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GI
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29
Medical
Graduate
09/16/2012

Additional Medical Flashcards

 


 

Cards

Term
Gastrin
Definition

Source: G cells (antrum of stomach)

 

Action:

  • increase gastric H+ secretion
  • increase growth of gastric mucosa
  • increase gastric motility
  • increase HCl secretion by parietal cells
  • increase pepsinogen secretion by chief cells
  • increase histamine secretion by ECL cells (enterochromaffin like cells)

Regulation:

  • increased by stomach distention/alkalinization, amino acids, peptides, Calcium in lumen of stomach, vagal stimulation via GRP.
  • decreased by stomach pH < 1.5.

Notes:

  • highly increased in Zollinger-Ellison syndrome.
  • Phenylalanine and tryptophan are potent stimulators.

member of the gastrin-CCK family

Term
Cholecystokinin
Definition

Source:

  • I cells (duodenum and jejunum)

Action:

  • increases pancreatic secretion
  • increases gallbladder contraction
  • decreases gastric emptying, sphincter of Oddi relaxation

Regulation:

  • increased by fatty acids, amino acids

Notes:

  • CCK acts on neural muscarinic pathways to cause pancreatic secretion
Term
Secretin
Definition

Source: S cells (duodenum)

 

Action:

  • increases pancreatic HCO3- secretion
  • increases bile secretion
  • decreases gastric acid secretion

Regulation:

  • increased by acid, fatty acids lumen of duodenum

Notes:

  • increased HCO3- neutralizes gastric acid in duodenum, allowing pancreatic enzymes to function.
Term
Somatostatin
Definition

Source: D cells (pancreatic islets, GI mucosa)

 

Action:

  • decreases gastric acid and pepsinogin secretion
  • decreases pancreatic and small intestine fluid secretion
  • decreases gallbladder contraction
  • decreases insulin and glucagon release

Regulation:

  • increased by acid
  • decreased by vagal stimulation

Notes:

  • Inhibitory hormone
  • antigrowth hormone effects (digestion and absorption of substances needed for growth)
Term

Glucose dependant insulinotropic peptide

 

aka

 

Gastric inhibitory peptide (GIP)

Definition

Source: K cells (D,J)

 

Action:

  • Exocrine: decreases gastric H+ secretion
  • Endocrine: increases insulin release

Regulation:

  • increased by fatty acids, amino acids, and oral glucose

Notes:

  • An oral glucose load is used more rapidly than the equivalent given by IV
Term
Vasoactive intestinal polypeptide (VIP)
Definition

Source: Parasympathetic ganglia in sphincters, gallbladder, small intestine

 

Action:

  • increases intestinal water and electrolyte secretion
  • increases relaxation of intestinal smooth muscle and sphincters

 

Regulation:

  • increased by distention and vagal stimulation
  • decreased by adrenergic input

 

Notes:

  • VIPoma - non-alpha, non-beta islet cell pancreatic tumor that secretes VIP. copious diarrhea.
Term
NO
Definition

Action:

  • increased smooth muscle relaxation, including lower esophageal sphincter

 

Notes:

  • Loss of NO secretion is implicated in increased lower esophageal tone of achalasia
Term
Motilin
Definition

Source: small intestine

 

Action: Produces migrating motor complexes (MMCs)

 

Regulation: increased in fasting state

 

Notes: Motiilin receptor agonists are used to stimulate intestinal intestinal peristalsis

Term
Intrinsic Factor
Definition

Source: Parietal cells (stomach)

 

Action: Vitamin B-12 binding protein (required for B-12 uptake in terminal ileum)

 

Notes: Autoimmune destruction of parietal cells -> chronic gastritis and pernicious anemia

Term
Gastric acid 
Definition

Source: Parietal cells of stomach

 

Action: decreases stomach pH

 

Regulation:

  • increased by histamine, ACh, and gastrin
  • decreased by somatostatin, GIP, Prostaglandin, and secretin

 

Notes: Gastrinoma - gastrin secreting tumor that causes continuous high levels of acid secretion and ulcers

 

Term
Pepsin
Definition

Source: Chief cells

 

Action: Protein digestion

 

Regulation: increased by vagal stimulation, local acid

 

Notes: inactive pepsinogen -> pepsin by H+

Term
HCO3-
Definition

Source: mucosal cells (stomach, duodenum, salivary glands, pancreas) and brunner's glands (duodenum)

 

Action: neutralizes acid

 

Regulation: increased pacreatic and biliary secretion with secretin

 

Notes: HCO3- is trapped in mucus that covers the gatric epithelium.

Term
H2 Blockers
Definition

Mechanism: Reversible block of histamine H2 receptors - decrease in H+ secretion by parietal cells

 

Use: peptic ulcer, gastritis, mild esophageal reflux.

 

Toxicity:

  • Cimetidine is a potent inhibitor of P-450;
  • it also has antiandrogenic effects (prolactin release, gynecomastia, impotence, decreased libido in males);
  • it can cross blood brain barrier (confusion, dizziness, headaches) and placenta.
  • Both cimetidine and ranitidine decrease renal excretion of creatinine.
  • othe H+ blockers are relatively free of these effects

Examples: Cimetidine, ranitidine, famotidine, nizatidine

(take H2 blockers before you dine)

Term
Proton Pump Inhibitors (PPIs)
Definition

Mechanism: Irreversibly inhibit H+/K+ATPase in stomach parietal cells.

