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Lipid Metabolism Sources and Functions
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Lipid Metabolism Sources and Functions

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Questions and Answers

What is the primary function of lipoprotein lipase in relation to exercise?

  • It enhances the transport of glucose into the bloodstream.
  • It breaks down plasma triglycerides for fatty acid uptake. (correct)
  • It facilitates the uptake of amino acids in muscles.
  • It provides energy directly to the brain during strenuous activities.

    • What role do GLUT4 and FAT/CD36 play during physical activity?

  • They coordinate the transport of nutrients to ensure enough fuel is available. (correct)
  • They are responsible for the synthesis of lipoprotein lipase.
  • They inhibit the uptake of glucose and fatty acids.
  • They increase the production of plasma triglycerides.

    • How does electrical stimulation via the sciatic nerve influence transport proteins?

  • It enhances the function of fatty acid transport proteins. (correct)
  • It decreases the transport efficiency of amino acids.
  • It disrupts the coordination of insulin signaling.
  • It leads to the breakdown of glycogen stores.

    • What did the study involving cycling at 60% VO2 max specifically focus on regarding response to exercise?

    <p>The regulation of fatty acid transporters similar to GLUT4.</p> Signup and view all the answers

    What effect does increased total lipoprotein lipase (LPL) in muscle have during exercise?

    <p>It enhances the uptake of fatty acids from triglycerides.</p> Signup and view all the answers

    What is the primary function of stored lipids in the body?

    <p>They serve as the main form of stored energy.</p> Signup and view all the answers

    Which of the following plays a role in the mobilization of lipids from adipose tissue?

    <p>Hormone-sensitive lipase (HSL)</p> Signup and view all the answers

    How is fatty acid transport in muscle affected by insulin and exercise?

    <p>Insulin and contraction stimulate FA transport in an additive manner.</p> Signup and view all the answers

    What are the possible fates of fatty acids in adipose tissue?

    <p>Release, re-esterification, and oxidation.</p> Signup and view all the answers

    Which component is primarily responsible for the uptake of fatty acids in muscle?

    <p>FAT/CD36</p> Signup and view all the answers

    What is a significant change in lipolysis due to training?

    <p>Increased sensitivity of HSL to stimulation by Epi.</p> Signup and view all the answers

    Which statements about dietary lipids as a fuel during exercise are correct?

    <p>Lipids cannot be used in anaerobic conditions.</p> Signup and view all the answers

    What role do albumin-bound free fatty acids play in lipid metabolism?

    <p>They act as a means of transport for fatty acids in the blood.</p> Signup and view all the answers

    What role does carnitine palmitoyl transferase 1 (CPT1) play in fatty acid entry into mitochondria?

    <p>It facilitates the transport of fatty acyl carnitine across the mitochondrial membrane.</p> Signup and view all the answers

    Which statement is true regarding lipid utilization during exercise?

    <p>Intramuscular lipid breakdown occurs primarily during exercise recovery.</p> Signup and view all the answers

    What happens to the contribution from fat oxidation in exercise-trained subjects?

    <p>It increases at a given workload.</p> Signup and view all the answers

    What key factor was historically considered rate limiting for fatty acid entry into mitochondria?

    <p>The action of CPT1.</p> Signup and view all the answers

    Why might carnitine not be necessary as some fat-burning supplements claim?

    <p>Other transport mechanisms may be sufficient.</p> Signup and view all the answers

    During a low-intensity running session, what is observed regarding plasma free fatty acids (FFA) with aerobic training?

    <p>FFA release into the plasma increases.</p> Signup and view all the answers

    In the context of mitochondrial lipid utilization, what has been a recent area of debate among researchers?

    <p>The presence of FAT/CD36 on the inner mitochondrial membrane.</p> Signup and view all the answers

    What impact does prolonged aerobic training have on fat oxidation rates at a constant workload?

    <p>It progressively increases, enhancing fat utilization.</p> Signup and view all the answers

    What explains the lower circulating free fatty acid (FFA) levels in trained individuals during aerobic exercise?

    <p>Higher reliance on intramuscular triglycerides (IMTGs)</p> Signup and view all the answers

    How do trained muscles compensate for lower plasma FFA levels?

    <p>By increasing extraction of FFAs from the blood</p> Signup and view all the answers

    What physiological adaptation relates to increased fat oxidation with training?

    <p>Enhanced content of β-oxidation and ETC enzymes</p> Signup and view all the answers

    What is one paradox associated with intramuscular triglycerides (IMTGs) in endurance-trained athletes?

