GI PBL 1 Flashcards
What makes up the upper GI tract?
The oesophagus, the stomach and the duodenum
How long is the oesophagus?
Roughly 25cm
What is the function of the oesophagus?
To transport food from the pharynx to the stomach
Where does the oesophagus originate?
The inferior border of the cricoid cartilage (C6)
Where does the oesophagus finish?
The stomach at the level T11
What is the oesophagus made up of?
The adventitia, muscular layer, submucosa and mucosa
What is the adventitia?
The outer layer of connective tissue
What is the muscular layer?
An external layer of longitudinal muscle and an internal layer of circular muscle
What types of muscle make up the outer layer of muscle?
Superior third: Voluntary striated muscle
Middle third: voluntary striated and smooth muscle
Inferior third: smooth muscle
What is the mucosa?
Non-keratinised stratified squamous epithelium
What type of epithelium line the stomach?
Columnar epithelium
How is food transported through the oesophagus?
peristalsis
What is peristalsis?
Rhythmic contractions of the muscle which moves food down the oesophagus
What are the oesophageal sphincters?
Upper and Lower oesophageal sphincters
What is the function of the oesophageal sphincters?
They help to prevent the entry of air and the reflux of gastric contents
What type of sphincter is the UOS?
A striated muscle sphincter
Where is the UOS?
The junction between the pharynx and the oesophagus
What muscle produces the UOS?
The cricopharyngeal muscle
Is the UOS usually constricted or relaxed?
Constricted to prevent the entrance of air into the oesophagus
What type of sphincter is the LOS?
A physiological sphincter - it doesn’t have a specific sphincter muscle
Where is the LOS located?
The gastro-oesophageal junction (between the stomach and the oesophagus situated to the left of the T11 vertebra)
How is the LOS formed?
- The oesophagus enters the stomach at an acute angle
- The walls of the intra-abdominal section of the oesophagus are compressed when there is a positive intra-abdominal pressure
- The folds of mucosa present aid in occluding the lumen at the gastro-oesophageal junction.
- The right crus of the diaphragm has a pinch-cock effect
When is the LOS relaxed?
During peristalsis to allow food to enter the stomach
What supplies blood to the thoracic portion of the oesophagus?
branches of the thoracic aorta and the inferior thyroid artery
What is the venous drainage of the oesophagus?
branches of the azygous veins and the inferior thyroid vein
What supplies blood to the abdominal portion of the oesophagus?
Left gastric artery (branch of the coeliac trunk) and left interior phrenic artery
What is the venous drainage of the abdominal portion of the oesophagus?
- portal circulation via the left gastric vein
- systemic circulation via the azygous vein
What is the innervation of the oesophagus?
- the oesophageal plexus combination of parasympathetic and sympathetic nerve fibres
What are the four main divisions of the stomach?
cardia, fundus, body, pylorus
What is the cardia?
The area that surrounds the superior opening of the stomach at the T11 level
What is the fundus?
The rounded often gas filled portion superior to and left of the cardia
What is the body of the stomach?
The large central portion inferior to the fundus
What is the pylorus of the stomach?
the area that connects the stomach to the duodenum
What is the pylorus divided into?
The pyloric antrum and the pyloric sphincter
What is the stomach wall composed of?
Serosa, muscularis, submucosa and mucosa
What are the layers of the muscularis
Oblique, circular and longitudinal
What is the function of the muscularis
The layers of muscle contract rhythmically to break up food in the stomach
What is the submucosa made up of?
Made up of connective tissue and a vascular plexus
What is the function of the submucosa
Allows the mucosa to move freely over the deeper structures
What is the mucosa?
the deepest layer of the stomach made up of three layers
What are the three layers of the stomach mucosa?
Epithelium, lamina propria, muscularis mucosae
Why is the internal surface of the stomach folded?
To form millions of gastric pits
What is the lamina propria?
Loose connective tissue that lies between the muscularis mucosae and the outer layer
What does the lamina propria of the stomach contain?
Capillaries, lymphatic vessels and nerves and gastric glands
What is the muscularis mucosae of the stomach?
A thin layer of smooth muscle that lies between the lamina propria and submucosa
What is the function of the muscularis mucosae in the stomach?
when it contracts, it compresses the gastric glands and helps to push their contents into the stomach
Where does the greater omentum hang from?
The greater curvature of the stomach
What is the function of the greater omentum?
Has many lymph nodes and can adhere to inflamed areas so helps minimise the spread of infections
Where is the lesser omentum found?
