HDL and LDL cholesterol refers to the lipoproteins that carry cholesterol in the blood. HDL is a high-density lipoprotein (HDL for the acronym in English high density lipoprotein), while LDLs are low-density lipoproteins (LDL) low density lipoprotein).
This classification of lipoproteins is due to the technique used to separate it: ultracentrifugation. In this technique, the blood plasma is centrifuged at high speed in a tube and the lipoproteins are separated by their density, leaving the densest (HDL) at the bottom of the tube and the least dense (LDL and other lipoproteins) floating at different levels. of the tube.
Cholesterol is a lipid molecule that is not soluble in water. Lipoproteins are spherical particles composed of proteins and lipids that carry cholesterol and other lipids through the blood. The major lipoproteins in cholesterol transport are HDL and LDL.
|Definition||High density lipoprotein.||Low density lipoprotein.|
|Density (gr / ml)||1,063-1,210||1,019-1,063|
|Cholesterol||24-45% of total lipids.||47-51% of total lipids.|
|Diameter||120-70 angstrom||250 angstrom|
What is HDL Cholesterol?
HDL or HDL cholesterol (HDL-C) are lipoproteins that transport cholesterol from cell membranes to the liver. They are also known as good cholesterol, although this statement is wrong, as HDL not only contains cholesterol.
Origin of HDL
HDL originates from the Apo A1 protein which is synthesized in extracellular space. This protein circulates through the tissues capturing cholesterol and phospholipids from the membranes, and once it enters the circulation, it exchanges proteins and cholesterol esters with other lipoproteins.
Characteristics of HDL
- It has a higher percentage of protein than lipids.
- Density between 1,063 and 1,210 gr / ml.
- Diameter from 70 to 120 angstroms, is the smallest of the lipoproteins.
Structure of HDL
HDL, like other lipoproteins, is a spherical particle, made up of:
- An outer layer of phospholipids, proteins and cholesterol.
- A hydrophobic liquid center with triglycerides and cholesterol ester.
HDL proteins can be recognition proteins such as Apo A1 and Apo A2 and enzymes such as LCAT.
The main function of all lipoproteins is to solubilize fats in the blood. HDL is the lipoprotein responsible for transporting cholesterol from extrahepatic tissues to the liver. It is what is known as the reverse transport of cholesterol.
In the liver, cholesterol is converted into bile acids for elimination by the gut, or recycled.
HDL values in human blood
High HDL cholesterol levels are associated with protection against cardiovascular disease (CVD). Normal HDL values for an adult should be between 40 and 60 mg / dl (1.04-1.55 mmol / L in SI units). Values greater than 60 mg / dl are recommended to prevent CVD. HDL values below 40 mg / dl are high risk for CVD.
What is LDL cholesterol?
LDL or LDL cholesterol (LDL-C) are lipoproteins that transport cholesterol from the liver to extrahepatic tissues. They are also known as bad cholesterol, as high levels of this lipoprotein are deposited in the arteries, producing atherosclerotic plaque.
Origin of LDL
LDLs are derived from the VLDLs (much lower density lipoproteins that are larger and richer in triglycerides) that are formed in the liver. These VLDLs travel through the bloodstream, delivering triglycerides to the tissues. In this way, they are reduced in size and gain in cholesterol content, until they are transformed into LDL.
Characteristics of LDL
- It has a higher percentage of lipids than proteins.
- Density between 1,019 and 1,063 g / ml.
- Diameter around 250 angstrom.
- The characteristic protein of LDL is the apolipoprotein B100.
Structure of LDL
LDLs are also spheroidal particles, larger than HDLs. Present:
- an outer layer of phospholipids, cholesterol and Apo B100 protein.
- A fat center full of cholesterol and triglycerides.
The main protein in LDL is the apo B100, which is a recognition protein by cellular receptors.
LDLs carry cholesterol to the tissues that need it. VLDLs loaded with triglycerides and cholesterol come out of the liver. Triglycerides are released as they pass through the circulation. LDLs are the result of a reduction in the size of these VLDLs.
LDL apo B100 protein binds to cellular receptors and enters the cell by endocytosis. The cell can thus use cholesterol to form membranes and other compounds.
LDL values in human blood
Elevated LDL cholesterol levels are associated with cardiovascular disease (CVD). Optimal LDL values for an adult should be below 100 mg / dl (less than 2.6 mmol / L, SI). Values between 130-159 mg / dl (3.36-4.11 mmol / L, SI) are of extreme risk for CVD, while above 159 mg / dl. the person has a high risk of ECV.
People with high LDL levels should consult with their doctor to implement measures that lead to a reduction in cardiovascular risk.
Good cholesterol and bad cholesterol
Cholesterol is an important molecule for the functioning of animal cells and organisms. This compound is the precursor to steroid hormones, such as sex hormones and corticosteroids. In addition, it is part of the cell membranes, interspersed between the phospholipids of the lipid bilayer, regulating the fluidity of the membranes.
To say that there is good or bad cholesterol is an oversimplification of the role that transporter lipoproteins play. Cholesterol that builds up in the arteries promotes the formation of fat plaques or atheromas, leading to atherosclerosis.
Cholesterol-carrying lipoproteins in the arteries (LDL) are called bad cholesterol, while membrane-taking lipoproteins (HDL) are called good cholesterol.
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