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L11_Digestion - Digestion Overview of Digestion...

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Digestion Overview of Digestion Assimilation – process of nutrient acquisition Takes place along gastrointestinal (GI) tract Contiguous with external environment Composed of many cell types Secretory cells Absorptive cells Muscle cells Neurons Egestion – Excretion of undigested food Diets Provide Energy (Fig 11.2) Energy content of diet must match metabolic demands of animal Caloric equivalent Energy content of a gram of a specific macromolecule Protein and carbohydrates = 4 kcal/gm Fat = 9 kcal/gm Some food is indigestible or unmetabolizable Energy is lost in feces or urine Some energy is spent digesting food Specific dynamic action (SDA) or heat increment Increase in metabolic rate during digestion Important source of thermal energy Vitamins (Fig 11.1: know A, D, E, K and ascorbic acid functs and sympts of D, K, and ascorbic acid) Group of unrelated molecules with diverse functions Many participate in catalysis as cofactors for enzymes Usually categorized based on solubility Fat-soluble – vitamins A, D, E, K (K for clotting) Water soluble – vitamins B (coenzymes), C Obtained in diet or from bacteria living in the GI tract Minerals Metallic elements that participate in protein structure Calcium Phosphorus Iron
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Copper Zinc Most are absorbed along GI tract by specific transporters Amino Acids Animals use 20 amino acids to build proteins Most can be produced by the animal Eight essential amino acids must be obtained in diet (sometimes more) Diets deficient in any essential amino acid lead to developmental defects and slow growth Protein quality amino acid profile of dietary protein animal tissue provides higher protein quality than plant tissue some plants lack specific amino acids Fatty Acids Animals can make almost all fatty acids from acetyl CoA cannot produce sufficient amounts of omega-3 ( ϖ 3) or omega-6 ( ϖ 6) fatty acids Omega-3 fatty acids must be ingested as linolenic (18:3 ϖ 3 acid) Found in cold-water fish and flax seed Omega-6 fatty acids must be ingested as linoleic (18:2 ϖ 6) Found in plant seeds Digestive Enzymes convert macromolecules to forms that can be absorbed and processed Lipases   Break down triglycerides and phospholipids into fatty acids Proteases Break down proteins into shorter polypeptides  Amylases Break down polysaccharides into oligosaccharides Nucleases Break down nucleic acids into nucleotides Most digestion takes place extracellularly Symbiotic Organisms and Digestion Digestion in many animals benefits from the assistance of symbiotic organisms
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bacteria, fungi, and photosynthetic organisms Three main types of symbionts participate in digestion
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