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Questions and Answers
What does the resulting answer in mg/dL represent in the serum sample?
What does the resulting answer in mg/dL represent in the serum sample?
The amount of HDL in the serum sample.
What is the purpose of the centrifugation separation step?
What is the purpose of the centrifugation separation step?
It is not required in direct methods.
What is the function of the first reagent in Method one of direct methods?
What is the function of the first reagent in Method one of direct methods?
It is an antibody to apolipoprotein B-100 that binds LDL and VLDL in the sample.
What is the purpose of the second reagent in Method one of direct methods?
What is the purpose of the second reagent in Method one of direct methods?
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What is the function of the first reagent in Method two of direct methods?
What is the function of the first reagent in Method two of direct methods?
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What is the purpose of the second reagent in Method two of direct methods?
What is the purpose of the second reagent in Method two of direct methods?
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What type of specimen is used in HDL measurement methods?
What type of specimen is used in HDL measurement methods?
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What can interfere with precipitation methods?
What can interfere with precipitation methods?
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What is the advantage of direct methods over older methods?
What is the advantage of direct methods over older methods?
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What is the principle of the direct methods?
What is the principle of the direct methods?
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Study Notes
Lipids and Lipoproteins
- Lipids are compounds that yield fatty acids when hydrolyzed or complex alcohols that can combine with fatty acids to form esters.
- Lipids are carried in the bloodstream by complexes known as lipoproteins because they are not soluble in plasma water.
Fatty Acids
- There are two types of fatty acids: saturated and unsaturated.
- Saturated fatty acids have no double bonds in their hydrocarbon chain.
- Unsaturated fatty acids have one or more double bonds in their hydrocarbon chain, which cause a kink or bend in the chain.
Triacylglycerols
- Triacylglycerols are made up of three fatty acids ester-linked to glycerol.
Phosphoacylglycerols (Phospholipids)
- Phosphoacylglycerols are similar in structure to triacylglycerols, except one of the alcohols of glycerol is esterified by phosphoric acid instead of a fatty acid, forming phosphatidic acid (PA).
Steroids
- Steroids are based on a fused ring system, are rigid in structure, and have no ester linkages.
- Examples of steroids include hormones (testosterone, progesterone, estrogen) and cholesterol.
- Cholesterol is a common membrane lipid, almost exclusive to animal cells, and is very hydrophobic but amphiphilic.
Lipoproteins
- Lipoproteins are classified according to density and electrophoresis migration.
- Lipoproteins differ in their sizes, weights, chemical composition, and atherogenicity (association with heart disease).
- There are four main types of lipoproteins: chylomicrons, VLDL, LDL, and HDL.
Chylomicrons
- Chylomicrons are produced by the intestine and transport dietary lipid from the intestine to fat/muscle cells.
- They are the largest lipoproteins, mostly composed of lipid (almost 90% triglyceride), with 1% protein (mainly Apo-B48, C-II, and E).
VLDL
- VLDL is produced by the liver and transports liver-synthesized fat (mostly triglyceride) to fat/muscle cells.
- VLDL is mainly lipid (55% triglyceride), with 10% protein (Apo-B100, C-II, E), and remnants are cleared by liver Apo-B/E receptors.
LDL
- LDL is produced from IDL with a loss of Apo C-II and transports cholesterol to tissue.
- LDL is taken up by Apo-B receptors, and cholesterol is released; in the liver, this decreases cholesterol synthesis.
- LDL can also be taken up by scavenger receptors on macrophages, leading to the formation of foam cells.
HDL
- HDL is the smallest and most dense lipoprotein, synthesized by the liver and intestine.
- HDL is mainly protein (Apo A-I, A-II), with lipid (cholesterol, phospholipid), and is involved in "reverse transport" of cholesterol from tissue to liver.
Apolipoproteins
- Apolipoproteins are proteins that differ in composition from one lipoprotein class to another.
- Functions of apolipoproteins include activating enzymes involved in lipid metabolism, maintaining structural integrity of lipid/protein complex, delivering lipids to cells via recognition of cell surface receptors.
Laboratory Diagnosis and Reference Ranges
- Total Cholesterol: desirable < 200 mg/dL (< 5.2 mmol/L), borderline high 200-240 mg/dL (5.2-6.2 mmol/L), and high > 240 mg/dL (> 6.2 mmol/L).
- LDL cholesterol can be calculated or measured directly using methods such as Friedewald Calculation or Derived Beta-Quantification, or direct methods that selectively react with HDL cholesterol.
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Description
Test your knowledge of lipids and lipoproteins, including their classification, functions, and physiological changes. Covers apolipoproteins, lipoprotein function, and abnormalities in lipid metabolism.
