gastric secretions Flashcards
what is secreted in the saliva?
amylase lysozyme bicarbonate growth factors trans cobalamin II water
what does amylase do?
breaks polysaccharides to disaccharides
what does lysozyme do?
lyses bacterial membranes
what does bicarbonate do?
neutralizes food and bacterial acids
what do growth factors in the saliva do?
stimulate epithelial proliferation to protect the oesophageal epithelium from breaking down.
what does transcobalamin II do?
binds to vitamin B12: prevent breaking down stomach
what is found in gastric secretions?
mucous, acid, pepsinogen, chymosin, lipase and intrinsic factor
what secretes mucus and what does it do?
mucus - coats and lubricates gastric surface and protects the epithelium
what is secreted by parietal cells and what does it do?
HCl
activates pepsinogen –> pepsin
inactivates ingested microorganisms
what secretes pepsinogen?
mucus cells and chief cells
what does pepsinogen do?
activated to pepsin by acid to digest proteins
what secretes chymosin?
chief cells
what does chymosin do?
coagulates milk protein
what secretes lipase?
chief cells
what secretes intrinsic factor?
parietal cells and chief cells
what does intrinsic factor do?
binds vitamin B12 in the intestine so it can be absorbed
explain how vitamin b12 is absorbed
binds to salivary haptocorrin complexed with stomach IFs absorbed in the terminal ileum transported in portal circulation transferred to transcobalamin degraded in lysosome to allow function in metabolism
what do surface mucus cells secrete?
mucus, trefoil peptides (associated with mucus), bicarbonate
what is the function of mucus neck cells?
stem cell compartment
what do parietal cells secrete?
secrete acid and intrinsic factor
what do ECL cells secrete?
secrete histamine
what do chief cells secrete?
secretes pepsinogen, chymosin and lipase
what do G cells secrete?
hormones such as gastrin
explain the process of gastric acid secretion
carbonic acid –> CO2 and H2O
H2O –> OH- and H+
CO2 and OH- become bicarbonate ion
H+ pumped into lumen via H+/K+ pump on apical membrane
Cl- pumped into lumen via CFTR channel
HCl formed and turns pepsinogen –> pepsin
where is the H+/K+ pump found?
apical membrane of the parietal cell
what are canaliculi and what do they do?
secretory network in the parietal cells
transport protons to the top of the cell so it can be secreted through the mucus layer into the lumen
why is mucus important in acid control?
acts as a physical and chemical barrier to stop acid from interacting with cells directly
what effect does histamine have on acid secretion and how?
stimulates acid secretion by binding to a H2 receptor on parietal cells
what effect does gastrin have on acid secretion and how?
activates ECL through CCK2 receptor which stimulates acid secretion
explain the role of G cells in acid secretion?
detect whether protein rich foods have been digested thoroughly
secrete gastrin
what is the function of D cells?
monitor acid levels and use somatostatin to regulate acid levels
what effect does somatostatin have on acid secretion and how?
inhibits acid secretion by inhibiting ECL and parietal cells
what effect does ACh have on D cells?
stops them from producing somatostatin so that acid can be secreted
what complications might occur when NSAIDs are prescribed to a patient and why?
stops prostaglandins being produced
increases stomach acid secretion
medication needs to be prescribed to counteract this
what causes Zollinger-ellison syndrome?
gastric acid hypersecretion
caused by a neuroendocrine tumour
what is a gastrinoma?
neuroendocrine tumour
what part of the body does Zollinger-Ellison syndrome normally affect?
duodenum or the pancreas
what complications can Zollinger-Ellison syndrome lead to?
severe gastroesophageal peptic ulcer disease
what are the phases of neural control of gastric secretion?
cephalic
gastric
intestinal
explain the cephalic phase of neural control of gastric secretions
Conditioned reflexes feed into the cerebral cortex –> oral and chemical mechanoreceptors feed into the medullary nuclei –> secretion of acid into the stomach
which nervous system is mainly involved in the cephalic phase
parasympathetic system
mainly the vagus
what is the purpose of the gastric phase?
as long as there is food in the stomach (gastric distension), the cycle loops back on itself
what is the purpose of the intestinal phase?
needed to stop digestion
what is the main nerve in the intestinal phase?
sympathetic nerves from the spinal cord
vagus has some involvement
which two hormones control bile secretion?
CCK
secretin
what nerve stimulates bile production?
parasympathetic impulses along the vagus nerve
what organ produces bile?
the liver
what stimulates the secretion of CCK into the blood?
Fatty acids and amino acids in the chyme entering the duodenum
what stimulates the secretion of secretin into the blood?
Acidic chyme entering duodenum
how does CCK impact bile secretion?
causes contraction of the gall bladder and relaxation of the sphincter of Oddi
how does secretin impact bile secretion?
enhances flow of bile rich in HCO3- from liver by stimulating biliary ductal cells
what type of bacteria is H. pylori and where is it found?
gram negative found in the duodenum and stomach
what complications can helicobacter pylori lead to?
peptic ulcers
describe the stages of H. pylori infection
H pylori tunnels through mucus layer to epithelial layer
urease converts water and urea to form CO2 and ammonia
ammonia neutralises gastric acid and de-gels mucin
environment changes
other H pylori can be recruited
mucosal damage
inflammation and cell death
how is h pylori infection diagnosed?
urea breath test
CLO test
blood antibody test
stool antigen test
explain how the urea breath test works
urea C14 is given to patient and H. Pylori converts urea C14 to ammonia (NH3) + C14O2
explain how the CLO test works?
mucosa biopsy taken from the antrum put into urea medium with an indicator urease from h pylori hydrolyses urea to ammonia raises pH colour changes from yellow to red
explain the colour changes in the CLO test
yellow - negative
red - positive
name the treatments for peptic ulcer disease
histamine h2 antagonists
proton pump inhibitor
antibiotics
name histamine antagonists and explain how they work
cimetidine, ranitidine, famotidine
Block H2 receptors on parietal cell
Reduce acid secretion
name proton pump inhibitors and explain how they work
omeprazole
Prevent H+/K+ ATPase on parietal cell
Reduces acid secretion
name antibiotics used to treat peptic ulcer disease and explain how they work?
Amoxycillin + Clarithomycin
kill bacteria
what treatment of h pylori infection is no longer performed?
vagotomy
what is GORD?
a condition when the reflux of stomach contents causes symptoms and/or complications
what is reflux?
retrograde flow of gastric contents into the oesophagus
what are some of the causes of GORD?
excessive reflux - increased frequency of TLOSRs
weakened oesophageal epithelium
hiatus hernia
hypersensitivity of oesophageal pain sensing nerves
how is GORD treated?
proton pump inhibitors e.g. omeprazole
neurological drugs e.g. baclofen to reduce TLOSRs
Gaviscon and other antacids
how do alginates work?
forms protective raft over the stomach to prevent acid reflux
what is a surgical option for GORD?
fundoplication
explain how a fundoplication works
tightens and reinforces the lower oesophageal sphincter
Upper part of the stomach is wrapped around the outside of the lower oesophagus to strengthen the sphincter
