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GI II > Liver metabolism- urea cycle > Flashcards

Liver metabolism- urea cycle Flashcards

1
Q

Where is bilirubin from

A

heme from broken down RBC

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2
Q

Where is heme taken up to be processed first

A

reticoendothelial cells of the spleen to form unconjugated bilirubin (lipid soluble) via heme oxygenate

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3
Q

How is unconjugated bilirubin transported to the liver

A

attached to albumin in the blood stream

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4
Q

What happens to unconjugated bilirubin in the liver

A

addition of glucuronic acid to produce conjugated bilirubin which is water soluble

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5
Q

What enzyme is responsible for the conjugation of bilirubin in the liver

A

UDPGT

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6
Q

Where is conjugated bilirubin converted into urobilinogen

A

intestines by intestinal bacteria

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7
Q

what forms of urobilinogen are excreted in stool

A

urobilin and stercobilin, oxidized forms

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8
Q

How does bile get recycled to liver

A

must be bound to albumin because not very water soluble

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9
Q

What does the van den berg test for

A

measures blood levels of conjugated and unconjugated bilirubin

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10
Q

Describe what the Intestine does to ocnjugated bilirubin

A

hydrolyzed back to unconj.
in distal ileum and colon the flora reduce unconjugated bilirubin to urobilinogen and then also oxidation makes the unconj.bilirubin brown colored

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11
Q

Urobilinogen is a collective term for what 3 tetrapyrroles

A

stercobilinogen
mesobilinogen
urobilinogen

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12
Q

where does the 20% of reabsorbed urobilinogen go

A

entero-hepatic circulation

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13
Q

how much bilirubin ends up in urine

A

2-5%

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14
Q

How much of total bilirubin is conjugated

A

<0.2 mg/dL

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15
Q

how do you calculate unconjugated bilirbuin

A

total - conjugated

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16
Q

What happens with elevations of serum bilirubin

A

deposition in sclera of eyes and tissue– icterus and jaundice

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17
Q

When does jaundice appear (what serum level)

A

2-3 mg/dL

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18
Q

What are the causes of jaundice

A

excessive production of bilirubin
reduced hepatocyte uptake
impaired bilirubin conjugation
impaired bile flow

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19
Q

At what serum level in infants will the result be kernicterus

A

15-20 mg/dL

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20
Q

What causes pre hepatic jaundice

A

hemolysis

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21
Q

what causes hepatic jaundice

A

viral hepatitis, drugs, alcohol, cirrhosis, recurrent cholestasis
enzyme mutations, defective secretion

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22
Q

What causes post hepatic jaundice

A

common duct stones, carcinomas of bile duct pancreas ampulla, biliary stricture
sclerosing cholangitis
pancreatic pseudocyst

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23
Q

In hemolytic anemia which bilirubin is elevated

A

unconjugated

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24
Q

In hepatitis what bilirubin is elvated

A

both unconj and conjugated

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25
Q

with a biliary duct stone what bilirubin is elevated

A

conjugated

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26
Q

Describe pre-hepatic jaundice

A

excessive bilirubin presented to liver, too much
causes hemolysis of RBC and results in increased serum unconjugated bilirubin
Increase in urinary urobilinogen

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27
Q

Describe Intra-hepatic jaundice

A

abnormal hepatocyte function

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28
Q

What genetic disorders cause intra-hepatic jaundice

A

Gilbert’s, Cirgler-Najjar type I, Dubin-Johnson

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29
Q

describe findings in someone with Gilberts

A

stress activated. total bilirubin is not elevated but increased unconjugated bill with increased urine urobilinogen

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30
Q

describe findings in someone with Crigler-Najjar syndrome I

A

unconj bili in serum is above 5 mg/dL and there is an increased urinary urobilinogen

