DSA GI Regulatory Substances Flashcards
What regulate the functions of the GI tract?
Hormones, neurocrines, paracrines
What make up Gastrointestinal Peptides?
Hormones (released in portal circulation to liver–>systemic–> carried back to target organs)
Paracrines (act locally within same tissue that secretes them)
Neurocrine (synth in neurons of GI, released after AP)
What GI peptides are classified as hormones?
Gastrin
CCK (cholecystokinin)
Secritin
GIP
What GI peptide is classified as paracrine?
Somatostatin (inhibitory)
What GI peptides are classified as neurocrine?
ACh, NE, VIP, NO, GRP, enkephalins, substance P
What criteria must be met to qualify as a GI hormone?
1: must be secreted in response to stimulus and carried to distant site via bloodstream
2: fxn has to be independent of neural activity
3: must be isolated, purified, identified, synthesized
Fxn of Gastrin
promotes H+ secretion by parietal cells (G cells) in stomach
What is the minimum fragment necessary for gastrin biological activity?
C-terminal tetrapeptide
What stimulates secretion of gastrin?
Ingestion of food
—> neurocrine GRP released as part of vagal reflex, distention of stomach, Phe and Trp
What inhibits secretion of gastrin?
- low pH of stomach
- Somatostatin
What are the major actions of gastrin?
- stimulates H+ secretion by gastric parietal cells
- stimulates growth of gastric mucosa
Zollinger-Ellison Syndrome
gastrin-secreting tumor (gastrinoma, usually in head of pancreas)—> increased H+ secretion, inactivation of pancreatic lipase–> steatorrhea
treat w/ H+ pump inhibitors (omeprazole) among others
Fxn of CCK
promote fat digestion and absorption
What is the minimum fragment of CCK necessary for activity?
C-terminal heptapeptide
Where are CCK secreted?
I cells of deodenal and jejunal mucosa
What stimulates CCK secretion?
fatty acids (not TAGS) and small peptides/amino acids (tell I cells that you just ingested a meal with fat and protein)
What are the 5 actions of CCK?
1: contraction of GB to eject bile into SI
2: secretion of pancreatic enzymes (lipase and amulase)
3: secretion of bicarbonate from pancreas
4: growth of exocrine pancreas and GB
5: inhibition of gastric emptying to allow time to digest and absorb
What secretes secretin?
S cells of duodenum
What stimulates secretion of secretin?
H+ and fatty acids in lumen of SI (when acidic contents arrive from stomach~pH 4.5)
Fxn of secretin
promote secretion of pancreatic and biliary bicarbonate
—-> neutralizes H+ so you can digest fat via lipase (pH 6-8)
Where is GIP secreted?
K cells of duodenal and jejunal mucosa
What stimulates GIP secretion?
glucose, amino acids, fatty acids
Fxn of GIP
Stimulation of insulin secretion by pancreatic B cells
inhibition of gastric H+ secretion and emptying
Due to its fxn, what is GIP also classified as?
Incretin–> GI hormone that promotes secretion of insulin
