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Human Digestive System DIGESTION Topic:6.1 Explain why digestion of large food molecules is essential. Explain the need for enzymes in digestion. State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase Draw and label a diagram of the digestive system. Outline the function of the stomach, small intestine and large intestine. Distinguish between absorption and assimilation. Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion. NUTRITION Nutrition: The process by which an organism takes the matter and energy from its environment. All organisms need nutrient to survive. There are two main types of nutrition. 1- Autotrophic nutrition 2- Heterotrophic Nutrition Classification of Nutrition Heterotrophic Nutrition Autotrophic Nutrition photosynthesis Holozoic nutrition Parasitic nutrition Saprotrophic Nutrition chemosynthesis AUTOTROPHIC NUTRITION Autotrophic organisms are self feeding organisms. They can produce their own food by using inorganic substances. 1- Photosynthetic nutrition: Organisms produce their own food by using light energy and inorganic substances. Plants, Protista, Bacteria 2- Chemosynthetic nutrition: Organisms produce their own food by using energy from oxidation of inorganic substances and inorganic substances. Chemosynthetic Bacteria HETEROTROPHIC NUTRITION Heterotrophic nutrition: feeding on complex ready-made food. Feeding on other organisms. 1-Holozoic nutrition: Animals take large food pieces into the digestive system and digest them in the gut. 2-Parasitic nutrition: Organisms feed on/in a host organisms. They take digested nutrients from host organisms. These organisms do not have digestive enzymes. Example: tape worm, thick, lice …….. 3-Saprotrophic Nutrition: Organisms feed on dead bodies. They convert them into inorganic molecules. Bacteria and fungi WHAT IS FOOD? Foods can be divided into six groups according to its composition A- carbohydrates. B- lipids C- proteins D- vitamins E- minerals F- water All of the molecules above are essential for a balanced diet. Which group of foods are macromolecules? Foods are a. ingested b. digested c. absorbed d. assimilated e. egested Explain why digestion of large food molecules is essential. a. Ingestion: food taken into mouth for processing in the gut. b. Digestion: Process in which large molecules of foods are broken down into smaller pieces to cross plasma membrane easily c. Absorbtion: Soluble products of digestion are taken into the blood/lymph circulation. d. Assimilation: Products of digestion are absorbed from blood into body cells and used or stored. e. Egestion: Undigested food and dead cells of the gut, together with bacteria from the gut flora, expelled from the body as faeces. What do we need for digestion of food? • Digestion is a hydrolysis reaction. • Enzymes are required. • Water is required for hydrolysis Do we use ATP for digestion? Does digestion take place outside of the body? Where does digestion take place in the body? In the cell or outside of the cell? DIGESTION Mechanical digestion: Physical breakdown of the food (cheewing by teeth, muscular contraction of stomach…) Chemical digestion: chemical breakdown of the food into smaller molecules (sub units) usually by the help of the enzymes Where does digestion take place? 1- Intracellular digestion: Large molecules are digested in the food vacuole by lysosome enzymes. Some unicellular organisms digest food by intracellular digestion. Foods are taken into the cell by phagocytosis and digested by lysosme. Disadvantage: They cannot benefit from the bigger molecules than they cannot take into cell. 2- Extracellular Digestion: Animals take the food into a body cavity that is continuous with the outside environment, into which they secrete digestive enzymes. Enzymes act on food, reducing it to nutrient molecules that can be absorbed by the cells lining the cavity. e.g: all vertebrates, some protists and some invertebrates Advantage: They can benefit from the complex molecules that are present in the environment. What are the organs of human digestive system In the digestive system there are mouth, pharynx, esophagus, stomach, small and large intestines. There are glands that secrete enzymes to assist digestion such as salivary glands, gastric glands (stomach), intestinal glands, liver and pancreas. Figure 21.UN02 a. g. b. h. c. d. e. i. j. f. k. l. Figure 21.4_2 Nasal cavity Oral cavity (mouth) Tongue Salivary glands Pharynx Esophagus Liver Esophagus Sphincters Gallbladder Stomach Pancreas Small intestine Large intestine Rectum Anus Small intestine DIGESTIVE ORGANS Mouth: mechanical digestion by chewing food and chemical digestion of the starch into maltose. Oesophagus: connects mouth to stomach. Food is transported by peristalsis ( wave like Movement to push food to Stomach). Stomach: It is the largest portion of the digestive system. It is saclike structure between esophagus and intestine. . Functions of stomach; • To store ingested food • To produce gastric juice and continue the digestion of food • To split nucleoproteins to nucleic acid and protein • To activate pepsin and rennin • To kill bacteria in the ingested food • To denaturate proteins Small Intestine: The human small intestine is 5-6 meters. It has 3 parts. • duodenum • jejunum • ileum Duodenum: 26cm in length, 3-4 cm in width. Wirsung channel (from pancreas) attached to the duodenum. It has important