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31
Q

describe findings in someone with dubin johnson syndrome

A

increased serum conjugated bill from defective secretion of hepatocyte

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32
Q

What are the findings in someone with hepatitis causing jaundice

A

increased direct and indirect bilirubin with total levels 5-10 mg/dL

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33
Q

What are the findings of someone with impaired excretion of bilirubin

A

increased serum AND urine conjugated bilirubin
decreased urobilin and stercobilin (pale stool)
no urinary urobilinogen

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34
Q

Malaria can cause what type of jaundice

A

pre-hepatic

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35
Q

In which type of jaundice is there and increase in fat in the stool

A

intra-hepatic

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36
Q

What liver function enzymes will be impaired in someone with an intrahepatic jaundice

A

SGOT and SGPT

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37
Q

What is kernicterus

A

brain encephalopathy referring to the yellow staining of basal ganglia
caused by excessive jaundice

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38
Q

how does bilirubin cross blood brain barrier in a newborn

A

the barrier is not fully formed

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39
Q

What causes the prolonged jaundice in newborns

A

polycythemia

Rh incompatability with mom

40
Q

What are inherited disorders of bilirubin metabolism

A

gilberts, crigler-najjar type I and II

lucey-driscoll, dubin-johnson, rotors syndrome

41
Q

What genetic conditions can you suspect in someone with elevated conjugated bilirubin

A

Dubin-johnson and rotors

42
Q

What is mutated in someone with Gilbert’s syndrome

A

UDPGT- low activity

43
Q

What is mutated in Crigler najjar syndrome type I

A

incomplete absence of UDPGT

high high levels of unconjugated bilirubin

44
Q

What type of inheritance is Crigler najjar syndrome type I

A

autosomal recessive

45
Q

What is the Tx for crigler najjar syndrome I

A

liver transplant within first year of life

46
Q

What type of inheritance is crigler najjar type II

A

autosomal dominant

47
Q

What mutation is in crigler najjar type II

A

partial deficiency of UDPGT

48
Q

What is the Tx for crigler najjar syndrome type II

A

responds to phenobarbital and normal life can be expected

49
Q

What type of inheritance is dubin johnson

A

autosomal recessive

50
Q

Impairment of the excretion of various conjugated anions and bilirubin into bile reflects what in dubin johnson syndrome

A

underlying defect in cnalicular excretion

51
Q

What does the liver look like in someone with dubin johnson

A

dark brown pigment in hepatocytes and kupffer cells

52
Q

How do you rule out rotors from dubin johnson

A

does not have pigmented liver, non itching jaundice

53
Q

What is alcohols mech of leading to jaundice

A

decreased excretion of bilirubin into bile. hyperbilirubinemia

54
Q

What are the various sources for aa

A

body protein, de novo synthesis from carbon and Nitrogen, dietary aa

55
Q

What can aa be turned into

A

body protein, urea and O2 and biosynthesis of N compounds like creatine, hormones, nucleotides etc

56
Q

What 3 circumstances lead to aa oxidative catbolism

A

leftover aa from normal protein
dietary aa that exceed need
proteins in body that are broken down (starvation, DM)

57
Q

What 2 key processes does the liver do in metabolic nitrogen elimination

A

transamination of aminotransferase reactions

release of nitrogen from glutamate and conversion into urea by the urea cycle

58
Q

how does the liver assist in ammonia detoxification

A

urea cycle

59
Q

which molecular group is removed from aa first before any breakdown

A

the amino group

60
Q

all aminotransferases rely on what cofactor

A

the pyridoxal phosphate cofactor

61
Q

which compound accepts the amino groups

A

alpha ketoglutarate

62
Q

What aa is a temporary storage for nitrogen

A

L glutamine, will donate if amino group needed for biosynthesis

63
Q

What is the role of glutamate dehydrogenase

A

aketoglutarate and NH4–> glutamate with help of NADH–>NAD+

64
Q

What two enzymes are involved in non-hepatic removal of ammonia

A

glutamate dehydrogenase and glutamine synthetase

65
Q

What two enzymes in the liver are involved with excreiton of N via urea production

