Lecture_Five

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					Lecture Five
Lipids
       -Organic compounds (CnHnOn) that contains more C and H in proportion to O
       than does CH2O
       -Insoluble in water, but soluble in organic solvents (ether, acetone, benzene)
       -Supplies 40% of the calories in American diets
       -Source of essential fatty acid
       -Necessary for fat soluble vitamins A, D, K and E
       -Concentrated form of energy
               -1g of fat = 9.45kCal
               -1g of protein or CH2O = 4.1 kCal
               -On average  2.25 times more energy in fat than CH2O or protein
                       -Important for hibernating animals
       -Simple Lipids
               -Esters of fatty acids and alcohol (glycerol)
               -Fats and oils = esters of fatty acids and glycerol
               -Waxes = esters of fatty acids and alcohol (not glycerol)
       -Compound Lipids
               -Esters of fatty acids, also containing nonlipid substances (P, CH2O,
               proteins)
                       -Phospholipids (phosphoric acid, N) membranes,
                       transport/emulsification
                       -Glycolipids (CH2O, N)
                       -Lipoproteins carriers in blood and tissues (LDL, HDL, VHDL)
       -Derived Lipids
               -Substances derived from simple and compound lipids by hydrolysis
       -Sterols
               -Lipids with complex phenanthrene type ring structure
       -Terpenes
               -Isoprene type structures
       -Structure of Lipids
               -Fatty Acids
                       -Carbon chains from 2-24 in length
                               -Even numbered straight chained in most animal tissue
                               -Some branched in ruminants
                       -Carboxyl group at the end of each
                       -RCOOH general structure (R stands for fatty acid chain)
                       -CH3CH2COOH is acetate
                       -Double bond vs. H Saturation
                               -Stearic C18:0  number of double bonds
                               -Linolenic C18:3 number of double bonds
                       -Isomers
                               -Cis
                               -Trans (margarine, other hydrogenated fats)
               -Glycerol is an alcohol
                       -Mono, Di, and triglycerides are esters of fatty acids and glycerol
          -Mono, Di, and triglycerides
                -Typically are mixed triglycerides (98%)
                -Chain length, degree of saturation determines physical properties
                        -TG of C10:0 or longer = solid at room temperature
                        -TG of less than C10 = liquid at room temperature
                        -TG with each fatty acid saturated = solid
                        -TG with more unsaturated fatty acids = liquid
                        -Fats can have 10 or more different fatty acids
-Lipids
       -Phosopholipids
               -Usually contain fatty acids (hydrophobic), phosphoric acid
               (hydrophilic), a glycerol, a nitrogenous base
               -Higher in unsaturated fatty acids than lipids in adipose tissue
               -Widely dispersed in body fluids
               -Emulsifying properties that help to function in lipid transport
       -Sterols
               -Phenanthrene type ring
               -Cholesterol, ergosterol, 7-dehydrocholesterol, androgens,
               estrogens, progesterone
-Lipid Functions
       -Energy supply
               -2.25 times that of CH2O and protein
       -Source of essential fatty acids (EFA)
               -Can not be synthesized in adequate amounts
                        -Linoleic Acid (C18:2) and linolenic acid (C18:3)
                        -Arachidonic acid (C20:4) can be synthesized from linoleic
                        acid
               -Involved in maintenance of skin integrity in nonruminants
               -Young ruminants require essential fatty acids in diet (just like non
               ruminants)
       -Carriers of fat soluble vitamins
               -Vitamins A, D, E and K
                        -Absorption is a function of digestion and absorption of fats
                        -Mixed micelles containing monoglycerides and FFA’s
                        higher rate of vitamin uptake
       -Source as insulation and protection as well as heat generation
-Lipid Absorption
       -Site of major fat processing—upper small intestine
       -Fats (mostly triglycerides) mix with bile and pancreatic and intestinal
       secretions
       -Bile salts act as emulsification agents (detergent like action)
               -Particle size decreases increasing surface area and exposure to
               lipases
       -Lipases attach fatty acid in 1 and 3 positions result in beta
       monogylcerides and free fatty acids
        -Monoglycerides + FFA + bile salts + phospholipids + cholesterol=mixed
        micelles
                 -Bile Salts
                         -Secreted in large quantities, reabsorbed in jejunem and
                         ileum, recycled in liver
                         -Facilitate digestion and absorption of lipids
                         -Absorption of fat soluble vitamins
                         -Cholesterol absorption
        -Mixed micelles combine with cholesterol and fat soluble vitamins =
        larger mixed micelles
        -Main site of absorption is upper jejunem, some absorption in duodenum
        and ileum
        -Upon entering mucosal cell
                 -Fats are reassembled into triglycerides
                 -Protein coating takes place to form chylomicrons (triglycerides,
                 phospholipids, cholesterol, esters, and protein)
                 -Chylomicrons enter lacteals via intercellular space lymphatic
