Lecture 9 - stomach Flashcards
What is responsible for the stomachs gastric mobility?
The abundant smooth muscle
Cells of the gastric mucosa secrete gastric juice which include?
- HCl (protein digestion)
- pepsinogen (pepsin - protein digestion)
- intrinsic factor (vitB12 absorption in ileum)
- mucus (protects gastric mucosa from H+: ph1-2)
What are the cells in the body of the stomach and what do they secrete?
parietal cells - secrete HCl and intrinsic factor
Chief cells - secrete pepsinogen
What are the cells in the antrum of the stomach and what do they secrete?
G cells - secrete gastrin into the circulation
D cells - secrete somatostatin
Function of HCl in the stomach ?
Hydrophobic acid which creates a pH of 2 in the stomach. It inhibits bacteria and so proteins lose their shape.
What id 90 % of stomach is missing?
Just take vit b12 pill
What are pits in the stomach?
Gastric secretions that come from gastric invaginations
What are pits lined with?
different secretory cells:
- Parietal cells (secrete Hal and intrinsic factor)
- Chief cells (secrete pepsinogen)
- G cells (secrete gastrin into the circulation)
- D cells (secrete somatostatin)
- mucus neck cells (secrete mucus, bicarbonate)
regional differences occur in the number of cell types that line the gastric pit, what are these differences?
Near lower oesophagus and pyloric sphincter - mucus, HCO3-
Rest of stomach - digestive secretions (H+, pensinogen)
What is at the base of the pits?
parietal cells
What is lining the duct of the pits?
chief cells, d cells, g cells and at the top the mucous neck cells.
Function of parietal cell?
Secrete acid –> coagulate protein
What is at the apical membrane of a parietal cell?
H+ and K+ ATPase, Cl- channels
H+ is secreted into the lumen of the stomach via primary active transport and Cl- follows H+ into the lumen
What is at the basolateral membrane of a parietal cell?
Na+ and K+ ATPase, Cl- and HCO3- exchanger
HCO3- is moved into the interstitial space in exchange for Cl-. Na + goes into the stomach
What do the epethial cells contain?
contain carbonic anhydrase which catalyses CO2 +O2 into H2CO3 (source of H2CO3)
What stimulates H+ secretion?
PNS -
- ) neurotransmitter ACh
- ) secretes into M3 receptor
- ) Gq
- ) Ca2+ or IP3 (calcium concentration increases)
- ) PKA
- ) increased ATPase (H+ to K+)
Histamine -
- ) released from enterochromaffin like cells in gastric mucosa
- ) binds to nearby parietal cells
- )binds to histamine H2 receptor
- )Gs protein
- )cAMP
- ) PKA
- ) increased ATPase activity
Gastrin -
- ) G cells
- ) into circulation
- ) cholecystokinin B (CCKB) receptor
- ) Gs
- ) increased calcium concentration (IP3)
- ) PKA
- ) increased ATPase activity
What inhibits potassium hydrogen ATPase?
omeprazole
Potentiation of the stimulus occurs with ….. between the 3 stimulation
cross talk
What inhibits H+ secretion?
Somatostatin (produced by D cells): Direct pathway: 1.) inhibits parietal cells 2.) binds to receptor 3.) Gi 4.) reduced cAMP 5.) reduced H+ secretion indirect pathway: 1.) inhibits histamine release from ECL cells 2.) inhibits gastrin release from G cells
Response to a meal, first step ?
Vagus nerve innervation:
- ) parietal cells directly (ACh) release HCl
- ) G cells (GRP, gastrin releasing peptide) releases gastrin into circulation which is carried by bloodstream to parietal cells which releases HCl indirectly.
- ) muscarinic blocking agent (atropine) does not fully block HCl secretion
Response to meal, step 2 - cephalic phase?
- ) accounts for 30 % of total HCl secretion
- ) stimulates by smell, taste and it is a conditioned reflex. Anticipation of food
- ) mechanism - direct and indirect
Response to meal, step 2 - gastric phase?
- ) accounts for 60% of total HCl secreted
- ) stimulus - distension of stomach, presence of amino acids and small peptides
- ) mechanism - distension direct and indirect vagal stimulation of parietal cells (gastrin). AA and peptides: direct effects on G cells (gastrin)
Response to meal, step 3 - intestinal phase?
- ) accounts for 10 % of total HCl secretion
2. ) stimulus - AA and peptides stimulate G cells to release gastrin then parietal cells release HCl.