A

aminotransferase and glutamate dehydrogenase

66
Q

How is excess ammonia transported in tissues because is toxic

A

attaches to glutamine via glutamine synthetase

enters blood to liver where NH4 is liberated in mitochondria by glutaminase

67
Q

How many steps are there in the urea cycle

A

4

68
Q

Describe first step in urea cycle

A

carbamoyl phosphate combined with ornithine form citrulline so can pass into cytosol

69
Q

describe the second step in urea cycle

A

citrulline is converted to arginino-succinate thorugh a citrullyl-AMP intermediate

70
Q

describe the third step of the urea cycle

A

argininosuccinate is cleaved via argininosuccinase to yield fumarate and arginine which enters the citric acid cycle

71
Q

describe the fourth step of the urea cycle

A

formation of urea- arginine is converted to urea and ornthinine via arginase

72
Q

What is the link between the citric acid cycle and urea cycle

A

arginosuccinate can be converted to fumurate (which can then be converted to malate) and enters citric acid cycle

73
Q

Where is the most common site of the urea cycle

A

liver and sometimes kidney

74
Q

toxic ammonia is quickly recaptured by what

A

carbamoyl phosphate and passed into urea cycle

75
Q

how is nitrogen added to urea cycle

A

carbamoyl phosphate and aspartate

76
Q

what are the enzymes of urea cycle that are in the mitochondria

A

carbamoyl phosphate synthestase

ornithine trans carbamylase

77
Q

What are the enzymes in the cytosol of urea cycle

A

arginino-succinate synthase
arginino- succinase
arginase

78
Q

Complete loss of urea cycle enzymes cause what

A

death shortly after birth

79
Q

deficiencies in urea cycle enzymes lead to what

A

hyperammonemia (elevated ammonia in blood)

also lead to build up of glutamine and glutamate which can cause brain swelling

80
Q

How are urea cycle disorders Tx

A

restricting dietary protein intake to limit nitrogen

metabolic substrates given to increase biosynthesis of nitrogen containing compunds that are excreted

81
Q

What do we Tx people with argininosuccinase deficiency

A

high doses of L arginine

82
Q

What causes phenylketonuria

A

problem with phenlyalanine hydroxyls PAH which converts phenylalanine to tyrosine and epinephrine

83
Q

What inheritance is phenylketonuria

A

autosomal recessive

84
Q

What is the result of a defective PAH

A

increase phenylpyruvate which is harmful

85
Q

people who do not stick to low phenylalanine diet with phenylketonuria develop what

A

AHDH

86
Q

What common food source contatins high phenylalanine

A

Nutrasweet, artificial sweetener. has aspartame

87
Q

What are common liver function tests

A

ALT, AST, ALP, albumin, bilirubin, GGT, LDH and PT

88
Q

describe alanine transaminase (ALT)

A

enzyme in liver cells that metabolize protein
low levels in blood
released into blood when liver is damaged

89
Q

describe aspartate transaminase (AST)

A

metabolizes alanine and is found in high [ ] in liver, if elvels increase further indicative of liver damage

90
Q

describe alkaline phosphatase (ALP)

A

in liver and bile ducts as well as other tissues.

highger than normal levels indicate liver damage or disease

91
Q

Low levels of albumin and total protein are indicative of what

A

liver damage because this shows how well liver is making proteins to fight infections and perform functions

92
Q

What is the gamma-glutamyltransferase test for

A

measures amount of enzyme in blood. If elevated suggest liver or bile duct damage

93
Q

L -lactate dehydrogenase test is for what

A

elevated levels may indicate liver damage, found in other tissues too

94
Q

Why is the prothrombin time aliver function test

A

measures clotting time. Increased PT indicates liver damage since liver produces thrombin and fibrinogen

95
Q

why does liver damage lead to increased plasma ammonia

A

blood is shunted away from liver–> ammonia catabolism is decreased

GI II (12 decks)

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