Clinical Chemistry 1 - Lipids and Lipoproteins Flashcards

Comprehensive vocabulary flashcard set covering lipids, lipoproteins, laboratory measurement methods, apolipoproteins, electrophoretic mobility, clinical calculators, and clinical lipid disorders.

Lipids

Organic biomolecules composed primarily of carbon and hydrogen, and sometimes oxygen, which are insoluble in water but soluble in organic solvents such as chloroform and ether.

Lipoproteins

Spherical carrier complexes composed of lipids and proteins that transport water-insoluble lipids through the bloodstream.

Lipolysis

The metabolic process of breaking down stored lipids to produce energy in times of carbohydrate depletion.

Lipogenesis

The biochemical process involved in the formation and synthesis of lipids in the body.

Fat-Soluble Vitamins

Essential organic compounds (Vitamins A, D, E, and K) whose intestinal absorption depends on the presence and digestion of lipids.

Nonpolar Covalent Bonds

Chemical bonds formed by carbon-hydrogen ($\text{C-H}$) links in lipids, imparting hydrophobic properties and insolubility in water.

Organic Solvents for Lipids

Nonpolar chemical liquids, specifically chloroform and ether, capable of dissolving hydrophobic lipid molecules.

Fatty Acids

Linear chains of carbon-hydrogen bonds terminating with a carboxyl group ($\text{-COOH}$).

Carboxyl Group

The terminal acidic functional group ($\text{-COOH}$) present on fatty acid chains.

Short-Chain Fatty Acids

Fatty acid chains containing $4$ to $6$ carbon atoms.

Medium-Chain Fatty Acids

Fatty acid chains containing $8$ to $12$ carbon atoms.

Long-Chain Fatty Acids

Fatty acid chains containing more than $12$ carbon atoms.

Saturated Fatty Acid

A fatty acid chain containing no carbon-carbon double bonds ($\text{C=C}$), which tends to be solid at room temperature.

Unsaturated Fatty Acid

A fatty acid chain that contains one or more carbon-carbon double bonds ($\text{C=C}$).

Monounsaturated Fatty Acid

An unsaturated fatty acid containing exactly one carbon-carbon double bond ($\text{C=C}$).

Polyunsaturated Fatty Acid

An unsaturated fatty acid containing two or more carbon-carbon double bonds ($\text{C=C}$).

Cis Unsaturated Fatty Acids

Unsaturated fatty acids where spatial bends at double bonds cause them to form liquid oils at room temperature.

Triglycerides

Neutral fats consisting of three fatty acid molecules attached to one glycerol molecule by ester bonds; the primary storage lipid in human adipose tissue.

Glycerol

A three-carbon molecule containing three hydroxyl groups that forms the structural backbone of triglycerides and most phospholipids.

Ester Bonds

Covalent linkages formed between the hydroxyl groups of glycerol and the carboxyl groups of fatty acids in triglycerides and phospholipids.

Adipose Tissue

The primary human tissue dedicated to storing excess energy in the form of triglycerides.

Phospholipids

Lipids composed of a glycerol backbone, two fatty acids, and an attached phosphate group; major structural constituents of cell membranes.

Assessment of Fetal Lung Maturity

Clinical laboratory measurement of amniotic fluid phospholipid ratios used to determine if a fetus can survive delivery without respiratory distress.

Phospholipid Bilayer

The amphiphilic structural arrangement of cell membranes consisting of outer hydrophilic phosphate heads facing water and inner hydrophobic fatty acid tails facing each other.

Amphiphilic

Possessing both hydrophilic (water-attracting) polar regions and hydrophobic (water-repelling) nonpolar regions.

Hydrophilic Head

The polar, water-attracting phosphate region of a phospholipid molecule positioned on the exterior surface of lipid bilayers.

Hydrophobic Tail

The nonpolar, water-fearing fatty acid chains of a phospholipid situated internally within the lipid bilayer.

Lecithin

Phosphatidylcholine; the most abundant phospholipid in lipoproteins and cell membranes, constituting approximately $70\%$ of total phospholipids.

Sphingomyelin

A major membrane phospholipid ($20\%$ of total) derived from the amino alcohol sphingosine rather than glycerol, enriched in nerve sheaths, RBC membranes, and ocular lenses.

Sphingosine

An amino alcohol that forms the structural backbone of sphingomyelin instead of glycerol.

Acid Sphingomyelinase

A lysosomal enzyme responsible for converting sphingomyelin into ceramide.

Niemann-Pick Disease

A lysosomal storage disorder caused by a deficiency of acid sphingomyelinase, leading to massive accumulation of sphingomyelin in the liver, spleen, and other tissues.

Ceramide

The lipid compound formed when sphingomyelin is degraded by the enzyme acid sphingomyelinase.

Cephalin

A group of phospholipids constituting approximately $10\%$ of total phospholipids, including phosphatidylethanolamine, phosphatidylserine, lysolecithin, and inositol phosphatide.

Cholesterol

An unsaturated steroid alcohol consisting of four fused rings (A, B, C, D) with a polar hydroxyl group at position C3; serves as a precursor for bile acids, steroid hormones, and Vitamin D3.

