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Pathophysiology Exam 3 > Lecture 25 > Flashcards

Lecture 25 Flashcards

1
Q

What are the two mechanisms for removal of LDL from plasma?

A
  1. Mediated by an LDL receptor
  2. Receptor for oxidized LDL (scavenger receptor)
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2
Q

Chylomicrons

A

Carry diet-derived lipids to body cells

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3
Q

VLDLs

A

Carry lipids synthesized by the liver to body cells

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4
Q

LDLs

A

Carry cholesterol around the body

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5
Q

HDLs

A

Carry cholesterol from the body back to the liver for breakdown and excretion

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6
Q

What state are these aggregates in within circulation?

A

State of constant flux, changing in composition and physical structure as the peripheral tissues take up the various components before the remnants return to the liver

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7
Q

What are the beneficial metabolic consequences of bariatric surgery?

A

Sodium is a key factor; gastric bypass decreases the amount of sodium normally brought into the intestine with bile (impairs intestinal glucose uptake via sodium-glucose cotransport)

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8
Q

How is the alimentary limb impacted with gastric bypass?

A
  • SGLT1
  • Low sodium
  • With gastric bypass, the bile, and hence the sodium, is deprived
  • Sodium-glucose co-transport is blunted in bile-deprived alimentary limb
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9
Q

What limb is glucose absorbed in with Roux-en-Y gastric bypass?

A

Common limb: sodium-glucose co-transport

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10
Q

How does sodium addition impact glucose uptake in the alimentary limb?

A

Sodium addition restores glucose uptake

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11
Q

How does Roux-en-Y gastric bypass impact postprandial glucose response?

A

Decreases

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12
Q

Choleresis

A

Liver cells secrete bile that contains bile salts, cholesterol, lecithin, bilirubin, electrolytes, and water (bile salts emulsify fats)

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13
Q

Colipase

A

Amphipathic protein makes fat droplets covered with emulsifying agents accessible to water soluble lipase

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14
Q

Lipase

A

Breaks down triglycerides

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15
Q

Fat Droplet

A

division of large droplets into smaller emulsion droplets (~1mm to increase the surface area and accessibility to lipase action) occurs by mechanical disruption of contractile activity of lower portion of stomach

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16
Q

Explain the digestion and assimilation of dietary fats in the lumen of small intestine.

A
  1. Fat Droplets
  2. Bile salts, phospholipids
  3. Colipase: emulsion droplets
  4. Bile salts, pancreatic lipase
  5. Micelles
  6. Free molecules of fatty acids and monoglycerides
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17
Q

Explain the digestion and assimilation of dietary fats in the epithelial cell.

A
  1. Free molecules of fatty acids and monoglycerides diffuse into epithelial cells
  2. Triglyceride synthetic enzymes in ER
  3. Droplets of triglyceride enclosed by membrane from the ER coated with amphipathic proteins
  4. Lacteal: chylomicron
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18
Q

What molecules carry fat from intestine to liver via general circulation?

A

Chylomicrons (triglycerides, phospholipids, cholesterol, apolipoproteins)

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19
Q

Lipoproteins

A

Assembled in enterocytes and hepatocytes and constantly modified as they circulate, transport cholesterol and other lipids between tissue

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20
Q

What mediates binding of lipoproteins to receptors in tissues?

A

Apoproteins/ apolipoproteins

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21
Q

Apoproteins

A
  • Synthesized and secreted by many tissues (liver and intestines)
  • Determine: overall structures, interactions with receptor molecules, metabolism of lipoproteins in liver and peripheral tissues
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22
Q

What is the lipoprotein associated with apoprotein A-I?

A

HDL, chylomicrons

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23
Q

What is the source of apoprotein A-I?

A

Liver, intestine

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24
Q

What is the biological role of apoprotein A-I?

A

Activates lecithin-cholesterol acyltransferase in HDL

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25
Q

What is the lipoprotein associated with apoprotein B-48?

A

Chylomicrons

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26
Q

What is the source of apoprotein B-48?

A

Intestine

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27
Q

What is the biological role of apoprotein B-48?

A

Serves as structural protein for chylomicrons

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28
Q

What is the lipoprotein associated with apoprotein B-100?

A

VLDL, LDL

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29
Q

What is the source of apoprotein B-100?

A

Liver

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30
Q

What is the biological role of apoprotein B-100?

