Overview of the Human Digestive System

Feb 1, 2025

Human Digestive System Overview

Key Functions of the Digestive System

  1. Ingestion: Intake of food.
  2. Digestion: Breakdown of large biomolecules into building blocks.
    • Mechanical Digestion: Physical breakdown through chewing.
    • Chemical Digestion: Enzymatic breakdown, e.g., salivary amylase breaks down carbohydrates.
  3. Absorption: Uptake of nutrients by the body.
  4. Elimination: Expulsion of undigested substances.

Process of Digestion

Ingestion

  • Begins in the mouth.
  • Saliva: Contains enzymes and buffers, starts chemical digestion.
  • Enzymatic Action: Salivary amylase in the mouth begins digestion of carbohydrates.
  • Mechanical Digestion: Teeth grind food.
  • Formation of Bolus: Food becomes a bolus for swallowing.
  • Epiglottis: Prevents food from entering the trachea.
  • Peristalsis: Muscle contractions move bolus down the esophagus.

Stomach

  • Can hold about 2 liters.
  • Chemical Digestion: Done by gastric juices (HCL and pepsin).
  • Mechanical Digestion: Churning mixes food with gastric juices to form chyme.
  • Sphincters:
    • Lower Esophageal Sphincter: Prevents acid reflux.
    • Pyloric Sphincter: Controls passage to small intestine.

Small Intestine

  • Three Sections:
    • Duodenum: Chemical digestion with pancreatic enzymes and bile; absorbs iron and minerals.
    • Jejunum: Main site for nutrient absorption, aided by villi.
    • Ileum: Absorbs vitamin B12, bile salts, and fat-soluble vitamins (A, D, E, K).
  • Mnemonic: Digestive Juices Intake (Duodenum, Jejunum, Ileum).

Large Intestine

  • Sections:
    • Ascending Colon: Absorbs water/salts.
    • Transverse Colon: Further absorption/storage.
    • Descending Colon: Moves waste to rectum.
  • Mnemonic: Ascending absorbs, Transverse transports, Descending drives down.

Accessory Organs

  • Liver: Produces bile, metabolizes carbohydrates and proteins.
  • Gallbladder: Stores bile.
  • Pancreas: Produces enzymes and bicarbonate for digestion.

Key Hormones and Enzymes

  • Gastrin: Stimulates gastric glands; aids in protein digestion.
  • Cholecystokinin (CCK): Stimulates bile release and pancreatic enzymes.
  • Secretin: Regulates pH; stimulates bicarbonate production.
  • Insulin: Facilitates glucose uptake; lowers blood sugar.
  • Glucagon: Raises blood sugar by breaking down glycogen.
  • Bile: Emulsifies fats for digestion.

Conclusion

  • Understanding the gastrointestinal system is crucial for AITs exams.
  • Additional resources available at Nurse Chun's Store.