    <p>Higher IMTG content is associated with insulin resistance.</p> Signup and view all the answers

    What might explain differences in plasma FFA levels at higher exercise intensities?

    <p>Increased catecholamine response</p> Signup and view all the answers

    Which molecules are indicated to interfere with insulin signaling and lead to insulin resistance?

    <p>Diacylglycerols and ceramides</p> Signup and view all the answers

    What was the observed level of total ceramide in athletes compared to their sedentary counterparts?

    <p>Lower in athletes</p> Signup and view all the answers

    In which group was total DAG reported to be lowest?

    <p>Obese sedentary</p> Signup and view all the answers

    What role does the protein Akt2 play in insulin signaling?

    <p>It phosphorylates AS160</p> Signup and view all the answers

    How do ceramides influence the energy production in the presence of fatty acids during insulin signaling?

    <p>They reduce insulin sensitivity</p> Signup and view all the answers

    What effect do diacylglycerols have on insulin receptor signaling?

    <p>They lead to receptor desensitization</p> Signup and view all the answers

    What is the relationship between imbalanced fatty acid metabolism and insulin signaling?

    <p>It alters lipid signaling pathways</p> Signup and view all the answers

    What metabolic state is characterized by high levels of ceramides and impaired insulin signaling?

    <p>Insulin resistance</p> Signup and view all the answers

    Study Notes

    Lipid Metabolism Sources

    • Adipose triacylglycerol (TAG) or triglyceride (TG)
    • Intramuscular TAG or TG (IMTG)
    • Blood-borne
      • Albumin-bound free fatty acids (FFA or FA) from adipose
      • TAGs from chylomicrons (intestinal-derived) or VLDL (liver)

    Lipids as Fuel

    • The body’s main form of stored energy
    • Spares carbohydrate reserves
    • Cannot be used anaerobically but contributes to high-intensity exercise

    Sites of Regulation

    • Mobilization from adipose tissue
    • Uptake by muscle
    • Mitochondrial uptake and oxidation

    Mobilization from Adipose Tissue

    • Lipolysis is the breakdown of stored triglycerides into free fatty acids (FFA) and glycerol
    • Lipolysis is regulated by hormones, including epinephrine (Epi), norepinephrine, and glucagon
    • Hormonal sensitivity increases with training, enhancing lipolysis

    Muscle Fatty Acid Uptake

    • Fatty acid transporter proteins facilitate the uptake of fatty acids into muscle cells
    • Key transport proteins include:
      • FAT/CD36 (fatty acid translocase)
      • FABPpm (fatty acid binding protein)
      • FATP1-6 (fatty acid transport family)

    FAT/CD36 and Exercise

    • Two separate pools of FAT/CD36 translocate in response to insulin and exercise
    • Translocation to the plasma membrane and fatty acid uptake are partially additive
    • Insulin and contraction stimulate FA transport in an additive manner

    Intramuscular Lipid Utilization

    • During prolonged exercise, intramuscular lipid utilization increases
    • Type II muscle fibers do not break down lipids during exercise, but do during recovery

    Mitochondrial Membrane Transport

    • Fatty acid entry into the mitochondrion is a complex process
    • Requires carnitine palmitoyl transferase 1 (CPT1) and carnitine
    • Fatty acids are activated by acyl CoA-synthetase to form FA acyl-CoA
    • Fatty acyl CoA is converted to fatty acyl carnitine, which can cross the mitochondrial membrane
    • FAT/CD36 may also be present on the inner mitochondrial membrane

    Fat Oxidation and Training

    • Fat oxidation is increased with training. This includes:
      • Increased sensitivity of adipose HSL to epi
      • Increased lipoprotein lipase content
      • Increased FA transporters at the plasma membrane
      • Increased content of beta-oxidation, Krebs cycle, and electron transport chain enzymes
      • Increased IMTG content

    IMTG and Insulin Sensitivity

    • Intramuscular triglycerides (IMTG) are associated with insulin resistance, but this is not always the case in endurance-trained athletes
    • Diacylglycerols and ceramides interfere with insulin signaling leading to insulin resistance.
    • Athletes have reduced total ceramide levels which may contribute to their insulin sensitivity despite high IMTG content

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    Description

    Explore the various sources of lipids and their roles in metabolism. This quiz covers lipid functions as fuel, regulation sites, and the mobilization process from adipose tissue. Understand the hormonal influence on lipolysis and muscle uptake mechanisms.

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