GI Session 1 Flashcards
What are the three narrowings of the oesophagus?
Cricopharyngeal sphincter
Broncho-aortic constriction
Inferior oesophageal sphincter
Is the inferior oesophageal sphincter a true sphincter?
No, physiological caused by diaphragmatic constriction and angle made with junction of stomach
How far is oesophagsatric mucosal junction from the incisors?
40 cm
What is visible on endoscopy of the oesophagus at the oesophagogastric mucosal junction?
Pale pink squamous epithelium –> dark red gastric epithelium
What is hiatus hernia?
Where the cardia and fundus of the stomach push through the oesophageal opening in the diaphragm
What is Barrett’s oesophagus?
Chronic acid exposure cause metaphase of squamous epithelium to gastric columnar epithelium
What are the five regions of the stomach?
Cardia Fundus Body Pyloric antrum Pylorus
Where is gastric ulceration most commonly seen in the the stomach?
At the lesser curvature
Which part of the stomach is removed in sleeve gastrectomy in bariatric surgery?
Greater curvature
Where do peptic ulcers which bleed slower than those in the duodenum develop?
Pyloric canal
Describe the nervous control of the oesophagus.
Superior 1/3 voluntary
Inferior 2/3 autonomic
What gives arterial supply to the superior 2/3 of the oesophagus?
Systemic arteries: inferior thyroid and aortic branches
What gives venous drainage to the superior 2/3 of the oesophagus?
Systemic veins: inferior thyroid and Azygos branches
What gives arterial and venous drainage to the inferior 1/3 of the oesophagus?
Portal system: L gastric branch of coeliac trunk, L inferior phrenic artery, drains into L gastric vein
What causes oesophageal varices?
In portal hypertension blood can’t pass through portal hepatic vein so there is a reversal of blood flow through porto-systemic anastomoses –> oesophageal submucosal veins dilate with increased flow
What controls entry of stomach contents into the duodenum?
Pyloric sphincter at the end of the pyloric canal formed by muscular thickening
What are rugae in the stomach?
Longitudinal gastric folds that allow for expansion of the stomach
What overlaps the first portion of the duodenum?
Liver and gallbladder
Describe the position of the second part of the duodenum.
Descends retroperitoneal around the head of the pancreas
What is the significance of the embryological origin of the second part of the duodenum?
Marks transition from embryonic foregut to midgut therefore receives blood supply from coeliac trunk and SMA
Describe the passage of the third part of the duodenum.
Runs transversely at L2/3 level crossing the aorta below SMA origin
Describe the position of the fourth part of the duodenum.
Retroperitoneal and ascends to left of midline where it turns to form the duodenojejunal flexure
What happens to the duodenum as it forms the duodenojejunal flexure?
Becomes intraperitoneal and has a mesentery
Why is the first part of the duodenum most likely to ulcer?
Lack of mucus and acidity of contents which is yet to be neutralised by addition of HCO3-
What happens if a duodenal ulcer in the first part of the duodenum erodes anteriorly or posteriorly?
Anteriorly –> peritonitis
Posteriorly –> perforates gastroduodenal artery causing massive haemorrhage or erodes into pancreas causing severe pain in lumbar region
What an lead to gallstone ileus?
Erosion of a gallstone causing a choledocoduodenal fistula which the stone can then pass through
What supports the duodenojejunal flexure?
Ligament of Treitz
What signifies the opening of the main pancreatic duct into the duodenum?
Major duodenal papilla
What controls release of contents from the pancreatic duct into the duodenum?
Sphincter of Oddi
What does ulceration in the second part of the duodenum suggest?
Pancreatic disease
Zollinger-Ellison syndrome
What is Zollinger-Ellison syndrome?
Gastrin-secreting tumour stimulates parietal cells to maximal activity
What can form in the third part of the duodenum if either the aorta or duodenum is diseased?
Aorto-duodenal fistula
What is seen following dramatic weight loss in the third part of the duodenum?
SMA syndrome where aorta and SMA press on the third part of the duodenum causing partial/complete obstruction
What an happen in the duodenum in deceleration injury?
Traction injury caused by ligament of Treitx pulling of duodenojejunal flexure and causing subsequent perforation
Where does the ligament of Treitz descend from?
Right crus of diaphragm
What does contraction of the ligament of Treitz aid?
Persistalsis
Describe the passage of the common bile duct.
Passes behind duodenum to run in a groove within the pancreas entering the duodenum at the Ampulla of Vater
Where can the Pringle manoeuvre to control hepatic haemorrhage be applied?
Along the free edge of the lesser omentum where the common bile duct, portal vein and artery run
What are the components of the biliary tree?
