Lipids & Lipoproteins
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What are lipids?
Substances insoluble in water because they contain nonpolar C-H bonds.
What do lipids include?
Fats, steroids, phospholipids, others
What is the lipid composition of food?
98% TG (95% fatty acid and 5% glycerol) 2% cholesterol, phospholipids, steroids, fat soluble vitamins
List the functions of lipids
Energy source Hormone, hormone precursor Cell membrane components Assist in digestion
What are the three phases of lipid physiology?
Digestive phase Absorptive phase Transport phase
What happens on the digestive phase?
TG are broken down by lipase in the liver with the help of cholic acid from liver bile. Lipids are surrounded by bile acid which emulsifies them into micelles.
What happens in the absorptive phase?
Lipids are absorbed freely in the small intestine in the form of free fatty acids and monoglycerides (glycerol with one FA tail).
What is a monoglyceride?
Glycerol containing one FA tail.
What happens in the transport phase?
Long fatty acids and cholesterol are reassembled and transported as chylomicrons and moved through the lymphatic system of the small intestine , transported to tissue for use or storage. Short fatty acids are bound to albumin to head to all tissues as free fatty acids. They are moved out of adipose tissues after lipolysis from stored TG.
What is cholesterol?
Lipid made by hepatocytes of the liver fro, two acetate groups; acetatyl coa and acetoacetyl-coa. (90% of it)
What are the functions of cholesterol?
• Hormone precursor for cortisol, estrogen, testosterone. - Cell membrane constituent
How does cholesterol circulate?
In the form of cholesterol esters
In what form is cholesterol trasnsported?
HDL LDL
What about dietary cholesterol?
Only a small amount of it is absorbed.
Described the physiology of cholesterol
• Firstly, cholesterol must be solubilized (emulsified) into micelle form by bile acids (detergent) • After being absorbed, cholesterol is packed in chylomicrons. • Chylomicrons carry cholesterol to the liver and rest of the body.
What cells make cholesterol?
All cells, especially those of the liver.
What is the enzymatic committing and rate limiting step in the formation of cholesterol?
HMG COA reductase
What is the drug that usually inhibits this hmg coa reductase enzyme?
Statin
What happens to cholesterol in tissues?
Cholesterol is esterified and bound to a lipoprotein core in the circulation and moved into cells for various functions
What happens to cholesterol in the liver?
It is converted to bile acids in the liver, then recycled or excreted in feces.
What are triglycerides?
Lipids made up of fatty acid and glycerol. Can be long or short
What are the functions of triglycerides?
Organ insulation Energy source Storage (offering free FA to the Krebs cycle)
What percentage of stored fat is TG?
95%
What is the physiology of TG?
When eaten, they are digested by lipase, emulsified, and then reformed in the intestinal cells and packaged into chylomicrons.