Lipid Metabolism

Question 1

What is the function of triglycerides?

Answer 1

used in energy metabolism

Question 2

What is the function of cholesterol?

Answer 2

Precursor of steroid hormones, necessary for cell membrane synthesis, and metabolic precursor of bile acids

Question 3

What are chylomicrons?

Answer 3

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

Question 4

What is the rate limiting step in cholesterol synthesis?

Answer 4

involves the enzyme 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase. Statins inhibit HMG-CoA reductase.

Question 5

Describe lipoproteins

Answer 5

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

Question 6

Describe VLDL

Answer 6

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

Question 7

What is responsible for removing LDL from the circulation?

Answer 7

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

Question 8

What can happen as a result of LDL uptake by macrophages in the arterial wall?

Answer 8

Insoluble cholesterol esters, formation of foam cells, and atherosclerosis

Question 9

What is the function of HDL?

Answer 9

Facilitates the clearance of cholesterol from atheromatous plaques and transports it to the liver, where it may be excreted. inhibits cellular uptake of LDL

Question 10

What increases and decreases HDL?

Answer 10

regular exercise and moderate alcohol consumption increase HDL levels. Smoking and the metabolic syndrome decrease levels of HDL

Question 11

What are apoproteins?

Answer 11

synthesized in the small intestine and the liver. regulate lipid transport and metabolism. genetic defects in apoproteins are involved in hyperlipidemia and accelerated atherosclerosis

Question 12

Describe the process of atherosclerosis

Answer 12

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

Question 13

How are lipids metabolized?

Answer 13

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.

Question 14

What are saturated fatty acids?

Answer 14

have single bonds between the carbon atoms. Most animal fat (and coconut oil) is saturated

Question 15

What are monosaturated fatty acids?

Answer 15

contain only one double bond. Example, oleic acid as found in olive oil

Question 16

What are polyunsaturated fatty acids?

Answer 16

contain two or more double bonds. Includes most vegetable fats: Vegetable oils like soybean, sunflower ,corn, safflower.Fish like tuna, salmon, herring

Question 17

What is ketosis?

Answer 17

result of the liver converting fat into fatty acids and ketone bodies (which can be used for energy as an alternative to glucose)

Question 18

When does ketosis occur?

Answer 18

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

Question 19

Surprise! What is Waterhouse-Friderichsen syndrome?

Answer 19

adrenal gland failure due to bleeding into the adrenal glands, commonly caused by Neisseria meningitidis. Presents with stiff neck, rash, low BP, and high temp