Lecture on Chemical Digestion and Gastric Conditions

Introduction to Protein and Fat Digestion

• Protein Digestion
  • Begins with hydrochloric acid denaturing protein molecules.
  • Converts pepsinogen to pepsin, which breaks peptide bonds to form peptides.
• Fat Digestion
  • Continues in the stomach, particularly in infants where the pH is 5-6.

Role of Hydrochloric Acid

• Kills microbes in food.
• Mucous cells protect the stomach walls with a 1-3 mm thick layer of mucus.

Mechanical Digestion

• Gentle mixing waves every 15-25 seconds.
• Produces about two quarts of gastric juice daily.
• Gastric juice combines with the bolus to form chyme, a soupy substance.
• Vigorous waves and intense waves near the pylorus help in the digestion process.
• Pyloric sphincter controls the release of chyme to the small intestine, optimizing surface area contact.

Vomiting (Emesis)

• Forcible expulsion of upper GI tract contents.
• Vomiting from the duodenum can cause an alkaline taste.
• Prolonged vomiting can lead to acid-base imbalances and dehydration.

Peptic Ulcers

• Crater-like lesions in the GI tract's mucous membrane.
• Complications include anemia from bleeding.
• Causes include:
  • Bacterium Helicobacter pylori
  • Non-steroidal anti-inflammatory drugs (e.g., aspirin)
  • Hypersecretion of hydrochloric acid

Helicobacter pylori

• Can live in acidic stomach conditions.
• Invades mucous layer to epithelial cells, converting urea and water into ammonium, neutralizing stomach acid.
• Infection leads to loss of mucosal protection, allowing acid and pepsin damage.
• Cytotoxins and ammonia contribute to cell damage.

Potential Outcomes of H. pylori Infection

• <1% develop mucosa-associated lymphatic tissue (MALT) lymphoma.
• 100% develop acute or chronic gastritis.
• 5% develop gastric atrophy.
• 1% develop gastric cancer.
• 10% develop gastric or duodenal ulcers.

Historical Context of Ulcer Research

• Initially believed ulcers were caused by stress and acidic foods.
• Barry Marshall and Robin Warren identified H. pylori as a cause of gastric ulcers in 1982, winning the Nobel Prize in 2005.
• Their research faced skepticism and resistance, especially from pharmaceutical interests.
• Marshall self-experimented by ingesting H. pylori to prove its role in causing gastritis.

H. pylori and Cancer Risk

• Infection in childhood increases risk of gastric cancer.
• Infection in adulthood increases risk of ulcers.

Lecture Goals

• Draw and label the stomach's different regions.
• Describe mechanical and chemical digestion occurring in the stomach.
• List enzymes and substances in gastric juice aiding digestion.
• Describe histology of gastric mucosa.
• Define terms: chyme, pyloric stenosis, pylorospasm, parietal cell, chief cell, G cell, gastrin, Zollinger-Ellison syndrome, peptic ulcer, emesis.