Flashcards in Lipid Metabolism Deck (19):
What is the function of triglycerides?
used in energy metabolism
What is the function of cholesterol?
Precursor of steroid hormones, necessary for cell membrane synthesis, and metabolic precursor of bile acids
What are chylomicrons?
Largest protein molecules. Synthesized in the small intestine. Involved in the transport of dietary triglycerides (TG) and cholesterol. After transferring TG to cells, the remnant particles containing cholesterol are taken up by the liver
What is the rate limiting step in cholesterol synthesis?
involves the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Statins inhibit HMG-CoA reductase.
fat carrying proteins that encapsulate cholesterol and trigylcerides. Because fats are less dense than proteins, as the proportion of triglycerides (TG) decreases, the density increases
synthesized in the liver. Provide pathway for transport of endogenous TG. Initially TG content of VLDL is high and decreases due to enzyme activity as it is carried to fat/muscle cells. Resulting IDL fragments are main source of LDL
What is responsible for removing LDL from the circulation?
LDL receptors (70%) on hepatocytes or by non-receptor mechanisms involving scavenger cells such as macrophages. The amount of LDL that is removed by the scavenger pathway is directly related to the plasma cholesterol level
What can happen as a result of LDL uptake by macrophages in the arterial wall?
Insoluble cholesterol esters, formation of foam cells, and atherosclerosis
What is the function of HDL?
Facilitates the clearance of cholesterol from atheromatous plaques and transports it to the liver, where it may be excreted. inhibits cellular uptake of LDL
What increases and decreases HDL?
regular exercise and moderate alcohol consumption increase HDL levels. Smoking and the metabolic syndrome decrease levels of HDL
What are apoproteins?
synthesized in the small intestine and the liver. regulate lipid transport and metabolism. genetic defects in apoproteins are involved in hyperlipidemia and accelerated atherosclerosis
Describe the process of atherosclerosis
accumulation of lipoproteins within the arterial wall. activates macrophages which ingest oxidized lipoproteins and form foam cells that contribute to fatty lesions. Fatty lesions progress to fibrous plaques. Fissures may develop in a plaque, exposing the underlying tissue to platelets. Platelet adhesion and aggregation lead to thrombus formation, occluding the vessel lumen
How are lipids metabolized?
emulsified by bile in duodenum. packaged into micelles which are taken up by mucosal cells and used in the synthesis of chylomicrons. chylomicrons enter the blood at the thoracic duct.
What are saturated fatty acids?
have single bonds between the carbon atoms. Most animal fat (and coconut oil) is saturated
What are monosaturated fatty acids?
contain only one double bond. Example, oleic acid as found in olive oil
What are polyunsaturated fatty acids?
contain two or more double bonds. Includes most vegetable fats: Vegetable oils like soybean, sunflower ,corn, safflower.Fish like tuna, salmon, herring
What is ketosis?
result of the liver converting fat into fatty acids and ketone bodies (which can be used for energy as an alternative to glucose)
When does ketosis occur?
when the rate of formation of ketones by the liver is greater than the ability of tissues to oxidize them. Excess ketone bodies will decarboxylate into acetone: Starvation or when large amounts of fat are eaten in the absence of carbs