Digestive System-primary level (for school students))
- 1. THE DIGESTIVE SYSTEM BY AREEBA RIZVI
- 2. THE DIGESTIVE SYSTEM • Digestion is the process of breaking down food into nutrients our body can use. • Alimentary canal is a tube that runs from the mouth to the anus.
- 3. • Mouth • Esophagus • Stomach • Small Intestine • Large Intestine • Rectum & Anus Main Parts of the Digestive System
- 4. 1. Mouth – Chewing and saliva start digestion. 2. Esophagus – A tube that pushes food to the stomach. 3. Stomach – Acid and muscles break food into mush. 4. Small Intestine – Nutrients are absorbed. 5. Large Intestine – Water is absorbed. 6. Rectum and Anus – Waste is removed from the body. Step-by-Step Process
- 5. Mouth Chemical digestion (amylase converts starch to maltose) Physical digestion (teeth break food down into smaller pieces) Oesophagus Connects mouth to stomach Stomach Liver Produces bile for the digestion of fats Gall bladder Stores bile Holds the food for a while Physical digestion Chemical digestion Pancreas Produces digestive juices Small intestine Chemical digestion Absorption of nutrients into blood Appendix Large intestine Elimination of waste Absorption of water Rectum Stores waste Anus
- 6. MOUTH • The food is broken down by the teeth and mixed with saliva. • Saliva is excreted by three pairs of glands. • Saliva contains water, mucus and the enzyme salivary amylase.
- 7. Functions of the Tongue •Taste •Chewing •Swallowing
- 8. Tongue Taste Centres Epiglottis Bitter Sour Salt Sweet Taste Buds Papillae
- 9. Oesophagus • The food passes into the pharynx (a muscular tube behind the mouth) and down the oesophagus. • The epiglottis, a small flap of cartilage blocks the entrance to the larynx, this stops the food going down the wrong way and prevents choking.
- 11. Stomach Structure • It is a J-shaped, elastic organ. • Food enters it from the oesophagus through the cardiac sphincter. • Food leaves the stomach through the pyloric sphincter into the duodenum (first part of the small intestine).
- 12. Functions of The Stomach • It digests protein through the action of enzymes. • It churns food with the gastric juices. • It helps lubricate the food by producing mucus. • It absorbs alcohol. • It kills bacteria by producing hydrochloric acid. • Hydrochloric acid neutralises bacteria and activates pepsin. • Pepsin is an enzyme that breaks down proteins into peptones.
- 13. Structure of the Small Intestine • It is seven metres long. • It is divided into three parts: The duodenum The jejunum The ileum • The walls has four layers
- 14. Functions of The Small Intestine Digestion • Pancreatic juice is secreted into the duodenum and contains the following enzymes: Trypsin: converts proteins into shorter chains. Lipase: converts fats into fatty acids and glycerol. Amylase: converts starch into disaccharides. • Bile: emulsifies fats (breaks them into smaller droplets).
- 16. What is the Large Intestine • It deals with waste. • It is about 1.5m long. • It consists of the following: The caecum: a small pouch; the ileum empties its contents into the caecum through the ileo-caecal valve. The colon: ascending, transverse, descending colon. The appendix: narrow tube attached to the caecum. The rectum. The anus.
- 17. Functions • Whatever remains of the food, is passed into the large intestine. • To reabsorb water and vitamins left in digestive waste. • It secretes mucus to help the movement of faeces. • Short term storage of faeces in the rectum. • Many bacteria live in the large intestine, they are harmless in the colon and may be useful e.g. produce Vitamin K. • Defecation: peristalsis pushes waste along the colon and then it is passed out of the body.
- 18. ENZYMES • An example of a digestive enzyme is amylase. • Amylase is present in saliva. • Amylase chemically breaks down starch. • Amylase converts starch into a sugar called maltose. STARCH MALTOSE
- 20. ENZYMES • The substance that an enzyme works on is known as its substrate. • The substance formed by the enzyme is known as its product. • Therefore starch is the substrate for amylase and maltose is its product.
- 21. STAGES OF NUTRITION There are four stages in human nutrition: 1. Eating (also called “ingestion”) 2. Digestion 3. Absorption of digested food into the blood 4. Elimination of undigested food (also called “egestion”)