The digestive system breaks down food into simple substances the body can absorb for energy and growth. Its organs and enzymes are common biology exam questions.
Path of Food (Alimentary Canal)
Food travels through the mouth, oesophagus, stomach, small intestine and large intestine. Undigested waste leaves through the anus.
Key Organs and Their Roles
- Mouth: teeth crush food; saliva contains salivary amylase that digests starch.
- Stomach: secretes HCl and the enzyme pepsin to digest protein.
- Small intestine: main site of digestion and absorption.
- Large intestine: absorbs water.
Liver and Pancreas
- The liver is the largest gland; it produces bile, which breaks fat into small droplets.
- The pancreas secretes digestive enzymes and the hormone insulin.
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Enzymes in Digestion
- Amylase: digests carbohydrates.
- Pepsin and trypsin: digest proteins.
- Lipase: digests fats.
Important Facts
The small intestine is the longest part of the alimentary canal, about 6 metres. Its inner walls have finger-like villi that increase surface area for absorption. HCl in the stomach kills germs and makes the medium acidic for pepsin.
Quick Revision Points
- Liver is the largest gland in the body.
- Liver produces bile for fat digestion.
- Stomach secretes HCl and pepsin.
- Most digestion happens in the small intestine.
- Villi help absorb nutrients.
- Saliva contains amylase for starch.
- Large intestine mainly absorbs water.