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Friday, December 19, 2014

LDL Cholesterol (Bad) And HDL Cholesterol (Good)

What is cholesterol ?


Cholesterol is an organic compound and a fatty substance. Cholesterol belongs to the group of the sterols (modified steroids). It is an essential building block in the development of animal cell membranes where it is a celverstevigend element and contributes significantly to the permeability of the cell membrane.

Cholesterol is the building block of steroid hormones, vitamin D and bile. Gallstones consist of 80% cholesterol.

In animals, acts as primary sterol cholesterol: cholesterol synthesis in vertebrates occurs mainly in the liver, and in small amounts in the adrenal and intestine. In the testes, it is produced by the endoplasmic reticulum.

Plants, fungi, bacteria and the membranes of mitochondria contain no cholesterol. But they have other, structurally similar to cholesterol, sterols.

Cholesterol is only 2% directly absorbed from the diet.

Cholesterol Transport in the body


Lipids (including cholesterol and fat) are not soluble in water. Therefore, these substances are transported in the blood by means of lipoproteins: small spheres having a hydrophobic interior consisting of triglycerides and cholesterol esters surrounded by a hydrophilic exterior consisting of phospholipids and apoproteins. Lipoproteins are classified according to fractions having difference in density. Lipoproteins from low to high density are: chylomicrons, very-low-density-lipoprotein (VLDL), intermediate-density lipoprotein (IDL), low-density-lipoprotein (LDL) and high-density-lipoprotein (HDL).

In the liver, cholesterol is formed. This is used together with triglycerides packed in a VLDL-particle, after which it is released into the blood. In the blood, the VLDL particles are smaller due to the activity of the lipoprotein lipase, triglycerides which liberates from these particles. These triglycerides can be absorbed by the tissues. Eventually these LDL particles, which then mainly contains cholesterol. 70-80% of the LDL is taken up in the liver, adrenal glands and the gonads (testes and ovaries). The LDL that remains in the bloodstream, is finally taken up by cells (macrophages / foam cells), which can provide fatty degeneration of the vessel wall by lodging in the vessel wall (atherosclerosis). LDL cholesterol is sometimes called "bad" cholesterol, because high concentrations of LDL is a marker can cause the risk of heart attack and ruptured blood vessels.

HDL allows for transport of "excess" cholesterol from cells back to the liver (reverse cholesterol transport). HDL is formed in the liver, where it ends up in the blood circulation and absorbs cholesterol from the cells. For this purpose it is a compound with ATP-binding cassette transporter A1 (ABCA1). Cholesterol is removed in the liver from the HDL via the scavenger receptor-BI (SR-BI). In the liver, cholesterol in the bile from the body to be removed. HDL is also called "good" cholesterol, because an increased concentration of HDL associated with a reduction in the incidence of cardiovascular disease.

The role of HDL is more complex, it also plays a role in inflammation, infections, blood clotting, and even more processes.

Hyperlipidemia


Elevated cholesterol levels in the blood is called hypercholesterolemia. Hypercholesterolemia is a part of a group of disorders that are mentioned in the medicine hyperlipidemias. In hyperlipidemias are in the patient increased concentrations of cholesterol and / or triglycerides found in the blood. These hyperlipidemias are classified into primary and secondary hyperlipidemias:

-Primary: familial hypercholesterolemia, familial defective ApoB100, polygenic hypercholesterolemia, familial dysbetalipoproteinemia, familial combined hyperlipidemia, familial hypertriglyceridemia, familial apoCII Lipoprotein lipase deficiency or deficiency (and other, rarer forms).
-Secondary: kidney disease, liver disease, thyroid disease, diabetes mellitus, Cushing's syndrome, use of glucocorticoids, dysglobulinemie, acute intermittent porphyria and (excessive) alcohol.

The doctor always close all forms of secondary hyperlipidemia, before he starts searching for the primary forms of hyperlipidemia. In the group of primary hyperlipidemias a number of inherited disorders present and some that are inherited as well as depending on lifestyle.

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Lipid profile


In order to check whether there is a disorder is a lipid profile is determined in the fat metabolism. This means that the concentration of cholesterol and triglycerides in the blood is determined. The tests which are hereby be carried out are:

-Total cholesterol
-HDL cholesterol
-LDL cholesterol
-Triglycerides
-Ratio cholesterol / HDL

Since the concentration of triglycerides in the blood to a large extent determined by the concentration Chylomicrons in the blood, which immediately after a meal are quite high, it is important that the patient is fasted. Also for the concentration of LDL, it is important that the patient is fasting since it is often calculated from the concentration of cholesterol, HDL and triglycerides. As a measure for the number of atherogenic particles APO-B100, the concentration may be used. For this test, the patient does not have to be sober.

Interpretation "good" and "bad"


For some time, it is known in the literature that HDL and LDL-cholesterol appear in different subclasses. HDL example, can be divided into five subclasses, with the biggest 3 if they contribute is that cardiovascular disease (CVD) less prevalent. The smaller two variants do not have this protective effect. For LDL does something similar. LDL is based on the type often separated into two categories: the "small dense LDL" (pattern B) and the "large buoyant LDL" (pattern A). Of small dense LDL (sdLDL) is known to be associated with an increased risk of the development of cardiovascular disease. The height of the plasma cholesterol concentration is a reflection of the amount present LDL. The amount of triglycerides corresponds to the amount of VLDL. At elevated triglyceride concentrations decreased HDL levels in the blood (negative correlation). The combination of "small dense LDL" low HDL levels and high triacylglycerol values one also calls it "atherogenic lipoprotein profile" meaning (roughly translated) the "atheromabevorderende blood lipid profile," and this condition is partly hereditary. The opposite is also true, the combination of larger particle LDL, increased HDL concentration and reduced triglyceride levels in the blood gives a significant reduction in the risk of atherosclerotic diseases and cardiovascular diseases in general. The evaluation of hyperlipidemias and thus the risk of cardiovascular disease, the doctor watches on multiple laboratory results: HDL, LDL cholesterol, triglycerides and cholesterol / HDL ratio. On the basis of this data in combination with data from the Standard Cardiovascular Risk, the doctor looks at the potential for the development of cardiovascular diseases and, if necessary, a matching set for therapy.

LDL size by the Adult Treatment Panel III (US) is increasingly seen as a relevant risk factor for heart - disease. It is certainly not just the cholesterol that affects the risk of cardiovascular disease; all kinds of properties of fats in the food and fats in the blood are important.

Cholesterol and cardiovascular disease


Some studies have shown in the 70 that increased levels of LDL are associated with a high risk of a heart attack. It should be noted that these studies have paid and are held by the pharmaceutical companies that sell cholesterol level lowering agents. HDL is assumed that it has a protective effect on cardiovascular disease, but there is little evidence to support this assumption.

By saturation of bile with cholesterol can precipitate cholesterol and gallstones may occur. In western countries are cholesterol stones about 80% of gallstones.

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