Stacy Gaugler and Lindsey Heiser April 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.

 Any Further Questions?