## Adrenal Cortical Zones — Histological Identification ### Zona Fasciculata Architecture **Key Point:** The zona fasciculata is the widest zone of the adrenal cortex and is composed of columnar cells arranged in parallel cords separated by sinusoidal capillaries. **High-Yield:** These cells are lipid-rich (appear pale/vacuolated in H&E staining due to lipid extraction during processing) and contain abundant smooth endoplasmic reticulum (SER) for steroid synthesis, particularly glucocorticoids (cortisol). ### Comparative Histology of Adrenal Zones | Zone | Cell Arrangement | Lipid Content | ER Type | Primary Hormone | | --- | --- | --- | --- | --- | | **Zona Glomerulosa** | Glomerular/arched clusters | Moderate | SER | Aldosterone | | **Zona Fasciculata** | Columnar cords, parallel | **High (lipid-rich)** | **Abundant SER** | **Cortisol** | | **Zona Reticularis** | Irregular anastomosing cords | Low | Moderate SER | Androgens | | **Adrenal Medulla** | Polygonal chromaffin cells | Minimal | Rough ER | Catecholamines | **Clinical Pearl:** The pale, vacuolated appearance of zona fasciculata cells in routine H&E sections is due to lipid droplet dissolution during tissue processing — lipids are the substrate for steroid hormone synthesis. **Mnemonic:** **GFR** = **G**lomerulosa (Aldosterone), **F**asciculata (cortisol), **R**eticularis (sex steroids). Fasciculata = **F**at-rich (lipid-laden). [cite:Robbins 10e Ch 24] 
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