How does the human digestive system work, and what are its main organs?

The digestive system breaks food into molecules small enough for the body to absorb. It uses two types of digestion:

• Mechanical: Physical breakdown chewing, churning
• Chemical: Enzyme and acid breakdown of proteins, carbohydrates, and fats

The journey of food:

1. Mouth: Teeth crush food; saliva adds amylase to begin starch breakdown; tongue forms a bolus for swallowing
2. Esophagus: 25 cm muscular tube; peristalsis pushes food downward; no digestion occurs here
3. Stomach: Gastric acid (pH 1.5–3.5) kills bacteria and activates pepsin for protein breakdown; food becomes liquid chyme (takes 2–4 hours)
4. Small intestine (6–7 meters): Main site of digestion and absorption:
   • Duodenum receives bile and pancreatic enzymes
   • Jejunum absorbs most nutrients into the bloodstream
   • Ileum absorbs remaining nutrients including vitamin B12
5. Large intestine (1.5 meters): Absorbs water and salts; gut bacteria ferment remaining material; waste becomes solid feces
6. Rectum and anus: Store and expel feces

Accessory organs: Liver, Gallbladder, Pancreas