PED2006 Flashcards
what is the importance of gastrointestinal importance
- function - major metabolic and endocrine system
- pathology - wide range of disease
- economic - £5 million per year in Newcastle
what is the pharmacological importance of the gastrointestinal system
- gastric secretion
- vomiting (emesis)
- bowel motility
what is included in the GI tract hormonal innervation
- endocrine secretions (bloodstream)
- paracrine secretions (local)
what hormones are included in endocrine secretions
gastrin
cholecystokinin - synthesis in endocrine cells of mucosa
what hormones are included in paracrine secretions
- histamine
- acetylcholine
what is the function of parental cells in the walls of the gastric gland
to keep pH between 6-7
what is the structure of parietal cells in the walls of the gastric gland
canalicular membrane
canaliculus - releases HCL
tubulovesicles - release hydrogen and potassium
mitochondria
basolateral membrane
what is the action of the proton pump in the canalicular membrane
- H+/K+ ATPase
- Cl- co-transporter
- release isotonic HCl
- requires extrinsic stimulation
what is the action of the hydrogen potassium pump
pulls potassium back in and hydrogen out, keeping the pH isoelectrically neutral
gastrin is a key driver in this process
how does gastrin control acid secretion
- peptide hormone
- stimulates acid secretion, pepsinogen secretion (indirectly), blood flow and increases gastric motility
- increases cytosolic ca2+
how does acetylcholine control acid secretion
- neurotransmitter
- released from vagal neurones
- increases cytosolic ca2+
how does histamine control acid secretion
- sub-type specific action (H2 receptors)
- increases cAMP
what diseases are associated with acid dysregulation
- dyspepsia
- peptide ulceration
- reflex oesophagitis
- zoloinger-ellison syndrome
what is dyspepsia
- indigestion
- upper abdominal pain
- bloating
- nausea
what causes peptide ulceration
- prolonged excess acid secretion leading to gastric and duodenal ulceration
what is reflux oesphagitis
- damage to oesophagus by excess acid secretion
what is Zollinger-Ellison syndrome
- gastrin producing tumour
how do we decrease secretion of gastric acid
- reducing proton pump function
- blocking histamine receptor function (H2 receptor antagonism
- neutralising acid secretion with antacids
what is the action of proton pump inhibitors
- irreversibly inhibit H+/K+ ATPase
what are example drugs of proton pump inhibitors
omeprazole
lansoprazole
what conditions are proton pumps used to treat
peptide ulcers
reflux oesophagitis
Zollinger-ellison
what are the pharmacokinetics of proton pump inhibitors
- inactive at neutral pH
- weak bases - allows accumulation in acidic environment
- degraded rapidly at low pH (enteric coating)
- single dosing –> 2-3 day acid secretion inhibition
what are the adverse effects of proton pump inhibitors
headache, diarrhoea, rash
can mask the symptoms of gastric cancer
care must be taken in high risk groups - i.e. liver failure and pregnancy
what are histamine H2 receptor antagonists
- competitive inhibitors of H2 histamine receptors