🍽️ Digestion, Absorption & Nutrition

Digestion is the mechanical and biochemical hydrolysis of complex macromolecular food substances into simple, diffusible, and absorbable nutrient monomers.

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1. 🔬 Alimentary Canal Histology (Outer to Inner)

🔬 Alimentary Canal Transverse Histology (Concentric 4-Layer Wall)

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2. 🧪 Digestive Secretions & Enzyme Cascades

🧪 Master Digestive Juice Enzymes & Enteric Cascades

2.1 Enteric Hormonal Regulation

1. Gastrin (G-cells of stomach): Stimulates gastric glands to secrete $HCl$ and pepsinogen.
2. Secretin (Duodenal S-cells, First discovered hormone by Bayliss & Starling): Stimulates pancreas to secrete water and bicarbonate ions ($HC{O}_3^{-}$) to neutralize gastric acid.
3. Cholecystokinin (CCK-PZ): Stimulates gallbladder contraction to release bile and pancreatic acinar cells to secrete pancreatic digestive enzymes.
4. Gastric Inhibitory Peptide (GIP / Enterogastrone): Inhibits gastric secretion and motility.

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3. 🧈 Digestion & Absorption of Lipids

Lipids are insoluble in water and require sequential emulsification, micellar solubilization, and chylomicron packaging:

$$\text{Triglycerides}\underset{\text{Bile Salts (Sodium taurocholate/glycocholate)}}{\overset{\text{Emulsification}}{\to }}\text{Fine Lipid Droplets}\stackrel{\text{Pancreatic Lipase}}{\to }\text{Monoglycerides}\mathbf{+}\text{Free Fatty Acids}$$

🧈 Lipid Digestion, Micelle Solubilization & Chylomicron Lymphatic Delivery