13.9: What are Steroids?By- Katherine Kauffman

Vanessa Witmer

Brief Steroid InformationSteroids are the third major class of lipids.Their structure is basically four rings.It starts with three cyclohexane rings

connected together and ends with a fused cyclopentane ring.

Cyclohexane

Cyclohexane

Cyclohexa

ne

Cyclopentane

Cholesterol and YouCholesterol is the most important steroid in

the human body.Most people don’t really even think of

cholesterol as being a steroid.The one thing people ‘know’ about

cholesterol is that it’s bad but in actuality it is extremely necessary for human life.

Cholesterol Functions

Cholesterol has many functions one of which is to serve as a plasma membrane component in, for example, red blood cells.

Cholesterol is also a raw material for the synthesis of other steroids.

Ex- Sex hormones, adrenocorticoid hormones and bile salts.

Where does Cholesterol come from?Cholesterol is constantly going through your

blood and is in a dynamic state.So despite the fact people try and stay away

from cholesterol you can’t really escape from it.Your liver is currently making cholesterol that

satisfies your needs even if you aren’t eating anything that contains cholesterol.If cholesterol level goes over 150 mg/100 mL,

cholesterol synthesis in the liver is reduced to half the normal rate of production.

Gallstones are basically pure cholesterol.

LipoproteinsCholesterol is hydrophobic as are esters of

cholesterol.Due to being hydrophobic , cholesterol needs

a water-soluble carrier to go through the blood.

This carrier is none other then the lipoproteins

Lipoproteins contain both lipid and protein molecules and not only transports cholesterol but fat as well.

There are four different types of lipoproteins

High-density LipoproteinsAbbreviated HDL and also called ‘good

cholesterol’HDL consists of 33% protein and 30%

cholesterolHDL particles are able to remove cholesterol

from arteries and send it back to the liver.A person with high HDL levels is less likely to

have cardiovascular disease while people with lower levels of HDL are at risk for the disease.

Women in the pre-stages of menopause have more HDL then men.

This puts women at a lower risk for coronary heart disease.

Low-density LipoproteinsAbbreviated LDL also called ‘bad cholesterol’Contains 25% protein and 50% cholesterolHigh levels of type B LDL particles are shown

to increase the risk heart disease and other health problems.

Type A LDL particles due the exact opposite.

Very-low-density lipoproteinsAbbreviated VLDLVLDL’s mainly carry triglycerides that are

synthesized by the liver.VLDL’s transport not only triglycerides but

also phospholipids, cholesteryl esters and of course cholesterol.

ChylomicronsChylomicrons carry dietary lipids that are

synthesized in the intestines.They consist of 85%-92% triglycerides6%-12% phospholipids1%-3% cholesterolAnd 1%-2% proteinsThey are produced in the absorptive cells on

the small intestines.

Transportation of Cholesterol From VLDL to LDLWhen cholesterol is transported from the

liver, it starts as a VLDL particle.The VLDL core has triglycerides, cholesteryl

esters, and cholesteryl linoleate.The core of VLDL is surrounded by a polar

coat of phosolipids and proteins.When capillaries reach muscle of fat,

proteins, except apoB-100, are removed from the VLDL, and the lipoprotein shrinks and leaves only cholesteryl esters, turning it into an LDL.

Cholesterol in LDLLDL’s carry cholesterol to the cells that have

LDL-receptors that line the cell surface in concentrated areas (coated pits).

The LDL proteins bind the LDL receptors in the coated pits.LDL is then taken into the endocytosis (inside) of the cell and are broken down by enzymes.

Cholesterol in LDL The cholesterol is separated from the

cholesteryl esters and then used as a component of the membrane.

Cholesterol builds up in blood when the LDL receptors don’t have the right amount in number.

Genetics and diet both determine cholesterol levels in the blood.

How HDL moves cholesterolHigh-density lipoproteins move cholesterol

from the peripheral tissues to the liver and moves the cholesterol to the LDL.

Free cholesterols in HDL are turned into cholesteryl esters when in the serum.

Bile acids and steroid hormones are synthesized in the liver from the esterfied cholesterols.

How HDL moves cholesterolThe HDL sticks to the liver cell surface and

moves the cholesterol ester to the cell in a selective lipid uptake.

The HDL reenters the circulation after it has been taken from the lipid content.

You want high HDL levels in the blood because it removes cholesterol from the blood stream.

Levels of LDL and HDLCholesterol is insoluble in waterWhen cholesterol is high, plaque deposits

form on the inner surfaces of the arteries and can slow blood flow (atherosclerosis)

Atherosclerosis and high blood pressure leads to heart attack, stroke, or malfunctioning kidneys

Levels of LDL and HDLMyocardial infarction- the death of a heart

muscle because of lack of oxygenCholesterol is usually transported in low-

density lipoproteins When the concentration of cholesterol in a

cell is low, the synthesis of LDL receptors increases

Levels of LDL and HDLFamilial hypercholesterolemia is a disease

where the cholesterol level in the plasma is 680 mg/100 mL, which is unlike normal levels.

The normal level is 175 mg/100 mL.When a person has a high LDL level and a

low HDL level it means that there was a faulty cholesterol transport and are at risk for atherosclerosis.

It is best to have high HDL levels and low LDL levels in the bloodstream.

Serum Cholesterol LevelsThe amount of cholesterol synthesized in the

liver is determined by the serum cholesterol level.

Synthesize of cholesterol is low when the serum cholesterol level is high.

Synthesize of cholesterol is high when the serum cholesterol level is low.A low cholesterol diet can lower the serum

cholesterol level and some drugs can inhibit the synthesis of cholesterol.

LDL DrugsStatin drugs block the synthesis of

cholesterol in cells which leads to the synthesis of LDL receptor proteins.

Example of some statin drugs- Lipitor and Zocor

The more LDL in the cells the lower amount of cholesterol in the arteries.