It is continuous with the peritneal layers of the stomach, it attaches to the liver
What is the function of the lesser omentum?
To attach the stomach and duodenum to the liver
What is the main arterial supply of blood to the stomach?
The coeliac trunk and its branches
what is the innervation of the stomach?
parasympathetic and sympathetic
- Parasympathetic supply – arises from the anterior and posterior vagal trunks, derived from the vagus nerve
- Sympathetic supply – arises form the T6-T9 spinal cord segments and passes to the coeliac plexus via the greater splanchnic nerve. It also carries some pain transmitting fibres.
What is the duodenum?
The most proximal portion of the small intestine
Where does the duodenum go?
From the pylorus of the stomach to the duodenojejunal junction
What is the function of Brunner’s glands?
To produce mucous and bicarbonate to neutralise stomach acid
Are Brunner’s glands present in the rest of the small intestine?
no
What is the function of mucous cells?
to produce mucous
What is the function of parietal cells?
To produce HCl acid
What is the function of mucous neck cells?
To produce mucin which turns into mucous when combined with water
What is the function of ECL cells?
To produce histamine
What does histamine do in the GI tract?
stimulates acid secretion by acting on parietal cell via H2 receptor and by acting on D cell via H3 receptor (inhibits somatostatin production)
What is the function of D cells?
To produce somatostatin
What is the function of somatostatin in the GI tract?
inhibits parietal cell acid secretion and inhibits ECL cell histamine secretion
What is the function of chief cells?
To produce pepsinogen (converted to pepsin in the presence of acid)
What is the function of G cells?
To produce gastrin
What is the function of gastrin in the GI tract?
stimulates ECL cell to produce histamine and stimulates parietal cell to produce acid
What is the effect of prostaglandins in the GI tract?
stimulate mucus and bicarbonate secretion as well as vasodilation of nearby bloody vessels.
What is the location of gastrin?
The gastric antrum, duodenum
What is the function of CCK in the GI tract?
- Stimulates gallbladder contraction
- stimulates release of pancreatic enzymes
- relaxes the sphincter of Oddi for release of bile and enzymes
What is the location of CCK?
Duodenum, jejunum
What is the function of secretin in the GI tract?
- Stimulates secretion of HCO3 from the pancreas
- inhibits gastrin and gastric acid secretion
What is the location of secretin?
Duodenum and jejunum
What is the function of Vasoactive intestinal peptide (VIP)?
- Increases water and electrolyte secretion from the pancreas and gut
- relaxes smooth muscle (via NO) of the gut
What is the location of VIP?
Enteric nerves
What is the function of gastric inhibitory polypeptide (GIP)?
- reduces gastric acid secretion and intestinal motility
- stimulates insulin release
What is the location of GIP?
Duodenum, jejunum
What is the function of motilin in the GI tract?
Increases small bowel motility (MMC during fasting) and gastric emptying
What is the location of motilin?
throughout the gut
What is the function of somatostatin in the GI tract?
inhibits secretion and action of many hormones
What is the location of somatostatin?
Stomach, small intestine, and pancreas
What is a peptic ulcer?
A break in the mucosal lining of the stomach or duodenum more than 5mm in diameter, with depth to the submucosa.
What is it called when an ulcer is smaller than 5mm and doesn’t have appropriate depth?
An erosion
What is an erosion?
Ulcers smaller than 5mm and without depth to the submucosa
How do peptic ulcers arise?
An imbalance between factors promoting mucosal damage.
This can include gastric acid, pepsin, H. Pylori infection, non-steroidal anti-inflammatory drug use
What other mechanisms can cause peptic ulcers?
Mechanisms promoting gastroduodenal defence (prostaglandins, mucous, bicarbonate, mucosal blood flow)
What are the most common causes of peptic ulcers?
NSAIDs and H. Pylori bacterial infection
Why do NSAIDs cause peptic ulcers?
- topical irritant effect of these drugs on the epithelium
- impairment of the barrier properties of the mucosa
- suppression of gastric prostaglandin synthesis
- reduction of gastric mucosal blood flow
- interference with the repair of superficial injury
How does H. Pylori cause peptic ulcers?
causes an inflammatory response with neutrophils, lymphocytes, plasma cells, and macrophages within the mucosal layer and causes epithelial cell degeneration and injury
what are the three layers of the inner wall of the GI tract?
- The innermost epithelial layer
- the middle layer - the lamina propria
- the outermost layer - the musclaris mucosa
What is the function of the innermost epithelial layer of the GI tract?
