Here’s a complete and easy-to-understand explanation of the human digestive system—from start to finish—highlighting what happens at each stage:

1. Mouth – Where Digestion Begins

• Mechanical Digestion: Teeth break down food into smaller pieces by chewing.

• Chemical Digestion: Saliva (from salivary glands) contains an enzyme called amylase that starts breaking down carbohydrates (like bread and rice) into sugars.

• The tongue helps in mixing the food and forming a soft ball called a bolus which is swallowed.

2. Esophagus – The Food Transporter

• A muscular tube connecting the mouth to the stomach.

• Uses a wave-like motion called peristalsis to push the bolus down.

• A valve called the lower esophageal sphincter opens to let food into the stomach and closes to prevent acid reflux.

3. Stomach – The Churning and Breaking Chamber

• Mechanical digestion: Muscles churn the food.

• Chemical digestion: Stomach lining releases:

  • Hydrochloric acid (HCl) to kill bacteria and activate enzymes.

  • Pepsin, an enzyme that starts digesting proteins.

• Food is turned into a semi-liquid mixture called chyme.

4. Small Intestine – The Main Absorption Zone

It has three parts: duodenum, jejunum, and ileum.

• Duodenum:

  • Bile (from liver and stored in the gallbladder) emulsifies fats (breaks large fat into smaller droplets).

  • Pancreatic juices (from the pancreas) contain enzymes to digest carbohydrates, proteins, and fats.

• Jejunum and Ileum:

  • Nutrients are absorbed through the villi (finger-like projections) into the bloodstream.

  • Vitamins, minerals, sugars, amino acids, and fatty acids are absorbed here.

5. Large Intestine (Colon) – Water Absorption & Waste Prep

• Absorbs water, salts, and some vitamins.

• The remaining undigested food is turned into feces.

• Good bacteria here help break down some materials and produce Vitamin K and B.

6. Rectum and Anus – The Exit

• Rectum: Stores feces temporarily.

• Anus: The final part where feces are expelled through defecation.

Summary of What Happens:

• Food gets chewed, mixed, broken down by acids and enzymes.

• Nutrients are absorbed in the small intestine.

• Water is absorbed in the large intestine.

• Waste exits through the rectum and anus.