Stacy Gaugler and Lindsey Heiser April 28,2011. The third major class of lipids is the steroids. They are compounds containing: ◦ 17 carbon atoms.

Stacy Gaugler and Lindsey HeiserApril 28,2011

The third major class of lipids is the steroids.

They are compounds containing:◦ 17 carbon atoms ◦ 1 five-membered ring◦ 3 six-membered rings

Steroids are closely related in structure but highly diverse in function.

The most abundant and most important steroid in the body.

Only a small change in steroid structure can lead to large changes in hormonal action.

Cholesterol is also used to build cell membranes, many of which contain about 25% by mass of this steroid.

Our livers make cholesterol that satisfies our needs without dietary consumption.

Cholesterol is converted into many different compounds.◦ Progesterone: helps control menstrual cycle and

pregnancy

◦ Testosterone: Male sex hormone

◦ Estradiol: Female sex hormone

Cholesterol, along with fat, is carried along by lipoproteins.

A lipoprotein is best defined as: spherically shaped clusters containing both lipid molecules and protein molecules.

Picture of VLDL

High-density lipoprotein (HDL) (Good Cholesterol)-◦ Consists of about 33% protein and about 30%

cholesterol.

Low-density lipoprotein (LDL) (Bad Cholesterol)-◦ Contains only 25% protein and 50% Cholesterol.

Very-low-density lipoprotein (VLDL)-◦ Mainly carries triglycerides, which are fats,

synthesized by the liver.

Chylomicrons-◦ Carries dietary lipids synthesized in the intestines.

The transport of Cholesterol starts out as a VLDL particle.

When the fat is removed from the VLDL particle it becomes LDL.

The LDL carries the cholesterol to the cells, where specific LDL:◦ Receptor molecules line the cell surface in certain

concentrated areas called the coated pits.

If the LDL receptors are not sufficient in number, cholesterol accumulates in the blood.◦ This can happen even with a low intake of dietary

cholesterol◦ Genetics and Diet play a big role in determining

cholesterol levels in the blood.

High-density lipoproteins transports cholesterol from peripheral tissues to the liver and transfers cholesterol to LDL.

The free cholesterols in HDL are converted to cholesteryl esters, while in the serum.

The cholesterol uptake from HDL differs from that noted with LDL.

Note:◦ It is desirable to have a high level of HDL in the

blood because of the way it removes cholesterol from the bloodstream.

*Cholesterol is insoluble in water. If your level of cholesterol is elevated in the

blood serum, plaque-like deposits may form on the inner surfaces of the arteries.

The resulting decrease in the diameter of the blood vessels may, in turn, decrease the flow of blood.◦ Athersclerosis can result from this.

Athersclerosis if accompanying high blood pressure may lead to:◦ Heart Attack◦ Stroke◦ Kidney Dysfunction

Athersclerosis may increase the chance of blockage of some arteries by a clot at the point where your arteries are constricted by the plaque.

Once constricted they may deprive the cells of oxygen, which may cause them to stop working. ◦ The death of the heart muscles due to oxygen deprivation

is known as myocardial infarction.

The most common drug treatment to prevent it still involves the reduction of serum cholesterol by:◦ Preventing absorption from the

intestines◦ Inhabiting cellular synthesis of

this steroid. These treatments can

decrease serum cholesterol levels by about 50%.

It is generally considered desirable to have high levels of HDL and low levels of LDL in the bloodstream.

HDL levels can be increased by exercise and weight loss.

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