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Low density lipoprotein or LDL containing 47% cholesterol. Form of VLDL triglycerides and lose that free protein. Are the main transporter of cholesterol to tissues. LDL can be oxidized becoming harmful agents capable of initiating the atherosclerotic lesion.

Therefore, high levels of LDL are inconvenient in that it represents a higher probability of generating potentially harmful oxidized LDL particles.

High density lipoprotein HDL, contain proportionately more protein, 50% and 19% mostly esterified cholesterol. Are heterogeneous, several subclasses have been described, according to their density and protein composition. They are formed in the liver and intestine as small particles, rich in proteins, which contain relatively little cholesterol.

After release into the bloodstream, the nascent HDL collected free cholesterol, phospholipids and apoproteins of other lipoproteins such as chylomicrons and VLDL. They bind to the cell surface of peripheral tissues and induce the transfer of free cholesterol

from the cell into the particle. Thus, nascent HDL is converted to mature HDL, high cholesterol, which deliver cholesterol to the liver and steroidogenic tissues (adrenal gland, ovaries and testes). In the liver, cholesterol is mainly used for bile secretion, as well as free cholesterol or bile salts.

Mobilized cholesterol by HDL from peripheral tissues to the liver is the phenomenon known as reverse cholesterol transport. The beneficial effect of high levels of HDL cholesterol is derived from the ability of HDL to remove excess cholesterol from peripheral tissues and return it to the liver for disposal.

Source: www.bio.puc.cl/vinsalud/boletin/42hdl.htm
image source: http://futurity.org/wp-content/uploads/2010/05/good_cholesterol.jpg