Organ-Structure-Function Comparison
| Feature | Stomach | Small Intestine | Large Intestine |
|---|---|---|---|
| Characteristic structure | Rugae (mucosal folds) | Villi + Microvilli (brush border) | Haustra (sacculations) |
| Primary function | Protein digestion + churning | Digestion + nutrient absorption | Water absorption + faeces formation |
| Key enzyme | Pepsin (pH 1.5–2.0) | Brush border enzymes (pH 7–8) | No digestive enzymes |
| Key secretion | HCl (parietal cells) | Pancreatic juice + bile | None (bacterial vitamins) |
| Length | ~25 cm | ~6–7 metres | ~1.5 metres |
Absorption Route Comparison
| Nutrient | Mechanism | Transport Vehicle | Route | Passes Liver First? |
|---|---|---|---|---|
| Glucose | Active transport (SGLT + ) | Free (dissolved) | Blood capillary → portal vein | YES |
| Amino acids | Active transport (various co-transporters) | Free (dissolved) | Blood capillary → portal vein | YES |
| Fatty acids/glycerol | Passive diffusion → chylomicrons | Chylomicron | Lacteal → thoracic duct | NO (bypasses liver) |
| Water | Osmosis | Free | Blood capillary (large intestine) | YES |
| Fat-soluble vitamins | With fats in chylomicrons | Chylomicron | Lacteal → thoracic duct | NO |
Complete Enzyme Activation Cascade
Hormonal Sequence for a Fatty Meal
Attribution: National Cancer Institute (NCI), Public Domain, via Wikimedia Commons