Intrahepatic ducts –> R and L hepatic ducts –> common hepatic duct –> +cystic duct from gallbladder –> common bile duct
What do S/S of jaundice, dark urine and pales stool indicate?
Blockage of the common bile duct causing disruption of entero-hepatic bile salt
What is painless obstructive jaundice commonly secondary to?
Tumour: carcinoma of head of pancreas, cholangiocarcinoma, adenocarcinoma of duodenum, liver tumour causing extrinsic pressure
What does painful obstructive jaundice suggest?
Gallstone disease
What attaches the small bowel to the posterior abdominal wall?
15 cm long mesentery from DJ flexure to R sacroiliac joint
Why does the jejunum have a thicker wall than the ileum?
More, larger and taller pliae circulares
Why is the jejunum deeper red than the ileum?
Greater blood supply
What atrophies in coeliac disease?
Deep crypts with tall villi of jejunal wall
What can cause luminal obstruction of the ileum in lymphoma?
Enlargement of the abundant Peyer’s patches
What are Peyer’s patches which are found in the ileum?
Aggregates of lymphoid tissue
What is Meckel’s diverticulum?
Embryological remnant in distal ileum with gastric mucosa that secretes acid
What is the rule of 2s that Meckel’s diverticulum follows?
Seen in 2% of the population
2 inches long
Presents at 2 y.o.
2 ft from iliocaecal valve
Which quadrants is the jejunum mainly located in?
L and R upper quadrants
Which quadrants is the ileum mainly situated in?
R and L lower quadrants
Is the colon longer in males or females?
Females
How long is the colon typically?
100-180 cm
What forms the taenia coli?
3 longitudinal bands of muscle along the length of the colon
Where do the taeni coli converge and what is the result of this?
In appendix which makes its lumen look triangular
What forms saculations in the colon?
Longitudinal bands of muscle being shorter than the colon
What prevents back flow of colonic contents during persistalsis?
Iliocaecal valve
Why is the rectum lumen circular?
Due to thick circular muscle needed to for formed stool passage
What breaks the appearance of the circular lumen of the rectum?
Haustral folds
What is the dentate/pectineal line formed by?
Valves of Ball from vertical columns of Morgagni
What is the significance of the pectineal line?
Watershed for supply and drainage
What supplies and drains the rectum above the pectineal line?
IMA
Visceral pelvic splanchnic nerves
IMV
Mesenteric nodes
What supplies and drains the rectum below the dentate line?
Internal iliac artery
Inferior rental nerve
Internal iliac vein
Iliac and inguinal nodes
How does pain sensed above and below the dentate line compare?
Above is dull and poorly located, below is sharp and well localised
Describe the position of the transverse colon with relation to surface markings.
Lies at umbilicus but may hang down into pelvis, esp in women
What forms the iliocaecal valve?
Oblique entrance a partial invagination of the ileum
How long is the ascending colon?
12-20 cm
How long is the transverse colon?
45 cm
How long is the descending colon?
22-30 cm
Where is the appendix found?
3 cm below the iliocaecal valve
Where does the caecum lie?
R iliac fossa
What are the fat filled peritoneal tags on the colon called?
Appendices epiploicae
How long is the sigmoid colon?
37 cm usually but can be up to 70 cm
How do colonic tumours in the caecum present?
Mass
Change in bowel habit
Decreed iron levels –> anaemia
Pain
What causes the caecum to dilate or perforate in large bowel obstruction?
Iliocaecal valve preventing back flow of air and colonic contents which cannot pass distally
Where does the rectum extend from and to?
S3 –> anal canal
Where is the most common location of colonic diverticulum?
Arterial entry point of sigmoid colon
Are colonic diverticuli in the sigmoid colon true diverticuli?
No because they do not involve the entire thickness of wall of parent organ
What can occur as a result of the length and loose mesenteric attachment of the sigmoid colon?
Sigmoid volvulus
What are the S/S of sigmoid volvulus the same as?
Large bowel obstruction with clack cal radiological appearance
How is sigmoid volvulus treated?
Flexible sigmoidoscopy
Where do 50% of colon cancers arise?
Rectum
Are tumours the same above and below the dentate line and why?
No, above has hindgut origin so is columnar epithelium and below is ectoderm so stratified squamous epithelium
What causes haemorrhoids?
Varices in portal hypertension due to porto-systemic anastomoses in rectum
How do haemorrhoids above and below the pectineal line compare?
Above are relatively painless so can be injected/banded
Below are very painful
How long is the oesophagus?
25 cm
What forms the alimentary canal?
Mouth Tongue Pharynx Oesophagus Stomach Small intestine Colon Appendix Rectum Anus
What are the accessory organs to the alimentary canal?
