Which of the following histological features is characteristic of the zona glomerulosa of the adrenal cortex?

Explanation

## Histological Architecture of the Adrenal Cortex The adrenal cortex is divided into three functional zones, each with distinct histological and ultrastructural features. ### Zona Glomerulosa (Outermost Zone) **Key Point:** The zona glomerulosa is characterized by cells arranged in **columnar clusters or ovoid glomerular groups**, with mitochondria containing **tubular cristae** — a hallmark ultrastructural feature of this zone. **Ultrastructural Features:** - Cells arranged in columnar clusters (or compact ovoid groups) - Mitochondria contain **tubular (vesicular) cristae** — distinguishing them from the lamellar cristae of zona fasciculata and reticularis - **Sparse rough endoplasmic reticulum (rER)** - Few lipid droplets compared to zona fasciculata - Produces **aldosterone** (mineralocorticoid) ### Why Option C is Correct Option C states "cells arranged in columnar clusters with mitochondria containing tubular cristae" — this precisely matches the standard histological description of the zona glomerulosa per Junqueira's Basic Histology and Wheater's Functional Histology. ### Why Option B is Incorrect Option B states "few mitochondria and sparse rough endoplasmic reticulum." The zona glomerulosa does NOT have few mitochondria — it has mitochondria with **tubular cristae**, which is a defining feature. Stating "few mitochondria" is factually wrong and contradicts standard histology texts. ### Comparative Histology of Adrenal Zones | Feature | Zona Glomerulosa | Zona Fasciculata | Zona Reticularis | |---------|------------------|------------------|------------------| | **Arrangement** | Columnar clusters / glomerular groups | Long parallel cords | Anastomosing reticular network | | **Mitochondrial cristae** | **Tubular** | Lamellar | Lamellar | | **Lipid droplets** | Few | Abundant (spongiocytes) | Moderate | | **rER** | Sparse | Moderate | Extensive | | **sER** | Moderate | Abundant | Abundant | | **Hormone** | Aldosterone | Cortisol, androgens | Androgens | **High-Yield:** The **tubular cristae** of mitochondria in zona glomerulosa is the key ultrastructural identifier. At the light microscopic level, the compact glomerular/columnar clustering distinguishes it from the loose parallel cords of zona fasciculata. **Clinical Pearl:** Aldosterone synthesis in zona glomerulosa is regulated by the **renin-angiotensin system** and serum potassium — not ACTH. This functional independence is reflected in its unique histological and ultrastructural organization. **Mnemonic:** **GFR** — **G**lomerulosa (glomerular/columnar clusters, tubular cristae), **F**asciculata (parallel cords, lamellar cristae, lipid-laden spongiocytes), **R**eticularis (anastomosing network, extensive rER). [cite: Junqueira's Basic Histology 14e Ch 21; Wheater's Functional Histology 6e Ch 14]