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The Digestive System The Digestive System Types of nutrition Autotrophic: an organism that can make its own food (plants) Heterotrophic: an organism that cannot make its own food (all animals) Types of nutrition Herbivores: animals that only eat plants. Carnivores: animals that eat other animals Omnivores: animals that eat plants and animals What is digestion? • Digestion is the break down of food into smaller particles, This allows the food to be absorbed into the bloodstream. Two types of digestion: 1) Mechanical digestion 2) Chemical digestion What is the alimentary canal? • Starts at the mouth and ends at the anus. Events in human digestion: 1) 2) 3) 4) Ingestion: food enters mouth Digestion: Breakdown of food Absorption: food absorbed into the blood Egestion: removal of unwanted waste The digestion process - What happens to your food as it travels through your body until it exits? - YouTube Mouth Mechanical digestion in the mouth Types of teeth • • • • Incisors: cut, slice and bite Canines: Tear and grip food Premolars: crush and chew food Molars: crush and chew food Human dental formula 2 (I - C - PM - M - ) Digestion in the mouth Mechanical digestion = food broken down into smaller pieces by your teeth. Chemical digestion: the enzyme amylase breaks down the food in the mouth. Chemical digestion in the mouth Saliva: softens and dissolves the food. Saliva consists of water, salts, and enzymes (amylase). Lysozyme: destroys any harmful micro organisms. Amylase (pH 7) Starch Maltose Oesophagus • Carries food from the mouth to the stomach. • Food is moved along the alimentary by the muscular action called peristalsis. • Peristalsis helps break down food mechanical. Peristalsis... not for those with a weak stomach...lol – YouTube Peristaltic Wave in the Gastric Antrum - YouTube Peristalsis in the Oesophagus Role of fibre • Plant cell walls contain cellulose, which provides us with fibre. • Sources of fibre: cereals, vegetables. • Fibre helps us to absorb water from large intestine. • Fibre helps stimulate peristalsis. Role of Fibre • Fibre is believed to help reduced the risk of cancer, as waste produces will leave your system faster. Stomach • Muscular bag that stores food and digests food. • Churns food causing mechanical digestion. • Creates a mixture known as chyme. Stomach • Food enters and leaves the stomach through the sphincter muscle. • Stomach lining (mucosa) releases gastric juices. What is in gastric juices: • Mucous: prevents self digestion of the stomach. • Pepsinogen: inactive enzyme when released (does not digest cells in stomach). • Pepsinogen is converted to active pepsin when reacting with acid. Videos on the stomach • Stomach Digestion – YouTube • A Gastric Prepyloric Benign Ulcer – YouTube • Parasites - Round Worm Found in Human Colon - YouTube Stomach • Hydrochloric acid in the stomach has a pH of 1-2. • This acid can kill any bacteria that may cause harm to the body. • HCl activates Pepsinogen to form pepsin. • Pepsin (protease) is an enzyme that digests proteins. Protection from self digestion • Mucous lines the stomach • Mucous is alkaline which reduces acidity near the cell wall. • Pepsin is released as inactive pepsinogen. • Cells that line the stomach are tightly packed and are replaced rapidly. Stomach Wall Glands associated with small intestine Pancreas • Secretes pancreatic juice containing sodium bicarbonate (sodium hydrogen carbonate) • Sodium bicarbonate neutralises the chyme from the stomach in the duodenum. Dual Role of Pancreas - YouTube Pancreatic Juice • Also contains the enzymes amylase and lipase which are secreted into the duodenum to aid digestion. • Both these enzymes work best at the pH of 7. Amylase Starch Maltose Lipase Lipids Fatty acids and glycerol Liver Functions • Produces bile • Breaks down excess amino acids to form urea • Converts excess carbohydrates to fats • Converts glucose to glycogen for storage • Stores vitamins like vitamin D • Produces heat to warm the blood • Makes chlorestol to form hormones Liver 01 Liver Video - YouTube Bile • Formed from the remains of dead red blood cells. • Yellow/ green liquid. • Made in liver and stored in gall bladder. What are gallstones: They form in the bile duct and prevent the release of bile. Bile and Gall stones Gallstones - YouTube Functions of bile: 1) It emulsifies Fats ( breaks down fats and oils into tiny droplets). This increases the surface area for the enzyme digestion. 2) Contains sodium bicarbonate which helps neutralise the chyme from the stomach. Small Intestine Consists of two parts: • Duodenum --- 25 cm long --- carries out digestion • Ileum --- 5.5 metres long --- absorption of food Duodenum • Carries out digestion • Products of liver and pancreas enter the duodenum Structure of small intestine • Inner lining of small intestine contain many infoldings called villi. • Each villi have 600 microvilli. • Villi increase surface area for digestion (duodenum) and absorption (ileum) . Villi and Micro villi End products of digestion Food Digested to Carbohydrates Monsaccharides (glucose) Proteins Amino acids Lipids Fatty acids and glycerol Videos on villi • Digestive System: Small Intestine – YouTube • Villi Model - YouTube Substance Made in Active in Preferred pH Substrate Product Amylase (enzyme) Salivary glands Mouth 7–8 Starch Maltose Pepsin (enzyme) Stomach lining Stomach 2 Protein Peptides Amylase (enzyme) Pancreas Duodenum 7–8 Starch Maltose Lipase (enzyme) Pancreas Duodenum 7 -8 Lipids Fatty acids and glycerol Bile Salts Liver Duodenum Lipids Lipid droplets Sodium hydrogen carbonate Liver/ pancreas Duodenum Acid Neutralises acid Hydrochloric acid Stomach lining Stomach Bacteria Kills bacteria and softens food Ileum • Food entering ileum is fully digested. • Ileum absorbs the nutrients into the blood. Villi • Small intestine consist of many villi • Villi increase surface area for absorption • Villi absorb glucose, amino acids, vitamins and minerals. Adaptions of the villi • It is very long • Numerous villi and microvilli • Rich supply of blood to carry away products • Villi are only one cell thick (very thin) • Each villi has a lacteal to carry away fats. Lacteal • Each villi contains a lacteal • Each lacteal contains lymph liquid. • Fatty acids and glycerol enter the lacteals and are transported away in the lymph fluid to the bloodstream. Liver, small intestine and hepatic portal vein • Nutrients are carried from the small intestine to the Liver by the hepatic portal vein. Liver, small intestine and hepatic portal vein • Amino acids cannot be stored in the body. • Amino acids are broken down in the liver to form urea (deamination) • Urea and other waste leaves the liver in the hepatic vein which travels to the heart and then the kidneys. Large Intestine • Only 1.5 metres long. • Food stays in large intestine for 10 hours to a few days. Caecum and appendix: • These organs have lost their functions (vesitigal organs) • Herbivores use them to digest cellulose. Colon • Colon is used to reabsorb water. • Contains faeces (its colour is due to the bile). • Faeces is stored in the rectum. NOTE: Diarrhoea is formed when not enough water has been reabsorbed. Constipation occurs when to much water is reabsorbed. Large Intestine Symbiotic bacteria in the digestive system Symbiosis: where two organisms live in a close association with each other and at least one benefits. • Symbiotic bacteria feed on waste products to produce vitamins B and K. • Symbiotic bacteria break down food (cellulose) which is absorbed into the body. • Symbiotic bacteria help prevent the growth of disease causing bacteria. What is a balanced diet: • A balanced diet consists of the right amount of each of the following foods: 1) 2) 3) 4) 5) 6) 7) Proteins Carbohydrates Lipids Vitamins Minerals Fibre Water