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Human alimentary canal Section II Structures and functions in living organisms Syllabus recognise the structures of the human alimentary canal and describe in outline the functions of the mouth, oesophagus, stomach, small intestine, large intestine, and pancreas understand the processes of ingestion, digestion, absorption, assimilation and egestion explain how and why food is moved through the gut by peristalsis Syllabus understand the role of digestive enzymes to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases recall that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralising stomach acid and emulsifying lipids explain how the structure of a villus helps absorption of the products of digestion in the small intestine Terminology Ingestion Taking food into the alimentary canal Digestion The chemical and physical process where large molecules are broken down to small molecule, so that the body can use them to build and nourish cells, and to provide energy. Chemical digestion involves a chemical change from one sort of molecule to another. Mechanical digestion involves the teeth and churning movements of the alimentary canal. Terminology Absorption Assimilation The uptake of a substance into the cells of an organism’s body. The incorporation of absorbed food into various parts of the body Egestion The removal of indigestible food from the body The Human Digestive System Structures Alimentary canal is a muscular tube, running from mouth to anus Oral cavity Mouth Teeth tongue Oesophagus Stomach Structures Liver Pancreas Small intestine Duodenum ileum Large intestine Bile duct Colon Rectum Anus Functions Mouth Ingestion of food here Bolus formed here. Bolus is a ball of food formed after chewing. Physical digestion Tongue and teeth use to masticate the food Mastication = mechanical grinding action of teeth Chemical digestion Saliva released contains salivary amylase which breaks down carbohydrates Functions of the digestive system Oesophagus Carry the food from mouth to stomach Peristalsis – rhythmic waves of contraction by smooth muscles in the wall of the canal that move the food Functions Stomach Physical digestion Churning food of the stomach helps break down the Chemical digestion Hydrochloric acid released Protease breaks down proteins Accessory Digestive Organs Functions Liver Bile duct = bile (yellowish-green watery liquid) used in mechanical digestion of lipids Large fat droplets broken down, increasing the surface area = emulsification contains NO enzymes Functions Liver Functions of: maintenance of a constant glucose level in bloodstream detoxification of drugs & alcohol production of bile (acts as emulsifier – begins fat breakdown destruction old RBC & converts haemoglobin to bilirubin regulation of cholesterol & other fats Hepatic portal system: drains blood from digestive tract Metabolic functions: storage, synthesis, chemical processing Liver - Assimilation Defined as the incorporation of absorbed food into various parts of the body The hepatic portal vein delivers the sugars and amino acids to the liver. The liver ensures the right nutrients are sent to the right cells so that various bodily functions can occur eg. Amino acids are made into new proteins for growth & repair OR glucose which is used for respiration Accessory Organs: Aid Digestion and Absorption Pancreas: exocrine functions Produces pancreatic juice contains digestive enzymes: Amylase Protease lipase Secretes sodium bicarbonate to neutralize the stomach acids Gallbladder: stores bile Functions Small Intestine Functions: Digestion: neutralize acid from stomach, add digestive enzymes and bile, break proteins, carbohydrates and lipids to absorbable materials Absorption: 95% of food absorbed here Small Intestine Very long ~5 metres (adult), more time for the food to be absorbed Highly folded, increases the surface area for absorption Hepatic portal vein carries the amino acids and sugars to the liver, where they are sorted and redirected to be used by the body or if in excess stored. Excess sugar stored as GLYCOGEN Excess amino acids deaminated (broken down) to GLYCOGEN and UREA Small Intestine Two parts Duodenum Food is mixed with Bile Pancreatic juice Ileum Food is mixed with Intestinal juice Maltase Protease (peptides to amino acids) Where absorption occurs Inner surface folded and covered in villi Structure of the small intestine Villus Function Increase the surface area that can absorb food Structure Capillary network Blood - to collect the sugars and amino acids Lacteal (lymph vessels) - collect the fatty acids and glycerol One cell thick Goblet cells Produce mucus which protect lining of gut Absorption of Proteins and Carbohydrates Absorption of Fats Major enzymes of digestive system Carbohydrates Amylase Proteins Protease Mouth & duodenum Substrate = starch Product = maltose Stomach (pepsin) & duodenum (trypsin) Substrate = proteins & polypeptides Product = polypeptides (Stomach) & amino acids Lipids Lipase Duodenum & ileum Substrate = emulsified fats Product= fatty acids and glycerol Functions Large Intestine Functions: absorbs nutrients and water, and eliminates waste Substances found in large intestine = mostly water, dead bacterial cells, cellulose fibers, other indigestible materials, lubricated by mucus Anus Where egestion of waste occurs