⚡ Endocrine System Lesson

ENA: the adrenal medulla hormones

The adrenal medulla isn't a typical endocrine gland — it's made of modified sympathetic nerve cells that release hormones directly into the blood instead of at a synapse.

Epineph.

Norepin.

Adrenaline

📖 Full Breakdown

Fight-or-flight hormones, and how they differ from the cortex's hormones

Fast, brief, and directly wired to the sympathetic nervous system — a completely different mechanism from the adrenal cortex.

Epinephrine (80%)

The dominant catecholamine

Increases heart rate, causes bronchodilation, raises blood glucose via glycogenolysis, and dilates blood vessels in skeletal muscle — this is the mechanism behind an EpiPen for anaphylaxis.

Norepinephrine (20%)

The vasoconstrictor

Primarily causes vasoconstriction, raising blood pressure. It also functions as a neurotransmitter in the central nervous system, separate from its hormonal role here.

Mechanism

Modified sympathetic neurons

Because the adrenal medulla is essentially specialized sympathetic tissue, its hormone release is fast and directly triggered by the nervous system — unlike the slower, hormonally-regulated adrenal cortex.

🩺 Clinical / Exam Application

A patient has episodes of sudden severe headache, heart palpitations, and profuse sweating that come and go unpredictably. This classic triad points toward pheochromocytoma — a tumor of the adrenal medulla that intermittently releases massive amounts of epinephrine and norepinephrine. Because the medulla's hormones act fast and powerfully on heart rate and blood vessels, episodic tumor secretion produces episodic, dramatic symptoms rather than a constant baseline change.

⚠️ Exam Alert

A key structural distinction commonly tested: the adrenal cortex responds to hormonal signals (ACTH) and produces slow, sustained steroid effects, while the adrenal medulla responds to direct sympathetic nervous system input and produces fast, brief catecholamine effects — different triggers, different timescales, different hormone classes entirely.

🚧 Common Trap

Don't assume the adrenal medulla works like the adrenal cortex just because they share the same gland. The cortex is a true hormonal gland responding to ACTH; the medulla is essentially nervous tissue that releases hormones the way a neuron releases neurotransmitters — just into the blood instead of a synapse.

✅ Quick Check

Why does the adrenal medulla respond so much faster than the adrenal cortex to a stressful stimulus?

📝 Exam Prep

Common Exam Questions

❓ What are the two main hormones released by the adrenal medulla, and what triggers their release?

✅ Epinephrine (80%) and norepinephrine (20%), released in response to sympathetic nervous system activation during stress or a fight-or-flight response.

❓ What is pheochromocytoma and what symptoms does it cause?

✅ Pheochromocytoma is a tumor of the adrenal medulla causing excess catecholamine release. It classically causes episodic hypertension, headache, palpitations, and sweating.