Lecture on the Human Stomach

Overview

• The human stomach can hold up to 4 liters of food at any given time
• The stomach processes food received from the oral cavity and esophagus

Functions of the Stomach

1. Receives food: Receives bolus (ball of food) from the esophagus
2. Mechanical breakdown: Muscle walls squeeze and break down the bolus into smaller pieces
   • Uses muscle contractions and enzymes for hydrolysis
3. Formation of chyme: Mixture of broken down food, stomach enzymes, and juices
   • Stored temporarily before being released into the duodenum (first part of the small intestine)

Anatomy of the Stomach

• The stomach is lined with folds to increase surface area
• Contains a layer of cells responsible for secreting components of gastric juice

Types of Cells in the Stomach

1. Parietal Cells: Secrete hydrochloric acid (HCl)
   • HCl is very corrosive, more acidic than battery acid
2. Chief Cells: Secrete pepsinogen (inactive form of the enzyme pepsin)
   • HCl converts pepsinogen to pepsin, which is active and helps in protein hydrolysis
3. Mucous Cells: Secrete mucus (mucin), which protects the stomach lining from being digested by HCl and pepsin

Chemical Process

• Pepsinogen to Pepsin Conversion:
  • Requires HCl to convert pepsinogen to pepsin
  • Pepsin breaks down peptide bonds in proteins, aiding in protein digestion

Protection Mechanisms

• Mucus layer protects the stomach lining
• Without this protection, the stomach could develop ulcers or begin to digest itself

Summary

• The stomach performs mechanical and chemical breakdown of food
  • Uses muscle contractions and enzymes for processing
  • Stores food in the form of chyme until it is ready to be moved to the small intestine