Absorbs and secretes mucus and digestive enzymes
What is the function of the middle layer of the inner wall of the GI tract?
contains blood and lymph vessels
What is the function of the outermost layer of the inner wall of the GI tract?
contracts and helps with the breakdown of food
What are the four regions of the stomach?
cardia, fundus, body and antrum
What keeps the food inside the stomach to be digested?
The pyloric sphincter
What type of organism are H. Pylori
Gram negative bacteria
What damaging substances do H. pylori release?
Proteases
What effect do proteases have on the gastric mucosa?
damages them
Where does the majority of damage happen?
The antrum
How do NSAIDs cause ulcers?
They inhibit COX which affects the synthesis of prostaglandins
What is Zollinger Ellison syndrome?
when a neuroendocrine tumour in the duodenal wall or pancreases causes an abnormal amount of gastrin to be secreted which stimulates parietal cells to release HCL which overwhelms normal defence mechanisms and allows ulcers to develop
What are the symptoms of peptic ulcers?
- Epigastric pain
- bloating
- vomiting
- pain that increases with eating (gastric ulcers)
- Pain that decreases with eating (duodenal ulcers)
- weight loss (gastric ulcer)
- weight gain (duodenal ulcers)
What are potential complications of peptic ulcers?
- If an ulcer erodes all the way through the wall of the stomach or duodenum then this can result in a perforation, this can allow GI contents into the space surrounding
- Very deep ulcers can erode into blood vessels and cause bleeding which is particularly dangerous when there is an artery nearby. This can lead to haemorrhage into the GI tract, which in turn can lead to shock.
- Long standing duodenal ulcers near the pyloric sphincter if there is a lot of edema or scarring it may obstruct normal passage of the gastric contents into the intestines resulting in gastric outlet obstruction. This can quickly lead to nausea or vomiting since the food cant get past
What is an advantage of serology to diagnose peptic ulcers?
It is the only test not influenced by PPIs and antibiotic use
What is a disadvantage of serology to diagnose peptic ulcers?
Cannot confirm the cure
What is an advantage of the urea breath test to diagnose H. pylori?
Can confirm cure
What is a disadvantage of urea breath test to diagnose H. pylori?
Accuracy is affected by PPI and antibiotic use
What is an advantage of faecal antigen testing to diagnose H. pylori?
Confirms cure
What is a disadvantage of faecal antigen test to diagnose H. pylori?
Accuracy is affected by PPI and antibiotic use
What is an advantage of Rapid urease test to diagnose H. pylori?
inexpensive, confirms cure
What is a disadvantage of rapid urease test to diagnose H. pylori?
Requires endoscopy, less accurate or after use of PPIs
What is an advantage of histology to diagnose H. pylori?
permits visualisation, confirms cure
What is a disadvantage of histology to diagnose H. pylori?
requires endoscopy, less accurate, affected by PPI and antibiotic use
What is an advantage of culture to diagnose H. pylori?
allows determination of antimicrobial sensitivity, confirms cure
What is a disadvantage of culture to diagnose H. pylori?
Requires endoscopy, result takes several days, affected by PPIs and antibiotic use
How does the urea breath test work?
- Patient swallow’s urea labelled with C13/14
- If H. pylori is present, then urease will have split/metabolized the urea
- When the patient exhales and their breath is tested, the presence of isotope marked CO2 will show if they have H. Pylori or not
How are peptic ulcers treated?
Reducing acid secretion
How do PPIs work?
Irreversibly block the H+/K+ ATPase enzyme or the gastric proton pump, which is found within the parietal cells of the stomach and is the final step of acid production
Why does preventing secretion of acid heal peptic ulcers?
gives damaged tissue time to heal
How long is the plasma T1/2 of PPIs?
short (30-60 minutes)
What can happened when people stop taking PPIs?
can result in high levels of gastrin when the patient stops taking them meaning they will potentially get some reflux symptoms
What is Vonoprazan?
A competitive potassium channel blocker at the proton pump (P-CAB)
Is Vonoprazan more or less effective than PPIs?
The acid suppression effects of Vonoprazan are considerable more potent than PPIs
What are H2 receptor antagonists?
- H2 blockers stop the acid-making cells in the stomach lining from responding to histamine
Why would antibiotics be used to treat peptic ulcers?
can be used to kill H. Pylori if it’s the underlying cause of the ulcers
What antibiotics can be used to treat H. Pylori?
amoxicillin, clarithromycin, tetracycline
What is a vagotomy?
The vagal nerve is severed
