Lecture Notes on Digestion and the Human Digestive System

Introduction to the Platypus

• Platypus is a unique mammal that lays eggs and has venomous spurs (in males).
• Stomach Definition:
  • If defined strictly (organ with gastric glands producing gastric juice), the platypus lacks a stomach.
  • This raises questions about its digestive system, which is broader than just the stomach.

Human Digestive System Overview

• Focus on four major tasks:
  1. Ingestion: Taking in food.
  2. Digestion: Breaking down biomolecule polymers into building blocks (chemical and physical).
  3. Absorption: Nutrients are absorbed into the body.
  4. Elimination: Waste removal from the body.

Ingestion

• Begins in the mouth:
  • Saliva plays a crucial role (contains enzymes like salivary amylase for carbohydrate breakdown).
  • Mechanical digestion occurs via teeth grinding food.
  • Saliva also helps in buffering acidity and lubricating food into a bolus.
  • Epiglottis: Prevents food from entering the trachea during swallowing.

Digestion in the Stomach

• The stomach can store about 2 liters of food/liquid.
• Chemical Digestion: Involves gastric juices (hydrochloric acid and pepsin).
• Mechanical Digestion: Churning of the stomach contents into a mixture called chyme.
• Protective mucus layer prevents the stomach from digesting itself.

Digestion in the Small Intestine

• Consists of three parts: duodenum, jejunum, and ileum (mnemonic: DJ Ivan).
• Chemical Digestion: Significant breakdown of carbohydrates, lipids, proteins, and nucleic acids.
• Absorption: Most nutrients absorbed here (glucose, amino acids, vitamins, etc.).
  • Villi and microvilli increase surface area for absorption.
  • Nutrients enter capillaries for transportation.

Large Intestine (Colon)

• Hosts beneficial bacteria that aid in digestion and vitamin production.
• Major function: Water Reabsorption to prevent dehydration.
• Feces are composed of undigested contents and bacteria.
• Ends with the rectum where feces are stored until elimination.

Accessory Organs in Digestion

• Liver: Largest internal organ; involved in carbohydrate and protein metabolism; produces bile for lipid breakdown.
• Gallbladder: Stores bile.
• Pancreas: Produces pancreatic juices with enzymes that aid digestion and neutralize gastric acids.

Hormones and Disorders in Digestion

• Various hormones regulate digestive processes.
• Common digestive disorders:
  • Celiac Disease: Issues with the small intestine.
  • Diverticulitis: Issues with the large intestine.
  • Heartburn (GERD): Stomach contents entering the esophagus.

Conclusion

• Understanding the human digestive system is crucial for recognizing and addressing digestive disorders.
• Emphasis on curiosity and further exploration of the topic.