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bioc192 > Lecture 24: ABSORPTION AND TRANSPORTATION OF FATS > Flashcards

Lecture 24: ABSORPTION AND TRANSPORTATION OF FATS Flashcards

1
Q

What do bile acids do?

A

Solubilize fats in the gastrointestinal tract by intercalating non-covalently

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2
Q

How are bile acids synthesised?

A

From cholesterol in the liver and stored in the gall bladder as bile

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3
Q

Where are bile acids secreted?

A

Into the small intestine in response to cholecystokinin

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4
Q

What are bile salts described as?

A

Powerful detergents with hydrophobic and hydrophilic surfaces

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5
Q

What do bile salts form?

A

Micelles with triacylglycerols to increase surface area for digestion

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6
Q

What does bile contain?

A

Water, bile acids, electrolytes, phospholipids, cholesterol and bile pigment (bilirubin)

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7
Q

What are examples of bile acids?

A

Glycocholic acid and taurocholic acid

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8
Q

What is the result of increased cholesterol?

A

Gall stones

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9
Q

What are hormones involved in regulation of digestion?

A

Cholecystokinin, gastrin and secretin

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10
Q

What is the source of cholecystokinin?

A

Duodenum

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11
Q

What is the major stimulus for production for cholecystokinin?

A

Fats and amino acids in the duodenum

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12
Q

What are the major actions of cholecystokinin?

A

Stimulates release of pancreatic enzymes and release of bile from the gall bladder

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13
Q

What is the source of gastrin?

A

Stomach

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14
Q

What is the major stimulus for production of gastrin?

A

Protein-containing food in the stomach, also parasympathetic nerves to the stomach

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15
Q

What are the major actions of gastrin?

A

Stimulates secretion of gastric juices

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16
Q

What is the source of secretin?

A

Duodenum

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17
Q

What is the major stimulus for production of secretin?

A

HCl in the duodenum

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18
Q

What are the major actions of secretin?

A

Stimulates secretion of alkaline bile and pancreatic juices

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19
Q

What happens with lipids?

A

They are emulsified by bile salts to form micelles

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20
Q

What does the pancreatic lipase/colipase enzyme system do?

A

Bonds to lipid/aqueous interface of micelles and hydrolyses triacylglycerols

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21
Q

What does pancreatic lipase do?

A

Hydrolyses fatty acids at position 1 and 3 of backbone of triacylglycerol to give free fatty acids and 2-monoacylglycerol

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22
Q

What is the result of pancreatic lipase hydrolysing fatty acids?

A

Smaller micelles form containing bile salts, free fatty acids, monoacylglycerol (and glycerol)

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23
Q

What happens with micelles?

A

They are absorbed across the intestinal cell membrane

24
Q

What does the small intestine have?

A

Specialised structures that create a vast surface area for absorption

25
Q

What are the specialised structures of the small intestine?

A

Villi and microvilli

26
Q

What does fat malabsorption lead to?

A

An excess of fat and fat soluble vitamins in the faeces

27
Q

What is fat malabsorption caused by?

A

Conditions that interfere with bile or pancreatic lipase secretion - pancreatitis, gall bladder or liver diseases

28
Q

What is a potent inhibitor of the pancreatic lipase active site?

A

Xenical (orlistat)

29
Q

How does xenical inhibit pancreatic lipase?

A

By forming a covalent bond

30
Q

What do lipoproteins help?

A

Solubilise lipids for transport in blood to tissues

31
Q

What do lipoproteins provide?

A

A delivery system for transporting lipids into and out of cells

32
Q

What are the important functions of apoproteins?

A

Structural for assembly (apoB), ligands for cell surface receptors (apoE and apoB) and enzyme cofactors (appCII for lipoprotein lipase)

33
Q

What is the general lipoprotein structure?

A

Phospholipids, unesterified cholesterol, esterfied cholesterol and apoproteins with hydrophobic interior and hydrophilic exterior. Triacylglycerides found inside

34
Q

What are the four main lipoprotein classes (from high lipid content to low)?

A

Chylomicrons, very low density (VLDL), low density (LDL), high density (HDL)

35
Q

What is the process of TAG synthesis?

A

2-monoacylglycerol + free fatty acids in activated coenzyme form&raquo_space;> diacylglycerol + free fatty acids in activated coenzyme form&raquo_space;> triacylglycerol + apoproteins + other lipids&raquo_space;> chylomicrons

36
Q

What are the lipid transport pathways?

A

Exogenous chylomicron pathway (uptake of dietary fat) and endogenous VLDL/LDL pathway (endogenously synthesised fat)

37
Q

What do triacylglycerols and other lipids combine with?

A

apoB int he ER to form chylomicrons

38
Q

Where are chylomicrons secreted?

A

From intestinal epithelial cells and enter the bloodstream via the lymphatic system

39
Q

What appearance do chylomicrons give plasma?

A

A milky appearance after a fat-rich meal

40
Q

What is lipoprotein lipase?

A

An enzyme found on endothelial surfaces

41
Q

What does lipoprotein lipase do?

A

Hydrolyses TAG in lipoproteins to glycerol and fatty acids

42
Q

Where is lipoprotein lipase the most active?

A

In the heart, skeletal muscle and adipose tissue

43
Q

What is lipoprotein lipase activated by?

A

apoCII

44
Q

What do defects (by mutation) in either apoCII or lipoprotein lipase lead to?

A

Elevated levels of chylomicrons and plasma triacylglycerol

45
Q

How is LDL determined?

A

total cholesterol - triaclyglyceride/5 - HDL

46
Q

How is VLDL determined?

A

triacylglyceride/5

47
Q

What are some inherited lipid disorders?

A

Familial ApoCII deficiency and familial hypercholesterolaemia

48
Q

What is familial hypercholesterolaemia?

A

A common form of hyperlipidaemia which leads to premature atherosclerosis

49
Q

What is familial hypercholesterolaemia cause by?

A

Defect in LDL receptor gene (many different mutations)

50
Q

What type of disorder is familial hypercholesterolaemia?

A

Dominant

51
Q

What do LDL (‘bad’ cholesterol) levels in familial hypercholesterolaemia do?

A

Are 2-3x higher than normal

52
Q

What is familial hypercholesterolaemia treated with?

A

Statins to lower LDL and increase HDL (‘good’ cholesterol)

53
Q

What is a symptom of familial hypercholesterolaemia?

A

Xanthomas - fatty growths under the skin

54
Q

What can patients with high blood triglyceride levels be treated with?

A

Tricor (fenofibrate)

55
Q

What are high blood triglyceride levels indicated by?

A

Milky plasma in centrifuged blood

bioc192 (38 decks)

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