Human Gas Exchange: Human Gas Exchange
8.2 Human Digestive System
Why Food Must Be Digested
- Large, insoluble molecules → broken into small, soluble molecules.
- Allows absorption into blood and transport to cells.
Types Of Digestion
- Physical digestion: food broken into smaller pieces (teeth, stomach churning). No chemical change.
- Chemical digestion: enzymes break large molecules into small soluble ones.
Human Teeth
| Tooth Type | Structure | Function |
|---|---|---|
| Incisors | Sharp, chisel-shaped | Cutting food |
| Canines | Pointed | Tearing food |
| Premolars | Broad surface | Crushing/grinding |
| Molars | Large, flat surface | Grinding food |
Tooth structure: enamel (hard), dentine, pulp (nerves + blood), cement, gum.
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Regions Of Digestive System
| Region | Function |
|---|---|
| Mouth | Ingestion, chewing, amylase in saliva digests starch |
| Salivary glands | Produce saliva (amylase) |
| Oesophagus | Moves food by peristalsis |
| Stomach | Churns food, protease digests protein, HCl kills bacteria |
| Liver | Produces bile (emulsifies fats, neutralises acid) |
| Gall bladder | Stores bile |
| Pancreas | Produces enzymes (amylase, protease, lipase) |
| Small intestine (duodenum + ileum) | Enzyme digestion, absorption by villi |
| Large intestine (colon) | Absorbs water |
| Rectum + anus | Stores and removes faeces (egestion) |
Enzymes In Digestion
| Enzyme | Substrate | Product |
|---|---|---|
| Amylase | Starch | Maltose |
| Maltase | Maltose | Glucose |
| Protease (pepsin, trypsin) | Protein | Amino acids |
| Lipase | Lipids | Fatty acids + Glycerol |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Other Key Points
- Hydrochloric acid in stomach → kills bacteria, provides acidic medium for protease.
- Bile → emulsifies fats (larger surface area for lipase).
- Peristalsis → wave-like contractions move food.