Lipid Transport Lipid Transport and Storageand Storage

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LIPIDS ARE TRANSPORTED IN LIPIDS ARE TRANSPORTED IN THE PLASMA AS THE PLASMA AS LIPOPROTEINSLIPOPROTEINS

Lipoproteins Consist of a Nonpolar Core & a Single Surface Layer of Amphipathic Lipids

The Distribution of Apolipoproteins Characterizes the Lipoprotein

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FREE FATTY ACIDSFREE FATTY ACIDS ARE RAPIDLY ARE RAPIDLY METABOLIZEDMETABOLIZED

TRIACYLGLYCEROLTRIACYLGLYCEROL IS IS TRANSPORTED FROM THE TRANSPORTED FROM THE INTESTINES IN CHYLOMICRONS & INTESTINES IN CHYLOMICRONS & FROM THE LIVER IN VERY LOW FROM THE LIVER IN VERY LOW DENSITY LIPOPROTEINSDENSITY LIPOPROTEINS

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Composition of the lipoproteinslipoproteins in plasma of humans.

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CHYLOMICRONSCHYLOMICRONS & VLDLVLDL ARE RAPIDLY CATABOLIZED

Triacylglycerols of Chylomicrons & VLDL Are Triacylglycerols of Chylomicrons & VLDL Are Hydrolyzed by Hydrolyzed by Lipoprotein LipaseLipoprotein Lipase

The Action of Lipoprotein Lipase Forms The Action of Lipoprotein Lipase Forms Remnant LipoproteinsRemnant Lipoproteins

The The LiverLiver Is Responsible for the Uptake of Is Responsible for the Uptake of Remnant LipoproteinsRemnant Lipoproteins

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Metabolic fate ofMetabolic fate of chylomicronschylomicrons

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Metabolic fate of Metabolic fate of VLDLVLDL and production of and production of LDLLDL

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LDLLDL IS METABOLIZED VIAIS METABOLIZED VIATHE THE LDL RECEPTORLDL RECEPTOR

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HDLHDL TAKES PART IN BOTH TAKES PART IN BOTHLIPOPROTEIN LIPOPROTEIN TRIACYLGLYCEROLTRIACYLGLYCEROL

& & CHOLESTEROLCHOLESTEROL METABOLISM METABOLISM

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CLINICAL ASPECTSCLINICAL ASPECTS

Imbalance in the Rate of TG Formation & Export Causes Fatty LiverFatty Liver

Ethanol Also Causes Fatty LiverFatty Liver

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ADIPOSE TISSUEADIPOSE TISSUE IS THE MAIN STOREOF TGTG IN THE BODY

The Provision of Glycerol 3-PhosphateGlycerol 3-Phosphate Regulates Esterification: Lipolysis Is Controlled by Hormone-Sensitive LipaseHormone-Sensitive Lipase (Figure 25–7)

Increased GlucoseGlucose Metabolism Reduces the Output of Free Fatty Acids

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HORMONESHORMONES REGULATEFAT MOBILIZATION

InsulinInsulin Reduces the Output of Free Reduces the Output of Free Fatty AcidsFatty Acids

Several HormonesSeveral Hormones Promote Lipolysis Promote Lipolysis

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LipolysisLipolysis increased by:

Epinephrine Norepinephrine Glucagon ACTH TSH Thyroid hormone

GH MSH Vasopressin Caffeine Theophylline Leptin

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LipolysisLipolysis decreased by:

Insulin Nicotinic acid Prostaglandin E1

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BROWN ADIPOSEBROWN ADIPOSE TISSUE TISSUEPROMOTES PROMOTES THERMOGENESISTHERMOGENESIS

Brown adipose tissue is involved in metabolism particularly at times when heat generation is necessary

Though not a prominent tissue in humans, it is present in normal individuals, where it could be responsible for “diet-induced thermogenesis.”

It is noteworthy that brown adipose tissue is reduced or absent in obese persons.

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The tissue is characterized by: well-developed bloodblood supply

high content of mitochondriamitochondria and cytochromescytochromes

but low activitylow activity of ATP synthase.

A thermogenic uncoupling protein, thermogeninthermogenin, acts as a proton conductance pathway dissipating the electrochemical potential across the mitochondrial membrane

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Thermogenesis increased by:

NorepinephineNorepinephine

FFAFFA

Acyl-CoAAcyl-CoA

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Thermogenesis decreased by:Thermogenesis decreased by:

Purine nucleotidesPurine nucleotides

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THE ENDTHE END