 

Clinical use: peptic ulcer, gastritis, esophageal reflux, Zollinger-Ellison syndrome.

 

Examples: Omeprazole, lansoprazole

Term
Bismuth, sucrasulfate
Definition

Mechanism: binds to ulcer base, providing physical protection, and allows HCO3- secretion to reestablish pH gradient in the mucous layer.

 

Use: increased ulcer healing, traveler's diarrhea.

 

Triple therapy of H. pylori ulcers - Metrinidazole, Amoxicillin (or Tetracycline), Bismuth. also, PPI.

 

Please MAke Tummy Better.

 

 

Term
Misoprostal
Definition

Mechanism: a PGE1 analog. Increased production and secretion of gastric mucous barrier, decreased acid production.

 

Use: prevention of NSAID-induced peptic ulcers; maintenance of a patent ductus arteriosus. Also used to induce labor.

 

Toxicity: Diarrhea. contraindicated in women of childbearing potential (abortifacient).

Term
Muscarinic antagonists
Definition

Mechanism: block M1 receptors on ECL cells (decreased histamine secretion) and M3 receptors on parietal cells (decreased H+ secretion).

 

Use: peptic ulcer (rarely used)

 

Toxicity: tachycardia, dry mouth, difficulty focusing eyes

 

examples: Pirenzepine, propantheline

Term
Octreotide
Definition

Mechanism: Somatostatin analog

 

Use: Acute variceal bleeds, acromegaly, VIPoma, and carcinoid tumors

 

Toxicity: Nausea, cramps, steatorrhea

Term
Antacids
Definition
  • can effect absorption, bioavalability, or urinary excretion of other drugs by altering gastric and urinary pH or by delaying gastric emptying. 
  • over use can cause:
    • Aluminum hydroxide - constipation and hypophashatemia; proximal muscle weakness, osteodystrophy, seizures
    • Magnesium hydroxide - diarrhea, hyporeflexia, hypotension, cardiac arrest
    • calcium carbonate - hypercalcemia, rebound acid increase
    • all can cause hypokalemia
Term
Infliximab
Definition

Mechanism: monoclonal Ab to TNF, proinflammatory cytokine.

 

Use: Crohn's disease, rheumatoid arthritis.

 

Toxicity: Respiratory infection (including reactivation of latent TB), fever, hypotension.

Term
Sulfasalazine
Definition

Mechanism: A combination of sulfapyridine (antibacterial) and 5-aminosalicyclic acid (antiinflammatory). Activated by colonic bacteria.

 

Use: ulcerative colitis, Crohn's disease

 

Toxicity: malaise, nausea, sulfonamide toxicity, reversible oligospermia.

Term
Ondansetron
Definition

Mechanism: 5-HT3 antagonist. Powerful central acting antiemetic.

 

Use: control vomiting postoperatively and in patients undergoing cancer chemotherapy.

 

Toxicity: headache, constipation.

 

Term
Metoclopramide
Definition

Mechanism: D2 receptor antagonist. Increased resting tone, contractility, LES tone, motility. Does not influence colon transport time.

 

Use: Diabetic and post-surgery gastroparesis

 

Toxicity: increased parkinsonian effects. Restlessnes, drowsiness, fatigue, depression, nausea, diarrhea, Drug interaction with digoxin and diabetic and diabetic agents. Contraindicated in patients with small bowel obstruction.

Term
Antiemetics
Definition


5HT3 antagonists

  •  (Ondansetron, Granisetron, dolasetron)
  • may act in chemoreceptor trigger zone and in peripheral sites.

DA antagonists

  • (Phenothiazine, metoclopiramide) 
  • blocks D2 receptors in chemoreceptor trigger zone.
  • metoclopiramide is also a prokinetic agent

Cannabinoids

  • (Dronabinol) 
  • active ingredient in marijuana.
Term
Emetics
Definition

Ipecac

  • locally irritates the GI tract and stimulates the chemoreceptor trigger zone
  • if emesis does not occur in 15-20 minutes, lavage must be used to remove ipecac

Apomorphine

  • Dopamine-receptor agonist that stimulates the chemoreceptor trigger zone
  • vomiting should occur within 5 min. 
Term
Brunner's glands
Definition

secrete alkaline mucus to neutralize acid contents entering the duodenum from the stomach.

 

located in the duodenal submucosa (thesse are the only GI submucosal glands). 

 

Hypertrophy of these glands is seen in peptic ulcer disease.

Term
trypsinogen
Definition
Converted to active trypsin by enterokinase/enteropeptidase, and enzyme secreted from the duodenal mucosa. Trypsin activates other proenzymes and itself.
Term
Carbohydrate digestion
Definition
  1. Salivary amylase (ptyalin) - starts digestion, hydrloyzes alpha1-4 linkages to yield disaccharides (maltose and dextrans)
  2. pancreatic amylase - highest concnetration in duodenal lumen, hydrolyzes starch to oligosaccharides and disaccharides.
  3. oligosaccharide hydrolases - at brush border of intestine, the trate-limiting step in carbohydrate digestion, produces monasaccharides from oligo- and disaccharides.
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