Nutrients in Humans (5078 syllabus)

Nutr ient s in Humans 1 Nutrients in Humans Define: Digestion: breakdown of large insoluble complex food molecules to smaller soluble (simpler) molecules which will be absorbed into the bloodstream Anatomy Mouth and buccal cavity: teeth Chewing action Increases surface area to volume ratio Salivary glands secretes saliva into tongue through via salivary duct Tongue Rolls the food into bolus Starch → maltose (salivary amylase) Oseophagus helps move food (bolus) along the long tube with peristalsis Stomach churns the bolus secrete gastric juice to break down food into simpler substances Hydrochloric acid:

Nutr ient s in Humans 2 stops the action of salivary amylase. changes inactive forms of enzymes to active forms (e.g pepsinogen is activated by hcl into pepsin), providing an acidic medium for action of gastric enzymes. kills potentially harmful microorganisms in food. proteins → polypeptides (protease) Small intestine helps to further digest proteins and starch and emulsified fats Enzymes remaining proteins → amino acids polypeptides →amino acids starch → trypsin (enterokinase) maltase → glucose (maltose) sucrose → glucose and fructose (sucrase) lactose → glucose and galactose (lactase) fats → fatty acids and glycerol (lipase) Large intestine absorbs excess water and mineral salts Pancreas Secretes pancreatic juices

Nutr ient s in Humans 3 Rectum stores undigested and unabsorbed food before its discharged as faeces through the anus Function of enzymes: Salivary amylase: starch → maltose Maltase: maltose → glucose Protease: proteins → polypeptides polypeptides → amino acids Lipase: fats → fatty acids and glycerol Lactase: lactose → galactose and glucose Sucrase: sucrose → glucose and fructose Rennin: caesinogen → caesin Trypsinogen: pepsin → trypsin Digestive Enzymes Liver + Gall bladder in Fat digestion Liver regulates blood glucose concentration after a meal produces bile for emulsification stores iron synthesizes protein deaminate excess amino acids to form urea detoxification of alcohol Gallbladder stores bile produced by the liver. Role of Liver:

Nutr ient s in Humans 4 1. metabolism of glucose Too much glucose after a meal: stimulates islets of Langerhans in pancreas secrete insulin insulin is transported to the liver excess glucose → glycogen by insulin (stored in the muscles and the liver cell) Too little glucose when fasting: stimulate islets of Langerhans in pancreas secretes glucagon Glucagon transported to the liver glycogen → glucose by glucagon (goes into the bloodstream) 2. metabolism of amino acids and formation of urea metabolism of amino acids deaminate amino acids formation of urea amino group, NH2, →ammonia ammonia → urea 3. breakdown of alcohol detoxifies alcohol, by converting it with alcohol dehydrogenase into acetaldehyde which is then broken down into compounds used in respiration Adaptation of small intestine: finger-like structure (villi and microvilli) to increase surface area to volume ratio and absorb nutrients into the bloodstream Epithelium of a villi is one-cell thick Long to allow sufficient time for absorption Many capillaries in intestinal walls and villi