How does digestion occur in the human body step by step?

Digestion in the human body is a systematic process involving multiple organs that break down food into simple, absorbable nutrients.

Step-by-step process of digestion:

1. Ingestion (Mouth)
Food is taken in through the mouth. Teeth perform mechanical digestion by chewing, while saliva (containing the enzyme amylase) begins the breakdown of starch into simple sugars.

2. Swallowing and transport (Esophagus)
Food is swallowed and moves through the esophagus to the stomach via peristalsis (wave-like muscle contractions).

3. Digestion in the stomach

• The stomach churns food mechanically.

• Gastric juices containing hydrochloric acid (HCl) and pepsin begin protein digestion.

• Food is converted into a semi-liquid substance called chyme.

4. Digestion in the small intestine

• Bile (from liver) emulsifies fats.

• Pancreatic enzymes break down carbohydrates, proteins, and fats.

• Intestinal enzymes complete digestion into simple forms:

  • Glucose

  • Amino acids

  • Fatty acids and glycerol

5. Absorption (small intestine)
Digested nutrients are absorbed through villi into the bloodstream and lymph.

6. Water absorption (large intestine)
The large intestine absorbs water and salts, forming solid waste.

7. Egestion (elimination)
Undigested waste is expelled from the body through the rectum and anus.

Key outcomes:

• Conversion of food into usable nutrients

• Energy production and body maintenance

In simple terms: Digestion starts in the mouth, continues in the stomach and small intestine, nutrients are absorbed, and waste is finally removed.