Correct Answer: A) Medulla
🧠 Explanation:
This is a classic histology-based identification question involving ultrastructural (electron microscopy) features of adrenal gland cells.
🔬 Let’s break it down:
Chromaffin cells are the hallmark of the adrenal medulla, not the cortex. These are neuroendocrine cells derived from neural crest cells, and they function similarly to postganglionic sympathetic neurons.
They store and secrete catecholamines: epinephrine and norepinephrine.
The electron microscopy of chromaffin cells shows:
Moderately electron-dense granules: typically contain epinephrine.
Highly electron-dense granules: typically contain norepinephrine.
These granules are membrane-bound and serve as a key identification feature on EM.
Thus, a tissue with chromaffin cells + electron-dense granules most certainly belongs to the adrenal medulla.
❌ Why the other options are incorrect:
C) Zona glomerulosa:
This is the outermost layer of the adrenal cortex. It produces mineralocorticoids (mainly aldosterone) and does not contain chromaffin cells. The cells here are arranged in small rounded clusters, not rich in dense granules.
D) Zona reticularis:
This is the innermost layer of the adrenal cortex and produces androgens (e.g., DHEA). The cells are known for a more irregular, branched appearance and lipid-rich cytoplasm—not electron-dense granules.
E) Zona fasciculata:
Middle layer of the cortex, responsible for glucocorticoid (cortisol) production. The cells appear pale under light microscopy due to lipid droplets and have a “spongy” appearance. They also lack chromaffin cells and electron-dense granules.
B) None of these:
This is incorrect because medulla is the correct answer and is indeed listed.