A

Serves as structural protein for VLDL and LDL; contains LDL receptor-binding domain

31
Q

What is the lipoprotein associated with apoprotein C-II?

A

HDL, VLDL, chylomicrons

32
Q

What is the source of apoprotein C-II?

33
Q

What is the biological role of apoprotein C-II?

A

activates extrahepatic lipoprotein lipase

34
Q

What is the lipoprotein associated with apoprotein C-III?

35
Q

What is the source of apoprotein C-III?

36
Q

What is the biological role of apoprotein C-III?

A

Inhibits lipoprotein lipase and hepatic lipase; inhibits hepatic uptake (catabolism) of triglyceride-rich particles

37
Q

What is the lipoprotein associated with apoprotein E?

A

VLDL, chylomicron remnants

38
Q

What is the source of apoprotein E?

39
Q

What is the biological role of apoprotein E?

A

Mediates uptake of chylomicron remnants by the liver

40
Q

What is the most obvious change in protein composition as chylomicrons undergo delipidation?

A

Acquisition of Apo-E

41
Q

Explain lipoprotein metabolism.

A
  1. Chylomicrons enter the bloodstream via thoracic duct
  2. Once in the blood, chylomicrons are subject to delipidation by enzyme lipoprotein lipase (LPL)
  3. With apolipoprotein ApoC-II as a co-factor, lipoprotein lipase hydrolyzes chylomicron triglycerides allowing the delivery of free fatty acids to muscle and adipose tissue
  4. More triglyceride removal -> formation of low-density lipoprotein (LDL)
  5. Enough lipid (triglycerides) has been lost and additional apolipoproteins (ex: ApoE) gained -> chylomicron remnant -> taken up by the liver
42
Q

What happens to chylomicron remnants and LDL in the liver?

A

Resynthesized into HDL and VLDL and put back into circulation

43
Q

What happens due to a mutation in apolipoprotein E (ApoE)?

A

Familial dysbetalipoproteinemia (remnant hyperlipidemia/ remnant removal disease): increased LDL, cholesterol, and triglyceride levels and decreased HDL levels

44
Q

What occurs with a genetic defect in the synthesis of apolipoproteins B-48 and B-100?

A

Abetalipoproteinemia: condition lipids not properly absorbed because chylomicrons cannot be formed and transported normally

45
Q

What happens when enough triglycerides are hydrolyzed?

A

Additional apolipoproteins (ex: ApoE) gained

46
Q

Where is VLDL assembled?

A

In the liver from triglycerides, cholesterol, and apolipoproteins

47
Q

Where are nascent VLDL released from and what do they contain?

A

From the liver and contain ApoB100, ApoC-I, ApoE, cholesterol, cholesteryl esters, and triglycerides

48
Q

What does nascent VLDL pick up as it circulates in blood?

A

ApoCII and additional ApoE donated from HDL

49
Q

What happens when a VLDL particle reaches the capillaries of adipose tissue or muscle?

A

It is cleaved by lipoprotein lipase (with ApoCII as a cofactor); process extracts most of the triglycerides -> IDL (enriched in cholesteryl esters) -> retains two (B100 and E) of the three apoproteins

50
Q

What happens to IDL not taken up by the liver?

A

Further metabolized to remove most of the remaining triglycerides -> cholesterol-rich LDL particles

51
Q

Where is LDL taken up?

A

By the liver via receptor-mediated transport via LDL receptor

52
Q

What is the result of a deficiency of LDL receptor?

A

Hypercholesterolemia (familial hypercholesterolemia (dyslipidemia))

53
Q

What happens when chylomicron remnants in blood are the appropriate size to enter the space of Disse?

A
  1. Taken up by hepatocytes via LDL receptor
  2. Acquire additional ApoE and taken up by LDL receptor-related protein
54
Q

What does the LDL receptor recognize?

A

Both apoproteins B-100 and E

55
Q

What is the function of ApoE?

A

Moiety required for rapid hepatic removal

56
Q

What inhibits ApoE?

A

C apolipoproteins (ApoC-I)

57
Q

What causes the termination of lipolysis?

A

The loss of ApoCII (as a cofactor activates extrahepatic lipoprotein lipase, LPL)

58
Q

Explain the process of the removal of chylomicron remnants and LDL.

