenteric artery supply?

Answer 12

Supplies the distal part of the duodenum, all of the jejunum and ileum, the ascending colon, and the proximal 2/3 of the transverse colon

The proximal part of the duodenum is supplied by the gastroduodenal artery and superior pancreaticoduodenal artery (which comes from the gastroduodenal artery)

The distal duodenum is supplied by the inferior pancreaticoduodenal artery from the superior mesenteric artery.

Question 13

What is the blood supply to the appendix?

Answer 13

Appendicular artery is a branch of ileocolic artery

Question 14

What are the branches of the inferior mesenteric artery?

Answer 14

1. Marginal artery
2. Left colic artery
3. Sigmoid arteries

Question 15

What does the inferior mesenteric artery supply?

Answer 15

Supplies distal 1/3 of transverse colon, descending colon, sigmoid colon, proximal rectum

Question 16

What is the venous drainage of the gut?

Answer 16

Nutrient-rich blood from the gut is drained into:

• Splenic vein
• Superior mesenteric vein
• Inferior mesenteric vein
• (and other veins)

These all drain into the Hepatic Portal Vein, bringing nutrients and toxins to the liver for processing.

Question 17

Describe the liver

Answer 17

The liver has ligaments- double-layer folds of peritoneum that attach it to the body wall or to other organs:

1. Falciform ligament - attaches the liver to the body wall. Ligamentum teres is a remnant of embryonic umbilical vein
2. Coronary ligament (forms right and left triangular ligaments) - Attaches the liver to the diaphragm, and the right kidney and adrenal gland. Forms the right and left triangular ligament

Bare area of the liver: the region of the liver not covered with peritoneum, where the liver is connected to the diaphragm directly with loose connective tissue.

You cannot have ascites in the bare area because there is no peritoneal space there for fluid to build up.

If you see fluid between the posterior liver and diaphragm, it is a pleural effusion.

The portal triad sits inside the hepatoduodenal ligament on the edge of the lesser omentum.

The liver can be further divided into 8 hepatic segments based on their functions.

Coeliac trunk -> common hepatic artery -> hepatic artery proper -> left and right hepatic arteries

Question 18

What are the Portal Caval Anastomoses?

Answer 18

There are 3 portal caval anastomoses:

• oesophagus
• umbilicus
• rectum

Purpose: When there is a blockage of the portal system, portocaval anastomosisenables the blood to still reach the systemic venous circulation.

Question 19

Explain the portal caval anastomoses?

Answer 19

The anastomosis between theleft gastric veins,which are portal veins, and the lower branches ofoesophageal veinsthat draininto theazygosandhemiazygos veins, which are systemic veins. The site of this anastomosis is the lower oesophagus.

The anastomosis between thesuperior rectal veins, which are portal veins, and theinferiorandmiddle rectal veins, which are systemic veins. The site of this anastomosis is the upper part of theanal canal.

The anastomosis between theparaumbilical veins,which runin the ligament teres as portal veins, andsmall epigastric veins, which are systemic veins. The site of this anastomosis is the umbilicus

Question 20

What is the blood supply of the spleen?

Answer 20

The splenic artery is the largest branch of the coeliac trunk. Travels along the superior border of the pancreas to reach the spleen

Question 21

What is the blood supply of the pancreas?

Answer 21

Head of Pancreas: Anterior and posterior superior pancreaticoduodenal arteries from common hepatic art.; ant and post. and inferior pancreaticoduodenal artery from the superior mesenteric artery

Body and Tail: Dorsal pancreatic artery and greater pancreatic artery from splenic art

Question 22

What is the venous drainage of the spleen and pancreas?

Answer 22

The splenic vein forms from several tributaries at the hilum of the spleen.

It travels behind the pancreas. It is joined by several pancreatic veins and the inferior mesenteric vein, then joins with the superior mesenteric vein to form the portal vein

Question 23

What is the innervation of the stomach?

