Lecture on Digestive System

Platypus and Digestion

• Unique features of the platypus:
  • Mammal that lays eggs.
  • Males have venomous spurs.
  • Lacks a conventional stomach as it does not contain gastric glands.

Overview of Human Digestive System

• Focus on four main tasks:
  1. Ingestion: Taking in of food.
  2. Digestion: Breakdown of biomolecule polymers physically or chemically.
  3. Absorption: Nutrients are absorbed and delivered to cells.
  4. Elimination: Removal of undigested waste.

Ingestion and Mouth

• Food enters through the mouth.
• Salivary glands release saliva containing:
  • Enzymes (e.g., Amylase) for chemical digestion.
  • Buffers to counteract acidity.
  • Lubrication for swallowing.
• Mechanical digestion via teeth.
• Formation of bolus, swallowed and moved down the esophagus.

Esophagus to Stomach

• Epiglottis: Flap preventing food from entering the trachea.
• Peristalsis: Wave-like muscle movements moving food down.
• Stomach stores up to 2 liters of food/liquid.
• Chemical digestion with gastric juices (HCL, pepsin).
• Mechanical digestion through stomach churning.
• Chyme formation.

Stomach Structure and Function

• Sphincters:
  • Esophageal sphincter: Separates esophagus and stomach.
  • Pyloric sphincter: Separates stomach and intestines.
• Stomach lining has protective mucus to prevent self-digestion.

Small Intestine

• Major parts:
  1. Duodenum
  2. Jejunum
  3. Ileum
• Significant chemical digestion of all biomolecules.
• Enzymes and juices from gallbladder, liver, pancreas.
• Peristalsis aids mechanical digestion.
• Absorption: Occurs via villi and microvilli with large surface area.
  • Absorbs glucose, fructose, amino acids, vitamins, etc.

Large Intestine (Colon)

• Home to beneficial bacteria.
• Main role: Reabsorb water to prevent loss.
• Feces: Undigested contents and bacteria.
• Ends with rectum for expulsion.

Accessory Organs

• Liver: Largest organ; involved in carbohydrate, protein metabolism, and bile production.
• Gallbladder: Stores bile.
• Pancreas: Produces enzymes and neutralizes acid chyme.

Hormones and Disorders

• Hormones regulate digestive processes.
• Common disorders:
  • Celiac disease (small intestine issue).
  • Diverticulitis (large intestine issue).
  • Heartburn/Gastroesophageal Reflux Disease (stomach contents entering esophagus).

Conclusion

• Understanding the digestive system aids in addressing its dysfunctions.
• Stay curious about biological systems.