N Topic 5.1 ammals in utrition M. Feeding/Ingestion Intake of food & processes that convert food substances into living matter Digestion Absorption Egestion.

N Topic 5.1 ammals in utrition M Feeding/Ingestion Intake of food & processes that convert food substances into living matter Digestion Absorption Egestion Assimilation The stages of Nutrition Feeding on ready-made complex organic matter: Holozoic nutrition Well developed organ system for nutrition in mammals (digestive system) Consists of the: Alimentary canal (gut) Associated glands Nutrition Mechanical breakdown of food into smaller particles Physical Enzymatic hydrolysis of food substances Digestion Chemical A journey through the gut: Overview A journey through the gut: The mouth & buccal cavity What happens when you chew a piece of bread for 1 minute? Food is chewed & mixed with saliva Jaws: Upper jaw is fixed Lower jaw is movable A journey through the gut: The mouth & buccal cavity Mastication: The mechanical process of breaking up food into small particles by the chewing action of the teeth 4 types: Incisors Canines Premolars Molars A journey through the gut: The teeth A journey through the gut: The mouth & buccal cavity Why is mastication important? Mixes food with saliva Food is more easily swallowed Increases surface area for enzyme action Saliva: Secreted by the salivary glands Saliva: Water & mucin softens food, lubricates food Saliva contains salivary amylase A journey through the gut: The mouth & buccal cavity StarchMaltose Salivary Amylase Slightly alkaline: Provides correct pH for amylase to work Helps to prevent tooth decay Tongue Mixes food with saliva Rolls food into a bolus (pleural: boli) Pushes food down into pharynx Has sense cells (taste buds) A journey through the gut: The mouth & buccal cavity Leads from the mouth to the: Oesophagus Trachea (windpipe) by the larynx (voice box) Junction of respiratory and digestive passages: common passage for food & air Think about it: Does food go into the lungs when we swallow? A journey through the gut: The pharynx A journey through the gut: Breathing & Swallowing A journey through the gut: Oesophagus Also known as the gullet A narrow, muscular tube Extends from the pharynx through the thorax & diaphragm to join the stomach Carries food to the stomach Does food drop into the stomach due to gravity? A journey through the gut: Oesophagus A journey through the gut: The layers of the gut: Pg 5 The muscular wall is made up of Outer longitudinal muscles Inner circular muscles A journey through the gut: Peristalsis The muscle layers cause rhythmic, wave-like contractions called peristalsis which move food along the gut A journey through the gut: Peristalsis The involuntary rhythmic waves of muscular contractions which pass along the gut to move the food along it The process is initiated by the presence of food A journey through the gut: Oesophagus Is it true that the oesophagus does not secrete anything? Wall produces mucin to lubricate food during peristalsis Salivary amylase continues to digest starch A journey through the gut: Stomach Stores food and digests protein A distensible, muscular bag with thick & well- developed muscular walls Very powerful muscular contractions (churning) Mixes food with gastric juice to form chyme A journey through the gut: Stomach Gastric glands secrete gastric juice: Hydrochloric acid Gastric enzymes Mucin A journey through the gut: Stomach Provides acidic medium (pH 2) for gastric enzymes to function Stops the action of salivary amylase Changes the inactive forms of gastric enzymes to active forms A journey through the gut: Stomach: Hydrochloric acid Denatures proteins, unfolding the polypeptide chains, exposing more peptide bonds to enzyme action Kills some bacteria / germs A journey through the gut: Stomach: Hydrochloric acid A journey through the gut: Stomach: Enzymes Prorennin Rennin Soluble milk Protein (Caseinogen) Insoluble milk Proteins (Casein) HCl Pepsinogen Pepsin ProteinsPolypeptides HCl Can remain in stomach long enough Proteases are produced in inactive forms Enzymes & acid are produced by different cells Mucus protects the stomach wall from enzyme action and corrosiveness of the acid A journey through the gut: Why doesnt the stomach digest itself? A journey through the gut: Stomach The food normally remains in the stomach for about 3 to 4 hours. The partly digested food becomes liquefied, forming chyme After 1 or 2 hours, the pyloric sphincter relaxes and opens at intervals to let the chyme into the duodenum A journey through the gut: Stomach Muscular valve where stomach joins the small intestine A journey through the gut: Stomach: Pyloric sphincter A journey through the gut: Small Intestine About 6 metres long! Consists of U-shaped duodenum (1 st part) Jejunum Ileum (very coiled) Liver & pancreas discharge secretions into the duodenum The intestinal wall also secretes intestinal juice A journey through the gut: Small Intestine Largest gland in the body Three blood vessels: Hepatic portal vein, Hepatic vein, Hepatic artery Liver cells secrete bile: Bile salts and pigments Greenish-yellow colour Alkaline Stored in gall bladder A journey through the gut: Associated Gland: Liver Produces pancreatic juice Contains digestive enzymes Produces insulin (hormone) Control of blood sugar levels Utilization of carbohydrates A journey through the gut: Associated Gland: Pancreas Liver & pancreas discharge their secretions via the bile duct & pancreatic duct respectively A journey through the gut: Liver & Pancreas The chyme stimulates The intestinal glands to secrete intestinal juice The pancreas to secrete pancreatic juice The gall bladder to release bile All 3 fluids are alkaline: Neutralize chyme (acidic) Provide suitable alkaline medium for enzyme action A journey through the gut: Duodenum A journey through the gut: Small Intestine NutrientsLiverPancreas Intestinal glands Carbohydrates-AmylaseMaltaseLactaseSucrase Proteins-Trypsin EnterokinaseErepsin FatsBileLipaseLipase A journey through the gut: SI: Carbohydrate digestion StarchMaltoseGlucose PancreaticAmylaseMaltase LactoseGlucose Lactase Galactose SucroseGlucose Sucrase Fructose A journey through the gut: SI: Protein digestion Protein Polypeptides Amino Acids Trypsin Erepsin Enterokinase Trypsinogen Glycerol A journey through the gut: SI: Fat digestion Fats Fat globules Fatty Acids Bile Pancreatic & IntestinalLipase Emulsification So far, what have we learnt? 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