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TAS Neonatal Medicine ✅ > Bilirubin Metabolism ✅ > Flashcards

Bilirubin Metabolism ✅ Flashcards

1
Q

How is bilirubin produced?

A

From the breakdown of RBCs in the reticuloendothelial system

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2
Q

What does the breakdown of RBCs in the reticuloendothelial system produce?

A

Haemoglobin

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3
Q

What is haemoglobin broken down into?

A
  • Fe
  • Globin
  • Carbon monoxide
  • Biliverdin
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4
Q

What is biliverdin converted into?

A

Bilirubin (unconjugated)

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5
Q

What happens to unconjugated bilirubin in the plasma?

A

It binds to albumin to form a bilirubin-albumin complex

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6
Q

What happens to the bilirubin-albumin complex?

A

It is taken up into the liver

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7
Q

What happens to the bilirubin once it has been taken up by the liver?

A

It is conjugated and excreted into bile

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8
Q

What happens to conjugated bilirubin in the gut?

A

Is is hydrolysed

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9
Q

What is produced when conjugated bilirubin is hydrolysed in the gut?

A
  • Stercobilinogen

- Urobilinogen

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10
Q

How is stercobilinogen removed from the body?

A

Excreted via faeces

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11
Q

How is urobilinogen removed from the body?

A

It is excreted via the kidney

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12
Q

What happens to bilirubin that is not hydrolysed in the gut?

A

It enters the enterohepatic circulation, and is taken up again into the liver

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13
Q

What molecules is haem present in?

A
  • Haemoglobin
  • Myoglobin
  • Cytochromes
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14
Q

What % of bilirubin is derived from haemoglobin?

A

80%

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15
Q

How many molecules of bilirubin are produced from 1 molecule of haem?

A

1

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16
Q

What increases red cell breakdown in neonates?

A

The high concentration of haemoglobin at birth

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17
Q

What is the normal haemoglobin at birth?

A

150-220g/L

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18
Q

Why is there a high concentration of bilirubin at birth?

A

It is a response to the relative hypoxia environment of the foetus

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19
Q

Why is there a breakdown of haemoglobin in early postnatal life?

A

Because of the increased oxygen concentration

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20
Q

What is the neonatal production rate of bilirubin?

A

100-120µmol/kg/day

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21
Q

What is the adult production rate of bilirubin?

A

50-70µmol/kg/day

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22
Q

How is fetal haemoglobin different from adult?

A

It has a shorter half life

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23
Q

What practice increases neonatal red cell mass?

A

Delayed cord clamping

24
Q

Where is the haem molecule broken down?

A

In reticuloendothelial cells

25
Q

What is the haem molecule broken down into?

A

Biliverdin

26
Q

What breaks haem down into biliverdin?

A

The enzyme haem oxygenase

27
Q

What enzyme converts biliverdin into bilirubin?

A

Biliverdin reductase enzyme

28
Q

What happens to iron released from the breakdown of haem?

A

It is used in haem synthesis again

29
Q

How much CO is produced from the breakdown of 1 mole of haem?

A

1 mole

30
Q

What % of endogenous CO is derived from haem?

A

80-90%

31
Q

What is the clinical relevance of haem breaking down into CO when considering jaundice?

A

The end-tidal CO can be used as a surrogate measurement for bilirubin production

32
Q

What kind of bilirubin does red cell breakdown produce?

A

Unconjugated

33
Q

What happens if the albumin binding capacity is exceeded?

A

Free bilirubin is released into the circulation

34
Q

What is the problem with free bilirubin being released into the circulation?

A

As it is lipid soluble, it can cross the blood-brain barrier and result in acute encephalopathy or kernicterus

35
Q

What happens to unconjugated bilirubin bound to albumin?

A

It is transported to the liver for conjugation

36
Q

What happens to bound bilirubin in the liver?

A

The albumin-bilirubin compound is dissociated, and the bilirubin is transported to hepatocytes

37
Q

Is the process of bilirubin being transported to hepatocytes active or passive?

A

Mostly passive process

38
Q

What is the process of transportation of bilirubin to hepatocytes dependant on?

A

Certain transporter proteins

39
Q

What happens to bilirubin within hepatocytes?

A

It is bound to cytosolic proteins known as glutathione S-transferases or ligandins within hepatocytes

40
Q

What enzyme is responsible for conjugation of bilirubin within hepatocytes?

A

Uridine disphosphate glucuronyltransferase (UGT)

41
Q

What is produced from the conjugation of bilirubin by UGT?

A

Mostly bilirubin diglucuronide, but also some bilirubin monoglucuronide

42
Q

Is excretion of conjugated bilirubin into the biliary system an active or passive process?

A

Active and energy-dependent

43
Q

What mediates the excretion of conjugated bilirubin into the biliary system?

A

Specific carrier proteins

44
Q

Can conjugated bilirubin cross the blood brain barrier?

A

No

45
Q

Why can’t conjugated bilirubin cross the blood brain barrier?

A

Because it is water soluble

46
Q

What happens to most of the conjugated bilirubin excreted in the bile?

A

It is hydrolysed back to unconjugated bilirubin

47
Q

What converts conjugated bilirubin back to unconjugated?

A

Beta-glucuronidase

48
Q

Where is beta-glucuronidase present?

A

In the intestinal mucosa

49
Q

What happens to conjugated bilirubin that is converted back to unconjugated in the gut?

A

It is absorbed in the terminal ileum and transported back to the liver via the portal circulation

50
Q

Why does the enterohepatic circulation play an important role in bilirubin metabolism?

A

It allows bile acids to be recycled

51
Q

What factors increase enterohepatic circulation?

A
  • Prolonged gut transit time
  • Delayed passage of meconium
  • Poor enteral feeding
  • Prematurity
  • Antibiotic treatment
52
Q

What happens to conjugated bilirubin that is not recycled in the gut?

A
  • Some is converted to stercobilinogen

- Small amount is converted to urobilinogen

53
Q

What converts conjugated bilirubin to stercobilinogen?

A

Colonic bacteria

54
Q

What happens to stercobilinogen?

A

It is further oxidised to stercobilin, which gives faeces its brown colour

55
Q

What happens to urobilinogen?

A

It is excreted into the urine following further oxidation to urobilin, which gives urine its colour

TAS Neonatal Medicine ✅ (35 decks)

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