Cholesterol

Cholesterol, a steroid alcohol, can be “free” or “unesterified” (“UC” as we say, which stands for unesterified cholesterol) which is its active form, or it can exist in its “esterified” or storage form which we call a cholesterol ester (“CE”). The diagram below shows a free (i.e., UC) molecule of cholesterol. An esterified variant (i.e., CE) would have an “attachment” where the arrow is pointing to the hydroxyl group on carbon #3, aptly named the “esterification site.”

Cholesterol is an unusual substance. Waxy and fat-like, it's classed as a steroid, a lipid (lipids are water insoluble hydrocarbons, like fat) and as an alcohol (normally water soluble). Curiously, it's almost completely resistant to water's solvent charms. 

This moisture-proof characteristic is one of the many properties that make it such an important component of our cellular environment. Let's look at a few of the roles it plays in our bodies before we examine how it got such a bad rap.

It's present in all of our cell walls, providing watertight integrity and structural support, and is especially essential to electrically conductive nerve and brain cells- we can't have moisture and wayward ions seeping in and short-circuiting things. 

This might explain why the nervous system is such a large repository of cholesterol, and why a diet that includes adequate amounts of it is a must for infants and small children with growing brains. Luckily, both human and bovine (cow's) milk contain plenty of it for just this purpose. 

Mood and behavior are also apparently linked to proper blood levels. Studies have shown a decrease in the number of serotonin receptors as cholesterol levels lower. Serotonin is a key neurotransmitter which figures heavily in depression, among other things.

Our digestive system relies heavily on bile salts to help emulsify and digest fats. The liver makes about a quart of these a day (just under a liter) with cholesterol as a major ingredient, storing a concentrated version in the gall bladder for controlled release as foods (especially fatty ones) enter the small intestine. 

Through a complex system of hormonal checks and balances, our bodies know when to make more cholesterol, and when to back off as dietary supply meets daily needs.

Forming the backbone for numerous steroid hormones manufactured in the ovaries, testicles and adrenal glands, cholesterol plays a critical role in controlling the body's stress response, defense system, sexual development, and numerous other metabolic functions.
(At right, sex hormone testosterone. Notice four ring structure typical of all steroids).