129b Lipid Digestion

Question 1

major component of dietary lipids

Answer 1

90% triglycerides (TG’s) - 3 fatty acids attached to glyceride via ester bonds

+ cholesterol esters, PL, Vit ADEK

Question 2

what happens to fat that is consumed?

Answer 2

Almost all is absorbed - stored in adipose tissue

most takes places in small intestine (minor in mouth and stomach via acid stable lipases)

Question 3

what is the basic process involved in fat absorption/digestin? what are the primary products that are transported into enterocytes?

Answer 3

hydrolysis through a variety of enzymes

FFA
2-MG
cholesterol

Question 4

digestion in small intestine

Answer 4

1) pancreas releases…
Lipase/colipase: TAG –> MAG + 2FFA
Cholesterol esterase: CE –> chol + ester
phospholipase A2: PL–>FA + lysoPL

2) Liver releases bile to soluble products in mixed micelles

Question 5

what does liver bile do?

Answer 5

solubilizes the lipid breakdown products (MAG, GGA, cholestrol) in mixed micelles

Question 6

after absorption, how do fats leave intestine?

Answer 6

chylomicrons via lymphatics

after reesterification of 2MG, lecithin, cholestrol with FFA to form TG/chol ester/PL

Question 7

how are TG absorped?

Answer 7

not by self - ester bonds must be broken to form

MG and 2 FFA

Question 8

what are bile acids made from?

Answer 8

cholesterol

Question 9

CMC

Answer 9

critical micelle concentration

concentration at which molecules self-associate to form micelles (1-2 mM for mixed bile salts)

Question 10

how are fats absorped in liver cells?

Answer 10

MG and FFA – passive diffusion across lipid bilayer

Question 11

what happens in liver cell?

Answer 11

remade into TG via MGT and DGT
packaged with chylomicrons and exocytosed into lymphatics (lacteals)

some FFA can be absorbed into portal blood (short and medium length (<C11))

Question 12

enterohepatic circulation

Answer 12

95% of bile acids are reabsorbed via ABST (apical Na dependent bile salt transporter b/c polar) in terminal illelium if not deconjugated

AND

passive absorption (when small intestine bacteria deconguate bile salts to form bile acids)

Question 13

CCK action

Answer 13

pancreas secretes lipase
sphincter of Oddi relaxes
contracts the gall bladder

Question 14

bile-acid independnet flow

Answer 14

constant level of production from heme breakdown and drug excretion

bile-acid dependent flow + ductular secretion (similar to pancreatic duct - bicarb fluid via secretin and CCK)