Lipoprotein Metabolism Overview
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Questions and Answers

Which of the following lipoproteins is primarily involved in transferring triglycerides from the intestine to tissues?

  • High density lipoproteins (HDL)
  • Very low density lipoproteins (VLDL)
  • Chylomicrons (correct)
  • Low density lipoproteins (LDL)

    • What role does apolipoprotein C play in chylomicron metabolism?

  • Modifies LDL receptors
  • Activates lipoprotein lipase (correct)
  • Enhances HDL activity
  • Facilitates the reesterification of fatty acids

    • Which lipoprotein class is NOT synthesized in the liver or intestine?

  • Intermediate density lipoproteins (IDL)
  • High density lipoproteins (HDL)
  • Very low density lipoproteins (VLDL)
  • Chylomicrons (correct)

    • Which apolipoprotein is primarily required for the secretion of chylomicrons?

    <p>Apo B</p> Signup and view all the answers

    What happens to the glycerol produced during chylomicron metabolism?

    <p>It enters the hepatic glycolytic pathway</p> Signup and view all the answers

    Which of the following is a primary feature of high density lipoproteins (HDL)?

    <p>Facilitate the uptake of cholesterol by cells</p> Signup and view all the answers

    Chylomicron remnants are primarily composed of which substances after they shrink in size?

    <p>Cholesterol and apo E</p> Signup and view all the answers

    What is the main function of lipoprotein lipase in the context of lipoprotein metabolism?

    <p>Releases fatty acids from triglycerides</p> Signup and view all the answers

    What is the primary function of HDL in cholesterol metabolism?

    <p>To transport cholesterol from non-hepatic cells to the liver</p> Signup and view all the answers

    What component is NOT part of the composition of nascent HDL?

    <p>Triglycerides</p> Signup and view all the answers

    Which condition is associated with the least amount of LDL receptors?

    <p>Familial monogenic hypercholesterolemia</p> Signup and view all the answers

    Which of the following contributes least to the development of dyslipidemias?

    <p>Infections and viruses</p> Signup and view all the answers

    What happens to nascent HDL as it accumulates cholesterol esters?

    <p>It becomes increasingly larger and spherical</p> Signup and view all the answers

    What is a common feature of primary hypercholesterolemia?

    <p>Defective cellular uptake of LDL</p> Signup and view all the answers

    Which type of hyperlipoproteinemia is characterized by elevated lipoprotein(a)?

    <p>Lipoprotein(a) elevation</p> Signup and view all the answers

    In which situation would plasma triglyceride concentrations likely be high?

    <p>Secondary hypercholesterolemia</p> Signup and view all the answers

    What is the typical total cholesterol concentration in homozygous patients with primary hypercholesterolemia?

    <p>800-1,000 mg/dL</p> Signup and view all the answers

    How does the number of LDL receptors in heterozygous patients with primary hypercholesterolemia compare to those in normal subjects?

    <p>Decreased by 50%</p> Signup and view all the answers

    What is the relative risk of developing ischemic heart disease in heterozygous patients with primary hypercholesterolemia compared to those with normal plasma concentrations?

    <p>10 to 20-fold higher</p> Signup and view all the answers

    Which of the following is NOT a common disorder that can cause secondary hypercholesterolemia?

    <p>Obesity</p> Signup and view all the answers

    What cholesterol level is typically used to define hypertriglyceridemia?

    <p>More than 200 mg/dL</p> Signup and view all the answers

    Familial endogenous hypertriglyceridemia is primarily caused by which condition?

    <p>Hepatic triglyceride overproduction</p> Signup and view all the answers

    Which of the following is associated with familial endogenous hypertriglyceridemia?

    <p>Glucose intolerance</p> Signup and view all the answers

    At what age does familial endogenous hypertriglyceridemia usually become apparent?

    <p>After the fourth decade</p> Signup and view all the answers

    What is the primary cause of true inherited lipoprotein lipase deficiency?

    <p>True deficiency of the enzyme</p> Signup and view all the answers

    Which condition is NOT associated with secondary hypertriglyceridemia?

    <p>Familial combined hyperlipidemia</p> Signup and view all the answers

    Which lipoprotein is characterized by the presence of apo E2/2 homozygosity?

