Digestion: Step-by-Step Breakdown of Carbohydrates, Proteins, and Fats

The Digestive Process

1. Mouth: Mechanical chewing + salivary amylase starts carbohydrate digestion.
2. Esophagus: Peristalsis transports bolus to stomach.
3. Stomach: Gastric juice (HCl + pepsin) denatures proteins, kills microbes; churns into chyme.
4. Duodenum (Small Intestine):
   • Pancreatic enzymes: amylase (carbs), proteases (proteins), lipase (fats).
   • Bile (from liver, stored in gallbladder) emulsifies fats.
   • Brush border enzymes (lactase, sucrase, peptidases) complete digestion.
5. Jejunum/Ileum: Nutrient absorption (villi/microvilli).
6. Large Intestine: Water/electrolyte absorption; microbiome ferments fiber → SCFAs; forms stool.
7. Defecation: Mass movements propel feces to rectum → expulsion.