LIPIDS. 2 Flashcards
LIPID METABOLISM
what are the 2 roles of lipids in the human body
- They are a rich source of energy and an efficient way for the body to store excess calories.
- They play an important structural role in cells as integral parts of cell membranes
Describe the dual role of lipids in the human body.
Lipids serve as both a rich source of energy and an efficient way to store excess calories.
What are the 4 principal lipids found in cells
- triglycerides
- phospholipids 3.cholesterol
- cholesteryl esters
Identify the principal lipids transported by lipoproteins
The lipids transported by lipoproteins include triglycerides, phospholipids, cholesterol, and cholesteryl esters
what is the role of pancrease lipase during the process of didestion
During the process of digestion, pancreatic lipase cleaves off fatty acids, converting dietary lipids into more polar compounds
What enzyme is responsible for cleaving off fatty acids during digestion?
Pancreatic lipase
How are dietary lipids converted into more polar compounds?
Triglycerides are broken down into monoglycerides and diglycerides, while cholesterol esters are converted into free cholesterol. Phospholipids transform into lysophospholipids.
What role do bile acids play in lipid metabolism?
Bile acids form micelles with lipids in the intestinal lumen, aiding their absorption.
How does cholesterol absorption occur?
Cholesterol absorption can happen via passive transfer or be mediated by the NPC1L-1 transporter.
What function do ABCG5 and ABCG8 transporters serve?
These transporters prevent excess absorption of dietary cholesterol and plant sterols.
split triglycerides
monoglycerides + diglycerides: cholesterol esters
what facilitates absorption of micelles (lysophospholipids + bile acids)
NPC1L-1
What doest NPC1L-1 transports
cholesterol
what transporters prevents excess absorption of dietary cholesterol and plant sterols
ABCG 5
ABCG 8
Explain exogenous pathway
- The newly synthesized chylomicrons in the iaskntestine enter the circulation by way of the thoracic duct to interact with proteoglycans, such as heparan sulfate
- The proteoglycans on capillaries also promote the binding of lipoprotein lipase (LPL), which hydrolyzes triglycerides on chylomicrons.
- The free fatty acids and glycerol generated by the hydrolysis of triglycerides by LPL can then be taken up by cells and used as a source of energy.
explain endogenous pathway
- Most triglycerides in the liver that are packaged into VLDL are derived from the diet after recirculation from adipose tissue
- A small fraction is synthesized de novo in the liver from dietary carbohydrate.
- VLDL particles, once secreted into the circulation, undergo a lipolytic process similar to that of chylomicrons.
- VLDL loses core lipids causing dissociation and transfer of apolipoproteins and phospholipids to other lipoprotein particles, primarily by the action of LPL.
- LPL activity results in converting VLDL to VLDL remnants or IDLs
- IDL persists for short periods of time and receives cholesterol esters from HDL in exchange for triglycerides via cholesteryl ester transport protein.
- About half of VLDL is eventually completely converted to LDL, and the remainder is taken up as VLDL remnants by the liver remnant receptors.
what is the difference between endogenous and exogenous pathway
- Exogenous pathway is from dietary sourses while endogenous the origin is the river
- In exogenous chylomicrons are formed in the intestinal epithelial cells (enterocytes) from absorbed fats and cholesterol while in endogenous pathway VLDL is repackaged in the liver from fats and cholesterol
- IN exogenous the lipoprotein lipase in peripheral tissues releases fatty acids and glycerol from chylomicronswhile in endogenous in peripheral tissue VLDL releases glycerol and fatty acids via LPL
- In exogenous chylomicron remnants are formed after unloading fats, and empty HDL is produced as a byproduct while in endogenous Empty HDL is produced as a byproduct.
- In endogenous VLDLs become smaller and transform into intermediate-density lipoproteins (IDLs)
How do newly synthesized chylomicrons enter circulation?
Chylomicrons enter circulation via the thoracic duct and interact with proteoglycans, such as heparan sulfate.
What role do proteoglycans play in capillaries during lipid metabolism?
Proteoglycans promote the binding of lipoprotein lipase (LPL), which hydrolyzes triglycerides on chylomicrons.
What are the products generated by LPL’s hydrolysis of triglycerides on chylomicrons?
free fatty acids and glycerol
Where are most triglycerides in VLDL derived from
Most triglycerides in VLDL come from the diet after recirculation from adipose tissue
How does VLDL undergo a lipolytic process similar to chylomicrons?
VLDL particles lose core lipids, leading to dissociation and transfer of apolipoproteins and phospholipids to other lipoprotein particles, primarily through LPL action
What is IDL, and how is it formed?
IDL (Intermediate-Density Lipoprotein) persists briefly after being formed from VLD
explain the reverse cholesterol transport pathway in simple terms
The Reverse Cholesterol Transport Pathway involves HDL (High-Density Lipoprotein) removing excess cholesterol from cells through various methods:
- HDL Role: HDL removes excess cholesterol from cells.
- Transport to Liver: Excess cholesterol is transported back to the liver.
- Excretion: It can be excreted into bile as free cholesterol or converted to bile acids.
- Cholesteryl Ester Formation: Free cholesterol binds to HDL and becomes trapped in lipoproteins after conversion to cholesteryl ester by LCAT (lecithin:cholesterol acyltransferase), which resides on HDL.
- Liver’s Role: The liver helps maintain overall cholesterol balance.1
explain the reverse cholesterol transport pathway
Reverse Cholesterol Transport Pathway:
1. HDL is believed to remove excess cholesterol from cells by multiple pathways
2. The principal way that peripheral cells maintain their cholesterol equilibrium
3. Excess cholesterol from peripheral cells is transported back to the liver, where it can be excreted into the bile as free cholesterol or after being converted to bile acids
4. Free cholesterol binds to HDL in the extracellular space, and it becomes trapped in lipoproteins after it is converted to cholesteryl ester by lecithin:cholesterol acyltransferase (LCAT), which resides on HDL
5.The liver acts as a buffer in helping the body maintain its overall cholesterol homeostasis