Answer 23

Coeliac plexus: nerve plexus near the aorta in the abdomen receiving the sympathetic and parasympathetic nerves (CN X) and conveying post-synaptic outputs to the abdominal viscera

Splanchnic nerves are from the sympathetic trunk and provide sympathetic innervation

Parasympathetic: anterior and posterior vagal trunks (coming through oesophageal hiatus)

Sympathetic: from the sympathetic trunk (T6-T9), the greater splanchnic nerve transmits presynaptic fibres to the coeliac ganglion, then postsynaptic arise from the coeliac plexus

Question 24

What is the innervation of the midgut?

Answer 24

Sympathetic innervation: arrises from sympathetic trunk, pre-synaptic nerves travel via lumbar splanchnic nerve to the superior mesenteric ganglion. Post synaptic fibres then travel to small intestine, ascending and proximal 2/3 transverse colon

T5-T12 forming splanchnic nerves supply foregut and midgut which synapse with coeliac ganglion.

Parasympathetic fibers: from vagus nerve, synapse on the gut itself

Question 25

What is the innervation of the hindgut?

Answer 25

Sympathetic innervation: arrises from sympathetic trunk, pre-synaptic nerves travel vial lumbar splanchnic nerve to the INFERIOR mesenteric ganglion. Post synaptic fibres then travel to distal 1/3 transverse colon, descending and sigmoid colon Parasympathetic fibers: from pelvic splanchnic nerves which arise from sacral spinal cord segments S2-S4 Descending colon and rectum get parasympathetic innervation from sacral, not vagus

Question 26

What is the ENS?

Answer 26

Two components: - Myenteric plexus (Aurbach’s plexus) in the muscular layer of the GI tract - Submucosal plexus (Meissener’s plexus) in the mucosa of the GI tract Controls mobility, secretion, fluid exchange independently of the parasympathetic and sympathetic nervous system

Question 27

What is Congenital megacolon?

Answer 27

Failure of migration of neural crest cells to form part of the enteric nervous system. Symptoms: Swollen belly, vomiting, failure to produce bowel movement within 48 hours of birth Treatment: bypass of effected region of colon

Question 28

What is the lymphatic drainage of stomach?

Answer 28

Gastric lymphatic vessels accompany the arteries along the greater and lesser curvatures of the stomach Drain to the gastric and gastro-omental lymph nodes along the curvatures of the stomach Ultimately drain to the celiac lymph nodes

Question 29

What are the lymphatics of the small intestine?

Answer 29

``` Superior mesenteric lymph nodes are situated near superior mesenteric artery. Lymph from the: -Colic lymph nodes -Ileocolic lymph nodes -Mesenteric lymph nodes -Superior central lymph nodes ``` Drain to the Superior mesenteric lymph nodes and then to the intestinal lymphatic trunk, and finally to the cisterna chyli Cisterna chyli - enlarged part of the thoracic duct, collects lymph and chyle (emulsified fat from digestion)

Question 30

What are the lymphatics of the large intestine?

Answer 30

Ascending colon and proximal 2/3 transverse: Drain to the Superior mesenteric lymph nodes via the colic lymph nodes Distal 1/3 transverse colon, descending, sigmoid colon: inferior mesenteric lymph nodes

Question 31

What are the lymphatics of the Liver?

Answer 31

Lymph from the posterior aspect of the liver (superficial and deep) flows toward the bare area to enter the phrenic lymph nodes Lymph from the anterior and inferior aspects flows toward the portal vein to enter hepatic lymph nodes in the lesser omentum.

Question 32

Why is pancreatic cancer so deadly?

Answer 32

Extensive drainage to relatively inaccessible lymph nodes + Rapid metastasis to the liver, via the portal vein = Surgical resection of the cancerous pancreas nearly futile Median survival time: 2–3 months after diagnosis (regardless of therapy)

Question 33

What are the lymphatics of the pancreas?

Answer 33

Pancreaticosplenic and back to coeliac nodes and superficial mesenteric nodes

Question 34

What is liver pain caused by?

Answer 34

Liver, Gallbladder and Duodenum: irritate the diaphragm, pain felt on neck (C3-5 dermatome) Commonly misdiagnosed