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Metabolism (Lipids (Made water soluble by binding to proteins, FFA bound…
Metabolism
Lipids
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4 major types: Chylomicrons, VLDL, LDL, HDL
Chylomicrons and VLDL - Converted to FFA by lipoprotein lipase, taken up by adipose tissue or muscle. Remnants and some VLDL taken up by liver & metabolised
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HDL - Transfers apoproteins to chylomicrons & VLDL to enhance lipid uptake, removes cholesterol from other cells & transfer to liver, cholesterol-rich HDL degraded & releases cholesterol - converted to bile salts or excreted in bile
Amino acids
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Used for protein synth, used for energy, conerted to fat/glycogen for storage
Degradation for energy leads to NH3, converted to urea by liver excreted in kidneys - Except herbores, transferred to gut for use by microbes
Introduction
Nutrients absorbed from small & large intestine as glucose, amino acids/di/tri peptides, triglycerides, VFAs
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Lipids enter circulation via lymphatic system, bypass liver
In carnivores metabolism varies between 2 phases: Absorptive state (energy from absorbed), post-absorptive (energy from stored)
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Post-absorptive state
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Liver: glycogenolysis, gluconeogenesis
Use of glucose reserved for brain, erythrocytes, kidneys and under anaerobic conditions skeletal muscle
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In pregnancy/lactation glucose essential for foetal metabolism/lactose synth hence maintenance of plasma glucose in post-absorptive v. important
Carbohydrates
Carnivores/omnivores: Absorbed as monosacc, mostly glucose
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Gluconeogenesis
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Omnivores - Sufficient glucose direct from diet
Carnivores - Diet low in CHO so gluconeogenesis dependent
Herbivores - CHOs fermented to VFAs, only propionic acid can serve as glucose pre-cursor
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Absorptive state
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Liver fills glycogen stores, synthesises lipids for export to other tissues
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Mobilisation of glycogen
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Liver: reduces anabolic activities, mobilising glycogen stores
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Lipids as energy source
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During post-absorptive VLDL synth from plasma FFA; FFA normally transported in blood bound to albumin
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Regulation of fat metab
Insulin -Tri-glys synthesised from glycerophosphates/FFA, inhibitions of FFA release into blood
Glucagon - Increases lipolysis in adipose tissues, mobilisation of tri-glys for ATP production
Comparative metabolism
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Ruminants require gluconeogenesis to occur in both states, primary source of energ in VFAs not glucose