⚡ Quick Revision: Introduction to Digestion
Digestion is the process of breaking down complex, insoluble food substances into simple, soluble molecules that can be absorbed by the body.
Alimentary Canal: A long, muscular tube extending from the mouth to the anus where digestion and absorption occur.
The 5 Stages of Nutrition
- 1 Ingestion: Taking food into the mouth.
- 2 Digestion: Breaking down food (Mechanical & Chemical).
- 3 Absorption: Uptake of nutrients into the blood.
- 4 Assimilation: Using absorbed food for energy/growth.
- 5 Egestion: Removing undigested waste from the body.
⚡ Quick Revision: The Mouth and Teeth
Mastication: The mechanical process of chewing food into smaller pieces by the teeth.
Types of Teeth
| Type | Number (Adult) | Function |
|---|---|---|
| Incisors | 8 | Biting and cutting food. |
| Canines | 4 | Tearing food. |
| Premolars | 8 | Crushing and grinding. |
| Molars | 12 | Strong grinding. |
Role of Saliva
- ✔ Produced by three pairs of salivary glands.
- ✔ Contains the enzyme Salivary Amylase which breaks starch into maltose.
- ✔ Moistens food to form a soft mass called bolus for easy swallowing.
⚡ Quick Revision: Oesophagus & Stomach
Peristalsis: The wave-like muscular contractions that push food down the alimentary canal.
The Oesophagus (Food Pipe)
- ✔ Connects the mouth to the stomach; no digestion occurs here.
The Stomach
- ✔ Hydrochloric Acid (HCl): Kills bacteria and activates pepsin.
- ✔ Pepsin: An enzyme that starts the digestion of proteins.
- ✔ Chyme: The thick, semi-liquid food mass produced after churning for 2-3 hours.
Mucus with HCl. Mucus protects the stomach lining from being digested by its own acid.
⚡ Quick Revision: Small & Large Intestine
The small intestine is the longest part of the alimentary canal and the primary site for complete digestion and absorption.
Small Intestine: The Hub of Absorption
- ✔ Villi: Finger-like projections that increase surface area for rapid nutrient absorption.
- ✔ Duodenum: The first part where bile (from liver) and pancreatic juice meet the chyme.
- ✔ Complete Digestion: Proteins → Amino Acids, Fats → Fatty Acids/Glycerol, Carbohydrates → Glucose.
Large Intestine
- ✔ Water Absorption: Absorbs water and minerals from undigested food.
- ✔ Egestion: Temporarily stores semi-solid waste (feces) in the rectum before elimination via the anus.
⚡ Quick Revision: The Digestive Glands
Digestive glands secrete chemical substances called enzymes that speed up the breakdown of food.
The Liver: The Largest Gland
- ✔ Secretes Bile, which is stored in the Gallbladder.
- ✔ Emulsification: Bile breaks large fat droplets into tiny ones for easier digestion.
The Pancreas
- ✔ Secretes Pancreatic Juice into the duodenum.
- ✔ Contains enzymes: Amylase (starch), Trypsin (proteins), and Lipase (fats).
The Liver makes bile; the Gallbladder only stores it. Bile does not contain enzymes but is essential for fat digestion.
⚡ Quick Revision: Healthy Habits & Disorders
Maintaining the digestive system is crucial for overall health and nutrient efficiency.
Common Digestive Disorders
- ✔ Indigestion: Difficulty in digesting food, often caused by overeating or spicy food.
- ✔ Constipation: Infrequent bowel movements and hard stool due to lack of fiber or water.
- ✔ Diarrhoea: Frequent watery stools often caused by infection or contaminated food/water.
Healthy Eating Habits
- Chew food thoroughly to aid mechanical digestion.
- Drink adequate water to prevent constipation.
- Include roughage (fiber) from fruits and vegetables in the diet.
Always remember the sequence: Mouth → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus.