Digestion
Digestion is the breakdown of large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood.
Organs of the Digestive System
| Organ | Function |
|---|---|
| Mouth | Mechanical chewing; saliva contains amylase (breaks down starch) |
| Oesophagus | Food tube connecting mouth to stomach; peristalsis moves food |
| Stomach | Churns food; gastric juice (HCl + pepsin) digests proteins |
| Small intestine | Main site of digestion and absorption; bile emulsifies fats; enzymes complete digestion |
| Large intestine | Absorbs water; compacts waste into faeces |
| Liver | Produces bile; detoxifies blood; regulates nutrients |
| Pancreas | Secretes digestive enzymes (amylase, lipase, protease) into small intestine |
Key Digestive Enzymes
| Enzyme | Substrate | Product | Site |
|---|---|---|---|
| Amylase | Starch | Maltose | Mouth, small intestine |
| Protease/Pepsin | Proteins | Amino acids | Stomach, small intestine |
| Lipase | Fats | Fatty acids + glycerol | Small intestine |
Absorption
The small intestine wall has millions of villi (tiny finger-like projections) that increase surface area for absorption. Digested nutrients pass through the villi walls into the bloodstream.