Secretion of the stomach and its control Flashcards
What are the four functions of the stomach?
Stores food
Mixes food with secretions
Regulates release of food into the duodenum
Secretes gastric juices
Name the five parts of the stomach (in order top to bottom)
Cardia Fundus Corpus Antrum Pylorus
Name the 7 layers of the stomach
Mucosa Muscularis mucosa Submucosa Oblique muscle Circular muscle Longitudinal muscle Peritoneum
What cells make up gastric glands?
Mucous neck cell Parietal cell EC like cell Chief cell D cell G cell
Where is the majority of acid produced in the stomach?
In the fundus and corpus
Where are there no parietal cells?
In the pylorus and antrum
What cells predominate the fundus and corpus?
Parietal and chief cells
What is the biological mechanism of acid secretion?
A parietal H-K pump embedded in the apical membrane
The pump exudes H+ into the lumen in exchange for K+
K+ is recycled by K+ channels
What role does carbonic anhydrase play in acid secretion?
Water is broken down into H+ and OH-
H+ excreted into the lumen
OH- combines with bicarbonate ion
What is the alkaline tide?
The release of HCO3 across the basolateral membrane into the blood stream
Name the direct regulators of acid secretion
Acetylcholine
Histamine
Gastrin
Name the indirect regulators of acid secretion
Acetylcholine
Gastrin-mediated histamine
What is somatostatin?
A peptide hormone made by D-cells
A direct and indirect inhibitor of acid secretion
Where is somatostatin produced?
D cells in the corpus of the stomach
D cells in the antrum of the stomach
Describe paracrine production of somatostatin
Triggered by neural and hormonal mechanisms
Corpus of the stomach
Describe endocrine production of somatostatin
Triggered by low intra-luminal pH
Antrum of the stomach
How does somatostatin inhibit acid secretion?
Binds to SST receptor on parietal cell
Inhibits adenylyl cyclase
Inhibits parietal cell
What intracellular signal-transduction pathway does acetylcholine use?
Binds to M3 muscarinic receptor
Activates PKC
What intracellular signal-transduction pathway does gastrin use?
Binds to cholecystokinin B receptor
Activates PKC
What intracellular signal-transduction pathway does histamine use?
Binds to the H2 receptor
Stimulates the enzyme adenylyl cyclase
Production of cAMP
Activates PKA
What are the two ways somatostatin indirectly inhibits acid secretion?
Somatostatin released by D-cells of the corpus inhibits the release of histamine from ECL cells in the corpus
Somatostatin released by D-cells of the antrum can inhibit the release of gastrin from G cells in the antrum