1. By- Katherine Kauffman Vanessa Witmer

2. Brief Steroid Information Steroids 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 Cyclopentane

3. Cholesterol and You Cholesterol 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.

4. 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.

5. 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.

6. Lipoproteins Cholesterol 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

7. High-density Lipoproteins Abbreviated HDL and also called ‘good cholesterol’ HDL consists of 33% protein and 30% cholesterol HDL 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.

8. Low-density Lipoproteins Abbreviated LDL also called ‘bad cholesterol’ Contains 25% protein and 50% cholesterol High 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.

9. Very-low-density lipoproteins Abbreviated VLDL VLDL’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.

10. Chylomicrons Chylomicrons carry dietary lipids that are synthesized in the intestines. They consist of 85%-92% triglycerides 6%-12% phospholipids 1%-3% cholesterol And 1%-2% proteins They are produced in the absorptive cells on the small intestines.

11. Transportation of Cholesterol From VLDL to LDL When 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.

12. Cholesterol in LDL LDL’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.

13. 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.

14. How HDL moves cholesterol High-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.

15. How HDL moves cholesterol The 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.

16. Levels of LDL and HDL Cholesterol is insoluble in water When 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

17. Levels of LDL and HDL Myocardial infarction- the death of a heart muscle because of lack of oxygen Cholesterol is usually transported in low-density lipoproteins When the concentration of cholesterol in a cell is low, the synthesis of LDL receptors increases

18. Levels of LDL and HDL Familial 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.

19. Serum Cholesterol Levels The 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.

20. LDL Drugs Statin 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.