Gut Basics
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Small Intestine: The Absorption Powerhouse
The small intestine is where the magic happens—95% of nutrient absorption occurs here.
Three sections:
1. Duodenum (first 10 inches)
- Receives chyme from stomach
- Pancreatic enzymes added
- Bile from gallbladder added
- pH neutralized (acid → alkaline)
2. Jejunum (middle 8 feet)
- Primary absorption site
- Carbohydrates and proteins absorbed
- Rich in blood vessels
3. Ileum (final 12 feet)
- Vitamin B12 absorption
- Bile salt reabsorption
- Connects to large intestine
Surface area optimization:
- Inner lining has millions of tiny finger-like projections (villi)
- Each villus has microvilli
- Total surface area: 250-400 square meters (size of a tennis court!)
Key enzymes:
- Lactase → breaks down lactose (milk sugar)
- Sucrase → breaks down sucrose
- Peptidases → break down proteins into amino acids
Problems here (inflammation, damage to villi, enzyme deficiencies) cause malabsorption.
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