Digestion And Absorption Of Dietary Lipids

Question 1

TAG percentage of dietary lipids

Answer 1

90-95%

Question 2

Types of TAGs

Answer 2

. Saturated
. Monounsaturated
. Polyunsaturated
. Trans-fat

Question 3

Lipid that compose other 5-10% dietary lipids

Answer 3

. Cholesterol esters
. Plant sterols and Stanols
. Phospholipids
. Vitamins ADEK

Question 4

Stomach digestion of TAGs

Answer 4

. Lingual lipase from mouth and gastric lipase from stomach hydrolyze TAG to release single FA
. DAG hydrolyzed into MAG w/ release of second FA
. Non-pancreatic lipase activity
. This w/ physical missing creates crude lipid emulsion that passes into small intestine

Question 5

Gastric lipase accounts for what percentage of total FA content of ingested dietary TAG?

Answer 5

10-30%

Question 6

Lipid digestion and absorption in small intestine

Answer 6

. Hormones: secretin and Cholecystokinin (CKK)
. Emulsification: smooth muscle and bile salts
. Enzymatic: pancreatic lipase, cholesterol esterase, phospholipase A2
. Michelle formation
. Absorption via passive diffusion. Fatty acid transport proteins, NPC1L1 and ABCG5/8

Question 7

Role of secretin and CCK

Answer 7

. Secretin in blood inc. pancreatic secretion of bicarbonate

. CCK in blood inhibits gastric motility and inc. pancreatic secretion of pancreatic enzymes and bile from gall bladder

Question 8

Emulsification

Answer 8

. Bile salts synthesized in liver and secreted into intestine
. Amphipathic structure permits bile salts to emulsify large lipid droplets
. Inc. efficiency of enzymatic digestion by inc. surface area

Question 9

Enzymatic digestion in small intestine

Answer 9

. Pancreatic lipase and colipase convert TAGs to DAG and MAG and FA
. Colipase forms 1:1 complex w/ pancreatic lipase to anchor it to lipid droplets and stabilize active confirmation
. Cholesterol esterase converts cholesterol ester + H2O to FA and cholesterol
. Phospholipase A2 converts phosphatidylcholine and H2O to fatty acid and lysosome-PC

Question 10

Micelle formation

Answer 10

. Products of lipid digestion, fat-soluble vitamins, and bile salts combine into micelles

Question 11

Micelle function

Answer 11

. Facilitates movement of hydrophobic products of lipid digestion across aqueous barrier

Question 12

Short-medium chain fatty acid absorption

Answer 12

. Diffuse directly across us stirred water layer for absorption and secretion into portal circulation

Question 13

Absorption of micelle from small intestine

Answer 13

. Transporters on Apical surface of enterocytes
. CD-36: fatty acids
. NPC1L1: cholesterol and plant sterols
. ABCG5/G8: heterotrimeric protein complex that excretes plant sterols and some cholesterol back into lumen
. SRB1: cholesterol or Vit. E

Question 14

What current lifestyle recommendations are there for lowing serum cholesterol

Answer 14

. Food w/ plant sterol esters

. Low in saturated fat and cholesterol

Question 15

Orlistat

Answer 15

. Not absorbed from intestine
. Inhibits gastric and pancreatic lipase
. Dec. enzymatic digestion of TAGs

Question 16

Bile acid-binding resins (Questran)

Answer 16

. Not absorbed in intestine
. Binds bile salts in intestines and prevents reabsorption in enterohepatic circulation
. Inc. hepatic conversion of cholesterol to bile

Question 17

Ezetimbe (Zetia)

Answer 17

. Inhibits NPC1L1-mediated uptake of cholesterol

. Combined w/ simvastatin has dual drug effect on cholesterol synthesis in liver and intestinal cholesterol absorption

Question 18

Diseases where lipid malabsorption occurs

Answer 18

. CF
. Celiac 
. Crohn’s 
. Pancreatitis 
. Cholelithiasis (gall stones)

Question 19

Pancreatic insufficiency of CF

Answer 19

. Accumulation of mucus causes exocrine pancreatic insufficiency leading to lipid malabsorption
. High protein and normal to high fat diet
. Enteric coated pancreatic enzymes for treatment

Question 20

Chylomicron synthesis

Answer 20

. Inside enterocytes
. TADs and cholesteryl esters Resynthesized from absorbed products of lipid digestion
. Microsomes triglyceride transfer protein (MTP) transfers resynthesized lipids to apolipoprotein B-48 in lumen of ER
. Lipidation of ApoB-48 w/ addition of phospholipids and vitamins makes chylomicron particle

Question 21

Where are chylomicron excreted?

Answer 21

. Across basolateral cell membrane into lymphatic system

. Pass into blood and deliver lipids to organs and tissues

Question 22

Abetalipoproteinemia

Answer 22

. Genetic disease w/ MTP mutation

. Infants w/ this has diarrhea, failure to thrice, and altered neurological function from lack of long-chain FA needed

Question 23

TAGs in breast milk function

Answer 23

. 50% calories
. Gives essential FA
. Provides long-chain polyunsaturated FA for development of brain and retina
. Serves as medium for absorption of fat-soluble vitamins

Question 24

Compensatory mechanisms in infants to facilitate optimal digestion and absorption of dietary fat

Answer 24

. Inc. digestion of lipids by gastric lipase
. Presence of bile salt-stimulated lipase (BSSL) in breast milk that activates in infants intestine
. Inc. gene expression for apo-B48 and MTP in enterocytes
. Location of palmitic acid in TAGs in breast milk that limit that formation of insoluble complexes w/ Ca