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LEARNING OUTCOMES ALL MUST… Know that enzymes are used in the digestion of food in the body, which can then be absorbed into the bloodstream LEARNING OUTCOMES ALL MUST… Know that enzymes are needed to break down (digest) large, insoluble molecules into small, soluble ones: View the photograph on the next slide and jot down • Where you would find it • What produced it • What it is The Human Digestive System The process of digestion has 5 functions: Ingestion: taking food into the body Digestion: breakdown of insoluble substances into soluble ones Absorption: uptake of soluble substances into cells Assimilation:how cells use food Egestion: removal of undigested waste Digestion Egestion faeces Ingestion Absorption Food is broken down into smaller pieces by biting, chewing, churning, bile action. These pieces are not soluble but have a large surface area for enzymes to work on. Surface area = 24 cm2 2cm Volume = 8 cm3 2cm SA : V ratio = 24:8 = 3:1 2cm Surface area = 6 cm2 Volume = 1 cm3 1cm 1cm SA : V ratio = 6:1 1cm Digestive enzymes break chemical bonds to make insoluble food particles soluble. Carbohydrases break down carbohydrates into sugars Proteases break down proteins into amino acids Lipases break down fats (lipids) into fatty acids and glycerol model gut experiment boiling tube LEARNING OUTCOMES ALL MUST… Label a diagram of the component parts of the digestive system and identify their function. LEARNING OUTCOMES to include: • buccal cavity - the mechanical digestion by teeth and the chemical digestion of starch by amylase; LEARNING OUTCOMES to include: • stomach - the production of gastric juice containing protease enzyme and acid, and the digestion of proteins; Pin the pancreas on the body What do you remember Add gall bladder, bile duct, sphincter Buccal cavity Salivary gland Oesophagus Liver Stomach Duodenum Pancreas Ileum Colon Appendix Anus Rectum Mechanical: chewing, biting Chemical: Saliva from the salivary glands contains the enzyme CARBOHYDRASE. Starch + carbohydrase sugar (maltose) The ball of food is called a bolus NO FOOD IS BROKEN DOWN HERE Muscles in the wall of the oesophagus contract, pushing food down to the stomach. This is called PERISTALSIS peristalsis Muscles in wall contract FOOD PERISTALSIS Oesophagus wall Food moves forwards The strong muscle walls contract to churn and mix food with stomach juices called GASTRIC JUICES. Cells in the stomach wall produce a protease enzyme that digests proteins, breaking them down into amino acids. The stomach cells also produce hydrochloric acid HCl, which • Lowers the pH for the protease enzyme to work • Kills bacteria • Stops salivary amylase from working A circular, sphincter muscle at the exit of the stomach opens to allow food into the small intestine. It controls release of food from the stomach. LEARNING OUTCOMES to include: • liver - the production of bile, its storage in the gall bladder and its actions in the duodenum in neutralisation of acids and emulsification of fats LEARNING OUTCOMES to include: • duodenum - enzyme production by the pancreas and the duodenal wall to include carbohydrases, lipases and proteases LEARNING OUTCOMES to include: • ileum - relate its structure to its function of absorption of digested food molecules and the ways it is adapted: large surface area (length, folds and villi), good blood supply, and thin and permeable membranes; LEARNING OUTCOMES SOME MAY… explain how the structure of a villus (finger-like shape, single layer of surface cells, capillary network and lacteal) is adapted for the efficient absorption of digested food molecules. Bile, made in the liver and stored in the gall bladder passes along the bile duct into the duodenum. Bile breaks fats into very small droplets, increasing the surface area for enzymes to work on. This is called emulsification. Bile is alkaline and therefore also neutralises acid from the stomach. bile made in the liver passes into the gall bladder gall bladder digestive enzymes produced in pancreas bile duct pancreatic duct duodenum ENZYMES are added to the duodenum from: • The pancreas • The wall of the duodenum Carbohydrases break down starch to sugars Proteases break down protein to amino acids Lipase breaks down fat to fatty acids and glycerol Main function is absorption. The walls are adapted for efficient diffusion of the soluble products of digestion. ridge covered with villi network of blood capillaries lacteal absorbs fatty acids single layer of epithelial cells villus muscle layer arteriole venuole A villus sugar ileum wall Made of epithelial cells amino acids fatty acids blood capillaries lacteal to liver • Long length (5m), folds and villi increase the surface area for absorption • Villi contain blood vessels to carry away absorbed nutrients • Villi contain lacteals to carry away absorbed fats • The walls are thin, one cell thick, and permeable to form a short diffusion distance The absorbed nutrients, amino acids and sugars are carried in the blood to the liver in the HEPATIC PORTAL VEIN. LEARNING OUTCOMES to include: • colon - large surface area for water absorption; • rectum & anus - storage and removal of faeces. NO DIGESTION OCCURS HERE The colon has a large surface area for the absorption of water from the fluid we drink, food we eat, mucus and digestive juices. It also absorbs mineral salts. Solid waste made up of undigested food, bacteria and cells from the gut forms faeces, which is stored in the rectum before passing out of the body through the anus. transverse colon descending colon ascending colon appendix rectum anus Summary bbc learning zone clip 4180 dvd Cut & stick activity