    <p>Familial dysbetalipoproteinemia</p> Signup and view all the answers

    What leads to the elevation of lipoprotein(a) particles?

    <p>The presence of apo (a) linked to apo B-100</p> Signup and view all the answers

    Which factor is often associated with secondary mixed hyperlipidemia?

    <p>Poorly controlled diabetes mellitus</p> Signup and view all the answers

    What is a key characteristic of familial combined hyperlipidemia?

    <p>Increased synthesis of both LDL and VLDL</p> Signup and view all the answers

    In which condition do VLDL particles migrate in a broad β region during agarose electrophoresis?

    <p>Familial dysbetalipoproteinemia</p> Signup and view all the answers

    What underlying issue primarily causes reduced activity of lipoprotein lipase in adults?

    <p>Apo C-II deficiency</p> Signup and view all the answers

    What is the primary initiating event in atherosclerosis related to apoB containing lipoproteins?

    <p>Infiltration and retention in the artery wall</p> Signup and view all the answers

    Which of the following best defines the consequence of macrophage internalization of apoB containing lipoproteins?

    <p>Formation of foam cells</p> Signup and view all the answers

    What role do smooth muscle cells play in atherosclerosis?

    <p>Produce the extracellular matrix</p> Signup and view all the answers

    What is associated with the rupture of the fibrous cap in vulnerable plaques?

    <p>Increased macrophage apoptosis</p> Signup and view all the answers

    How does HDL and apoA-I contribute to cardiovascular health?

    <p>Prevent inflammation and oxidative stress</p> Signup and view all the answers

    Which factor does NOT contribute to the risk of cardiovascular disease?

    <p>Low LDL cholesterol levels</p> Signup and view all the answers

    Which process occurs as a result of unresolved inflammation in atherosclerosis?

    <p>Necrotic cell death and collagen degradation</p> Signup and view all the answers

    What is the primary risk factor associated with the development of ischemic heart disease?

    <p>Raised plasma total and LDL-cholesterol concentrations</p> Signup and view all the answers

    What is the primary consequence of Lp(a) competing with plasminogen?

    <p>Promotion of clotting</p> Signup and view all the answers

    Which condition is characterized by an HDL cholesterol concentration of less than 40 mg/dL?

    <p>Hypoalphalipoproteinemia</p> Signup and view all the answers

    What is Tangier disease associated with in terms of HDL cholesterol levels?

    <p>Very low HDL levels as low as 1-2 mg/dL</p> Signup and view all the answers

    What clinical syndrome is associated with Apo B deficiency?

    <p>Steatorrhoea and progressive ataxia</p> Signup and view all the answers

    What primary dysfunction occurs due to LCAT deficiency?

    <p>Accumulation of free cholesterol in tissues</p> Signup and view all the answers

    What implication does acute hypoalphalipoproteinemia have on lipoprotein assessments?

    <p>They should be reassessed after recovery</p> Signup and view all the answers

    What is a common result of LCAT deficiency concerning systemic health?

    <p>Renal damage and premature atherosclerosis</p> Signup and view all the answers

    What happens to lipoproteins during severe physiological stress?

    <p>Temporary reduction of HDL and total cholesterol</p> Signup and view all the answers

    Study Notes

    Lipoprotein Metabolism

    • Lipoproteins are complexes of protein and lipids held together by noncovalent bonds.
    • They are classified into five classes:
      • High-density lipoproteins (HDL)
      • Low-density lipoproteins (LDL)
      • Intermediate-density lipoproteins (IDL)
      • Very low-density lipoproteins (VLDL)
      • Chylomicrons
    • Lipoproteins are synthesized in the liver or intestine.
    • After secretion, they are modified by enzyme-catalyzed reactions, and the remnants are taken up by receptors on cell surfaces.
    • These processes are regulated by the protein component of the particle (apolipoproteins).

    Apolipoproteins

    • Apolipoproteins (apo) are specific proteins found in lipoproteins.
    • Different apolipoproteins have different functions in lipoprotein metabolism.

    Exogenous Lipid Pathways

    • Fatty acids and cholesterol, released by digestion of dietary fat, are absorbed into intestinal mucosal cells.
    • They are re-esterified to form triglycerides and cholesterol esters.
    • These, along with phospholipids, apo A, and apo B, are secreted from cells into the lymphatic system as chylomicrons.
    • Chylomicron secretion depends on the presence of apo B.
    • Chylomicrons enter the systemic circulation via the thoracic duct.
    • Apo C and apo E derived from HDL are added to them in both lymph and plasma.

