What's Cholesterol?

Cholesterol is the most abundant sterols that the body requires as a  building block for cell membranes & hormones. The structure of cholesterol (C17H46O)-

Structure of cholesterol

Sources: 

Exogenous (Dietary)-The richest sources are egg yolk, red meat, liver, kidney, butter & brain.
Endogenous- Every cell can synthesize its own cholesterol. Plasma cholesterol is synthesized in the liver & intestine from fats, carbs & proteins.

Distribution of cholesterol:

It is widely distributed in all tissues but higher concentrations are present in the nervous tissue, liver, adrenals, gonads, skin & adipose tissue.

Plasma level of cholesterol: 

Normally it ranges from 120-200 mg/dL (30% as free cholesterol & 70% as cholesteryl-esters).

Excretion:  

It is mainly excreted from the body in bile in the form of bile salts. Less amounts are excreted as cholesteryl-esters & dihydrocholesterol.  In the large intestine cholesterol is reduced by intestinal bacteria to give coprostanol which is excreted mainly in stool.

Functions of cholesterol : 

1. It is converted into bile in the liver. Bile aids in digestion. It breaks down fats into fatty acids, which can be taken into the body by the digestive tract.
2. Precursor of steroid hormones including corticoids, sex hormones.
3. Essential for making the cell membrane & cell structures
4. Helps to maintain the integrity & fluidity of cell membranes.  At temperatures, cholesterol makes the membrane less fluid by limiting the movement of phospholipids. At low temperature cholesterol decreases the close packing of phospholipids, increasing fluidity & decreasing gel formation.
5. Important for vitamin D synthesis
6. It insulates nerve fibers