GI PUD/GERD Flashcards
What are the two types of cells present in the gastric pits?
a. Digestive cells (3)
1. Parietal (oxyntic) cells (secrete HCl)
2. Chief cells (secrete pepsinogen)
3. Endocrine cells (ECL, G, D cells)
b. Protective cells (3)
Mucous neck cells (secrete bicarb and mucus→protective barrier to prevent enzyme damage to stomach lining), Superficial epithelial cells, Stem/regenerative cells
What are the 3 stimulators of gastric acid secretion by parietal cells? What pump is responsible for acid secretion by parietal cells?
- Ach→M3-R’s
- Histamine→H2-R’s
- Gastrin→CCKB-R’s
The H+/K+ATPase (HKA) pumps H+ into the GI lumen, in exchange for K+.
What are the two pathways leading to gastric acid secretion by parietal cells?
- Direct pathway→Ach, gastrin, and histamine stimulate the parietal cell, triggering secretion of H+ into the llumen.
- Indirect pathway→Ach and Gastrin stimulate the ECL cell, resulting in secretion of histamine, which then acts on the parietal cell.
What are the 5 key receptors on the parietal cell involved in the regulation of gastric acid secretion, and how do they work?
- CCKB(gastrin)→Gq→PLC→IP3→Ca→HKA
- M3(Ach)→Gq→PLC→Ca→HKA
- H2→Gs→AC→cAMP→PKA→HKA
- Somatostatin→Gi→inhibits AC→decrease cAMP→reduced HKA activity
- Prostaglandin→Gi→inhibits AC→decrease cAMP→reduced HKA activity
Peptic Ulcer Disease (PUD) is ______ and ________?
Chronic (persistent) and Recurrent (it comes back after you treat it)
Difference in the etiologies of Gastric and Duodenal Ulcers in PUD?
PUD=digesting too much or protecting too little
- Gastric Ulcer: normal/reduced acid output, w/ altered/reduced mucosal resistance
- Duodenal: high acid output (esp at night), w/ inadequate bicarb to neutralize the increased acid
Major cause of non-NSAID PUD?
H. pylori infection→>90% of duodenal and 70% of gastric ulcers
Why is H. pylori resistant to the acidic environment of the stomach?
They produce UREASE which converts urea→ammonia(+bicarb)
Dx of H. pylori?
a. Urea Breath Test→tells you if you are currently infected
b. Blood Ab Test→tells you if you have ever been infected, not necessarily that you are currently infected
Other causes of PUD other than H. pylori?
a. NSAIDs (block PG synthesis by COX) (25% of gastric, some duodenal)
b. Cancer (Zollinger Ellison)
c. Other
Is H. pylori carcinogenic?
Yes, it is a Class I Carcinogen b/c it has been associated w/ the development of gastric corpus/antrum adenocarcinomas and MALT lymphomas
5 Classes of Drugs for PUD Rx? What type of regimen is used for management of H pylori infection?
- Antacids
- H2-Receptor Blockers
- Proton Pump Inhibitors (PPI’s)
- Mucosal Protective Agents (Cytoprotectives)
- Antibiotics
A Multi-drug regimen for H. pylori management
3 Goals for the Rx of PUD?
- Relief of Symptoms (antisecretory agents, antacids)
- Healing of Ulceration (PG agonists, Bismuth compounds, Sucrasulfate)
- Eradication of H. pylori in order to prevent recurrence (Abx)
Antacids MoA? (2)
- Weak bases that NEUTRALIZE gastric acid (bind up H+) in the stomach
NaHCO3 + HCl→ NaCl + CO2 + H2O - Goal is to raise pH>4 to prevent activation of pepsinogen to pepsin
Four ingredients used in antacids? Side effects if any?
Antacids come in Hydroxide and Carbonate forms
- Aluminum Hydroxide (constipation) + Magnesium Hydroxude (diarrhea)→usually used in combo so constipation/diarrhea cancel out
- Calcium Carbonate (Tums)→faster H+ neutralizer; can cause gas and acid reflux
- Simethicone-surfactant (basis for burping)
- Alginic Acids (often added to Al/Mg combo)→forms floating gel to prevent regurgitation, usually in anti-reflux antacids
Therapeutic uses of Antacids? (2)
- Simple dyspepsia
2. Adjuncts to primary therapy with H2 blockers or PPI’s
When should antacids be taken? DDI?
a. Should be taken 1 hr and 3 hr after a meal
b. Should also be taken at bedtime (bc of nocturnal secretion)
c. ADE: significant effects on the absorption of other drugs→do not take antacids w/in 1-2 hr of other drugs
What are the four H2 Receptor Antagonists?
- *the “-TIDINE’s”**
1. Cimetidine
2. Ranitidine
3. Nizatidine
4. Famotidine
H2 Antagonists MoA?
a. Competitive inhibitors of H2-R’s that block H2 stimulation by histamine, reducing both volume and H+ concentration of gastric acid secretion
c. They also reduce secretory response to gastrin and Ach due to loss of potentiation
Which phases of gastric acid secretion do H2 blockers inhibit?
They inhibit all phases→ inhibition of basal, food stimulated, and nocturnal gastric acid secretion
T/F: H2 blockers are associated with widespread ADEs? Why or why not?
False, they have minimal side effects b/c specificity for H2 (minimal H1 activity) and secondary importance of H2’s outside the stomach result in infrequent and mild ADEs.
Fundamental difference between the 4 H2 blockers?
Potency (they have equal efficacy but differ in potency)
Which H2 blocker is least potent/has shortest duration?
Cimetidine
Which H2 blocker is most potent/has longest duration?
Famotidine
Which H2 blocker has a unique issue?
CIMETIDINE→potent inhibitor of CYP450s and thus slows metabolism of many drugs. If interactions possible, choose a different H2 blocker.
What are the 5 PPI’s?
- *the “-PRAZOLE’s”**→the MOST POTENT inhibitors of gastric acid secretion
1. Omeprazole
2. Esomeprazole
3. Lansoprazole
4. Pantoprazole
5. Rabeprazole