Digestive system ↗Chewing fragments food
Teeth and tongue reduce particle size and mix food with saliva, increasing exposed surface.
DIGESTIVE / MOUTH TO COLON
Movement and chemistry
work together.
The gastrointestinal tract is a coordinated tube: motility exposes food to secretions, enzymes reduce large molecules, the mucosa transports usable units, and the colon reclaims water before elimination.
12-STAGE ROUTE
Transit creates
opportunity.
Transit is neither a conveyor belt at fixed speed nor a measure of absorption by itself. Neural, hormonal, muscular, structural, microbial, and meal factors interact.
Saliva starts starch digestion
Salivary amylase begins hydrolyzing starch while mucus helps form a swallowable bolus.
Peristalsis moves the bolus
Coordinated esophageal contractions propel material through sphincters toward the stomach.
The stomach meters chyme
Acid, pepsin and mixing begin protein processing while pyloric control meters delivery to the duodenum.
Bicarbonate neutralizes acid
Pancreatic and biliary bicarbonate supports a luminal environment where intestinal and pancreatic enzymes function.
Enzymes reduce macromolecules
Amylase, lipase and proteases work with brush-border enzymes to create absorbable units.
Bile disperses lipids
Bile acids support emulsification and micellar transport of lipid products and fat-soluble vitamins.
Villi expand transport area
Enterocytes, capillaries and lacteals provide distinct interfaces for nutrients entering blood or lymph.
The ileocecal junction meters entry
Remaining material moves into the colon; transit and microbial fermentation continue to reshape it.
Water and salts are reclaimed
Colonic transport concentrates luminal material while mucus supports passage and barrier function.
Microbes ferment substrate
Some nondigested carbohydrate becomes short-chain fatty acids, gases and other metabolites.
Defecation completes transit
Rectal filling and coordinated neural, sphincter and pelvic-floor control permit elimination.