Physiology Lesson 19: Gastric Secretions
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Questions and Answers

Which substance is essential for the absorption of vitamin B12 in the intestine?

  • Intrinsic Factor (correct)
  • Pepsinogen
  • Mucus
  • Gastric Acid

    • What is the primary function of hydrochloric acid (HCl) in the stomach?

  • To transport nutrients
  • To neutralize alkaline substances
  • To activate pepsinogen (correct)
  • To emulsify fats

    • Which factor is NOT considered a protective factor in gastric secretions?

  • Mucus
  • HCO3-
  • Pepsin (correct)
  • Prostaglandins (PGs)

    • What is the role of gastrin in gastric secretions?

    <p>To promote acid secretion by parietal cells</p> Signup and view all the answers

    What role does pepsin play in the digestive process?

    <p>It digests proteins</p> Signup and view all the answers

    Which of the following is a paracrine mediator involved in regulating acid secretion?

    <p>Somatostatin</p> Signup and view all the answers

    Which type of drug is commonly used to inhibit gastric acid secretion?

    <p>Histamine receptor antagonists</p> Signup and view all the answers

    Which condition may require treatments targeting H. pylori?

    <p>Peptic ulcers</p> Signup and view all the answers

    What role does HCl play in the stomach beyond digestion?

    <p>It helps maintain an acidic environment for enzymatic reactions.</p> Signup and view all the answers

    Which of the following substances is primarily responsible for the initial digestion of triglycerides in the stomach?

    <p>Lipase</p> Signup and view all the answers

    Which statement accurately describes the relationship between gastric secretions and the absorption of dietary iron?

    <p>Gastric acid may enhance the absorption of dietary iron.</p> Signup and view all the answers

    Which substance is secreted to help protect the stomach lining from aggressive factors?

    <p>Bicarbonate</p> Signup and view all the answers

    What effect does the surgical removal of the stomach have on nutrient absorption?

    <p>It does not affect absorption of non-vital nutrients.</p> Signup and view all the answers

    What role does intrinsic factor serve in gastric secretions?

    <p>It is crucial for the absorption of vitamin B12.</p> Signup and view all the answers

    Which of the following is a mechanism through which the stomach protects itself from harsh substances?

    <p>Secreting mucus and bicarbonate.</p> Signup and view all the answers

    Which component of gastric secretions is involved in the conversion of food proteins into smaller peptides?

    <p>Pepsinogen</p> Signup and view all the answers

    Which of the following substances is NOT produced by parietal cells in the stomach?

    <p>Lipase</p> Signup and view all the answers

    What is the mechanism by which gastric acid contributes to food sterilization?

    <p>By providing an acidic environment</p> Signup and view all the answers

    Which of the following drugs is specifically classified as a proton pump inhibitor?

    <p>Omeprazole</p> Signup and view all the answers

    Which aggressive factor mentioned contributes to potential damage to the stomach lining?

    <p>Caffeine</p> Signup and view all the answers

    What component of the gastric secretions is primarily responsible for the initial breakdown of triglycerides?

    <p>Lipase</p> Signup and view all the answers

    Which of the following negative regulators is associated with the inhibition of gastric acid secretion?

    <p>Somatostatin</p> Signup and view all the answers

    Which of the following factors is necessary for the absorption of dietary iron?

    <p>Hydrochloric Acid</p> Signup and view all the answers

    In the context of gastric secretions, which of the following substances forms a protective barrier in the stomach?

    <p>Mucus</p> Signup and view all the answers

    Study Notes

    Lesson 19: Gastric Secretions

    • The stomach is a muscular reservoir where food enters after being swallowed.
    • Gastric juices are the primary source of digestive capacity.
    • Digestive functions are not essential in the assimilation of a mixed meal; surgical removal of most of the stomach allows for adequate nutrition.
    • Some gastric secretion is required for B12 vitamin absorption and dietary iron.
    • Gastric secretions help sterilize food.

    Index

    • Gastric secretions: Introduction to the topic.
    • Regulation of acid secretion by parietal cells: Includes main mediators.
    • Drugs used to inhibit or neutralize gastric acid secretion: Classifies and includes drugs and indications.
    • Drugs that protect the mucosa: Details of medications.

    Main Mediators

    • HISTAMINE (paracrine): A stimulatory local hormone.
    • GASTRIN (endocrine): A stimulatory peptide hormone.
    • ACETYLCHOLINE: A stimulatory neurotransmitter.
    • PGE2, PGI2 (local hormones): Inhibit acid secretion
    • SOMATOSTATIN: An inhibitory peptide hormone.

    Gastric Secretion

    • The stomach produces substances that aid digestion and protect the stomach lining.
    • Hydrochloric acid (HCl): Produced by parietal cells; creates an acidic environment for initial food breakdown and has antimicrobial properties.
    • Pepsinogen: Secreted by chief cells; inactive precursor that converts to pepsin in the acidic stomach environment; essential for protein digestion.
    • Intrinsic factor: Also from parietal cells; essential for vitamin B12 absorption.
    • Mucus: Secreted by mucous cells; forms a protective layer.
    • Lipase: Produced by chief cells; contributes to triglyceride digestion.

