Lipid metabolism Flashcards
1
Q
Where does most of the body’s lipids come from?
A
80% from synthesis in the liver
20% from intake
2
Q
Metabolism of lipids - transportation
A
- lipids are absorbed as triglycerides, packaged with cholesterol, triglycerides are dropped off with help of lipoprotein and stored in peripheral tissue. Cholesterol is taken back to liver. Cholesterol in the liver functions as a source of energy, production of bile salts, and production of cholesterol based hormones
3
Q
Where can lipids go once they are in the blood as lipoproteins?
A
- can be excreted in feces
- synthesized from carbs and proteins
- oxidized for energy
- converted to brain and nerve tissue
4
Q
What is function of lipids that are stored in the adipose tissue?
A
- used for insulation
- support vital organs
- generate heat
- serve as energy reserve
5
Q
What are lipids and what are the 3 main categories of lipids?
A
- chemical substances composed of long chain fatty acids
- triglycerides
- phospholipids
- cholesterol
6
Q
How are triglycerides used?
A
- used in energy metabolism
7
Q
Function of phospholipids?
A
- impt structural components of lipoproteins, blood clotting components, myelin sheath and cell membranes
8
Q
Function of cholesterol?
A
- precursor of steroid hormones
- necessary for cell membrane synthesis
- metabolic precursor of bile acids
- obtained from diet and synthesized in liver and intestinal mucosa
- elevated levelare implicated in development of atherosclerosis
- est 41 mill Americans have significantly elevated serum cholesterol levels that could contribute to MI, CVA, PVD
9
Q
What are chylomicrons?
A
- largest of protein molecules
- synthesized in wall of small intestine
- involved in transport of dietary TGs and cholesterol that have been absorbed from the GI tract
- transfer their TG to cells of adipose and skeletal muscle tissue
- remnnant particles, which contain cholesterol are then taken up by the liver: cholesterol used in synthesis of VLDL or excreted in the bile
10
Q
How is cholesterol synthesized?
A
- rate limiting step in cholesterol synthesis involves enzyme 3- hydroxy-3-methylglutaryl coenzyme A reductase (if enzyme inhibited than unable to produce cholesterol)
- cholesterol and other lipids are transported in circulation as a component of lipoproteins.
11
Q
Importance of lipoproteins?
A
- because cholesterol and TGs are insoluble in plasma, they are encapsulated by special fat carrying proteins called lipoproteins
- named based on their protein content which is measured in density: because fats are less dense than proteins: as proportion of TG decreases, density increases
least dense = more TGs
12
Q
Five types of lipoproteins?
A
- chylomicrons: formed initially when fats absorbed in intestines
- VLDL: secreted mainly by the liver
- IDL
- LDL: main carrier of cholesterol
- HDL: garbage collector, in bloodstream picking up cholesterol
13
Q
what determines the cholesterol level in the blood?
A
- combo of factors and/or secondary causes
- genetics
- age
- dietary intake of saturated fat and cholesterol
- sedentary lifestyle
- poorly controlled DM: low HDL, hyperTG
- hypothyroidism: decreased metabolic rate
- nephrotic syndrome
- obstructive liver disease: cholesterol builds up within the liver
- alcoholism: metabolic dearrangement, and liver involvement
- drug therapy (cyclosporine, glucocorticoids)
14
Q
importance of VLDL’s?
A
- the liver synthesizes VLDL and HDL
- VLDLs contain large amounts of TGs
- provide the primary pathway for transport of endogenous TG produced in the liver
- the TG content of VLDL particles initially is high and decreases progressively as a result of enzyme activity in the bloodstream
- carry TG to fat and muscle cells where TG are removed: resulting IDL fragments are enriched in cholesterol and taken to the liver and recycled to form VLDL or converted to LDL in the vascular compartment
- IDLs are the main source of LDL
15
Q
Function of LDL (aka the bad cholesterol)?
A
- main carrier of cholesterol
- LDL is removed from circulation by either LDL receptors (70%) on hepatocytes or by non-receptor mechanisms involving scavenger cells such as macrophages
- therefore the liver plays an extremely impt role in LDL metabolism
- other non-hepatic tissues (adrenal glands, smooth muscle cells, endothelial cells, lymphoid cells) also use receptor dependent pathway to obtain cholesterol needed for membrane and hormone synthesis
16
Q
The amount of LDL that is removed by scavenger pathway is directly related to what?
A
- directly related to plasma cholesterol level
-
17
Q
What does the uptake of LDL by macrophages in arterial wall result in?
A
- accumulation of:
insoluble cholesterol esters - formation of foam cells
- development of atherosclerosis
18
Q
Function of HDL?
A
- good cholesterol
- synthesized in the liver
- participates in reverse transport of cholesterol, that is, carrying cholesterol from peripheral tissues back to liver
- studies show an inverse relation b/t HDL levels and development of atheroscelorsis
- HDL facilitates the clearance of cholesterol from atheromatous plaques and transports it to the liver where it may be excreted rather than used in the formation of VLDL
- also believed that HDL inhibits cellular uptake of LDL
19
Q
What increases HDL levels?
A
- regular exercise and moderate alcohol consumption increase HDL levels
20
Q
What decreases levels of HDL?
A
- smoking and metabolic syndrome
21
Q
What are apoproteins (or apolipoproteins)?
A
each type of lipoprotein consists of large molecular complex of lipids combined with proteins called apoproteins
- 6 major classes
- apoproteins control the interactions and ultimate metabolic fate of lipoproteins.. regulate lipid transport and metabolism
- research findings indicate that genetic defects in apoproteins are involved in hyperlipidemia and accelerated atherosclerosis
