Cholesterol metabolism

Ultra simplified explanation of the regulation of cholesterol in the organism. 

The objective is quite straightforward, the process aims to keep cholesterol levels at figures commensurate with the body requirements.

Therefore, as provided by the diet (external cholesterol ) is what is consumed daily and, depending on the food type, mobilizes a very complex mechanism that regulates the formation of cholesterol from the body (synthesis) and the removal of cholesterol excess, if any. 

Cholesterol that is consumed passes from the intestine to the liver, transported as lipid or fat particles, through special vessels and is released from the liver into the blood, where is carried by special proteins that form the complexes known as lipoproteins (LDL and VLDL) . Another complex, the HDL leads cholesterol  back to the liver for disposal. 

Organic synthesis (less than half of total cholesterol) is carried out in cells of the liver, intestine and to a lesser extent in cells of other organs, based on what is known as the energy cycle. Within these cells, at specialized sites in the cytoplasm. Part of the cholesterol produced turns to blood and the rest is stored in the cytoplasm, free or in capsules. 

Excess cholesterol is eliminated from the body through just an unique path, the bile, either as free cholesterol or converted into biliar acids. 

The amount of cholesterol in blood is regulated, as noted earlier, by several parallel mechanisms involved, blood level receptors or detectors, endocrine glands, hormones, special genes, enzymes and small intracellular organs. 

The outer surface of the cell membrane, in contact with bloodstream, has special extensions (like tiny wires) that "measure" continuously blood cholesterol level. These sensors give notice to the involved endocrine glands, pancreas and adrenal, which, depending on the situation, release hormones to increase or decrease cholesterol production in the cells (synthesis). To emphasize that, owing to its importance, one of the hormones involved is insulin. 

These hormones control the exposure of specific genes and the reading of genetic information (transcription) that stimulate (if necessary) enzymes production, which act as accelerators for the 

cholesterol production and its precursors or promoting HDL to remove cholesterol from the bloodstream. 

The reading of genetic information and the production of these enzymes, is carried out in small organs of the cytoplasm and the nucleus almost permanently, something very difficult to imagine, as a factory with an enormous amount of workers that do not stop at any time. They have periods of greater and lesser activity, but the alert and the mechanisms are always active. 

A similar but somewhat simpler mechanism, occurs in the liver for bile formation and cholesterol incorporation. 

I ask the scientists' indulgence and the readers' understanding due to that to write this post on the metabolism of cholesterol, I have had to shorten explanations so its accuracy and clarity are not the best.