Digestion is the process of breaking food into nutrients the body can absorb. It begins in the mouth and ends in the large intestine.

Digestive pathway:

1. Mouth — mechanical breakdown, salivary amylase begins starch digestion
2. Esophagus — transport only
3. Stomach — acid (HCl) denatures protein, pepsin begins protein digestion. Food becomes chyme.
4. Small intestine — 90% of nutrient absorption occurs here. Pancreatic enzymes and bile break down all macronutrients.
5. Large intestine — water absorption, gut bacteria ferment fiber, waste formation
6. Rectum/Anus — elimination

Key insight: The small intestine is ~20 feet long with a surface area the size of a tennis court — maximized for absorption.

Reference:

Wikipedia: Human digestive system

https://en.wikipedia.org/wiki/Human_digestive_system