Orris

feature of neuronal cells of medulla of adrenal gland

Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Loading Image
Reading File
I now have comprehensive content from multiple authoritative textbooks. Here is the full answer:

Neuronal (Chromaffin) Cells of the Adrenal Medulla

The cells of the adrenal medulla are called chromaffin cells (also called medullary cells). They are best understood as modified neurons. Here is a systematic breakdown of their features:

1. Embryological Origin

  • Derived from neural crest cells (neuroectoderm), the same precursors that give rise to postganglionic neurons of sympathetic and parasympathetic ganglia.
  • They migrate to colonize the adrenal medulla during development.
  • Langman's Medical Embryology confirms the suprarenal medulla originates from neural crest ectoderm.

2. Nature as Modified Neurons

  • Chromaffin cells are fundamentally modified sympathetic postganglionic neurons - they have lost their axons and dendrites and are instead specialized as secretory (endocrine) cells.
  • They are considered equivalent to postsynaptic neurons, but lack axonal processes in vivo.
  • In culture, they can extend axon-like processes, but in the intact gland, glucocorticoids from the adrenal cortex suppress axonal growth, maintaining the endocrine phenotype.
  • Because their secretory products enter the bloodstream via fenestrated capillaries rather than a synapse, they function as endocrine cells.
(Histology: A Text and Atlas, Ross & Pawlina)

3. Histological Features

  • Large, pale-staining, polyhedral (epithelioid) cells arranged in cords or clumps.
  • Supported by a reticular fiber network.
  • Profuse sinusoidal (fenestrated) capillaries run between the cords, enabling rapid hormone delivery to the bloodstream.
  • A few parasympathetic ganglion cells are scattered in the medulla.
  • On H&E: faintly stained cytoplasmic granules visible in most cells.
Adrenal Medulla - H&E and TEM
(Left: H&E showing pale chromaffin cells in cords with wide capillaries; Right: TEM showing electron-dense NE granules vs. less dense E granules - Junqueira's Basic Histology, 17e)

4. Ultrastructure (Electron Microscopy)

  • Contain many electron-dense secretory granules, 150-350 nm in diameter, for catecholamine storage and secretion.
  • Two cell types based on granule appearance:
    • Epinephrine (E) cells: granules are less electron-dense and generally smaller.
    • Norepinephrine (NE) cells: granules are more electron-dense (due to chromogranins binding catecholamines).
  • Granule contents: catecholamines (epinephrine or norepinephrine) + Ca²⁺ + ATP + chromogranins (49-kDa proteins) - stored as granular complexes.
(Junqueira's Basic Histology, 17e)

5. The Chromaffin Reaction (Naming Origin)

  • Named because they react with chromate salts (chromic acid or potassium dichromate) - the chromaffin reaction.
  • This reaction involves oxidation and polymerization of the catecholamines within the secretory vesicles.
  • Chromaffin cells are part of the APUD system (Amine Precursor Uptake and Decarboxylation).
(Histology: A Text and Atlas, Ross & Pawlina)

6. Innervation and Secretory Mechanism

  • Innervated by myelinated preganglionic sympathetic nerve fibers (via the greater splanchnic nerve, with cell bodies in the thoracic spinal cord).
  • Preganglionic fibers release ACh, which activates nicotinic receptors on chromaffin cells.
  • Upon activation, chromaffin cells release catecholamines directly into the circulation - acting like a "gang-lion in the blood."
(Costanzo Physiology, 7th Ed.)

7. Secretory Products and Proportions

Product% SecretedWhere Else Made
Epinephrine (adrenaline)~80%Only in adrenal medulla
Norepinephrine~20%Also sympathetic nerve endings
  • The conversion of norepinephrine → epinephrine requires the enzyme PNMT (phenylethanolamine-N-methyltransferase), which is present only in chromaffin cells of the adrenal medulla.
  • PNMT activity depends on cortisol supplied via the portal venous drainage from the adrenal cortex - this is why cortisol from the cortex controls the medullary phenotype in two ways: inhibits axon growth AND enables epinephrine synthesis.
(Costanzo Physiology, 7th Ed.)

8. Supporting Cells

  • Sustentacular cells support the chromaffin cells (analogous to glial/satellite cells in ganglia).
(Robbins, Cotran & Kumar - Pathologic Basis of Disease)

9. Paraganglion System

  • Chromaffin cells are not exclusive to the adrenal medulla. Scattered clusters exist in paravertebral and prevertebral sympathetic ganglia and viscera - collectively called paraganglia.
  • Extra-adrenal chromaffin cells typically secrete only norepinephrine (lack PNMT because they are distant from cortisol supply).

10. Clinical Relevance - Pheochromocytoma

A tumor of chromaffin cells. Key features follow the "rule of 10s":
  • 10% extra-adrenal (paragangliomas)
  • 10% in children
  • 10% bilateral/multiple
  • 10% not hypertensive
  • 10% malignant
  • 10% familial
  • 10% recur after surgery
  • Pheochromocytoma secretes mainly norepinephrine (tumor is too far from cortical cortisol to express PNMT effectively)
Summary in one sentence: Chromaffin cells are neural crest-derived, modified sympathetic postganglionic neurons that have traded their axons for secretory granules, are innervated by preganglionic cholinergic fibers, and secrete predominantly epinephrine (80%) into the blood under stress.
This is a shared conversation. Sign in to Orris to start your own chat.