Gastroenterology 3 Flashcards
What is Rotor’s syndrome similar to?
Similar to Dubin-Johnson but milder (impaired liver excretion of conjugated bilirubin)
What differentiates Rotor’s syndrome from Dubin-Johnson?
No black liver
What are 2 mechanisms of neonatal jaundice?
- ↑ bilirubin (more RBCs, shorter lifespan)
- ↓ UDP-glucuronyl transferase activity (Takes 14 weeks for enzyme to reach adult level of function)
Neonatal jaundice results in increased [conjugated/unconjugated] bilirubin. This can lead to what condition?
- Unconjugated
- Kernicterus
Who is at the greatest risk for Neonatal jaundice?
Preterm infants
What is the treatment for Neonatal Jaundice?
Phototherapy - Converts bilirubin to lumirubin (more water soluble, allows excretion without conjugation)
What 2 substances do neck cells of the stomach secrete?
Mucous and bicarbonate
Where are parietal cells found?
In the gastric glands within the lamina propria of the mucosal layer of the stomach
Parietal cells are stained [color] in H&E staining
Pink (eosinophilic)
What are the 3 stimuli for Stomach acid secretion?
- Gastrin (direct)
- Gastrin (indirect)
- Vagus nerve
What cells secrete gastrin? How does gastrin directly stimulate stomach acid secretion?
- G cells in the antrum (distal) stomach
- Binds to CCKb receptors on parietal cells
How does gastrin indirectly stimulate stomach acid secretion?
Gastrin binds to ECL cells → release histamine → stimulates parietal cells to release acid
How does the vagus nerve stimulate stomach acid secretion?
Releases ACh which activate M3 receptors on parietal cells
Acitvates G cells using gastrin releasing peptide (GRP) → gastrin secretion
What is a vagotomy? What was it previously used for?
- Surgical disruption of vagus nerve to stomach
- Old therapy for gastric ulcers
Why does atropine not work to suppress stomach acid secretion?
Blunts parietal stimulation by ACh but does not block stimulation by vagus nerve (GRP → gastrin secretion → HCL)
What cells secrete intrinsic factor?
Parietal cells
What 2 transporters are present on the luminal side of parietal cells?
H+/K+ ATPase, Cl- channel (separate secretion of H+ and Cl- for HCL)
Omeprazole, pantoprazole are classified under what drug class?
Proton pump inhibitor
H+ is formed by what enzyme in parietal cells?
Carbonic anhydrase (converts H2O and CO2 into HCO3- and H+)
What is the alkaline tide?
Increase of serum HCO3- after meals due to increase activity of carbonic anhydrase (to form HCL)
Vomiting can cause metabolic [acidosis/alkalosis]
Alkalosis
What are 2 mechanisms that explain how vomiting causes metabolic alkalosis?
- Loss of HCL
- Increased production of H
What are 2 mechanisms that explain how vomiting causes metabolic alkalosis?
- Loss of HCl
- Increased production of HCl leads to generation of HCO3-
Urinary [electrolyte] is useful in metabolic alkalosis with unknown cause.
Cl-
Unexplained metabolic alkalosis with low urinary Cl- suggests…
surreptitious vomiting
Unexplained metabolic alkalosis with high urinary Cl- suggests…
diuretic use (blocks NaCl resorption)
Parietal secretion is activated by what 3 gastrointestinal secretions?
- Gastrin
- ACh
- Histamine
Parietal secretion is inhibited by what 2 gastrointestinal secretions?
- Somatostatin
- Prostaglandin
*inhibits proton pump
What is the second messenger for ACh?
Gq- IP3/Ca2+
What is the second messenger for histamine?
Gs- cAMP
What is the second messenger for somatostatin?
Gi- cAMP
What is the second messenger for gastrin?
Gq- IP3/Ca2+
What is the second messenger for prostaglandin?
Gi- cAMP
Cimetidine, ranitidine, famotidine, and nizatidine are classified under what drug class? What effect will this have?
Histamine (H2) blocker, blunts acid secretion
Misoprostol is a [drug class]. What effect will this have on the GI system?
PGE1 analog, blunts acid secretion
_____ cells are found in the upper layers of the gastric glands and _____ cells are found in the deeper layers.
Parietal, Chief
Chief cells stain [color] on H&E staining.
dark colored (basophilic)
What do chief cells secrete?
Pepsinogen (converted to pepsin by H+)
What stimulates the release for pepsinogen?
vagus nerve (i.e. about to eat, thinking about eating)
What does pepsin do?
digest protein
What are 3 effects of gastrin?
- Stimulates H+ secretion by parietal cells (directly and indirectly)
- Stimulates growth of gastric mucosa
- Increases gastric motility
What is the most important parietal cell receptor?
histamine
Gastrin is released in response to [4]
- Stomach distention
- Alkalinization
- Amino acids (especially phenylalanine and tryptophan)
- Vagal stimulation (mediated by GRP)
Gastrin release is inhibited by [2]
- Low pH
- Somatostatin
What is Zollinger-Ellison Syndrome?
