Follow a meal through the gut, then zoom into its lining. Choose starch, protein or long-chain fat and discover why their next routes differ.
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Digestion changes material inside the gut. Absorption moves selected products across its lining. Food does not simply go into the stomach and then straight into the blood.
Does the swallowed meal travel through the liver before it enters the small intestine?
Food stays in the gut lumen. Liver secretions reach the intestine through ducts; many absorbed nutrients later reach the liver through portal blood.
Chewing breaks food into smaller pieces. Peristalsis moves contents along the tract; other contractions mix them. Enzymes break particular chemical bonds. Physical breakup and chemical digestion are related but different actions.
The main route is mouth → esophagus → stomach → small intestine → large intestine → rectum/anus. Liver, gallbladder and pancreas send secretions through ducts; swallowed food does not pass through those organs. The liver makes bile; the gallbladder stores and concentrates it.
Many sugars and amino acids enter capillary blood and reach the liver through portal circulation. Many long-chain dietary fats are absorbed, repackaged and enter lacteals, then lymph and eventually blood. Short-chain fatty-acid products can take a portal-blood route instead.
Small-intestinal folds, villi and microvilli increase exchange area at distinct scales. The magnified villus shows lumen, lining, capillary and lacteal. A villus is not a single cell, and it is not the same structure as a microvillus.
Bile helps disperse lipid droplets, increasing access for digestion. That physical process is different from an enzyme cleaving a molecule. In the virtual route, a label identifies the selected product rather than pretending every nutrient is the same bead.
Transport depends on nutrient species and cellular mechanisms. The selected routes do not cover all substances, uptake mechanisms or real motility. The progress bar names stages, not a universal digestion time, calorie calculation or blood-sugar response.
Link paper pieces as a starch chain, then put it inside a folded food parcel. Tear only the parcel into smaller pieces. The chain is still chemically unchanged.
Separate the chain at marked joins to represent chemical cleavage. Give the small products new labels. This step changes the represented molecule.
Draw a gut lining. Move a sugar card into capillary blood and a selected long-chain-fat card into a lymph route. Keep secretions and swallowed-food arrows separate.
Which step changes a molecule, and which changes its location?
A conceptual paper model, not actual digestion. No tasting, acid mixtures or food-based health tests are needed.
NIH institute overview of the tract, organ contributions, peristalsis and absorption.
NIDDK · Digestive systemNutrient-specific discussion and table 23.10 distinguish lipid routes and short-chain exceptions.
OpenStax · Digestion and absorptionAcademic definitions and mechanism descriptions.
OpenStax · Digestive processesIndependent subject review is pending.
Read the sources and model assumptions
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