--- title: "Digestion and Absorption in the Mammalian Gut" description: "Absorption is a transport problem set by surface area, gradient and the specific carriers in the membrane, and the small intestine is shaped by that problem. Co-transport of glucose with sodium is the" 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: 2026-09-12 --- > **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 Absorption is a transport problem set by surface area, gradient and the specific carriers in the membrane, and the small intestine is shaped by that problem. Co-transport of glucose with sodium is the case where the whole argument comes together. 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 your gut moves food into blood You get energy from food in four steps. First you take food in, then you break it down, then you move the small products into your body, and finally you get rid of what is left. Most breaking down finishes in your small intestine, and almost all moving across happens there too. Your large intestine has a narrower job: it takes back water and salts. Your small intestine is built for crossing. Its wall folds into finger-like villi, and each lining cell carries even tinier folds called microvilli. Together they multiply the surface many times over, so far more molecules can cross each second. The wall is thin, and rich blood waits right behind it to carry goods away. **Example.** Take glucose, a simple sugar from digested food. It often has to move into blood even when blood already holds more of it. It manages this by riding with sodium through a carrier in the membrane: sodium slides down its own gradient, and glucose is carried along. The sodium gradient supplies the pull, which is why this is called sodium-linked co-transport. **Tip.** Do not give villi jobs they lack. They do not digest food, and they do not pump most nutrients by themselves. They are a structural fix: huge thin area plus blood flow, which is exactly what the quantities in Fick's law reward. More area and a thinner barrier mean faster crossing. **Recap.** Your gut breaks food small, then a huge thin folded surface moves the pieces into blood. ## 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) - [Surface Area to Volume Ratio and Exchange Surfaces](https://lightmysky.com/learn/science/surface-area-to-volume-ratio-and-exchange-surfaces-mt_1TclgVUxfa) - [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) ## 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-)