Adrenal Medulla

Question 1

What is the primary function of the adrenal medulla?

Answer 1

The adrenal medulla secretes catecholamines (epinephrine, norepinephrine, dopamine) in response to stress.

Question 2

What are catecholamines, and how are they synthesized?

Answer 2

Catecholamines are stress-response biomolecules, synthesized as follows:
1. Tyrosine → L-DOPA (via Tyrosine Hydroxylase)
2. L-DOPA → Dopamine (via DOPA Decarboxylase)
3. Dopamine → Norepinephrine (via Dopamine β-Hydroxylase)
4. Norepinephrine → Epinephrine (via Phenylethanolamine-N-methyltransferase (PNMT), activated by cortisol)

Question 3

What are the physiological functions of catecholamines?

Answer 3

• Regulation of blood pressure & cardiac output
• Glycogenolysis & gluconeogenesis (glucose mobilization)
• Thermoregulation
• Fight-or-flight response

Question 4

How are catecholamines metabolized and excreted?

Answer 4

Catecholamines are degraded in the liver and excreted via urine as:
* Vanillylmandelic Acid (VMA) (major metabolite)
* Homovanillic Acid (HVA) (dopamine metabolism)
* Metanephrine & Normetanephrine (minor urinary metabolites)

Question 5

What are the key considerations for catecholamine sample collection?

Answer 5

• Avoid stress, caffeine, tea, chocolate, and certain medications 48 hours before testing.
• Use antioxidants (glutathione) to prevent catecholamine degradation.
• Collect blood in heparin/EDTA tubes or 24-hour urine with acidification.

Question 6

What are the main analytical methods used for catecholamine measurement?

Answer 6

• Colorimetry & Fluorimetry (less specific)
• High-Performance Liquid Chromatography (HPLC) with Electrochemical Detection (gold standard)
• HPLC-MS/MS (most sensitive technique)

Question 7

What are the normal reference values for plasma catecholamines?

Answer 7

• Epinephrine: 50–900 pmol/L
• Norepinephrine: 450–3000 pmol/L
• Dopamine: 50–600 pmol/L

Question 8

What are the normal reference values for urinary metabolites?

Answer 8

• VMA (Vanillylmandelic Acid): 2–5 mg/24h
• HVA (Homovanillic Acid): 3–8 mg/24h
• Free Catecholamines: 20–55 µg/24h
• Metanephrines: 1–2 mg/24h

Question 9

When is dynamic testing used in adrenal medulla exploration?

Answer 9

When static tests are inconclusive, especially in detecting pheochromocytoma.

Question 10

How does the Histamine/Glucagon Test work?

Answer 10

• Histamine/Glucagon injection induces temporary hypertension (HTN).
• Normal response: Blood pressure returns to normal in 2 minutes.
• Tumor presence: Hypertension persists for 5–15 minutes.

Question 11

What is the significance of the Oral Glucose Tolerance Test (OGTT) in adrenal tumors?

Answer 11

Pheochromocytoma patients often have a prediabetic glucose profile due to catecholamine-induced insulin resistance.

Question 12

How does the Regitine (Phentolamine) Test diagnose pheochromocytoma?

Answer 12

• Regitine blocks catecholamine receptors, leading to BP drop in normal patients.
• Pheochromocytoma: Blood pressure remains elevated for 5–15 minutes.

Question 13

What is the Clonidine Suppression Test, and how does it work?

Answer 13

• Clonidine suppresses sympathetic tone, reducing catecholamine levels.
• Pheochromocytoma: Catecholamine levels remain high despite clonidine administration.

Question 14

What is a pheochromocytoma?

Answer 14

A catecholamine-secreting tumor arising from chromaffin cells of the adrenal medulla.

Question 15

What are the key symptoms of pheochromocytoma?

Answer 15

Classic triad:
1. Hypertension (HTN) resistant to treatment
2. Tachycardia & palpitations
3. Excessive sweating (diaphoresis)
Other symptoms: Headaches, anxiety, weight loss, hyperglycemia.

Question 16

What biochemical findings confirm pheochromocytoma?

Answer 16

• ↑ Plasma Epinephrine (Adrenal tumor) or Norepinephrine (Extra-adrenal tumor).
• ↑ Urinary VMA, metanephrines, normetanephrines.
• ↑ Glucose levels (due to catecholamine-induced gluconeogenesis).

Question 17

What genetic syndromes are associated with pheochromocytoma?

Answer 17

• Von Hippel-Lindau Disease (VHL)
• Neurofibromatosis Type 1 (Recklinghausen disease)

Question 18

What is the treatment for pheochromocytoma?

Answer 18

Surgical resection (usually curative).

Question 19

What is a neuroblastoma?

Answer 19

A malignant tumor of neural crest cells, primarily affecting infants & young children.

Question 20

What are the main sites of neuroblastomas?

Answer 20

• Sympathetic ganglia (Sympathoblastoma)
• Adrenal gland (Adrenal Neuroblastoma)

Question 21

What are the key clinical features of neuroblastoma?

Answer 21

• No hypertension (unlike pheochromocytoma).
• Large abdominal mass (up to 1 kg).
• Metastases: Liver (Pepper syndrome), bones, orbit (Hutchinson syndrome → periorbital ecchymosis & exophthalmos).

Question 22

What are the biochemical markers for neuroblastoma?

Answer 22

• ↑ Dopamine (main precursor).
• ↑ Homovanillic Acid (HVA) (key urinary marker).
• ↑ Neuron-Specific Enolase (NSE) (neuroendocrine tumor marker).

Question 23

What conditions mimic neuroblastoma?

Answer 23

• Wilms’ Tumor (Nephroblastoma): Normal catecholamine levels.
• Hepatoblastoma: ↑ Alpha-Fetoprotein (AFP).

Question 24

How is dopamine linked to schizophrenia?

Answer 24

• Increased dopamine levels due to inhibition of dopamine β-hydroxylase.
• Dopaminergic hyperactivity is a key factor in schizophrenia.

Question 25

What is the role of dopamine in Parkinson’s disease?

Answer 25

• Dopamine deficiency due to neurodegeneration of dopaminergic neurons.
• Treatment: Levodopa (L-DOPA) (dopamine precursor).