Digestive System Overview

Introduction

• Humans consume on average 1 to 2.7 kg of food daily.
• This equals over 365 kg per year and more than 28,800 kg over a lifetime.
• The digestive system is a complex network of 10 organs, 9 meters long, with over 20 specialized cell types.

Main Components of the Digestive System

1. Gastrointestinal Tract
   • A twisting channel with an internal surface area of 30 to 40 sq meters.
2. Pancreas, Gallbladder, and Liver
   • Produce special juices to break down food.
3. Enzymes, Hormones, Nerves, and Blood
   • Collaborate to modulate the digestive process and deliver nutrients.
4. Mesentery
   • A large tissue that supports digestive organs in the abdomen.

Digestive Process

Pre-tongue

• Anticipation of food triggers saliva production (1.5 liters/day).

Mouth

• Chewing and saliva form a moist lump called bolus.
• Saliva enzymes begin starch breakdown.

Esophagus

• 25 cm long tube where peristalsis (muscular contractions) transports bolus to the stomach.

Stomach

• Muscular walls break bolus into chunks.
• Hormones trigger acids and enzymes to dissolve food and break down proteins.
• Hormones signal pancreas, liver, and gallbladder to prepare digestive juices and bile.

Small Intestine

• After 3 hours in the stomach, bolus becomes chyme.
• Duodenum:
  • Bile from the gallbladder helps dissolve fats in chyme.
  • Pancreatic and intestinal juices break fats into fatty acids and glycerol.
  • Proteins are broken into amino acids and carbohydrates into glucose.
• Jejunum and Ileum:
  • Villi increase surface area for absorption into the bloodstream.

Large Intestine (Colon)

• Absorbs remaining fluid, leaving a soft mass called stool.
• Stool is pushed into the rectum.

Conclusion

• The entire process typically takes 30 to 40 hours.
• Stool is expelled through the anus, completing digestion.