    Chylomicron Metabolism

    • Chylomicrons are metabolized in adipose tissue and muscle.
    • Lipoprotein lipase, located on capillary walls, is activated by apo C.
    • This enzyme hydrolyzes triglycerides into glycerol and fatty acids.
    • Fatty acids are taken up by adipose or muscle cells or bound to albumin in the plasma.
    • Glycerol enters the hepatic glycolytic pathway.
    • As the chylomicron shrinks, surface material containing apo A and some apo C and phospholipids are released and incorporated into HDL.
    • Small chylomicron remnants are composed mainly of cholesterol, apo B, and apo E.
    • They bind to hepatic chylomicron-remnant receptors, which recognize the constituent apo E.
    • The remnants enter the liver cells, where the protein is catabolized, and cholesterol is released.
    • At the end of this pathway, dietary triglycerides have been delivered to adipose tissue and muscle, and cholesterol to the liver.

    Endogenous Lipid Pathways

    • The liver is the main source of endogenous lipids.
    • Triglycerides are synthesized from glycerol and fatty acids, which may reach the liver from fat stores or glucose.
    • Hepatic cholesterol may be synthesized locally or derived from lipoproteins, such as chylomicron remnants, after they have been taken up by liver cells.
    • These lipids are transported from the liver in VLDL.

    VLDL Metabolism

    • VLDL is a large triglyceride-rich particle incorporating apo B, apo C, and apo E.
    • After secretion, it incorporates more apo C from HDL.
    • In peripheral tissues, triglycerides are removed after hydrolysis by lipoprotein lipase.
    • The VLDL remnant, or IDL, which contains triglycerides and cholesterol, as well as apo B and apo E, is either rapidly taken up by the liver or loses remaining triglycerides and apo E to become LDL.

    LDL Metabolism

    • LDL is a small cholesterol-rich lipoprotein containing only apo B.
    • It is taken up by specific receptors located on cell surfaces (LDL receptors).
    • Although these receptors are present on all cells, they are most abundant in the liver, and recognize apo B.
    • After entering cells, LDL particles are broken down by lysosomes.
    • Much of the released cholesterol contributes to membrane formation or to steroid synthesis in the adrenal cortex and gonads.
    • Most cells can synthesize cholesterol, but feedback mechanisms prevent intracellular accumulation.
    • Most of the plasma LDL is removed by LDL receptors.
    • If plasma concentrations are high, some LDL may also enter cells via a passive, unregulated route.
    • This can cause damage to tissues, such as the arterial wall.

    Role of High-Density Lipoprotein (HDL)

    • Cholesterol synthesized in cells would accumulate if not removed.
    • HDL is involved in transporting cholesterol from non-hepatic cells to the liver.
    • HDL is synthesized in hepatic and intestinal cells and secreted from them as small particles containing phospholipids, free cholesterol, and apo A and apo E (nascent HDL or discoidal HDL).
    • Nascent HDL picks up cholesterol from other lipoproteins and peripheral tissue cells and converts it to cholesterol esters, mediated by LCAT.
    • As HDL fills with cholesterol esters, it becomes spherical in shape.
    • HDL transports cholesterol to the liver.

    Disorders of Lipid Metabolism

    • Common disorders of lipid metabolism are associated with hyperlipidemia (abnormal serum lipids).
    • They can be caused by genetic abnormalities or environmental/lifestyle imbalances.
    • They may develop secondarily to other diseases.
    • Specific types of diseases include, but are not limited to: dyslipidemia, hyperlipoproteinemia, hypolipoproteinemia, predominant hypercholesterolemia, predominant hypertriglyceridemia, mixed hyperlipidemia, and lipoprotein (a) elevation.
    • Further subcategories exist for each of these categories.

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    Lipoprotein Metabolism PDF

    Description

    This quiz dives into the fundamentals of lipoprotein metabolism, detailing the types of lipoproteins, their synthesis, and function. It also covers the role of apolipoproteins and exogenous lipid pathways in the body. Test your knowledge on these critical processes in lipid management.

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