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How Digestion Breaks Down Food
Digestion Breaks Down Food
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Digestion is the process that turns food into small molecules the body can absorb and use. It matters because cells need glucose, amino acids, fatty acids, vitamins, minerals, and water to make energy, build tissues, and maintain health. The digestive system uses both physical actions, like chewing and churning, and chemical reactions, mostly from enzymes and acid. Each organ has a specialized job that moves food from the mouth to the intestines in an organized path.
Food is first broken into smaller pieces in the mouth, then pushed through the esophagus to the stomach by peristalsis. In the stomach, acid and enzymes begin protein digestion and turn food into a thick liquid called chyme. In the small intestine, bile emulsifies fats and pancreatic enzymes finish most chemical digestion. Nutrients pass through the villi into the blood or lymph, while the large intestine absorbs water and forms feces.
Key Facts
- Mechanical digestion breaks food into smaller pieces without changing its chemical structure.
- Chemical digestion uses enzymes to break large molecules into absorbable subunits.
- Carbohydrates break down into simple sugars such as glucose.
- Proteins break down into amino acids.
- Fats break down into fatty acids and glycerol.
- Peristalsis moves food through the digestive tract by waves of smooth muscle contraction.
Vocabulary
- Enzyme
- An enzyme is a biological catalyst that speeds up a specific chemical reaction in the body.
- Peristalsis
- Peristalsis is the wave-like contraction of smooth muscle that pushes food through the digestive tract.
- Chyme
- Chyme is the thick, partly digested mixture of food and stomach juices that leaves the stomach.
- Bile
- Bile is a fluid made by the liver that helps break large fat droplets into smaller droplets.
- Villi
- Villi are tiny finger-like folds in the small intestine that increase surface area for nutrient absorption.
Common Mistakes to Avoid
- Thinking digestion happens only in the stomach. This is wrong because digestion begins in the mouth and most nutrient absorption happens in the small intestine.
- Confusing mechanical digestion with chemical digestion. Mechanical digestion changes food size, while chemical digestion changes large molecules into smaller molecules.
- Saying bile is an enzyme. Bile helps emulsify fats, but it does not chemically cut molecules the way enzymes do.
- Assuming the large intestine absorbs most nutrients. The large intestine mainly absorbs water and salts, while the small intestine absorbs most digested nutrients.
Practice Questions
- 1 A meal contains 90 g of carbohydrate. If digestion converts all of it into glucose units, about how many grams of glucose-based material are available for absorption?
- 2 The small intestine is about 6 m long. If chyme moves through it at an average speed of 2 m per hour, how long does it take to travel through the small intestine?
- 3 Explain why a person who cannot produce enough pancreatic enzymes may have trouble gaining nutrients from food even if they eat a normal diet.