- Gastrin secretin tumor that occurs in the duodenum or pancreas
- Leads to excessive acid secretion and hypertrophy of mucosa
What are 4 common symptoms seen in Zollinger-Ellison Syndrome?
- Abdominal pain: improves with food
- Chronic diarrhea: low pH in intestine inactivates pancreatic enzymes + inhibits sodium/water absorption → poor digestion, steatorrhea
- Ulcers: most in distal duodenum
- Heartburn
What are 2 ways to diagnose a Gastrinoma?
- Fasting serum gastrin levels
- Secretin test
What are 2 ways to diagnose a Gastrinoma?
- Fasting serum gastrin levels
- Secretin test
What is a secretin test? What does it test for?
A secretin test measures the gastrin level in response to secretin administration. Normal G cells are inhibited by secretin, but Gastrinomas are stimulated by it.
What happens to gastrin levels after secretin administration?
Gastrin levels will rise after secretin administration.
What does the secretin test help differentiate?
It helps differentiate gastrinomas from other causes of increased gastrin.
What are 3 possible treatments for Gastrinomas?
- High dose proton pump inhibitor
- Octreotide (somatostatin analog)
- Surgical excision
What is pernicious anemia?
Pernicious anemia is an autoimmune gastritis that leads to the loss of parietal cells and intrinsic factor, resulting in the inability to absorb Vitamin B12.
What is a typical lab finding in pernicious anemia?
High gastrin levels leading to G-cell hyperplasia.
What cells release Cholecystokinin?
I cells in the small intestine.
What are 4 effects of Cholecystokinin?
- Stimulate gall bladder contraction
- Relaxation of sphincter of Oddi
- Stimulate pancreatic enzyme secretion
- Inhibits gastric emptying
How does Cholecystokinin stimulate pancreatic enzyme secretion?
It binds to CCK receptors in the vagus nerve, leading to ACh release which stimulates the pancreas.
What are 2 stimuli for Cholecystokinin release?
- Fatty acids and monoglycerides (not triglycerides)
- Amino acids
When is a HIDA scan performed?
To evaluate RUQ pain, usually when Ultrasound is non-diagnostic.
How is a HIDA scan performed? What information can be obtained?
Administer 99mTc-hepatic iminodiacetic acid, which should concentrate in the bladder and pass to the intestines. Radioactivity can be followed, and failure to fill the gallbladder suggests obstruction.
What GI hormone can sometimes be administered with a HIDA scan? What can this tell us?
Cholecystokinin can be administered to measure gall bladder ejection fraction before and after.
What cells release secretin?
S cells of the duodenum.
What stimulates secretin secretion?
- H+ in duodenum
- Fatty acids in duodenum
What are 4 effects of Secretin?
- Increases HCO3- secretion by pancreatic duct cells (raises pH in small intestine)
- Inhibits gastric H+ secretion
- Increases bile secretions
- Promotes pancreatic flow: water secreted with bicarb
What does somatostatin do to GI hormones?
Somatostatin inhibits most GI hormones.
Where is somatostatin found?
- Originally discovered in the hypothalamus
- Released by D cells throughout the GI tract
- Found in nerves throughout the body
What are the 2 stimuli for somatostatin secretion in the GI tract?
- Low pH (no food in stomach)
- Decreased vagus nerve stimulation
How does somatostatin regulate digestion/acid secretion?
When pH rises with food in the stomach, somatostatin release is inhibited, allowing other GI hormones to function. Acid in the stomach without food causes somatostatin release, shutting down other hormones.
What are 6 effects of somatostatin in the GI tract?
- Inhibit gastric H+ secretion
- Inhibits pepsinogen secretion
- Inhibit gall bladder contraction
- Inhibit intestinal fluid secretion
- Inhibit pancreatic fluid secretion
- Inhibit insulin and glucagon release
What drug class is Octreotide? What are 4 indications for this drug?
Octreotide is a somatostatin analog.
Indications include:
1. Acromegaly
2. GI bleed/bleeding varices
3. Carcinoid syndrome: can improve flushing and diarrhea
4. Gastrinoma/Glucagonoma
What is Acromegaly?
A hormonal disorder that results from excess growth hormone.
Not included in the provided text.
What are GI bleed/bleeding varices?
Conditions related to bleeding in the gastrointestinal tract, often due to varices.
What is Carcinoid syndrome?
A condition that can improve flushing and diarrhea.
What are Gastrinoma and Glucagonoma?
Types of neuroendocrine tumors that secrete gastrin and glucagon, respectively.
Why is Ocretotide used in GI bleeding?
Reduces splanchnic blood flow in bleeding varices.