Salivary glands
Liver
Gallbladder
Pancreas
What forms the mucosa of the gut wall?
Epithelium, LP with aggregations of lymphocytes in Peyer’s patches, muscularis mucosae
What forms the submucosa of the gut wall?
Layer of CT with glands, arteries, veins and nerves which are particularly on the outer edge near the muscle
What forms the muscularis externae of the gut wall?
Outer longitudinal and inner circular layers of muscle which spiral down the gut to create peristaltic waves
What forms the serosa of the gut wall?
CT covered by simple squamous epithelium which surrounds most but not all of the gut
What does the serosa of the gut wall form?
Mesentery which contains arteries, veins and nerves
What are the layers of the gut wall from innermost to outermost?
Mucosa
Submucosa
Muscularis externae
Serosa
What are the major functions of the GI tract?
Movement of food Absorb nutrients Mechanically disrupt food Port of food entry Eliminate residual waste material Temporarily store food Chemically digest food Sterility
Where is movement of food most rapid in the GI tract?
Oesophagus and rectum
What are the major steps in the digestion of food?
Physical and chemical disruption –> sterile, neutral pH, isotonic solution –> absorption
What causes physical and chemical disruption of food in the mouth?
Physical: teeth, tongue, muscles of mastication
Chemical: salivary amylase and lipase
What protects teeth in the mouth?
High calcium concentration of saliva
How much saliva is added to ingested food in the mouth?
1.5 l
What provides innervation to the oesophagus?
Submucosal and myenteric plexuses
Where is the myenteric plexus located?
Between circular and longitudinal layers of muscle in the oesophagus
What gives paracrine control of motility and secretion in the GI tract?
Histamine controls gastric acid
Vasoactive substances control gastric blood flow
Why is fluid balance in the GI tract delicate?
Large quantities that are vary variable are involved
What gives neural control of motility and secretion in the GI tract?
Somatic: mouth, 1/3 oesophagus, last sphincter of anus
Autonomic: everything else via submucosal and myenteric plexuses with lots of neurotransmitters
What gives endocrine control of motility and secretion in the GI tract?
Secretin, gastrin and CKK control gastric acid, alkali and enzyme secretion
How much fluid is added to ingested food by the stomach?
2.5 l of gastric secretions
Why does the stomach act as a necessary food store?
We eat faster than we can digest
What is the purpose of receptive relaxation in the stomach?
So pressure doesn’t rise as it stretches from 50 ml to 4 l
How does the stomach physically disrupt ingested food?
Contracts rhythmically to move dynamic rugae
What cells are found in the stomach and what do they secrete?
Chief - enzymes
Parietal - acid and intrinsic factor
Goblet - mucus
How does the stomach produce a hypertonic chyme?
Combines action of acid, enzymes and agitation increases the number of molecules present
What are the main functions of the duodenum?
Dilution
Neutralisation of chyme
Iron absorption
How much fluid is added to the contents of the duodenum?
9 l of water/alkali
Where is water drawn from in the duodenum to make chyme isotonic?
ECF
What is the function of Brunner’s glands, found above the Sphincter of Oddi?
Produce mucus rich alkaline solution to protect duodenum and inhibit gastric chief and parietal cell function
What do the accessory organs secrete into the chyme in the duodenum?
Liver releases bile containing water, alkali and bile salts
Pancreas secretes alkali and enzymes
How is digestion of chyme completed in the duodenum?
Secretion of enzymes by pancreas, liver and intestine
What so the function of the jejunum?
Absorption of most nutrients
What forms the jejunal mucosa?
Simple columnar epithelium
Lamina propria
Muscularis mucosa with microvilli and goblet cells
What are pliae circulares?
Permanent circular folds of mucosa and submucosa that project into the jejunal lumen
Why is gut transit reduced in the jejunum?
To give adequate time for absorption
Describe the absorption which takes place in the jejunum.
Most active takes place proximally
Absorbs mainly sugars and a.a.
What is the main function of the large intestine?
Drying of contents (although jejunum actually absorbs more water)
How are useful small molecules absorbed in the large intestine?
By bacteria involved in vitamin synthesis and enterocytes
What epithelium lines the large intestine?
Simple columnar with attached enzymes, crypts of Lieberkühn and lymphatic tissue
What vitamins are synthesised by bacteria in the large intestine?
K
B12
Thiamine
Riboflavin
What causes the urge to defecate?
Rapid propulsion of colonic contents into rectum causing it to stretch
What can overcome the urge to defecate?
Reverse peristalsis
How much water is removed from the colonic contents by the large intestine?
1.35 l
How much water is removed from the contents in the small intestine?
12.5 l
