1. 13.9 Cholesterol

2. Cholesterol Most abundant steroid in the human body
Two main functions:
Plasma membrane in all cells
Example: red blood cells
Raw material for synthesis of other steroids
Example: sex and adrenocorticoid hormones
Exists in free form and esterified with fatty acids
Example: gallstones contain free cholesterol

3. Necessary for human life
A body’s liver manufactures cholesterol to satisfy needs without dietary intake
Reduces production rate by half if cholesterol level exceeds 150mg/100mL
Cholesterol is constantly circulating in blood
Need water-soluble carrier to circulate in the aqueous medium of blood

4. *Lipoproteins: carriers of cholesterol
Cholesterol is transported by lipoproteins
4 kinds of lipoproteins
High-density lipoprotein (HDL) “Good Cholesterol”
Consists about 33% protein & 30% cholesterol
Low-density lipoprotein (LDL) “Bad Cholesterol”
Contains only 25% protein, but 50% cholesterol

5. Very-low-density Lipoprotein (VLDL) Chylomicrons
Carries triglycerides (fats) synthesized by the liver
Chylomicrons
Carry dietary lipids synthesized in the intestines

6. Transportation of Cholesterol in LDL
Transports cholesterol from liver starts as VLDL
Contains: triglycerides, cholesterol esters, cholesteryl linoleate
Surrounded by phospholipids and proteins
Carried to serum
Fat is removed, and density increases

7. LDL carries cholesterol to the cells
LDL receptors line the walls in concentrated areas
Coated pits
Enzymes break down the now formed lipoprotein
Freeing cholesterol from cholesteryl esters
Without a sufficient number of LDL receptors, cholesterol would accumulate in the blood

8. *Transportation of cholesterol in HDL
HDL transports cholesterol from peripheral tissues to the liver
Transfers cholesterol to LDL
Good to have a high level of HDL
Removes cholesterol from blood stream
Section D

9. *Levels of HDL and LDL Insoluble in water
Most cholesterol is transported by LDL
High cholesterol inside cells cause the synthesis of LDL receptor to reduce
And vice versa
High levels of LDL and low levels of HDL are symptoms of faulty transport
Greater risk of atherosclerosis
Leads to heart attack, stroke, of kidney dysfunction

10. Serum cholesterol levels control amount synthesized by liver
High levels mean that synthesis is low
Low levels mean that synthesis is high
High levels of HDL are good, and low levels of LDL
Atherosclerosis
Plaque build-up in the arteries that decrease blood flow
My cause heart attack, stroke, of kidney dysfunction