Human Digestive System: CBSE Class 7 & 10 Science Guide
The human digestive tract is a continuous 9-meter muscular tube that breaks complex dietary macromolecules into cellular nutrients.
Digestion is the biochemical conversion of complex, insoluble food molecules into simple, soluble molecules that can be absorbed through intestinal walls into the bloodstream.
In CBSE Class 7 and Class 10 Science, questions frequently center on specific digestive enzymes, their source organs, optimal pH environments, and the crucial role of microscopic intestinal villi.
Digestive Enzymes and Secretions Table
| Organ / Gland | Secretion | Substrate Acted Upon | End Product |
|---|---|---|---|
| Salivary Glands | Salivary Amylase (Ptyalin) | Cooked Starch | Maltose (Disaccharide sugar) |
| Gastric Glands | Pepsin + Hydrochloric Acid (HCl) | Dietary Proteins | Smaller Peptones & Proteoses (acidic pH) |
| Liver | Bile Juice (No enzymes) | Large Fat Globules | Emulsified fine fat droplets (alkaline pH) |
| Pancreas | Trypsin & Chymotrypsin | Proteins and Peptones | Peptides and Amino Acids |
| Pancreas | Pancreatic Lipase | Emulsified Fats | Fatty Acids and Glycerol |
| Small Intestine | Intestinal Enzymes | Carbs, Proteins, Fats | Glucose, Amino Acids, Fatty Acids |
Why Villi in the Small Intestine are Engineering Marvels
The inner wall of the ileum (small intestine) is not a smooth tube; it contains millions of microscopic, finger-like projections called villi, covered in thousands of even smaller microvilli.
This folding increases the effective internal surface area of the gut to over 250 square meters (the size of a tennis court!). Each villus is richly supplied with blood capillaries to absorb glucose and amino acids, and a central lymph vessel called a lacteal to absorb digested fats.
✨ Key Takeaways
- Digestion begins in the mouth with salivary amylase breaking starch into maltose.
- Hydrochloric acid in the stomach creates an acidic pH (1.5 - 2.5) necessary for enzyme pepsin to activate.
- Bile from the liver contains no enzymes; its job is fat emulsification and neutralizing stomach acid.
- Virtually all nutrient absorption occurs in the small intestine via finger-like villi.
- The large intestine reabsorbs surplus water before waste is expelled.