cholesterol
Meaning of cholesterol: There is no good or bad cholesterol, only good and bad carriers: the molecule is identical, and the particle transporting it differs.
Definition of cholesterol
Cholesterol is a waxy fat-like molecule that every animal cell needs. It stiffens and seals cell membranes and supplies the raw material for steroid hormones, vitamin D and the bile acids that digest fat. The liver makes most of what the body uses and food supplies the rest. Because it does not dissolve in water, it moves through blood inside protein-coated particles.
Why does it travel inside particles?
Blood is water, and fat does not mix with water. Cholesterol is therefore packaged into lipoproteins, droplets with a fatty core and a protein and phospholipid shell, and the routine cholesterol panel is really a measure of those particles rather than of the molecule loose in the blood vessel.
| Particle | Job | Association with arterial disease |
|---|---|---|
| LDL, low density lipoprotein | Delivers cholesterol from the liver to tissues | Higher levels track with more disease |
| HDL, high density lipoprotein | Collects surplus cholesterol and returns it to the liver | Higher levels track with less, though raising it by drugs has not proved protective |
| VLDL and chylomicrons | Carry triglycerides from the liver and the gut | Their remnants also enter the artery wall |
How does it damage an artery?
LDL particles cross into the artery wall, and the more particles there are in circulation, the more get in. Once inside they are chemically altered and scavenged by immune cells, which become bloated with fat and die there. The debris, muscle cells and calcium build a plaque beneath a fibrous cap. That plaque narrows the channel, and if the cap tears, a clot forms on the exposed surface and can close the artery within minutes.
What changes the level?
The liver adjusts its own production according to how much arrives from food, which is why swallowed cholesterol influences the blood level less than the amount of saturated and trans fat in the diet does. Body weight, physical activity, thyroid function, kidney and liver disease and several medicines all shift it. Genetics matters most at the extremes: familial hypercholesterolemia is an inherited fault in clearing LDL that produces very high levels from birth, long before any adult habit could account for them.
Used in a sentence
The lipid panel showed the patient's total cholesterol along with its major subtypes.
Good to know
Cholesterol is carried by several different particles, and those particles rather than the molecule itself account for the differing associations with arterial disease, which is why a lipid panel reports more than one number.
Word origin
Where “cholesterol” comes from
Formed from Greek chole, meaning bile, and stereos, meaning solid, reflecting its original identification in the solid material of gallstones.