Digestive System Lecture

Platypus Facts

• Platypus is a unique mammal:
  • Lays eggs.
  • Males have venomous spurs.
  • Doesn't have a stomach in the traditional sense (lacks gastric glands and gastric juice).
• Links provided for further reading on platypus evolution and digestion.

Human Digestive System Overview

• Four Major Tasks:
  1. Ingestion: Taking in food.
  2. Digestion: Breaking down food into building blocks.
  3. Absorption: Nutrients absorbed and transported to cells.
  4. Elimination: Removing undigested waste.

Detailed Process

Ingestion

• Food intake occurs in the mouth.
• Saliva in the mouth:
  • Contains enzymes (e.g., salivary amylase) that begin breaking down carbohydrates.
  • Has buffers to counteract acidity (prevent tooth decay).
  • Lubricates food.
• Mechanical digestion in the mouth by grinding food with teeth.
• Formation of a food ball (bolus) by the tongue.
• Bolus travels down the esophagus through peristalsis.
• Epiglottis blocks the windpipe (trachea) to prevent food from entering.

Stomach

• Stores up to 2 liters of food and liquid.
• Chemical digestion: gastric juices (HCL and enzymes like pepsin) break down proteins.
• Mechanical digestion: stomach churning mixes the contents with gastric juices.
• Chyme: resulting substance after digestion in the stomach.
• Stomach protected by specialized cells that produce a protective mucus layer.
• Sphincters control food passage between the esophagus, stomach, and intestines.

Small Intestine

• Sections: Duodenum, Jejunum, Ileum (mnemonic: DJ Ivan).
• Major site for chemical digestion and absorption:
  • Carbs, lipids, proteins, nucleic acids broken down.
  • Enzymes and digestive juices from the gallbladder, liver, and pancreas aid digestion.
• Mechanical digestion continues through peristalsis.
• Absorption through the intestinal lining (villi and microvilli increase surface area).
• Nutrients absorbed into capillaries for transport.

Large Intestine

• Reabsorbs water to prevent water loss.
• Home to beneficial bacteria (some synthesize vitamins).
• Feces formation from undigested contents and bacteria.
• Feces stored in the rectum and expelled through the anus.

Accessory Organs

• Liver: Largest internal organ, involved in carbohydrate and protein metabolism, bile production.
• Gallbladder: Stores bile.
• Pancreas: Produces pancreatic juices with enzymes, neutralizes chyme acidity.

Digestive System Disorders

• Celiac Disease: Small intestine issues.
• Diverticulitis: Large intestine issues.
• Heartburn/GERD: Stomach contents enter the esophagus.
• Further information available in video details.

Conclusion

• Understanding the digestive system aids in addressing dysfunctions.
• Stay curious!