The human digestive system is the body system responsible for taking in food, breaking it into simpler substances, absorbing nutrients, and removing undigested waste.
Digestion helps the body obtain:
- Energy
- Growth and repair materials
- Nutrients for body functions
What is Digestion?
Digestion is the process of converting complex food substances into simple, soluble forms that can be absorbed and used by the body.
Example:
| Complex Food | Simple Form |
|---|---|
| Carbohydrates | Glucose |
| Proteins | Amino acids |
| Fats | Fatty acids + Glycerol |
Human Digestive System – Main Parts
The digestive system consists of:
1. Alimentary Canal (Digestive Tract)
A long tube running from mouth to anus.
2. Digestive Glands
These glands release digestive juices.
Examples:
- Salivary glands
- Liver
- Pancreas
Flow of Food in Human Digestive System
Mouth → Buccal Cavity → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus
1. Mouth (Buccal Cavity)
Functions:
- Food enters the body.
- Teeth break food into smaller pieces (mechanical digestion).
- Saliva mixes with food.
Role of Teeth:
- Cutting
- Tearing
- Grinding
Role of Tongue:
- Mixes food with saliva
- Helps in swallowing
- Helps in tasting
Salivary Glands:
Produce saliva.
Saliva Contains:
- Salivary amylase enzyme
Function of Salivary Amylase:
Converts:
Starch → Sugar
2. Oesophagus (Food Pipe)
Function:
- Transfers food from mouth to stomach.
Process:
Food moves by Peristalsis.
What is Peristalsis?
Wave-like muscular movement that pushes food forward.
Important Point:
No digestion occurs here.
3. Stomach
The stomach is a muscular J-shaped organ.
Functions:
- Stores food temporarily
- Mixes food
- Starts protein digestion
Gastric Glands Secrete:
| Substance | Function |
|---|---|
| Hydrochloric Acid (HCl) | Creates acidic medium |
| Pepsin | Digests proteins |
| Mucus | Protects stomach wall |
Digestion:
Proteins → Simpler proteins
4. Small Intestine (Main Site of Digestion and Absorption)
This is the longest part of the digestive system.
Three Parts:
- Duodenum
- Jejunum
- Ileum
Functions:
- Completes digestion
- Absorbs nutrients
Secretions Entering Small Intestine:
A. Liver → Bile Juice
Function:
- Breaks large fat globules into smaller droplets (Emulsification)
B. Pancreas → Pancreatic Juice
Contains enzymes to digest:
- Carbohydrates
- Proteins
- Fats
C. Intestinal Glands → Intestinal Juice
Completes digestion.
Final Digestion
| Nutrient | Final Product |
|---|---|
| Carbohydrates | Glucose |
| Proteins | Amino acids |
| Fats | Fatty acids + Glycerol |
Absorption in Small Intestine
The inner wall contains Villi.
Villi:
Small finger-like projections.
Functions:
- Increase surface area
- Absorb digested food into blood
5. Large Intestine
Functions:
- Absorbs water
- Absorbs salts
- Forms semi-solid waste
Important:
No major digestion occurs.
6. Rectum
Function:
Stores waste temporarily.
7. Anus
Function:
Waste is removed from the body.
This process is called:
Egestion
Digestive Glands and Their Functions
| Gland | Secretion | Function |
|---|---|---|
| Salivary Gland | Saliva | Digests starch |
| Liver | Bile juice | Emulsifies fats |
| Pancreas | Pancreatic juice | Digests nutrients |
| Gastric Glands | Gastric juice | Protein digestion |
Process of Digestion – Summary Table
| Organ | Main Function |
|---|---|
| Mouth | Chewing and starch digestion |
| Oesophagus | Food transport |
| Stomach | Protein digestion |
| Small Intestine | Digestion and absorption |
| Large Intestine | Water absorption |
| Rectum | Waste storage |
| Anus | Waste removal |
Key Terms
- Digestion → Breaking food into simple substances
- Peristalsis → Wave-like food movement
- Absorption → Nutrients entering blood
- Assimilation → Use of absorbed nutrients
- Egestion → Removal of waste
Practice Questions with Answers
1. What is digestion?
Answer: Digestion is the process of converting complex food into simpler absorbable substances.
2. Which enzyme is present in saliva?
Answer: Salivary amylase.
3. Where does maximum digestion occur?
Answer: Small intestine.
4. What is the function of bile juice?
Answer: It emulsifies fats.
5. What are villi?
Answer: Finger-like projections that absorb nutrients.
Fill in the Blanks
- Digestion starts in the mouth.
- Hydrochloric acid is secreted in the stomach.
- Bile juice is produced by the liver.
- Nutrient absorption mainly occurs in the small intestine.
- Waste leaves the body through the anus.
10 MCQs (With Answers)
1. Digestion begins in:
A. Stomach
B. Mouth ✅
C. Liver
D. Intestine
2. Saliva digests:
A. Protein
B. Fat
C. Starch ✅
D. Vitamins
3. Peristalsis occurs in:
A. Oesophagus ✅
B. Teeth
C. Tongue
D. Liver
4. Gastric juice contains:
A. Pepsin ✅
B. Bile
C. Insulin
D. Glucose
5. Bile is secreted by:
A. Pancreas
B. Liver ✅
C. Stomach
D. Kidney
6. Main digestion occurs in:
A. Mouth
B. Small Intestine ✅
C. Rectum
D. Anus
7. Villi are found in:
A. Stomach
B. Small Intestine ✅
C. Mouth
D. Oesophagus
8. Protein digestion begins in:
A. Stomach ✅
B. Mouth
C. Rectum
D. Liver
9. Water is absorbed in:
A. Large Intestine ✅
B. Mouth
C. Liver
D. Pancreas
10. Removal of undigested food is called:
A. Absorption
B. Assimilation
C. Egestion ✅
D. Respiration
