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Intro to Lipids Classification of Lipids Lipid Tests Clinical Significance of Lipids and Lipoproteins

Lipid

A diverse group of biological molecules of varying composition that are all soluble in nonpolar solvents.

Fatty Acid

Long hydrocarbon chains of various lengths that end with a carboxylic acid group (-COOH). A lipid.

Saturated Fatty Acid

Long chain monocarboxylic acids with the general formula CH3(CH2)nCOOH. They contain only carbon to carbon single bonds & carbon hydrogen bonds.

Unsaturated Fatty Acid

Long chain monocarboxylic acids that contain one or more carbon to carbon double or triple bonds. This structure will not be 100% saturated w/ hydrogen atoms (hence unsaturated).

Phospholipids

Combination of a lipid and a phosphate group; a major form of lipid in cells.

Phosphoglyceride

Phospholipids derived from a glycerol.

Steroids

A naturally occurring family of lipids of importance to medicine. High molecular weight lipids that all contain a nucleus of 17 carbons over 4 fused rings of carbon atoms with two methyl groups.

Steroid Functions

Critical component of membranes, important to maintain membrane fluidity, serve as hormones, and are an integral component of bile acids.

Cholesterol

A common fat like steroid based alcohol found in animal fats. The most important steroid in animals. A major component of the cell membrane and provides memrane fluidity. A precursor for all steroid hormones.

Triglyceride (TG)

An organic compound consisting of three molecules of fatty acids esterfied to glycerol. Also called Triacylglycerol.

Glycerol

A liquid alcohol often found in the diet as a component of fat or triglycerides. Structural backbone onto which fatty acid molecules are attached to make triglycerides.

Lipoprotein

Combination of a lipid and a protein; major transportation form of lipids in the bloodstream. The lipid forms a hydrophobic core & the proteins form a hydrophilic surface. This allows the hydrophobic lipids to be efficiently transported within the hydrophilic environment of the bloodstream. 4 kinds classified by density.

Apolipoprotein

The protein component found in plasma lipoproteins.

Adipose

Fat stored within the body; stored within cells called adipocytes.

Lipase

An enzyme that hydrolyzes the ester linkage between glycerol and the fatty acids of triglycerides.

Glycolipids

Combination of a lipid and a carbohydrate group. Present on select cell surface membranes like brain and nervous tissue.

Metabolism

The sum of all biochemical reactions that occur within a cell. Includes the building up and breaking down of the four key biological molecules, carbohydrates, proteins, lipids, and nucleic acids.

Cortisol

Steroid hormone secreted from the adrenal gland when the human body is under stress. Helps the body deal with the stress by RAISING the blood glucose levels by increasing lipolysis and depressing the immune system.

Anabolic Steroids

Resemble testosterone in structure; Artificially stimulate the body to increase the amount of muscle mass, stimulate the healing of damaged muscle, and often increase competitive aggressiveness.

Major Lipids of the Human Body

Dietary Lipids and Biosynthesized (Lipid anabolism)

Dietary Lipids

Exogenous from the food an average person ingests, absorbs, and transports.

Biosynthesized (Lipid Anabolism)

Endogenous, made from the body in the cytoplasm when supplies exceeds demand and are stored in the adipocytes for later usage.

Exogenous Pathway

Occurs in three stages: Digestive, Absorption, and Transport.

Lipoprotein Lipase (LPL)

An enzyme present on the capillary surface. It Catalyzes the hydrolysis of triglycerides in the chylomicrons.

Chylomicrons

Very large lipoproteins formed after ingestion of dietary fat and contain mostly triglycerides; largest and least dense of the lipoprotein particles.

Chylomicrons

Formed in the intestinal mucosa, they are transported by the lymphatic system ot the bloodstream. Transport deitary triglycerides, cholesterol, fat soluble vitamins, and other lipids from the intestine to the liver and adipose tissue.

Chylomicrons

Presence of this after a meal often causes serum to have a milky appearance (lipemia) after a phlebotomy draw.

Very Low-Density Lipoproteins (VLDL)

Synthesized in the liver. Transports triglycerides produced in the liver to extra hepatic tissues such as adipose and muscle. Major carrier of endogenous triglycerides. Excess dietary intake of carbohydrate intake is converted to VLDL by the liver for storage.

Low Density Lipoproteins (LDL)

Transport cholesterol and cholesterol esters to the peripheral tissues and regulate de novo (new) synthesis of cholesterol at these sites. Contains more cholesterol and cholesterol ester than triglyceride in the lipoprotein core.

Low Density Lipoproteins (LDL)

Bad cholesterol. Permeate into the extracellular space of the vessel wall, where they can be oxidized & taken up by macrophages. Macrophages that take up too much lipid become filled with intracellular lipids and transform into foam cells.

High Density Lipoproteins (HDL)

Synthesized in the liver. Transports cholesterol from the peripheral tissues back to the liver for excretion in the bile. The smallest and most dense lipoprotein particle.

High Density Lipoproteins (HDL)

Good Cholesterol. The function of the reverse cholesterol pathway is to remove excess cellular cholesterol from peripheral cells and return it to the liver. Since most peripheral cells do not catabolize cholesterol, it can become toxic therefore HDL aids in cholesterol homeostasis.

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