    Regulation of Acid Secretion by Parietal Cells

    • Disturbances are important in peptic ulcer pathogenesis.
    • Parietal cells secretion: pH <1.
    • HISTAMINE (a stimulatory local hormone)
    • GASTRIN (a stimulatory peptide hormone)
    • ACETYLCHOLINE (a stimulatory neurotransmitter)
    • PGE2 and PGI2 (local hormones): Inhibit acid secretion.
    • SOMATOSTATIN (an inhibitory peptide hormone)

    Gastric Acid Secretion by ECL Cells

    • ECL cells (enterochromaffin-like cells) secrete histamine.
    • Histamine maintains basal histamine release.

    Gastrin

    • Synthesized by G cells, mainly in the pyloric antrum of the stomach, duodenum, and pancreas.
    • Its main action is stimulating HCl production.

    Acetylcholine

    • Stimulates muscarinic M3 receptors on parietal cells.
    • Elevates intracellular Ca2+ and stimulates proton (H+) release into the stomach.
    • Contributes to HCI production.

    Prostaglandins

    • Most importantly PGE2 and PGI2.
    • Increase bicarbonate secretion-helps neutralize stomach acid and protects the mucosal lining.
    • Increase protective mucin release.
    • Reduce gastric acid output.
    • Prevent vasoconstriction following injury or insult.

    Somatostatin

    • Peptide hormone released from D cells within the stomach.
    • Inhibits gastrin release, histamine release, and acid output on parietal cells.

    Drugs to Inhibit or Neutralize Gastric Acid Secretion

    • Histamine H2 Receptor Antagonists: Cimetidine, Ranitidine, Nizatidine, Famitidine.
      • Decrease basal and food-stimulated acid secretion.
      • Promote healing of gastric and duodenal ulcers
      • Relapses are possible after treatment stops.
      • Indications: peptic ulcer, reflux oesophagitis, Zollinger-Ellison syndrome, (NOTE: now also includes potentiation of effects of some oral anticoagulants and tricyclic antidepressants).
      • ADRs: diarrhoea, dizziness, muscle pain, alopecia, transient rashes, confusion (in elderly), and hypergastrinaemia.
    • Proton Pump Inhibitors: Omeprazole, Esomeprazole, Lansoprazole, Pantoprazole, Rabeprazole.
      • Irreversibly inhibit H+-K+-ATPase (proton pump).
      • Reduce basal and stimulated gastric acid secretion.
      • Indications: peptic ulcer, reflux oesophagitis, Part of therapy for H. Pylori and Zollinger-Ellison syndrome.
      • Pharmacokinetics: oral administration (enteric coated granules). Injectable preparations are possible.
      • Precautions: use with caution in people with liver disease or who are pregnant or breastfeeding, this may mask gastric cancer symptoms. *(Note: Capsules contain enteric-coated granules; injectable forms available).
    • Antacids: Hydrotalcite, salts of magnesium and aluminium (including magnesium hydroxide, magnesium trisilicate, magnesium carbonate, and aluminium hydroxide gel, colloidal aluminium hydroxide).
      • Neutralize gastric acid.
      • Inhibit peptic enzyme activity (ends up at pH 5).
      • Effective in healing duodenal ulcers, less so for gastric ulcers. *(Note: Preparations with high sodium content should be avoided in patients requiring sodium restriction.)
    • Alginates or Simethicone: Sometimes combined with antiacids.
      • Increase viscosity and adherence of mucus to the oesophageal mucosa (protective barrier).
      • Simeticone is an anti-foaming agent.
    • Misoprostol: Stable analogue of PGE2.
      • Promotes ulcer healing and prevents gastric damage from NSAIDs.
      • Inhibits basal gastric secretion, increases mucosal blood flow and mucus/bicarbonate secretion.
      • ADRs: diarrhoea, abdominal cramps, uterine contractions (not given during pregnancy).

    Helicobacter Pylori Infection

    • Infection of the stomach mucosa; it is a major cause of ulcers.
    • Diagnosis: Urea breath test, stool antigen test, biopsy during endoscopy, Blood Antibody Test.
    • Treatments consist of an antibiotic, proton pump inhibitor, and bismuth chelate.
      • Bismuth chelate=toxic effects on the bacillus; OTC remedy for mild gastrointestinal symptoms (also helps with eradication of H pylori).
    • ADRs: Very little is absorbed but if renal excretion is impaired it can cause encephalopathy, nausea, vomiting, and blackening of the tongue and faeces.

    Drugs Protecting the Mucosa

    • Sucralfate: Complex of aluminium hydroxide and sulfated sucrose.
      • Forms complex gels with mucus.
      • Stimulates mucus, bicarbonate, and prostaglandin secretion from the gastric mucosa.
      • Reduces absorption of other drugs (e.g fluoroquinolones, antibiotics, theophylline, tetracycline, digoxin and amitriptyline).
      • Requires an acidic environment for activation.

    Peptic Ulceration, GERD, and Zollinger-Ellison Syndrome

    • Peptic ulceration: A break in the lining of the stomach or duodenum.
    • GERD: Gastroesophageal reflux disease, when stomach acid moves back into the oesophagus causing damage.
    • Barrett's Oesophagus: Pre-cancerous condition that can develop from untreated GERD.
    • Zollinger-Ellison Syndrome: Rare hypersecretory condition caused by a gastrin-producing tumour. (New information added: GERD can progress to the pre-cancerous condition of Barrett's oesophagus.)

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    Lesson 19 - Gastric Secretions PDF

    Description

    Explore the functions of gastric secretions and their role in digestion, including the regulation of acid secretion and the impact of various hormones and medications. This quiz delves into the intricacies of how the stomach processes food and its importance in nutrient absorption.

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