The gut and its derivatives Flashcards
What is the arterial, venous and lymphatic drainage of the oesophagus?
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.
What is the innervation of the oesophagus?
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
What are the layers of the stomach?
Layers:
- Mucosa: innermost layer, releases stomach acid
- Submucosa: second layer, contains nerve endings and blood vessels
- Muscles
- Serosa: inner lining of GI tube
Stomach muscle has 3 layers: circular, longitudinal and oblique
What is the internal anatomy of the stomach?
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
What is a hiatal hernia?
Stomach protruding through oesophageal hiatus (T10) into the thorax
What are the functions of the different parts of the small intestines?
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
What are the different parts of the duodenum?
Superior, descending, horizontal, ascending
What is the blood supply to the gut?
Coeliac Trunk (T12) - supplies foregut
Superior Mesenteric artery (L1) - supplies midgut
Inferior Mesenteric artery (L3) - supplies hindgut
What is the blood supply to the stomach?
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
What are the branches of the coeliac trunk?
Coeliac trunk forms:
- Gastric arteries
- Splenic artery –> left gastroomental artery
- Commo hepatic artery –> hepatic artery proper and gastroduodenal artery
The gastroduodenal artery forms the right gastroomental artery
What are the branches of the superior mesenteric artery?
- Jejunal and ileal arteries
- Ileocolic artery
- Right colic artery
- Middle colic artery
What does the superior mesenteric artery supply?
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.
What is the blood supply to the appendix?
Appendicular artery is a branch of ileocolic artery
What are the branches of the inferior mesenteric artery?
- Marginal artery
- Left colic artery
- Sigmoid arteries
What does the inferior mesenteric artery supply?
Supplies distal 1/3 of transverse colon, descending colon, sigmoid colon, proximal rectum
What is the venous drainage of the gut?
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.
Describe the liver
The liver has ligaments- double-layer folds of peritoneum that attach it to the body wall or to other organs:
- Falciform ligament - attaches the liver to the body wall. Ligamentum teres is a remnant of embryonic umbilical vein
- 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
What are the Portal Caval Anastomoses?
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.
Explain the portal caval anastomoses?
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
What is the blood supply of the spleen?
The splenic artery is the largest branch of the coeliac trunk. Travels along the superior border of the pancreas to reach the spleen
What is the blood supply of the pancreas?
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
What is the venous drainage of the spleen and pancreas?
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
What is the innervation of the stomach?
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
What is the innervation of the midgut?
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
What is the innervation of the hindgut?
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
What is the ENS?
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
What is Congenital megacolon?
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
What is the lymphatic drainage of stomach?
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
What are the lymphatics of the small intestine?
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)
What are the lymphatics of the large intestine?
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
What are the lymphatics of the Liver?
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.
Why is pancreatic cancer so deadly?
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)
What are the lymphatics of the pancreas?
Pancreaticosplenic and back to coeliac nodes and superficial mesenteric nodes
What is liver pain caused by?
Liver, Gallbladder and Duodenum: irritate the diaphragm, pain felt on neck (C3-5 dermatome)
Commonly misdiagnosed
