Clinical Anatomy of the GI Tract Flashcards
Describe oesophageal anatomy
-Fibromuscular tube, 10 inches long, C6-T10
-Oesophageal plexus (vagus and sympathetics)
=Branch of vagus= left recurrent laryngeal nerve goes around aortic arch
-Vagal trunks (anterior and posterior)
-Oesophageal hiatus in diaphragm
-Right crus of diaphragm forms a sphincter-like sling= prevent reflux
What are the oesophageal constrictions (physiological narrowing)?
- Superiorly: level of cricoid cartilage, juncture with pharynx
- Middle: crossed by aorta and imprint of left main bronchus
- Inferiorly: diaphragmatic sphincter
Describe esophageal histology
-Mucosa =Stratified squamous, usually non-keratinizing =Muscularis mucosae prominent -Submucosa: mucous glands -Muscularis externa (circular skeletal muscle and longitudinal skeletal muscle layers with connective tissue in between) -Adventitia =Loose connective tissue =No serosa (unlike stomach)
How can histology help staging?
- Mucosa, muscularis mucosa and submucosa= T1
- Muscularis propria= T2
- Touches adventitia/ serosa= T3
- Tumour out of layers into nearby organs= T4
How is endoscopic ultrasound used in staging?
- Mucosal interface (hyperechoic= lighter)
- Mucosa (hypoechoic= darker)
- Submucosa (hyperechoic)
- Muscularis propria (hypoechoic)
- Adventitia (hyperechoic)
Where does the oesophagus tend to metastasize to?
- Lymph areas
- Bifurcation of trachea
- Lymph nodes between aortic arch and pulmonary artery
- Towards diaphragm
Why do patients present with a hoarse voice?
- Left recurrent laryngeal nerve related to movement of vocal chords
- If infiltrated affects vocal chords
- Advanced tumour
Describe the liver portal vein supply
-Superior mesenteric vein= draws blood from small bowel and right side of large bowel
-Inferior mesenteric vein= draws blood from left side of large bowel
-Joined by splenic vein from spleen
=All join to form portal vein
Other veins to know
- Left gastric vein takes blood from lesser curve of stomach and branches of this from fundus of stomach
- Coronary vein= blood from periesophageal plexus into portal vein
How does portal hypertension lead to varices?
- Nodular, stiff cirrhosis
- Blood from portal vein can’t get through easily so pressures increase
- Blood flow slows= collateral circulation= shunting of blood so portal vein to peri esophageal plexus= esophageal varices
- Collaterals drain into hemi-azygous and azygous veins= superior vena cava
- Reversal of flow in splenic vein= collateral forms in fundus to peri oesophageal plexus= gastric varices
How does vessel obstruction lead to varies?
- Clot in portal vein= portal vein thrombosis (slowed blood in cirrhosis)
- Blood from superior and inferior mesenteric veins and splenic vein can’t go through= bypass area by forming large varices in lower oesophagus
- Backflow in splenic vein= gastric varices
What happens if there is clotting in the splenic vein?
-Acute pancreatitis
-Blood no longer drains from spleen
=Collaterals to fundus of stomach
=Segmental portal hypertension, manifested with gastric varices
What happens when the is a clot in the superior mesenteric vein?
-Inflammation of small bowel (bowel ischaemia or trauma)
-Regional development of collaterals that manifest as varices in the small bowel
Blood bypasses by creating anastomosis with nearby vessels
How do we treat oesophageal varices?
- Endoscope
- Apply suction and place bands
- Thrombose/ clot areas to divert blood flow from very superficial layers into deeper layers to stop bleeding
- Ulceration heals
How do we treat gastric varices?
-Inject sclerosant/ thrombotic agent like thrombin
What are the regions of the stomach?
- Cardiac
- Fundus
- Corpus (body)
- Pyloric: antrum, canal, sphincter
Describe stomach histology
-Zones: cardiac, fundic, pyloric
-Glands in all zones have mucous cells and enteroendocrine cells
-Fundic glands
=Parietal (oxyntic) cells: HCl, intrinsic factor (B12 absorption)
=Chief (zymogenic) cells: pepsinogen, rennin, lipases
=Mucous neck cells
=Enteroendocrine cells: gastrin (secretion of acid), cholecystokinin (stimulates contraction of gall bladder to secrete bile), secretin, serotonin, glucagon
What are the vessels of the coeliac axis?
-Aorta= coeliac trunk= left gastric artery, common hepatic (branch of right gastric, proper hepatic into R L and middle, gastroduodenal and supraduodenal), splenic artery
Where is the coeliac axis?
-Left gastric artery supply upper part of stomach, lesser curve
-Splenic artery bhind to spleen
Gastro Duodenal= bulb and posterior first part of duodenum- area for duodenal ulcers
Describe how to liver in linked with the gallbladder
- Right and left lobe, right and left hepatic duct= common hepatic duct into gallbladder
- Cystic duct links gallbladder to common duct
- Lower end of bile duct goes through head of pancreas, drains in ampullary area, to sphincter of Oddi
- Pancreatic duct meets bile duct at level of ampulla
- When sphincter opens up, gallbladder contracts at same time= bile flows down to mix with food
Why is the gallbladder important clinically?
- Stones= if it leaves and goes down common bile duct= obstruction= bile in blood so jaundice
- Tumour at head of pancreas- stops flow of bile into duodenum= enlarged gallbladder as tumour grows very slowly so duct dilates= jaundiced but painless- presents with weight loss and back pain
- Tumour at ampulla
How do we image the bile duct?
-High resolution Liver MRI
Describe blood supply to the gut and how it can be clinically important
-Coeliac trunk to foregut
-Superior mesenteric artery= midgut
=Can often be narrowed= ischaemia= abdominal angina- abdominal pain after eating
-Inferior mesenteric artery= hindgut
Describe the caecum
- Right side
- Ileocaecal valve
- Area of appendix
