Enzyme-Source-pH Facts:
- Salivary amylase: salivary glands → starch → maltose → pH 6.8
- Pepsin: chief cells (as pepsinogen) → proteins → large peptides → pH 1.5–2.0
- Gastric lipase: chief cells → short-chain triglycerides → pH 4.0–5.0
- Enterokinase: DUODENAL MUCOSA (not pancreas) → trypsinogen → trypsin → pH 7.0–8.0
- Trypsin + Chymotrypsin: pancreas (as proenzymes) → proteins/peptides → smaller peptides → pH 7.5–8.5
- Carboxypeptidase: pancreas (as procarboxypeptidase) → C-terminal amino acid cleavage → pH 7.5–8.0
- Elastase: pancreas (as proelastase) → elastin → pH 8.0–8.5
- Pancreatic lipase: pancreas (active) → emulsified triglycerides → FA + monoglycerides → pH 7.5–8.0
- Pancreatic amylase: pancreas (active) → starch + glycogen → maltose → pH 7.0–8.0
- Maltase/Sucrase/Lactase: brush border → disaccharides → monosaccharides → pH 7.0–8.0
Bile — Critical Distinction:
- Produced: liver. Stored: gallbladder. Released by: CCK.
- Contains: bile SALTS (not enzymes) → emulsification ONLY
- Bile has ZERO enzymatic activity
Absorption Routes:
- Glucose + amino acids → active transport (SGLT, Na-dependent) → blood capillaries → portal vein → liver
- Fats (fatty acids + glycerol) → reassembled as triglycerides → chylomicrons → lacteals → thoracic duct → left subclavian vein (bypass liver)
- Water → osmosis → large intestine → blood capillaries
- Fat-soluble vitamins (A, D, E, K) → lacteals → thoracic duct (same as fats)
Structural Features:
- Stomach: rugae (longitudinal mucosal folds → expansion + secretory surface)
- Small intestine: villi + microvilli (brush border) → 600-fold surface area amplification
- Large intestine: haustra (sacculations → slow transit for water absorption)
GI Hormones:
- Gastrin: G-cells, pyloric stomach → stimulates HCl + pepsinogen
- Secretin: S-cells, duodenum, trigger = acid → stimulates pancreatic bicarbonate
- CCK: I-cells, duodenum, trigger = fats + amino acids → bile release + pancreatic enzymes
- GIP: K-cells, duodenum, trigger = fats + glucose → inhibits gastric acid + stimulates insulin
Disorders:
- Kwashiorkor: protein deficiency → oedema, distended belly (low albumin → low oncotic pressure → fluid leaks)
- Marasmus: total calorie + protein deficiency → extreme wasting, NO oedema
- Jaundice: excess bilirubin → yellow skin + sclera
- Vomiting: medullary vomiting centre (medulla oblongata)