Steroid Rings A, B, C, and D

The four fused hydrophobic carbon ring structures forming the core molecular framework of cholesterol.

Hydroxyl Group of Cholesterol

The polar, hydrophilic functional group present on ring A of cholesterol that faces outward to interact with water at membrane surfaces.

Primary Bile Acids

Cholic acid and chenodeoxycholic acid, which are synthesized from cholesterol in the liver and act as detergents to emulsify dietary fats in the intestine.

Cholic Acid

A primary bile acid synthesized in the liver from cholesterol to promote intestinal fat digestion and absorption.

Chenodeoxycholic Acid

A primary bile acid synthesized from cholesterol in the liver that assists in intestinal fat emulsification.

Vitamin D3 Conversion

The radiation-driven transformation of cholesterol in human skin upon sunlight exposure into active vitamin D3 to strengthen bones.

Lecithin-Cholesterol Acyltransferase

LCAT; a liver-synthesized enzyme activated by Apo A-1 that transfers a fatty acid from lecithin to unesterified cholesterol, converting it into cholesteryl ester.

Free Cholesterol

Unesterified cholesterol; the amphipathic form of cholesterol containing an unesterified polar hydroxyl group, located on the surface of lipoproteins.

Cholesteryl Ester

Esterified cholesterol; the completely hydrophobic storage form of cholesterol generated by LCAT esterification, located within the core of lipoproteins.

Lipoprotein Core

The internal hydrophobic region of a lipoprotein particle consisting of triglycerides and cholesteryl esters.

Lipoprotein Surface

The external amphipathic monolayer coat of a lipoprotein particle composed of unesterified cholesterol, phospholipids, and apolipoproteins.

Lipoprotein Size Range

The spherical diameter spectrum of human lipoproteins, ranging from $10\,nm$ to $1200\,nm$.

Arteriosclerosis

A vascular disease characterized by the thickening and narrowing of blood vessels, closely associated with elevated LDL and reduced HDL levels.

Apolipoproteins

Surface proteins on lipoproteins that provide structural integrity, serve as receptor ligands, and act as enzyme cofactors or inhibitors.

Anti-Atherogenic Property

The cardioprotective ability, specifically exhibited by HDL and Apo A-I, to remove excess cholesterol from peripheral cells and prevent arterial plaque formation.

Apo A-I

The primary structural protein of HDL ($28{,}000\,Da$) that activates LCAT and serves as an ABCA1 lipid acceptor.

Apo A-II

A structural apolipoprotein ($17{,}400\,Da$) located primarily on HDL with a normal plasma concentration of $20\text{--}50\,mg/dL$.

Apo A-IV

A structural apolipoprotein ($44{,}000\,Da$) present on chylomicrons, VLDL, and HDL with a plasma concentration of $10\text{--}20\,mg/dL$.

Apo B-100

A large structural protein ($5.4 \times 10^5\,Da$) synthesized by the liver, found on LDL and VLDL, which serves as the ligand for the LDL receptor.

Apo B-48

A truncated structural protein ($2.6 \times 10^5\,Da$) synthesized by the intestine, uniquely present on chylomicrons, which serves as the ligand for remnant receptors.

Apo C-I

A structural apolipoprotein ($6{,}630\,Da$) present on chylomicrons, VLDL, and HDL with a plasma concentration of $5\text{--}8\,mg/dL$.

Apo C-II

An apolipoprotein ($8{,}900\,Da$) located on chylomicrons, VLDL, and HDL that acts as an essential cofactor for lipoprotein lipase (LPL).

Apo C-III

An apolipoprotein ($9{,}400\,Da$) located on chylomicrons, VLDL, and HDL that acts as an inhibitor of lipoprotein lipase (LPL).

Apo E

A structural apolipoprotein ($34{,}400\,Da$) present on VLDL and HDL that serves as a ligand for the LDL receptor.

APOE4 Isoform

A specific genetic variant of apolipoprotein E associated with an increased risk of developing Alzheimer's disease.

Apo(a)

A structural glycoprotein ($(3\text{--}7) \times 10^5\,Da$) covalently linked to Apo B-100 in Lipoprotein(a) that acts as a plasminogen inhibitor.

Chylomicrons

The largest ($80\text{--}1200\,nm$) and least dense ($<0.93\,g/mL$) lipoproteins, produced in the intestine to transport exogenous dietary triglycerides.

Exogenous Triglyceride Pathway

The lipid transport pathway mediated by chylomicrons delivering absorbed dietary triglycerides from the intestines to peripheral tissues and liver.

Postprandial Turbidity

The milky or turbid appearance of blood plasma following a meal due to high concentrations of light-reflecting chylomicrons.

Creamy Top Layer

The floating layer of chylomicrons that separates at the top of a stored plasma sample left undisturbed overnight at $4\,^\circ\text{C}$.

Very Low-Density Lipoproteins

VLDL; triglyceride-rich lipoproteins ($30\text{--}80\,nm$, density $0.93\text{--}1.006\,g/mL$) synthesized by the liver to transport endogenous triglycerides.