                 system  thoracic duct
                 -Mammals absorb long chain fatty acid lipids via lymph (chickens
                 absorb directly into portal blood)
-Transport of Lipids
        -Blood lipids
                 -Chylomicrons
                 -Lipids arising from mobilized depot stores
                 -Lipids synthesized in body tissues (liver and adipose)
        -Transported as lipoproteins
                 -4 Major Classes
                         -Chylomicrons (highest ratio of lipids to proteins)
                         -VLDL (very low density by lipoproteins)
                         -LDL
                         -HDL
-Lipid Deposition
        -All tissues store triglycerides
        -Adipose tissues are most significant sites
                 -Can synthesize TG from CH2O and oxidize fats
        -TG are ready source of energy so, there is continous triglyceride
        deposition and mobilization
        -Energy intake in excess results in net deposition of TG. Reverse is also
        true
        -Fat depot=fatty acid characteristics for each animal
                 -Non ruminants= dietary fatty acid influences fat depot
                 -Ruminants= less responsive, bypass fats
-Fatty Acid and TG to Metabolism
        -Major sites of lipid metabolism
                 -Liver
                 -Mammary gland
                -Adipose tissue
        -Liver (example)
                -Synthesis of :
                        -Fatty acids from CH2O and amino acids
                        -Cholesterol
                        -Phospholipids
                        -Lipoproteins
                        -Ketones
                -Degradation of:
                        -Fatty acids, phospholipids
                        -Saturation, desaturation, lengthening, shortening, deposit
                        of liver lipids
-Biosynthesis of fatty acids
        -Active in adipose, liver and mammary tissues
                -Begins in Acetyl-CoA
                -Assembled in 2 carbon units
                -Animal tissue synthesizes up to 16 carbons
                -Desaturation in tissue is limited
                -Ruminant:
                        -Glucose propionate lactate acetate Acetyl-CoA
-Biosynthesis of Triglycerides
        -Acetyl-CoA + alpha-glycerol phosphate phospholipid + Acyl-CoA
        diglyceride + Acyl-CoA triglyceride
-Triglyceride Catabolism
        -Adipose tissue
                -Composed primarily of adipose tissue
                -Dynamic tissue= synthesis and degradation of triglycerides
                -Lipoprotein lipase= hydrolysis of TG
                        -Synthesized in many tissues
                        -Activity high in fed state, low in fasted state
                -Activity under hormonal control
                        -Lypolysis is stimulated by: beta-adrenergic agonists
                        (paylean), adrenocortcotropins, somatotropin (GH)
                        -Inhibited by: prostaglandins and insulin
                        -Lypolysis is “break down of lipids”
                -Control of net fat accretion involves complex regulatory systems
                that include lypolysis and lipogenesis
-Fatty Acid Catabolism
        -Fatty acids released from hydrolysis=transported to tissues as an
        oxidative energy source
        -Oxidation (beta oxidation and TCA cycle) occurs in the mitochondria
        (skeletal muscle, liver, cardiac muscle, adipose tissue, etc.)
        -Beta oxidation stepwise enzymatic removal of 2 carbon units (Acetyl-
        CoA) to be used for resynthesis of fatty acids, synthesis of steroids or
        ketones, entry into TCA cycle
        -Not reverse of synthesis process
        -Total energy with oxidation of a LCFA comes from both beta oxidation
        and Acetyl-CoA oxidation in TCA cycle
-Steroid Metabolism
        -Cholesterol = most abundant sterol and precursor to most others
                -Biosynthesis of Acetyl-CoA
                        -Partially controlled by dietary intake
                -Cholesterol excreted in bile
                -Used for sterol synthesis; progesterone, ACTH, testerone,
                estrogen
-Phospholipid Metabolism
        -Lecithin (phosphatidyl choline) is most abundant in animal tissue
-Ketone Metabolism
        -Formation of ketones is continous
        -Used as energy source in skeletal muscle and other peripheral tissue
        -Overproduction occurs in:
                -Disorders: diabetes mellitus
                -Low CH2O intake
-Abnormalities in Lipid Metabolism
        -Fatty Livers
                -Dairy cattle in negative energy balance
                -Associated with excessive fat mobilization from adipose tissue
                -Fat deposited in liver (5%) slower net loss
                -Transition period important
                -Feeding protected choline
        -Ketosis
                -Overly fat animals, often seen in dairy cattle
                -Rapid mobilization of fat depot
                -Reduced intakes
                -Lack of ability to metabolize Acetyl-CoA in TCA cycle fast
                enough
                -Acetyl-CoA Acetoacetic acid acetone and B-hydroxybutric
                acid
        -Obesity
                -Over consumption of calories is a factor
                -Genetics plays a major role
                        -Lipogenic enzyme activity in adipose tissue of obese
                        animals higher
                -Net deposition is greater than normal
                -Cell size and number
                        -Vary with species and individuals
                        -Proliferation can occur postnatally

				
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posted:4/18/2011
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