--- title: "Digestion and Absorption in the Mammalian Gut" description: "Explain how villi support absorption and how an ATP-powered pump maintains the sodium gradient used for glucose co-transport. Connect villus damage in coeliac disease with reduced nutrient absorption." canonical: https://lightmysky.com/learn/science/digestion-and-absorption-in-the-mammalian-gut-mt_xZ2-3ZClDa source: https://lightmysky.com/learn/science/digestion-and-absorption-in-the-mammalian-gut-mt_xZ2-3ZClDa.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Digestion and Absorption in the Mammalian Gut Explain how villi support absorption and how an ATP-powered pump maintains the sodium gradient used for glucose co-transport. Connect villus damage in coeliac disease with reduced nutrient absorption. Subject: Science · Area: Organisms & Life Processes · Ages 16 to 17 Page: https://lightmysky.com/learn/science/digestion-and-absorption-in-the-mammalian-gut-mt_xZ2-3ZClDa ## Ready when they can - Explain the structure of a villus in terms of the quantities in Fick's law - Describe glucose absorption as sodium-linked co-transport and say what supplies the gradient - Account for the symptoms of a named absorption disorder from the mechanism that fails ## Lesson: How nutrients cross the gut lining Ingestion takes food in. Digestion breaks large food molecules into smaller products. Absorption moves nutrients across the gut lining into the body. Elimination removes unabsorbed material. Most chemical digestion and nutrient absorption occur in the small intestine. The large intestine absorbs water and salts from the remaining contents. Absorbed nutrients can later supply respiration; digestion itself does not release energy into ATP. Villi are finger-like tissue projections of the small-intestinal lining. Microvilli are smaller membrane projections on its lining cells. Both increase surface area. Each villus has a one-cell-thick epithelium, blood capillaries and a lymph vessel called a lacteal. A short path supports diffusion. Lining cells also contain transport proteins and digestive enzymes, including enzymes on the microvilli. *(drawing: Blood flow can maintain a diffusion gradient by carrying absorbed solutes away. This is a causal summary, not an anatomical diagram.)* For diffusion, Fick's law gives rate proportional to surface area × concentration difference ÷ diffusion distance. Hold other factors steady when comparing rates. If area triples and distance doubles, rate becomes 3 ÷ 2, or 1.5 times the original. Villi add area, their thin epithelium shortens the path, and blood flow can maintain a concentration difference. Fick's law alone does not explain carrier-driven uptake. Glucose enters a lining cell from the gut lumen, the space containing digested food. A sodium-glucose co-transporter moves sodium and glucose into the cell together. Sodium moves down its electrochemical gradient, supplying energy for glucose to move against its own concentration gradient. This is secondary active transport. The movement described here is entry into the lining cell, not direct entry into blood. On the cell's blood-facing side, the sodium-potassium pump uses ATP to move sodium out and potassium in. Keeping sodium low inside helps maintain its inward gradient. Glucose leaves through a separate carrier by facilitated diffusion, down its concentration gradient towards the blood. The pump uses ATP directly; the glucose co-transporter uses the sodium gradient. Glucose exit does not itself pump sodium out. *(drawing: The boxes trace the transport mechanism. They do not draw the two sides of the cell.)* In coeliac disease, gluten triggers an immune response that damages the small-intestinal lining and can flatten villi. Reduced surface area contributes to poor nutrient absorption. Small nutrients may still be present in the gut, yet less enters the body. This can cause weight loss and nutrient deficiencies. Damage can also affect enzymes on lining cells. Absorption, digestion and cellular respiration are different processes. **Recap.** Villi support absorption. An ATP-powered pump maintains the sodium gradient for glucose entry into lining cells. Villus damage can reduce nutrient uptake and cause deficiencies. *This lesson, question bank and flashcards were written for this dataset.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [The Digestive System and Testing Food for Nutrients](https://lightmysky.com/learn/science/the-digestive-system-and-testing-food-for-nutrients-mt__mBJCQEqPS) - [Fick's Law and What Sets the Rate of Exchange](https://lightmysky.com/learn/science/ficks-law-and-what-sets-the-rate-of-exchange-mt_6JreZAFeb-) - [Active Transport Against the Gradient](https://lightmysky.com/learn/science/active-transport-against-the-gradient-mt_BQf1bgo9oM) ## Optional connections - [Surface Area to Volume Ratio and Exchange Surfaces](https://lightmysky.com/learn/science/surface-area-to-volume-ratio-and-exchange-surfaces-mt_1TclgVUxfa) ## Opens up - [Fuel Homeostasis and the Fed to Fasted Switch](https://lightmysky.com/learn/science/fuel-homeostasis-and-the-fed-to-fasted-switch-mt_zZrXwbWqw-)