physiology 1- GI regulatory substances Flashcards
Gastrin;- source
g cells
antrum of stomach
What gastrointestinal functions would be impaired in a model gastrointestinal tract without G cells?
Increased acid secretion, promotion of growth of the gastric mucosa, increased gastric motility
Name at least two stimuli for the release of gastrin
Distention, amino acids, vagal stimulation, alkalinization
What serves as negative feedback for gastrin release?
Acid secretion (a pH
A patient with PUD refractory to medical treatment has multiple gastric ulcers. Gastrin level is markedly elevated. Diagnosis?
Zollinger-Ellison syndrome due to ectopic production of gastrin
A patient chronically on proton pump inhibitors or chronic gastritis might have increased levels of this gastric hormone due to lack of negative feedback.
Gastrin
A man does not produce a hormone that inhibits insulin and growth hormone secretion. He is status post-small bowel resection. What happened?
Due to resection of the duodenum and jejunum, he has no I cells, which are responsible for synthesizing cholecystokinin
What are the actions of cholecystokinin?
Stimulation of gallbladder contraction & pancreatic enzyme secretion, slowing of gastric emptying, increase in sphincter of Oddi relaxation
The presence of fatty acids and amino acids in the duodenum ____ (increases/decreases) cholecystokinin secretion.
increases
In cholelithiasis, pain worsens after the ingestion of what type of foods?
Fatty foods (this is due to stimulation of cholecystokinin release, which causes gallbladder contraction)
A patient has a genetic defect in her neural muscarinic pathways. Will her gallbladder activity be affected?
Yes, as cholecystokinin uses those pathways to stimulate gallbladder contractions
Secretin is produced by which cells? Where are these cells found? What stimulates this hormone’s release?
S cells of the duodenum; acids and fatty acids
What are the actions of secretin?
Increases pancreatic bicarbonate secretion, increases bile acid secretion, decreases gastric acid secretion
A patient has S cell dysfunction. What kinds of substances can this patient not digest well in his duodenum? Why is this the case?
Fatty acids; without secretin from S cells, he cannot alkalinize duodenal gastric acid, thus pancreatic enzymes will not function properly
Secretin-stimulated pancreatic bicarbonate functions to neutralize ____ within the ____.
Gastric acid; duodenum
A patient who is unable to produce secretin would have difficulty with the activity of enzymes from which organ?
The pancreas (the enzymes would be denatured and nonfunctional in the acidic environment created by unopposed gastric acid)
A male has excess gastric acid, increased gallbladder contractions, and lots of insulin and glucagon release. What hormone does he lack?
Somatostatin
This overarching inhibitory hormone of the gastrointestinal system is made by which cells? Where are these cells found?
Somatostatin is made by D cells of pancreatic islets and gastrointestinal mucosa
If a patient is given somatostatin, how does this impact pepsinogen secretions?
Decreases them
If a patient is given somatostatin, how does this impact gastric acid secretions?
Decreases them
If a patient is given somatostatin, how does this impact pancreatic secretions?
Decreases them
If a patient is given somatostatin, how does this impact fluid secretions in the small intestine?
Decreases them
What effect does somatostatin have on the gallbladder?
Somatostatin decreases gallbladder contraction
The presence of what substance in the gut lumen causes increased somatostatin release?
Acid
What inhibits somatostatin release?
Vagal stimulation
Given the functions of somatostatin, why is it classified as an antigrowth hormone?
Somatostatin inhibits digestion and absorption of nutrients, preventing the body from receiving growth nutrients (encourages somatostasis)
Glucose-dependent insulinotropic peptide is made by which cells? Where are these cells found? What is another name for this hormone?
K cells of the duodenum and jejunum; gastric inhibitory peptide (GIP)
What is the exocrine regulatory effect of glucose-dependent insulinotropic peptide?
Decreased secretion of gastric acid
What is the endocrine regulatory effect of glucose-dependent insulinotropic peptide?
Increased release of insulin
Why is an oral glucose load used more rapidly by the body than an equivalent load that is given intravenously?
Oral (but not intravenous) glucose stimulates glucose-dependent insulinotropic peptide, which stimulates insulin release
Where is vasoactive intestinal polypeptide (VIP) secreted within the gastrointestinal tract?
Parasympathetic ganglia in sphincters, gallbladder, and small intestine
Vasoactive intestinal polypeptide (VIP) ____ (increases/decreases) intestinal water and electrolyte secretion.
Increases
What effect does vasoactive intestinal peptide (VIP) have on intestinal smooth muscle and sphincters?
Relaxation of these structures
What stimuli increase secretion of vasoactive intestinal peptide (VIP)?
Distention, vagal stimulation
What is a negative regulator of vasoactive intestinal peptide (VIP) release?
Adrenergic input
A patient presents with watery diarrhea, hypokalemia, and achlorhydria. What is the most likely tumor causing this syndrome?
VIPoma, a non-α, non-β islet cell pancreatic tumor that secretes vasoactive intestinal peptide (VIP)
A patient has profuse watery diarrhea. CT shows a pancreatic mass; labs show hypokalemia and achlorhydria. What nervous system is to blame?
This is a VIPoma causing WDHA syndrome (Watery Diarrhea, Hypokalemia, and Achlorhydria) due to parasympathetic ganglia
Which small messenger molecule causes an increase in smooth muscle relaxation in the gut, particularly in the lower esophageal sphincter?
Nitric oxide
A man with dysphagia has uncoordinated esophageal peristalsis and increased lower esophageal sphincter tone. What is the pathophysiology?
Achalasia causing increased lower esophageal sphincter tone secondary to loss of nitric oxide secretion
What is the function of motilin?
Production of migrating motor complexes (MMCs) in the small intestine, thereby promoting peristalsis
Motilin secretion is ____ (increased/decreased) in a fasting state.
Increased
What hormone is produced by the small intestine and associated with intestinal peristalsis?
Motilin
What does CCK act on, resulting in pancreatic secretion?
Neuronal muscarinic pathway
A man takes erythromycin for a bacterial infection. He develops diarrhea not due to gut flora depletion. Are his MMCs to blame?
Yes, as erythromycin is a potent stimulator of motilin receptors, which increase intestinal peristalsis, likely causing the man’s diarrhea
