What is the Digestive System?
The digestive system is the group of organs that break down food into nutrients your body can absorb and use for energy, growth and repair. It runs as one continuous tube — the GI tract — assisted by accessory organs that add enzymes and other digestive juices.
The digestive system ingests food, breaks it down mechanically and chemically, absorbs nutrients into the blood, and eliminates waste. Its main organs, in order, are the mouth, esophagus, stomach, small intestine and large intestine.
- 1↓MouthTeeth mechanically break food down; salivary amylase begins starch digestion.
- 2↓EsophagusPeristalsis (muscle waves) pushes the bolus down to the stomach.
- 3↓StomachGastric acid and pepsin break down proteins, churning food into chyme.
- 4↓Small IntestinePancreatic enzymes and bile digest nutrients; villi absorb them into the blood.
- 5↓Large IntestineWater and electrolytes are absorbed; gut bacteria ferment remaining fiber.
- 6Rectum & AnusWaste is stored as feces and eliminated from the body.
Step-by-step worked examples
Trace a bite of bread from the mouth to absorption in the bloodstream.
Mouth: chewing + salivary amylase start breaking down starch Esophagus: peristalsis carries the bolus to the stomach Stomach: gastric juices further break it into chyme Small intestine: pancreatic enzymes finish digestion; villi absorb glucose into the blood
Why does most nutrient absorption happen in the small intestine rather than the stomach?
The stomach mainly digests protein and has a thick protective mucosa, not built for absorption The small intestine's inner wall is covered in villi and microvilli This creates a huge surface area (about 30-40 m² in an adult), ideal for absorbing nutrients into the blood
Which accessory organs release digestive juices into the small intestine, and what do they do?
Pancreas: releases enzymes (amylase, lipase, trypsin) into the duodenum Liver: produces bile Gallbladder: stores and releases bile, which emulsifies fats so lipase can act on them
Flashcards
Quick quiz
Q1.Which organ absorbs the majority of nutrients?
Q2.What is chyme?
Q3.Where is bile produced?
Q4.What is the main job of the large intestine?
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Common mistakes
Thinking the gallbladder makes bile. — Correct: The liver makes bile; the gallbladder only stores and releases it.
Believing the stomach absorbs most nutrients. — Correct: The stomach mainly digests; the small intestine does almost all nutrient absorption.
Treating digestion and absorption as the same step. — Correct: Digestion breaks food into small molecules; absorption is a separate step that moves those molecules into the blood.
Assuming the large intestine chemically digests food. — Correct: The large intestine mostly absorbs water/electrolytes and ferments fiber — little chemical digestion happens there.
FAQ
What is the digestive system?
The digestive system is the set of organs — from mouth to anus, plus accessory organs like the liver and pancreas — that break down food, absorb nutrients and remove waste.
What are the digestive system organs in order?
Mouth, esophagus, stomach, small intestine, large intestine, rectum and anus, assisted by the salivary glands, liver, gallbladder and pancreas.
How does digestion work step by step?
Food is chewed and moistened in the mouth, moved by peristalsis through the esophagus, broken down in the stomach into chyme, digested and absorbed in the small intestine, then water is reclaimed in the large intestine before waste is eliminated.
What is the function of the digestive system?
To ingest food, digest it mechanically and chemically, absorb nutrients into the bloodstream, and eliminate indigestible waste.