Lecture 24: ABSORPTION AND TRANSPORTATION OF FATS

Question 1

What do bile acids do?

Answer 1

Solubilize fats in the gastrointestinal tract by intercalating non-covalently

Question 2

How are bile acids synthesised?

Answer 2

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

Question 3

Where are bile acids secreted?

Answer 3

Into the small intestine in response to cholecystokinin

Question 4

What are bile salts described as?

Answer 4

Powerful detergents with hydrophobic and hydrophilic surfaces

Question 5

What do bile salts form?

Answer 5

Micelles with triacylglycerols to increase surface area for digestion

Question 6

What does bile contain?

Answer 6

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

Question 7

What are examples of bile acids?

Answer 7

Glycocholic acid and taurocholic acid

Question 8

What is the result of increased cholesterol?

Answer 8

Gall stones

Question 9

What are hormones involved in regulation of digestion?

Answer 9

Cholecystokinin, gastrin and secretin

Question 10

What is the source of cholecystokinin?

Answer 10

Duodenum

Question 11

What is the major stimulus for production for cholecystokinin?

Answer 11

Fats and amino acids in the duodenum

Question 12

What are the major actions of cholecystokinin?

Answer 12

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

Question 13

What is the source of gastrin?

Answer 13

Stomach

Question 14

What is the major stimulus for production of gastrin?

Answer 14

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

Question 15

What are the major actions of gastrin?

Answer 15

Stimulates secretion of gastric juices

Question 16

What is the source of secretin?

Answer 16

Duodenum

Question 17

What is the major stimulus for production of secretin?

Answer 17

HCl in the duodenum

Question 18

What are the major actions of secretin?

Answer 18

Stimulates secretion of alkaline bile and pancreatic juices

Question 19

What happens with lipids?

Answer 19

They are emulsified by bile salts to form micelles

Question 20

What does the pancreatic lipase/colipase enzyme system do?

Answer 20

Bonds to lipid/aqueous interface of micelles and hydrolyses triacylglycerols

Question 21

What does pancreatic lipase do?

Answer 21

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

Question 22

What is the result of pancreatic lipase hydrolysing fatty acids?

Answer 22

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

Question 23

What happens with micelles?

Answer 23

They are absorbed across the intestinal cell membrane

Question 24

What does the small intestine have?

Answer 24

Specialised structures that create a vast surface area for absorption

Question 25

What are the specialised structures of the small intestine?

Answer 25

Villi and microvilli

Question 26

What does fat malabsorption lead to?

Answer 26

An excess of fat and fat soluble vitamins in the faeces

Question 27

What is fat malabsorption caused by?

Answer 27

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

Question 28

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

Answer 28

Xenical (orlistat)

Question 29

How does xenical inhibit pancreatic lipase?

Answer 29

By forming a covalent bond

Question 30

What do lipoproteins help?

Answer 30

Solubilise lipids for transport in blood to tissues

Question 31

What do lipoproteins provide?

Answer 31

A delivery system for transporting lipids into and out of cells

Question 32

What are the important functions of apoproteins?

Answer 32

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

Question 33

What is the general lipoprotein structure?

Answer 33

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

Question 34

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

Answer 34

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

Question 35

What is the process of TAG synthesis?

Answer 35

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

Question 36

What are the lipid transport pathways?

Answer 36

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

Question 37

What do triacylglycerols and other lipids combine with?

Answer 37

apoB int he ER to form chylomicrons

Question 38

Where are chylomicrons secreted?

Answer 38

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

Question 39

What appearance do chylomicrons give plasma?

Answer 39

A milky appearance after a fat-rich meal

Question 40

What is lipoprotein lipase?

Answer 40

An enzyme found on endothelial surfaces

Question 41

What does lipoprotein lipase do?

Answer 41

Hydrolyses TAG in lipoproteins to glycerol and fatty acids

Question 42

Where is lipoprotein lipase the most active?

Answer 42

In the heart, skeletal muscle and adipose tissue

Question 43

What is lipoprotein lipase activated by?

Answer 43

apoCII

Question 44

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

Answer 44

Elevated levels of chylomicrons and plasma triacylglycerol

Question 45

How is LDL determined?

Answer 45

total cholesterol - triaclyglyceride/5 - HDL

Question 46

How is VLDL determined?

Answer 46

triacylglyceride/5

Question 47

What are some inherited lipid disorders?

Answer 47

Familial ApoCII deficiency and familial hypercholesterolaemia

Question 48

What is familial hypercholesterolaemia?

Answer 48

A common form of hyperlipidaemia which leads to premature atherosclerosis

Question 49

What is familial hypercholesterolaemia cause by?

Answer 49

Defect in LDL receptor gene (many different mutations)

Question 50

What type of disorder is familial hypercholesterolaemia?

Answer 50

Dominant

Question 51

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

Answer 51

Are 2-3x higher than normal

Question 52

What is familial hypercholesterolaemia treated with?

Answer 52

Statins to lower LDL and increase HDL ('good' cholesterol)

Question 53

What is a symptom of familial hypercholesterolaemia?

Answer 53

Xanthomas - fatty growths under the skin

Question 54

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

Answer 54

Tricor (fenofibrate)

Question 55

What are high blood triglyceride levels indicated by?

Answer 55

Milky plasma in centrifuged blood