Where does most digestion and nutrient absorption take place?

The small intestine is where most chemical digestion and virtually all nutrient absorption occur. About 6-7 meters long in adults; three sections: duodenum (first 25 cm; receives bile from gallbladder and pancreatic enzymes), jejunum (next ~2.5 m; most absorption), ileum (final ~3.5 m; absorbs vitamin B12, bile salts, remaining nutrients). The inner surface is highly folded and lined with villi (finger-like projections) and microvilli (tiny projections on villi cells), creating enormous surface area (~250 m²) for absorption. Digestive process by organ: (1) Mouth — mechanical breakdown by teeth; saliva contains amylase (starts carbohydrate digestion); (2) Esophagus — peristalsis moves food to stomach; (3) Stomach — mechanical churning; HCl creates acidic environment; pepsin begins protein digestion; food becomes chyme; (4) Small intestine — bile (emulsifies fats), pancreatic enzymes (lipase for fats, amylase for carbs, proteases for proteins) complete digestion; absorption into blood (sugars, amino acids) and lymph (fats); (5) Large intestine (colon) — absorbs water and electrolytes; houses beneficial bacteria; forms feces; (6) Rectum/anus — stores and eliminates waste. Accessory organs: liver (produces bile, processes nutrients), gallbladder (stores bile), pancreas (digestive enzymes and insulin).