Liver Biochemistry

Question 1

structure of the liver

Answer 1

largest solid organ
weights 1500 g
2 lobes subdivided into multiple lobes and sinusoids
75% supplied by portal vein
25% by hepatic artery
biliary component made of bile ducts and gallbladder

Question 2

liver cell types

Answer 2

hepatocytes 
endothelial cells
kupffer cells 
hepatic stellate cells 
pit cells (lymphocytes)

Question 3

functions of the liver

Answer 3

primary receiving, distribution and recycling center 
lipid biosynthesis and management 
protein biosynthesis - albumin and IgG
nitrogen metabolism - urea cycle 
waste management - xenobiotic reactions 
bilirubin metabolism 
fuel management

Question 4

central receiving, distribution, and recycling center

Answer 4

major role: monitoring, synthesizing, recycling, distributing, and modifying metabolites
ingested material is retrieved by the liver and converted into a useful form
harmful products are converted into a safe product

Question 5

structural adaptations

Answer 5

enteric circulation - portal vein
periphery - hepatic a
lack basement membrane, has gap junctions and fenestrations and low portal blood pressure which allow greater access and increased contact b/w liver and blood

Question 6

hepatocytes

Answer 6

well developed, plasma membrane w/ endocytic and exocytic system, well developed ER, metabolically active cells, lots of mitochondria, lots of lysosomes

Question 7

features of isoprenoids

Answer 7

3 acetyl CoA used to generate IPP which serves as a building block for the synthesis of all isoprenoids including steroids and lipid soluble vitamins

Question 8

sources of acetyl CoA

Answer 8

oxidative decarboxylation of pyruvate
beta oxidation of FA
breakdown of AA
transported into cytoplasm via citrate shuttle

Question 9

cholesterol

Answer 9

precursors of: bile acids and salts, vit D, and steroid hormones

Question 10

fate of cholesterol - all tissues

Answer 10

incorporated into cellular membranes

Question 11

fate of cholesterol - liver

Answer 11

synth bile acids

Question 12

fate of cholesterol - adrenal glands, ovaries, testes

Answer 12

synth steroid hormones

Question 13

fate of cholesterol - skin

Answer 13

synth vit. D

Question 14

lipid rafts

Answer 14

microdomains enriched in cholesterol
detergent insoluble low buoyant density
local centers for signal transduction processes
sites for abnormal processing of proteins in neurodegenerative disorders

Question 15

direct inhibition

Answer 15

inhibited by FFA, bile acids, oxysterols

inhibited by statins (competitive inhibitors)

Question 16

covalent modification

Answer 16

active - de pi 
inactive - pi 
low energy leads to pi and inactivation 
glucagon inhibits by preventing de pi 
insulin activates by promoting de pi

Question 17

transcriptional control

Answer 17

SREBP-SCAP complex is retained in ER in the presence of cholesterol which leads to low transcription rate
low sterol promotes release

Question 18

translational and post-translational control

Answer 18

translation is reduced by vitamin E

cholesterol leads to interaction of INSIG which will release from ER

Question 19

role of liver in cholesterol homeostasis

Answer 19

cholesterol biosynthesis happens in liver
VLDL to LDL
cholesterol delivered to liver via chylomicron
major source of nascent HDL
helps clear bulk of lipoproteins
synthesizes bile acids and eliminates cholesterol into bile

Question 20

statins

Answer 20

lower cholesterol
strong competitive inhibitors of HMG CoA reductase
increase in SREBP maturation which leads to transcription of LDL R and increased clearance of cholesterol

Question 21

cytochrome P450 and drug interactions

Answer 21

converts linear isoprenoid squalene into cholesterol
detoxify stains
inhibition leads to toxic side effects of statins

Question 22

hepatic cholesterol

Answer 22

a precursor of bile acids and bile salts

Question 23

strong detergents

Answer 23

amphipathic with polar and non polar regions

Question 24

bile

Answer 24

made in hepatocytes

stored and concentrated in gallbladder

Question 25

lipid emulsifying mixture

Answer 25

acids in lipid digestion by forming micelles which increase surface area of lipids exposed to lipases

Question 26

gallstones

Answer 26

crystals made of bile supersaturated with cholesterol

treated with ursodeoxycholic acid

Question 27

cholelithiasis

Answer 27

insufficient secretion of bile salts or phospholipids or excess cholesterol secretion