Jiaogulan Herb
Cholesterol is a lipid
found in the cell
membranes of all tissues, and it is
transported in the blood
plasma of all animals.
Cholesterol is also considered a sterol
(a combination steroid
and alcohol).
Because cholesterol is synthesized by all eukaryotes,
trace amounts of cholesterol are also found in
membranes of plants
and fungi.
The name originates from the Greek
chole- (bile)
and stereos (solid), and the chemical
suffix
-ol for an alcohol, as researchers first
identified cholesterol in solid form in gallstones
by François Poulletier de la Salle in 1769.
However, it is only in 1815
that chemist Eugène
Chevreul named the compound "cholesterine".[2]
Most of the cholesterol is synthesized by the
body and some has dietary origin. Cholesterol is
more abundant in tissues which either synthesize
more or have more abundant densely-packed
membranes, for example, the liver,
spinal
cord and brain.
It plays a central role in many biochemical
processes, such as the composition of cell
membranes and the synthesis of steroid
hormones. Cholesterol is insoluble in blood,
but is transported in the circulatory system bound
to one of the varieties of lipoprotein,
spherical particles which have an exterior
composed mainly of water-soluble proteins. The
main types, low-density
lipoprotein (LDL) and high-density
lipoprotein (HDL) carry cholesterol from and
to the liver, respectively.
According to the lipid
hypothesis, abnormally high cholesterol levels
(hypercholesterolemia)
and abnormal proportions of LDL and HDL are
associated with cardiovascular
disease by promoting atheroma
development in arteries (atherosclerosis).
This disease process leads to myocardial
infarction (heart attack), stroke
and peripheral
vascular disease. As high LDL contributes to
this process, it is termed "bad
cholesterol", while high levels of HDL
("good cholesterol") offer a degree of
protection. The balance can be redressed with
exercise, a healthy diet, and
In blood
- See
also: Blood
cholesterol
Cholesterol is minimally soluble in water;
it cannot dissolve and travel in the water-based
bloodstream. Instead, it is transported in the
bloodstream by lipoproteins
- protein "molecular-suitcases" that are
water-soluble and carry cholesterol and triglycerides
internally. The apolipoproteins
forming the surface of the given lipoprotein
particle determine from what cells cholesterol
will be removed and to where it will be supplied.
Cholesterol is transported towards peripheral
tissues by the lipoproteins chylomicrons,
very
low density lipoproteins (VLDL) and low-density
lipoproteins (LDL). Large numbers of small
dense LDL (sdLDL) particles are strongly
associated with the presence of atheromatous
disease within the arteries. For this reason, LDL
is referred to as "bad cholesterol".
On the other hand, high-density
lipoprotein (HDL) particles transport
cholesterol back to the liver for excretion.
Having large numbers of large HDL particles
correlates with better health outcomes, and hence
it is commonly called "good
cholesterol". In contrast, having small
amounts of large HDL particles is independently
associated with atheromatous
disease progression within the arteries.
The 1987 report of National
Cholesterol Education Program, Adult Treatment
Panels suggest the total blood cholesterol level
should be: <200 mg/dl normal blood cholesterol,
200-239 mg/dl borderline-high, >240 mg/dl high
cholesterol.[6]
SEE
ALL INFORMATION PLEASE CLICK
| 