function in digestion, chemical digestion takes place in duedonum. Jejunum: Longest part. It carries out digestion and absorption in this part. Ileum: It is the final portion that connects small intestine to large intestine and absorption of nutrients takes place here.. Structure of small intestine; • Mucosa layer has fingerlike projections called villi. Mucosa cells secrete mucus and enzymes and absorbs the nutrients. • What is the difference between absorption and assimilation? Large Intestine: It is almost 1,5 – 2 meters in length and 6-8 cm width. It is seperated from the small intestine by a valve. Cecum: small portion water absorption takes place Colon: the mid part & Vit.K is produced by useful Rectum: the last part bacteria There is no villi in the large intestine. Mucosa contains lymphoid structures and glands. DIGESTIVE SECRETIONS Digestive secretions originate from the salivary glands, gastric glands, pancreas, gall bladder and small intestine. a) Salivary Glands and Their Secretions • They produce saliva and secrete into a special duct that open into mouth. Saliva contains amylase (ptyalin), P, Ca. FUNCTION: • The initiation of carbohydrate digestion • As a solvent for detection of taste • The formation of bolus by mixing food • Lubrication of the pharynx to swallow the food easily. b) Gastric Glands These glands secrete gastric juice. It is an acidic fluid, that has pH almost 1,5. Because it consist of HCl Function of HCl: • It converts pepsinogen pepsin • It stimulates secretion of pancreas and intestinal glands • It destroys bacteria that are ingested with food • It facilitates protein digestion by denaturation c) The LIVER and bile secretion [Click on the picture for liver animation] Liver has many lobules …Liver is the largest organ of the body (1,52 kg). It las four main lobes(each lobe has lobules) and gall bladder. The liver cells in the lobules receive double blood supply; Oxygenated blood from hepatic artery and blood containing newly absorbed nutrients from the gut (via hepatic portal vein). Also there are bile canals in the lobules and bile is sent to the bile duct via these canals. Bile and blood in the veins that goes to the central hepatic vein move in opposite directions. Liver is a multifunctional organ and has more than 100 functions Here are some major functions; • Formation and secretion of bile • Regulation of blood sugar level • Formation of fibrinogen and thrombinogen for blood clotting • Conversion of pro-vit. A into vit.A by the enzyme carotinase • Deposition of Fe, Cu, proteins and vit. A, D and K • Degradation of old RBC by Kuppfer cells • Elimination of foreign substances which enter the liver by the blood (alcohol, medicine…) • Detoxification of substances (H2O2 H2O + O2 ) • Synthesis of urea • Heparin secretion • Synthesis of RBC by reticulo endothelial cells. Functions of bile … • Bile has bile salts, water, pigments and cholesterol in it. • It neutralizes the acidity of chyme entering the duedonum from the stomach • It emulsifies lipids and facilitates the activity of enzyme lipase • It helps absorption of vit. A, D and K. • Excessive cholesterolin the bile may precipitate out of solution with calcium and bile salts, forming hard crystals called gallstones. Pancreatic secretions; • Digestive enzymes • HCO3- for neutralization of acidic food. Intestinal glands; • Mucus for protection • Digestive enzymes Pancreatic secretions; • Digestive enzymes • HCO3- for neutralization of acidic food. Intestinal glands; • Mucus for protection • Digestive enzymes DIGESTION OF FOODS CARBOHYDRATES: Mouth: Starch amylase maltose + dextrin Stomach: No chemical digestion of Carbs. Small Intestine: Digestion of Carbs. is completed in small intestine Dextrin + H2O amylase maltose Maltose+ H2O maltase glucose lactase Lactose+H2O Sucrose+H2O glucose+galactose sucrase glucose+ fructose PROTEINS They are digested in the stomach and small intestine. Stomach: Proteins+ H2O pepsin polypeptide Gastrin (hormone that secrete from stomach glands) Gastric gland HCL Pepsinogen pepsin Protein + H2O polypeptides Small intestine: Chyme duodenum cells Pancreas secretes; a) Tyripsinogen Enterokinase a) Chymotyripsinogen Secretin(hormone) İntestinal gland Enterokinase tyripsin chymotyripsin Tyripsin and chymotyripsin Proteins Polypeptides polypeptides aminopeptidase carboxypeptidase dipeptidase tripeptidase a.a’s Lipids: Lipids are digested only in small intestine Lipids+Lipase+Bile+water Glycerol F. acids Absorption of Nutrients a) Mouth: Some medicine, ions, drugs (cocaine) and some poisons are absorbed in the mouth b) Stomach: Alcohol, some medicine, ions, some poisons are absorbed c) Small intestine: Most of the nutrients are absorbed in the small intestine. Amino acids, glucose, minerals, water soluble vitamins are absorbed by epithelial cells of mucosa layer and are given to the capillary blood vessels. Before they enter the general circulation, they are transported into liver by portal vein. Glycerol, fatty acids and lipid soluble vitamins are absorbed by epithelial cells and they are combined with each other in the mucosa cells and they are called chylomicrons. Then, these chylomicrons are given to the lymph vessels (lacteals). That means they are transported by lymph vessel, not blood vessels. d) Large intestine: Water, electrolytes (Na, Cl, K) are absorbed. Bacteria produce Vit. B & K Figure 21.11 Heart Liver Hepatic portal vein Intestines