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• Chapter 41 – Animal Nutrition Food Types / Feeding Mechanisms • • • • • • Opportunistic Herbivore: eat autotrophs Carnivore: eat other animals Omnivore: both Feeding Adaptations Suspension-feeders: sift food from water (baleen whale) • Substrate-feeders: live in or on their food (leaf miner) (earthworm: deposit-feeder) • Fluid-feeders: suck fluids from a host (mosquito) • Bulk-feeders: eat large pieces of food (most animals) Homeostasis & Energy Budget • “Budget” – flow of energy into and out of an animal’s body • Regulated through homeostatic mechanisms, ex. Glucose • Blood glucose rises, pancreas secretes insulin, enhances transport of glucose into body cells and stimulates liver and muscle to store glucose as glycogen • Blood glucose falls, pancreas secretes glucagon, promotes breakdown of glycogen in liver and release into the blood stream Caloric Imbalance • Undernourishment – stores of fat and glycogen used up, body breaks down proteins for fuel, caloric deficiency • Overnourishment – body hoards fat instead of using it for fuel • Malnourishment – essential nutrient deficiency • Obesity – a global problem, lead to a variety of health problems • Science currently conducting research to discover homeostatic mechanisms for food intake Appetite Regulation • Most appetite regulatory hormones are proteins, dozens of genes have been identified that code for these hormones • Leptin – produced by adipose tissue, suppresses appetite as fat increases • PYY – small intestine, after meals, suppresses appetite • Insulin – pancreas, rise in sugar levels after a meal, suppresses appetite • Ghrelin – stomach wall, triggers feelings of hunger as mealtime approaches, as diet/lose weight, ghrelin levels increase • Many of these are feedback mechanisms that prevent people from becoming overweight or obese Nutritional Requirements • Essential nutrients: materials that must be obtained in preassembled form • Essential amino acids: the 8 amino acids that must be obtained in the diet • Essential fatty acids: unsaturated fatty acids • Vitamins: organic coenzymes • Minerals: inorganic cofactors Essential Vitamins Food Processing • 1-Ingestion: act of eating • 2-Digestion: process of food break down – – – – enzymatic hydrolysis intracellular: breakdown within cells (sponges) extracellular: breakdown outside cells (most animals) alimentary canals (digestive tract) • 3- Absorption: cells take up small molecules • 4- Elimination: removal of undigested material The Alimentary Canal • Primitive inverts have gastrovascular cavity – a digetive sac with a single opening, functions in digestion and distribution of nutrients (cnidarians and flatworms) • All others have an alimentary canal – a digestive tube extending between two openings, a mouth and an anus Mammalian digestion, I • Peristalsis: rhythmic waves of contraction by smooth muscle • Sphincters: ring-like valves that regulate passage of material • Accessory glands: salivary glands; pancreas; liver; gall bladder Mammalian digestion, II • Oral cavity: salivary amylase (hydrolyzes starch), bolus (ball of chewed food • Pharynx (the throat): epiglottis - a cartilaginous flap that moves up to cover the trachea (windpipe) during swallowing • Esophagus: conducts food from the pharynx down to the stomach by peristalsis Mammalian digestion, II cont. • • • • • • • Stomach – stores food and performs preliminary steps of digestion Churning and enzymes convert food to nutrient broth called acid chyme Secretion of enzymes – controlled by nerve impulses and hormone gastrin 3 types of secretory cells: Mucous cells, secrete mucin (thin mucous layer protects stomach lining) and gastrin (stimulates further secretion of gastric juice) Chief cells, secrete pepsinogen (inactive precursor of pepsin, becomes active when mixed with acid) Parietal cells, secrete HCl – – – gastric juice (HCl and pepsin) HC I- acidity (pH 1-4) kills bacteria, starts conversion of pepsinogen to pepsin pepsin – begins to split peptide bonds of large polypeptide chains Mammalian digestion, III • Small intestine – more than 6 meters in length in humans; where most enzymatic hydrolysis and absorption of nutrients occurs • 3 sections: – duodenum – 25 cm, acid chyme mixes with digestive juices from the pancreas, liver, gall bladder, and intestinal wall • pancreas – protease for protein digestion and bicarbonate to buffer the acid chyme • liver – bile for fat emulsification (stored in the gall bladder) • brush border – epithelial lining of duodenum, secretion of several different digestive enzymes – jejunum - begin the absorption of amino acids, sugars, fatty acids and glycerol – Ileum – significant absorption due to large number of villi Mammalian digestion, IV • Villi (large circular folds) contain microvilli – increase surface area to increase nutrient absorption; each villus contains microscopic blood vessels (capillaries) and a lacteal (a small lymphatic vessel) • Nutrients are absorbed across the intestinal epithelium and across the epithelium of the capillaries or lacteal • Hepatic portal vein – carries nutrient rich blood away from villi directly to the liver (can interconvert various organic molecules) Mammalian digestion, V • Hormonal Action: – – – – gastrin – stomach, gastric juice production secretin – small intestine, stimulates pancreas to release buffer (sodium bicarbonate) cholecystokinin (CCK) – small intestine, triggers release of bile from gall bladder and enzymes from the pancreas enterogastrone – small intestine, assists in fat hydrolysis by stopping peristalsis when fat rich acid chyme reaches the duodenum Mammalian digestion, III cont. Mammalian digestion, VI • Large intestine (colon) – site of water absorption • Cecum • Appendix • Feces • Rectum/anus Evolutionary adaptations • • • • Dentition: an animal’s assortment of teeth Digestive system length Symbiosis Ruminants