1. Alimentary tract

2. The four main roles of digestive system.

3. Organs in the digestive system

4. Starting at the top - INGESTION ●Physical digestion takes place in the mouth ●Salivary glands release saliva water & mucous the enzyme amylase ●Amylase breaks down starch to maltose

5. going down - DIGESTION & SECRETION ●The oesophagus is a muscular tube where food is pushed down to the stomach ●Peristalsis=muscular contractions propelling the food along the tract. ●The internal surface of the oesphagus has mucous layer to assist food movement. ●Further chemical digestion of starch

6. into the stomach -digestion continues ●Circular muscles regulate movement of food in and out of the stomach ●(eg pyloric sphincter) ●Muscular contractions of the stomach churn and mix the food and enzymes etc ●Gastric juices containing pepsin and protease in the stomach wall are released ●Protease breaks down proteins into amino acids

7. into the small intestine - digestion goes on ●The pancreas secretes pancreatic juice via the pancreatic duct which enters the duodenum at the top of the small intestine ●Pancreatic juice contains lipase and amylase which act on lipids and carbohydrates respectively. ●Bile is produced by the liver but is stored in the gall bladder ●Bile mechanically (physically) breaks down fats into smaller globules to increase surface area ●Lipase then chemically breaks down fat into glycerol and fatty acids

8. at last - ABSORPTION ●The products of digestion are small enough to be absorbed through the walls of the small intestine transported to cells. ●Villi are structures which increase the surface area for more efficient uptake ●Within the villi are capillaries - where glucose and amino acids are absorbed. ●The capillaries are interconnected with the lymphatic system - water absorption also takes place here ●Glucose and amino acids move from the small intestines into the blood circulation by diffusion and active transport ●Glycerol and fatty acids move into a parallel circulation called the lymphatic circulation Absorption of molecules in the villi

10. and now for - egestion The small intestine connects with the large intestine which consists of two main parts: 1. the colon 2. rectum Function of the large intestine is to compact undigested food and absorb water and salts back into the body Faeces are eliminated from the body through the anus

11. Overview of Digestion Nat Geog

12. BIOMACROMOLECULES Carbohydrates amylase maltose maltase glucose Protein pepsin peptides peptidase amino acids Lipids (Triglycerides) lipase glycerol + fatty acids Glucose Enzymes and the break down of biomacromolecules