Endogenous Triglycerides

Triglycerides synthesized in the liver from excess dietary carbohydrates and fatty acids, packaged into VLDL for systemic delivery.

Fasting Hyperlipidemic Turbidity

Plasma turbidity observed in fasting specimens primarily caused by elevated concentrations of VLDL particles.

Low-Density Lipoproteins

LDL; cholesterol-rich lipoproteins ($18\text{--}30\,nm$, density $1.019\text{--}1.063\,g/mL$) responsible for delivering cholesterol to peripheral tissues.

High-Density Lipoproteins

HDL; the smallest ($5\text{--}12\,nm$) and most dense ($1.063\text{--}1.21\,g/mL$) lipoproteins, synthesized by the liver and intestine, responsible for reverse cholesterol transport.

Reverse Cholesterol Transport

The physiologic pathway in which HDL extracts excess cholesterol from peripheral cell membranes and transports it to the liver for excretion.

HDL2

A larger, lipid-rich, and less dense subclass of HDL particles.

HDL3

A smaller, denser, and lipid-poorer subclass of HDL particles.

Lipoprotein(a)

Lp(a); an abnormal LDL-like particle containing Apo B-100 linked to Apo(a); elevated levels increase the risk for premature coronary heart disease and stroke.

Plasminogen Homology of Lp(a)

Structural similarity between Apo(a) and plasminogen, allowing Lp(a) to compete for binding sites, inhibit clot lysis, and promote thrombosis.

Lipoprotein X

LpX; an abnormal lipid-rich particle high in free cholesterol and phospholipids found in patients with obstructive jaundice or LCAT deficiency.

Obstructive Jaundice

A disease state caused by blockage of bile flow out of the liver, leading to the accumulation of abnormal Lipoprotein X in circulation.

Beta-VLDL

$\beta\text{-VLDL}$; an abnormal floating pre-beta lipoprotein rich in cholesterol that accumulates in Type 3 hyperlipoproteinemia.

Serum Specimen for Lipids

Serum collected in SST tubes, preferred for general lipid profile testing because it lacks fibrinogen interferences.

Fibrinogen Interference

Plasma protein artifact that can distort lipoprotein electrophoretic patterns and scatter light during spectrophotometric lipid assays.

EDTA Plasma for Lipoproteins

The anticoagulated blood sample preferred for specialized lipoprotein analysis using ultracentrifugation or electrophoresis.

Fasting Requirement for Lipid Testing

A required $12\text{--}14$ hour fast necessary for accurate measurement of triglycerides and calculated LDL cholesterol.

Chylomicron Clearance Time

The duration of $6\text{--}9$ hours required for circulating postprandial chylomicrons to be cleared from blood plasma.

Nonfasting Lipid Tests

Total cholesterol and HDL cholesterol measurements, which do not strictly require a fasting specimen.

Recumbence Posture Effect

A 20-minute recumbent position that can decrease serum concentrations of TC, LDL-C, HDL-C, Apo A-1, and Apo B by up to $10\%$.

NCEP Pre-Sampling Guideline

Standard practice requiring patients to sit for at least $5$ minutes prior to venipuncture to prevent hemoconcentration.

Hemoconcentration

A reduction in plasma volume relative to red blood cells, causing artifactual elevation of lipid test results.

Ultra-Low Storage Temperature

Preservation of serum or plasma samples at $-70\,^\circ\text{C}$ or lower for long-term lipid storage.

Short-Term Sample Storage

Storage of serum or plasma specimens at $-20\,^\circ\text{C}$ for up to one or two months.

Liebermann-Burchardt Reaction

A chemical colorimetric assay for cholesterol utilizing acetic anhydride, glacial acetic acid, and concentrated $\text{H}_2\text{SO}_4$ to form a green color.

Cholestadienyl Monosulfonic Acid

The green end-product compound produced in the Liebermann-Burchardt cholesterol reaction.

Salkowski Reaction

A chemical colorimetric method for cholesterol determination producing a red end-product compound.

Cholestadienyl Disulfonic Acid

The red end-product compound produced in the Salkowski cholesterol reaction.

GC-MS Cholesterol Method

Gas Chromatography-Mass Spectrophotometry; the definitive CDC reference method for measuring total cholesterol.

Abell, Levy and Brodie Method

The traditional reference chemical method for cholesterol using saponification with alcoholic KOH, hexane extraction, and Liebermann-Burchardt color reagent.

Cholesterol Oxidase Reaction

An enzymatic colorimetric reaction sequence commonly used in automated clinical analyzers to measure cholesterol.

Saponification

The chemical cleavage of ester bonds using alcoholic KOH to liberate cholesterol or fatty acids and glycerol.

CDC Reference Method for Triglycerides

A chemical method involving saponification with alcoholic KOH, extraction with chloroform, treatment with silicic acid, and measurement of a pink chromophore.

Van Handel and Zilversmith Method

A chemical colorimetric assay for triglycerides yielding a blue-colored chromogen.

Hantzsch Condensation

A fluorometric chemical method for triglyceride measurement that measures the fluorescent compound Diacetyl Lutidine.