Human Body — Digestive System
1. Why Do We Need Food?
Food provides:
- Energy for all body activities.
- Growth and repair of body tissues.
- Protection from diseases.
Balanced Diet
A BALANCED DIET contains ALL essential nutrients in the RIGHT proportions.
| Nutrient | Function | Sources |
|---|---|---|
| Carbohydrates | ENERGY | Rice, wheat, potatoes, sugar |
| Proteins | Growth and repair | Pulses, eggs, meat, milk, fish |
| Fats | ENERGY (stored), insulation | Butter, oil, ghee, nuts |
| Vitamins | Protection from deficiency diseases | Fruits, vegetables, milk |
| Minerals | Growth, bone health, blood | Vegetables, milk, salt |
| Roughage (Fibre) | Digestive health | Whole grains, fruits, vegetables |
| Water | All metabolic processes | Drinks, fruits, vegetables |
2. The Digestive System — Organs
The digestive system is a TUBE (alimentary canal) stretching from mouth to anus, with associated GLANDS.
Organs in Order
| Organ | Functions |
|---|---|
| Mouth | TEETH (chewing), TONGUE (tasting, mixing), SALIVA (starch breakdown) |
| Oesophagus | Food pipe — carries food to stomach by PERISTALSIS |
| Stomach | CHURNS food, HCL kills germs, PEPSIN breaks proteins |
| Small intestine | MAIN site of DIGESTION and ABSORPTION |
| Large intestine | ABSORBS water and minerals, forms FAECES |
| Rectum | Stores faeces |
| Anus | Eliminates faeces (egestion) |
3. Digestive Glands
These glands SECRETE digestive juices containing ENZYMES.
| Gland | Secretion | Enzyme(s) | Substance Digested |
|---|---|---|---|
| Salivary glands | Saliva | Amylase | Starch → Maltose |
| Gastric glands (stomach) | Gastric juice | Pepsin | Proteins → Peptides |
| HCl | Kills germs, activates pepsin | ||
| Liver | Bile (stored in GALL BLADDER) | NO enzymes | EMULSIFIES fats (breaks into droplets) |
| Pancreas | Pancreatic juice | Trypsin, Amylase, Lipase | Proteins, starch, fats |
| Intestinal glands | Intestinal juice | Various | Completes digestion of all nutrients |
4. Process of Digestion
- Mouth: Starch → Maltose (by amylase). Food mixed with saliva → BOLUS.
- Oesophagus: Peristalsis pushes bolus to stomach.
- Stomach: Proteins → Peptides (by pepsin). CHYME (semi-digested food) formed.
- Small intestine:
- Pancreatic juice: Digests proteins, starch, fats.
- Bile: Emulsifies fats.
- Intestinal juice: Completes digestion.
- VILLI (finger-like projections) ABSORB nutrients into blood.
- Large intestine: Water and minerals absorbed.
- Rectum/Anus: Faeces eliminated.
Absorption in Small Intestine
- VILLI increase the SURFACE AREA for absorption.
- Each villus has BLOOD CAPILLARIES and a LACTEAL (lymph vessel).
- Glucose, amino acids → blood capillaries.
- Fatty acids, glycerol → lacteals.
5. Deficiency Diseases
| Nutrient | Deficiency Disease | Symptoms |
|---|---|---|
| Vitamin A | Night blindness | Poor vision in dim light |
| Vitamin B₁ (Thiamine) | Beriberi | Weak muscles, nerve damage |
| Vitamin C | Scurvy | Bleeding gums, slow wound healing |
| Vitamin D | Rickets | Soft, bent bones in children |
| Calcium | Osteoporosis | Weak, brittle bones |
| Iron | Anaemia | Weakness, pale skin, fatigue |
| Iodine | Goitre | Swollen thyroid gland in neck |
6. ICSE Exam Focus
| Topic | Marks | Frequency |
|---|---|---|
| Digestive organs and their functions | 3 marks | Very High |
| Digestive glands and enzymes | 2-3 marks | High |
| Balanced diet and nutrients | 2 marks | High |
| Absorption in small intestine (villi) | 2 marks | Medium |
| Deficiency diseases | 2-3 marks | Very High |
Common Mistakes
- Saying bile digests fats (it EMULSIFIES fats — breaks them into droplets for lipase to act).
- Confusing the small and large intestine functions (small = absorption, large = water reabsorption).
- Forgetting that liver produces bile (stored in gall bladder).
- Writing 'vitamins provide energy' — they do NOT; they protect from diseases.
Self-Test (5 Questions)
Q1. Which enzyme breaks down starch in the mouth? (1 mark)
- A) Pepsin
- B) Amylase
- C) Trypsin
- D) Lipase
Q2. 'Name the finger-like projections in the small intestine that absorb nutrients.' (1 mark)
Q3. 'Which vitamin deficiency causes rickets in children?' (1 mark)
Q4. 'List the organs of the digestive system in order.' (2 marks)
Q5. 'What is the function of the liver in digestion?' (2 marks)
Answers
A1. B) Amylase (salivary amylase). A2. Villi. A3. Vitamin D deficiency (leads to soft, bent bones). A4. Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Rectum → Anus. A5. The liver produces BILE which is stored in the gall bladder. Bile EMULSIFIES fats (breaks large fat droplets into smaller ones) for easier digestion by lipase.
