Regarding the synthesis, secretion, and physiological effects of adrenal steroid hormones, all of the following are true EXCEPT:

Question

Accepted Answer

D. Epinephrine synthesis requires the enzyme phenylethanolamine N-methyltransferase (PNMT), which is located in the adrenal cortex and catalyzes the final step of catecholamine synthesis. ## Adrenal Steroid and Catecholamine Synthesis and Regulation

### Correct Statements (Options 0, 1, 2)

**Key Point:** Aldosterone is synthesized exclusively in the zona glomerulosa and is regulated by the renin-angiotensin-aldosterone system (RAAS) and serum potassium. Angiotensin II is the primary physiological stimulus; elevated K^+^ also stimulates aldosterone secretion directly [cite:KD Tripathi 8e Ch 31].

**Key Point:** ACTH activates the cAMP-dependent protein kinase A (PKA) pathway via G-protein coupled receptors on adrenocortical cells. This increases the activity of StAR protein and P450 enzymes, promoting cortisol synthesis [cite:Robbins 10e Ch 24].

**High-Yield:** Adrenal androgens (DHEA and androstenedione) are produced in the zona reticularis under ACTH stimulation. In females, these contribute to axillary and pubic hair growth and clitoral development. In males, testicular testosterone dominates secondary sexual characteristics, but adrenal androgens still contribute [cite:Harrison 21e Ch 375].

### The Incorrect Statement (Option 3)

**Warning:** This option contains a critical anatomical and biochemical error:

1. **PNMT location:** Phenylethanolamine N-methyltransferase (PNMT) is located in the **adrenal medulla**, NOT the adrenal cortex. The adrenal medulla is derived from neural crest tissue and is functionally distinct from the cortex.

2. **Catecholamine synthesis pathway:**
   - Tyrosine → L-DOPA (via tyrosine hydroxylase)
   - L-DOPA → Dopamine (via DOPA decarboxylase)
   - Dopamine → Norepinephrine (via dopamine β-hydroxylase) — occurs in adrenal medulla
   - Norepinephrine → **Epinephrine** (via PNMT) — final step, occurs in adrenal medulla

**Clinical Pearl:** The adrenal medulla secretes ~80% epinephrine and ~20% norepinephrine. Epinephrine synthesis requires PNMT, which is present only in chromaffin cells of the medulla. The cortex does not synthesize catecholamines [cite:Robbins 10e Ch 24].

**Mnemonic:** **DOPA** = **D**opamine → **O**xidized → **P**henylethylamine → **A**cetylated (by PNMT in the **medulla**, not cortex).

### Summary Table

| Adrenal Zone | Primary Hormones | Enzyme/Regulator | Location |
|--------------|------------------|------------------|----------|
| **Zona Glomerulosa** | Aldosterone | Aldosterone synthase (P450c11AS) | Cortex |
| **Zona Fasciculata** | Cortisol | 11β-hydroxylase (P450c11) | Cortex |
| **Zona Reticularis** | DHEA, Androstenedione | 17α-hydroxylase | Cortex |
| **Adrenal Medulla** | Epinephrine, Norepinephrine | PNMT, Dopamine β-hydroxylase | **Medulla** (neural crest origin) |

Answer

A. Adrenal androgens (DHEA and androstenedione) are produced primarily in the zona reticularis and contribute significantly to secondary sexual characteristics in females

Answer

B. ACTH stimulates cortisol synthesis by activating adenylyl cyclase and increasing intracellular cAMP, which then activates protein kinase A

Answer

C. Aldosterone is synthesized in the zona glomerulosa and its secretion is primarily regulated by angiotensin II and serum potassium concentration

Regarding the synthesis, secretion, and physiological effects of adrenal steroid hormones, all of the following are true EXCEPT:

Explanation

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