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Download The human Digestive system
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THE HUMAN DIGESTIVE SYSTEM Paula Emile LEARNING OUTCOMES identify the gross structure of the alimentary canal and associated organs (mouth, oesophagus, stomach, small intestine: duodenum and ileum, large intestine: colon and rectum, anus, pancreas, liver) define ingestion, digestion, absorption, assimilation and egestion WHAT HAPPENS TO THE FOOD WE EAT? THE GUT AS A PRODUCTION LINE WHAT HAPPENS TO THE FOOD WE EAT? Ingestion Intake of food by the living organism into the mouth by the help of teeth , lips and tongue WHAT HAPPENS TO THE FOOD WE EAT? Digestion Breaking down of large, insoluble food molecules into smaller soluble ones to be easily absorbed and transported By the help of enzymes Absorption Process by which Digested food molecules leave and pass across the wall of the small intestine into the blood stream Assimilation Uptake of food molecules by cells Egestion Removal of undigested food, in the form of faeces, from the body PUPIL ACTIVITY Label the diagram of the digestive system. Use the textbook supplied to help if needed Design a table to link the structure and function of different parts of the digestive system. mouth tongue Salivary glands oesophagus trachea liver stomach Gall bladder Small Duodenum intestine ileum appendix pancreas colon Large rectum intestine anus THE HUMAN ALIMENTARY CANAL IS LINED WITH : Epithelial cells: Small cells able to divide rapidly due to replace the worn out cells due to friction with the food Goblet cells: secrete mucus to reduce the friction between food and the alimentary canal THE HUMAN ALIMENTARY CANAL IS LINED WITH : Muscle cells: mainly circular and longitudinal to contract and relax in a movement called Peristalsis PERISTALSIS It is the rhythmic contractions of the muscles in the walls of the alimentary canal to squeeze the contents along THE PARTS OF THE ALIMENTARY CANAL The mouth DIGESTION IN THE MOUTH AND OESOPHAGUS Chewed food is mixed with saliva in the mouth Saliva (secreted by salivary gland) contains: Amylase is an enzyme which starts to digest starch into sugars (maltose)….PH ? Mucus helps soften the food making it easier to chew and swallow The bolus of food travels down the oesophagus with the aid of peristalsis PERISTALSIS IN THE GULLET Saliva also contains bicarbonates that create a suitable ph value for the enzyme amylase to act PHARYNX Common passage for both food and air Contains a part known as soft palate to close the nasal cavity during swallowing Epiglotitis closes trachea during swallowing to avoid the flow of food into the respiratory system http://www.youtube.com/watch?v=WtsTaNfodEQ OESOPHAGUS Transfers food from pharynx to stomach by peristalsis STOMACH Widest part in the alimentary canal Controlled by two sphincter muscles: cardiac sphincter: when it relaxes and food passes to stomach pyloric sphincter: when it relaxes the food passes to small intestine Secretes gastric or stomach juice STOMACH Components of gastric juice: 1.Hydrochloric acid: kill microbes activate pepsinogen enzyme 2.Pepsinogen:activated by HCl Acts on proteins and digest them to polypeptides 3.Mucus Protect the wall of the stomach against HCl and Pepsin STOMACH Mechanical digestion of the food in stomach makes the food semi fluid Churning movement is the contraction and relaxation of the stomach muscles SMALL INTESTINE Longest part(6 m) Function : 1. Complete digestion of food 2. Absorption of digested food SMALL INTESTINE 1. 2. 3. Juices received: Bile Pancretic juice Intestinal enzymes 1.BILE Fluid Formed in liver and stored in the gall bladder Yellowish green that gives the faeces its colour Are used to emulsify fats, break it down to Small particles Contains bicarbonates to neutralize the acidity From stomach EMULSIFICATION OF FATS Increasing the surface area by by converting it from large globule into small droplets 2.PANCREATIC JUICE COMPONENTS 1. Amylase: digest Starch 2. Lipase: act on Lipids(fats) maltose fatty acids and glycerol 3.bicarbonates: Neutralize the acid, remember these enzymes need slightly alkaline medium 4.Trypsinogen: (inactive form) Activated by chemicals on the wall of intestine to be converted to Trypsin (active) Polypeptides amino acids 3. INTESTINAL ENZYMES COMPONENTS Maltase: Digest Maltose glucose ASSIGNMENT Present a summary of the digestive tract enzymes in a creative way Due date: Wednesday 26th of November ABSORPTION OF DIGESTED FOOD Most absorption takes place in ileum , the lowest part of small intestine Adaptation of ileum for absorption: 1.Very long, as to provide enough time for absorption of food to take place 2.Surface of the ileum is highly folded, lining of the ileum is folded into hundreds of thousands of tiny finger like projections called villi VILLI STRUCTURE ADAPTATION OF VILLUS 1.lined with epithelial cells (one cell thick) very thin to make food pass easily 2.the epithelial cells of villi conatin microscopic projections known as micro-villi ADAPTATION OF VILLUS 3. contain network of blood capillaries to transport glucose and amino acids 4.contain lacteal vessels to transport fatty acids and glycerol LARGE INTESTINE Absorption of water from undigested food Rectum stores the food temporarily , and when full pushes the faeces outside (egestion) SUMMARY FOR THE TYPES OF DIGESTION 1. 2. 3. 4. Physical: Chewing by teeth Peristalsis Churning movement of stomach Emulsification of fats Chemical: Effect of enzymes :amylase , lipase, proteases LIVER AND ITS FUCTIONS Manufacture of Bile, which is important in emulsifying fats Storage of glucose as glycogen Removal of old red blood cells from blood and store the iron they contain Break down of alcohol and other toxic substance (toxins) in a process called Detoxification Break down of excess amino acids to urea excreted in urine (Deamination) Regulation of the level of glucose in blood REGULATION OF GLUCOSE IN BLOOD If blood glucose level is high: Pancreas secrete insulin hormone to stimulate liver cells to store the excess glucose as glycogen If blood glucose level is low: Pancreas secrete glucagon hormone to stimulate liver to break down stored glycogen to glucose EGESTION LARGE INTESTINE The small intestine absorbs most of the water in the contents of the gut. By the time the contents reach the end of the small intestine, most of the digested food has also been absorbed. The remaining material consists of: water bacteria (living and dead) cells from the lining of the gut indigestible substances - such as cellulose from plant cell walls LARGE INTESTINE AND ANUS The colon is the first part of the large intestine. It absorbs most of the remaining water. This leaves semi-solid waste material called faeces. The faeces are stored in the rectum, the last part of the large intestine. Egestion happens when these faeces pass out of the body through the anus.