A
  1. Space of Disse: hepatocytes
  2. VLDL: ApoC, ApoE, B-100
  3. Lipolysis of VLDL: lipoprotein lipase (-> fat cells or muscle)
  4. IDL: B-100, ApoE
  5. a) receptor mediated clearance of IDL
    b) LDL: B-100
  6. a) LDL receptor on liver cell
    b) Receptor mediated clearance of LDL (LDL receptor on liver cell) OR other clearance (scavenger receptor for oxidized LDL)
59
Q

What cell types possess high-affinity LDL receptors?

A

Fibroblasts, lymphocytes, smooth muscle, hepatocytes, and adrenocortical cells

60
Q

How are drugs for cholesterol homeostasis able to lower plasma cholesterol?

A

By increasing the number of LDL receptors (ex: Statins)

61
Q

Statins

A

Suppress intracellular cholesterol synthesis by inhibiting HMG CoA reductase -> allows greater synthesis of LDL receptors (lowered cholesterol removes negative feedback on LDL receptor synthesis)

62
Q

Summarize the process of lipoprotein metabolism.

A
  1. Chylomicrons from dietary fat absorption are taken up by the liver and resynthesized into VLDL and HDL and put back into circulation
  2. Triglycerides are removed for tissue use from VLDL -> IDL
  3. More triglyceride removal -> LDL
  4. LDL taken up by peripheral tissue to obtain cholesterol
  5. 70% of circulating LDL returns to liver
  6. HDL circulates to peripheral tissues and takes up excess cholesterol for transport back to the liver for excretion (reverse cholesterol transport)
63
Q

Where is nascent HDL produced and what is it composed of?

A

Produced in the liver and small intestines; composed of ApoA-I, phospholipid (lecithin) and lecithin-cholesterol acyltransferase (LCAT)

64
Q

Since cells cannot breakdown cholesterol, what happens?

A

Efflux of cholesterol from extra hepatic cells facilitated by ATP-binding cassette (ABC) proteins

65
Q

What happens to the cholesterol that is transferred out of cells?

A

Accepted by nascent HDL and esterified by LCAT -> cholesterol esters (CE) and triglycerides (TG) are exchanged between VLDL, IDL, and chylomicron remnants and HDL through the activity of cholesterol ester transfer protein (CETP)

66
Q

How does HDL transfer its cholesterol esters (CE)?

A

Transferred to the liver through interaction with HDL receptor, scavenger receptor B1 (SR-B1) on hepatocyte membrane -> CEs cleaved by hepatic hormone-sensitive lipase and the free cholesterol enters the bile salt pathway or is excreted as cholesterol -> HDL particles recycled

67
Q

What is reverse cholesterol transport?

A

A process by which plasma cholesterol is delivered to the liver for bile acid production and to adrenals and ovaries for steroid hormone production

68
Q

What can mutations in ApoA-I cause?

A

Result in complete absence of HDL -> increased coronary heart disease and xanthomas (deposition of yellowish cholesterol-rich material)

69
Q

What is the result of an HDL receptor deficiency?

A
  • Infertility
  • Scavenger receptor class B type 1 (SCAR-B1, SR-B1): lipoprotein receptor that is highly expressed in adrenals and ovaries
  • Variation of SCARB1 gene also appears to impact progesterone production in women
70
Q

What does a mutation in ApoB-48 or ApoB-100 cause?

A

Abetalipoproteinemia (Bassen-Kornzweig syndrome): rare autosomal recessive disorder caused by a mutation in triglyceride transfer protein -> deficiencies in the apolipoproteins B-48 and B-100 -> interferes with normal absorption of fat and fat-soluble vitamins

71
Q

Familial Hyperchylomicronemia Syndrome

A

Inactivating mutations in LPL or cofactor, ApoC-II -> pancreatitis, hepatosplenomegaly, lipemia retinalis, xanthomas

72
Q

What happens when there is an excess of ApoC-III?

A

Found in genetic variations may predispose to non-alcoholic fatty liver disease

73
Q

What happens when there is a mutation of ApoC-III?

A

Enhances break-down of triglycerides -> low circulating TG -> less risk for heart attack

74
Q

Familial Dysbetalipoproteinemia

A

(Type III hyperlipoproteinemia, remnant hyperlipidemia, broad beta disease, remnant removal disease) Mutation in ApoE resulting in accumulation of chylomicrons content-triglycerides and cholesterol (especially LDL) -> xanthomas, premature atherosclerosis

Pathophysiology Exam 3 (10 decks)

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