19. GI regulatory substances Flashcards
Gastrointestinal substance secreted by paietal cells
- HCL
2. intristrict factor
histamine stimulates H+ secretion via
H2 receptors
myenteric plexus vs submucudal plexus p=according to other name, location and primary function
Myenteric ( auerbach) –> muscularis externa –> motility
submucosal (meissner ) –> secretion and blood flow, receive information from chemo and mechanoreceptors
vagus induced gastric secretion - direct vs indirect pathway according to mechanism
direct –> vagus innervates parietal cells ( AcH)
indirect –> vagus innervates G cells via GRO -> H + secretion via
trypsinogen is converted to trypsin by
enterokinase / enteropepitidase a brush - border enzyme on duodenal and jejunal mucosa
stool are brown because of
stercobilin
glucose - dependend insuinotropic peptide ( gastric inhibitroy peptide (GIP) - SOURCE
K cells ( duodenum, jejunm )
satiety hormone
leptin
payer patches - mechanism / function
contain M cells that sample and present antigen to immun cells –> B cells stimulated to germinal centers and differentiate into Ig A - secreting plasma cells ( IL-5) which reside in lamina propria –> IgA receives protective secretory component and is then transported across the epithelium to the gut to deal with intraluminal antigen
B12 uptake - location
terminal ileum
appetite regulation - endocannabinoids mechanism of action
stimulate cortical reward centers –> icreased desire for high fat foods
Bilirubin - metabolism in gut
conjugated bilirubin ( direct) –> urobilinohen ( flora ) –> 80 in feces as stercobilin ( bown color of stool +220% back)
VIPOMA is AKA
WDHA ( watery diarrhea, hypokalemia, achlorhydria
parasympathetic vs sympathetic nervous system on GI according to function and structure
parasympathetic –> preganglionic fibers synapse in myenteric and submucosal plexus –> excitatory
sympathetic –> postganglionic fibers synapse in myenteric and submucosal plexus –> inhibitory
Bile is composed by
- bile salts ( bile acid conjugated with glycine or taurine ( making the water soluble)
- phospholipids
- cholesterol
- bilirubin
- water
- ions
glucose - depended inuslinotropic peptide ( gastric inhibtory peptide ( GIP )) - action
- exocrine –> decreases gastric H+ secretion
2. endocrine –> incrases insulin secretion
pancreatic secretions - a-mylase, proteases and lipases role
- a-mylase —> starch digestion
- lipases –> fat digestion
- proteases –> protein digestion
secretin and GIP structure
secretin : 27 AA ( 14 of the same as glucagon ). All AA are required for activity
GIP: 42 AA , homologous to secretin and glucagon
cholecystokinin - source
I cells ( duodenum, jejunum)
GI tract - circular vs longitudinal muscle according to action
circular –> decreased in diameter
longitudinal –> decreased in length
clinical situation with decreased Intrisinsic factor
autoimmune destruction of parietal cells –> chronic gastritis and pernicious anemia
Ghrelin - source
stomach
B12 absortption
terminal ileum with bile salts ( and requires intrinsic factor)
gastric acid - action
decreased stomach pH
pancreatic secretion - proteases include … ( and echanism)
include trypsin , chymotrypsin elasase , carboxypeptodases secreted as proenzymes ( AKA zymogens)
trypsin activates all poreases
saliva glands structure and function of every part
.
GI tract - mechanism of slow wave
cyclic opening of Ca2+ channels ( depolarization ) followed by opening of K+ channels ( repolarization)
secretin action
- increases pancreatic HCO3- secretion
- decreases gastric acid secretion
- incrases bile secretion
bile and pancreatic HCO3–> neutralizes gastric acid in duodenum –> allow pancreatic enzymes to function
glucose - depended insulinotropic peptide ( gastric inhibitory peptide ( GIP) - regulation
increased by 1. fatty acis 2. amino acis 3. oral glucose
enterocytes - galactose is taken up by
SGLT1 ( Na+ dependent) into the cells –> Glut-2 to blood
somatostatin - source
D cells ( pancreatic islets, GI mucosa)
Ghrelin action
- stimulates hunger 9 orexigenic effect)
2. GH release ( via GH secretagog receptor)
glucose-dependend insulinotropic peptide is AKA
gastric inhibitory peptide ( GIP_
COLON - K+/Na+
aldosteron –> Na+ absorption and K+ secretion
• The G cells of the stomach produce which hormone? Where are these cells found?
Gastrin; in the antrum of the 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 <1.5 will inhibit gastrin secretion)
• 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 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
• A patient eats a meal with a large load of fatty acids, amino acids, and glucose. What happens to activity levels of K cells?
They increase (all of these nutrients stimulate glucose-dependent insulinotropic peptide release)
• 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
