Week 16

Question 1

What is the structure and definition of heme?

Answer 1

Heme = iron (Fe²⁺) + protoporphyrin IX ring; prosthetic group in hemoglobin, myoglobin, cytochromes

Question 2

Where does heme synthesis occur?

Answer 2

Organs: Liver and bone marrow
Subcellular: Mitochondria + cytosol

Question 3

What are the initial substrates for heme synthesis?

Answer 3

Glycine + Succinyl-CoA

Question 4

What is the rate-limiting step in heme synthesis?

Answer 4

ALA synthase (glycine + succinyl-CoA → ALA)

Question 5

Which steps of heme synthesis are inhibited by lead?

Answer 5

• ALA dehydratase
• Ferrochelatase

Question 6

Enzyme deficiency causing porphyria cutanea tarda?

Answer 6

Uroporphyrinogen decarboxylase deficiency

Question 7

What is the inheritance pattern of porphyrias?

Answer 7

Mostly autosomal dominant (except congenital erythropoietic porphyria = AR)

Question 8

Key symptoms of porphyrias?

Answer 8

• Photosensitivity
• Abdominal pain
• Neuropathy
• Psychiatric symptoms
• Dark urine

Question 9

Management of porphyrias?

Answer 9

• Avoid triggers (alcohol, drugs, fasting)
• Hemin (↓ ALA synthase)
• Glucose loading
• Sun protection

Question 10

Where does heme catabolism occur? What do the enzymes do?

Answer 10

Occurs in macrophages (spleen, liver)
• Heme oxygenase: heme → biliverdin
• Biliverdin reductase: biliverdin → bilirubin

Question 11

What are biliverdin and bilirubin?

Answer 11

• Biliverdin: green breakdown product of heme
• Bilirubin: yellow breakdown product (unconjugated, lipid-soluble)

Question 12

What is bilirubin conjugation? Location, enzyme, purpose?

Answer 12

• Definition: bilirubin + glucuronic acid
• Location: liver
• Enzyme: UDP-glucuronyl transferase
• Purpose: make bilirubin water-soluble for excretion

Question 13

What are urobilinogen, stercobilin, and urobilin?

Answer 13

• Urobilinogen: formed in intestine
• Stercobilin: colors stool brown
• Urobilin: colors urine yellow

Question 14

Cause and symptoms of Gilbert syndrome?

Answer 14

• Cause: mild UDP-glucuronyl transferase deficiency
• Symptoms: mild unconjugated hyperbilirubinemia, benign

Question 15

Cause and symptoms of Dubin-Johnson syndrome?

Answer 15

• Cause: defective bilirubin excretion (MRP2 transporter)
• Symptoms: conjugated hyperbilirubinemia, black liver

Question 16

Common causes of prehepatic (hemolytic) jaundice?

Answer 16

• Hemolytic anemia
• Malaria
• Sickle cell disease
• Transfusion reactions

Question 17

Common causes of intrahepatic (hepatocellular) jaundice?

Answer 17

• Hepatitis
• Cirrhosis
• Drugs
• Alcohol liver disease

Question 18

Common causes of posthepatic (obstructive) jaundice?

Answer 18

• Gallstones
• Pancreatic cancer
• Bile duct obstruction
• Cholangiocarcinoma

Question 19

Which type of bilirubin is elevated in each type of jaundice?

Answer 19

• Prehepatic: unconjugated
• Intrahepatic: both
• Posthepatic: conjugated

Question 20

Cause of neonatal jaundice and what is kernicterus?

Answer 20

• Cause: immature UDP-glucuronyl transferase
• Kernicterus: bilirubin deposition in brain → neurologic damage

Question 21

Treatment of neonatal jaundice?

Answer 21

• Phototherapy
• Exchange transfusion (severe cases)
• Adequate feeding