S5 Functions Of The Stomach Flashcards
What are the 3 main functions of the stomach?
Store and disrupt food
Disinfect food
Activate proteases
Describe the different parts of the stomach
At the entrance is the cardia
Fundus is at the top
Below is the body
Antrum is near the pyloric sphincter
What are the functions of the upper and lower areas of the stomach?
Upper stomach: has regular sustained contractions creating a basal tone of flow down the tube to reduce reflux
Lower stomach: strong peristalsis mixes stomach contents, coordinated movements
What is receptive relaxation?
Vagally mediated relaxation of the orad stomach (fundus + top ½ of the body), allowing storage of food since we consume faster than we digest.
Which cells secrete which substance in the stomach?
Parietal - HCL and intrinsic factor G cell - gastrin Enterochromaffin like cells - histamine Chief cell - pepsinogen D cell - somatostatin Mucus cell - mucus
Which cells are found mainly in the cardia, fundus and pylorus?
Cardia- mucus
Fundus and body - mucus, HCl, pepsinogen
Pylorus - gastrin, somatostatin
How does gastrin cause HCL secretion?
Gastrin acts on CCK receptor on parietal cell which causes HCL secretion
How does histamine cause HCL secretion?
Enterochromafin cells release histamine which acts on H2 receptor on parietal cell causing HCL secretion.
How does ACh cause HCL secretion?
Vagus nerve releases ACh which binds to muscarinic receptor on parietal cell causing HCL secretion
How is gastrin secretion controlled?
G cells in antrum stimulated by peptides and vagal stimulation (ACh and GRP).
Inhibition is via somatostatin.
What happens in the cephalic phase of digestion?
Parasympathetic stimulation from chewing cause’s direct stimulation of parietal cell by vagus nerve, and stimulation of G cells by vagus nerve
What happens in the gastric phase of digestion?
Distension of stomach and presence of amino acids stimulates G cells and parietal cells
What happens in the intestinal phase of digestion?
Chyme stimulates CCK and secretin which help suppress secretion of gastrin.
How does the stomach epithelia protect itself?
Mucus forms an alkaline layer protecting the epithelia
High turnover of epithelial cells
Prostaglandins maintain mucosal blood flow to epithelium
What is GORD?
Excess reflux of stomach contents into oesophagus
What are the causes of GORD?
Issues with lower oesophageal sphincter
Obesity
What are the symptoms and complications of GORD?
Heartburn, sore throat, dysphasia
Barrett’s oesophagus
What is acute gastritis?
Acute mucosal inflammation
Can be due to NSAIDs or alcohol
What is chronic gastritis?
Mucosal inflammation caused by;
H. Pylori (can cause peptic ulcer or adenocarcinoma)
Antibodies inhibiting parietal cells
Chronic alcohol abuse
How can gastritis cause perinicous anaemia?
Inhibiton of parietal cells reduces the amount of intrinsic factor released which is needed for Vit B12 absorption
What is a peptic ulcer?
Mucosal injury that pierces through the muscularis mucosa layer, most commonly in the 1st part of the duodenum, also the lesser curvature of the stomach.
What can cause a peptic ulcer?
Stomach acid
H. Pylori
NSAIDs
What are the symptoms of a peptic ulcer?
Epigastric pain - esp following a meal
Bleeding
Weight loss
How are gastric ulcers, GORD and gastritis treated?
Eradicate H pylori: triple therapy of PPI + clarithromycin + amoxicillin
PPIs: eg omeprazole which inhibits the proton pump
H2RA: eg ranitidine which prevents histamine stimulating parietal cell
What is Zollinger-Ellison syndrome?
Non-beta islet cell, gastrin-secreting tumour of the pancreas.
Causes proliferation of parietal cells increasing acid production, severe ulceration of stomach
How might gastric pathologies be diagnosed?
GI endoscopy
Blood test for anaemia
Urease breath test for H Pylori
How does H pylori damage epithelia?
Produces urease which converts urea to ammonium which is toxic to epithelia and increases local pH.
Can also release cytotoxins and degrade the mucus layer
What is the effect of H pylori depending on where it is mostly distributed?
Antrum: affects G cells increasing gastrin secretion. Leads to duodenal ulceration
Body: gastric ulcer, cancer
Describe the presentation and risk factors of stomach cancer
Dysphagia, loss of appetite, malaena, weight loss, enlarged Virchow’s nodes
H. Pylori, infection, smoking
