Describe the process of digestion of food in human.

Physiological Mechanism of Human Food Digestion:

1. 1. Buccal Ingestion & Oral Digestion:
   • Mastication lubricated by saliva; Salivary Amylase (Ptyalin, pH 6.8) cleaves ~30% dietary starch into maltose disaccharides, forming a lubricated food bolus.
2. 2. Gastric Digestion (Stomach):
   • Parietal cells secrete Hydrochloric Acid (HCl, pH 1.5–2.0), activating zymogen Pepsinogen into active Pepsin to hydrolyze complex proteins into proteoses and peptones. Gastric mucus shields the mucosal lining. Yields acidic semi-fluid Chyme.
3. 3. Intestinal Digestion (Duodenum & Ileum - Primary Digestive & Absorptive Site):
   • Hepatic Bile: Bile salts (sodium glycocholate/taurocholate) emulsify dietary fats into micro-micelles.
   • Pancreatic Juices:
     • Trypsin & Chymotrypsin: Cleave polypeptides into oligopeptides.
     • Pancreatic Amylase: Polysaccharides → Disaccharides.
     • Pancreatic Lipase (Steapsin): Emulsified lipids → Fatty acids and monoglycerides.
   • Intestinal Succus Entericus: Terminal brush-border enzymes (Maltase, Lactase, Sucrase, Peptidases) reduce all macronutrients into monomers: Glucose, Amino Acids, and Fatty Acids.
4. 4. Absorption via Intestinal Villi:
   • Microvilli exponentially augment luminal surface area; monosaccharides/amino acids enter mesenteric capillaries while fatty acids enter central lacteals as chylomicrons.
5. 5. Large Intestine & Defecation: Absorption of residual water and electrolytes; compaction and egestion of fecal matter.