IGCSE Biology 0610
7.2 Digestive system
Diagram of digestive system is on the way 🙂
5 Stages of Food Through the Alimentary Canal
- Ingestion → The taking of substances (e.g. food and drink) into the body
- Digestion → The breakdown of food
- Absorption → The movement of nutrients from the intestines into blood
- Assimilation → The uptake and use of nutrients by cells
- Egestion → The removal of undigested food from the body as faeces
| Mouth → Ingestion → Mechanical digestion → Chemical digestion | Teeth chew food into smaller pieces, increasing the surface area:volume ratio (Mechanical digestion). Saliva from the salivary glands mixes with the food (Chemical digestion). Amylase enzymes in saliva break down starch into simple reducing sugars. The tongue rolls the food into a ball and the lubricated ball with saliva can be swallowed easily (Ingestion). |
| Oesophagus | The tube that connects the mouth to the stomach. The movement of food down the oesophagus is caused by a wave of muscular contraction called peristalsis. |
| Stomach → Mechanical digestion → Chemical digestion | The stomach is a muscular bag that churns the food while gastric juice which contains pepsin digests proteins into smaller polypeptides. Gastric juice also contains hydrochloric acid to kill bacteria (low pH denatures bacteria enzymes) and provide optimum pH for protease enzyme (pepsin) to work. |
| Small intestine → Chemical digestion → Absorption | The first section of the small intestine is called the duodenum. Food coming out of the stomach finishes digestion at the duodenum through enzymes from small intestine and pancreatic juice. The second section is the ileum, where food is absorbed The ileum is long and lined with millions of villi to increase the surface area for absorption. |
| Large intestine | Consists of 3 sections: colon, rectum, and anus (in order). The colon absorbs any water not absorbed by the small intestine. The faeces is stored in the rectum and egested through the anus. |
| Pancreas | Produces all 3 types of digestive enzymes: amylase (starch), protease (proteins), and lipase (fats). The enzymes are secreted in an alkaline fluid into the duodenum. The fluid raises the pH of acidic food from the stomach. |
| Salivary glands | Produce saliva that contain mucus and amylase |
| Liver | Produces bile to emulsify fats (breaking down large globules of fats into smaller globules). Bile is stored in the gall bladder and released into the duodenum by the bile duct. |
| Gall bladder | Stores bile |