A small cap that does a lot
Sitting on top of each kidney like a triangular hat is an adrenal gland — about the size of a walnut and weighing only a few grams. Despite that small size, it is wired into almost everything: your blood pressure, your blood sugar, your salt and water balance, your sex hormones, and your moment-to-moment response to danger. The trick is that one gland is doing two completely different jobs at once.
Slice an adrenal gland in half and you see two clearly different regions. The outer rim, the adrenal cortex, is yellowish and makes up most of the gland. The inner core, the adrenal medulla, is reddish-brown and much smaller. They look different because they ARE different — they come from different tissues in the embryo and speak in different chemical languages.
The cortex: a steroid factory
The adrenal cortex makes steroid hormones — fat-soluble molecules built from cholesterol. There are three families. [[endo-glucocorticoid|Glucocorticoids]], chiefly cortisol, manage stress, blood sugar and inflammation. [[endo-mineralocorticoid|Mineralocorticoids]], chiefly aldosterone, control salt and blood pressure. And [[adrenal-androgen|adrenal androgens]] like DHEA feed into the body's sex-hormone pool.
The medulla: an adrenaline launcher
The adrenal medulla makes catecholamines — epinephrine (adrenaline) and a smaller amount of norepinephrine. These are amine hormones, built from the amino acid tyrosine, not from cholesterol. The medulla is best thought of as a modified piece of the sympathetic nervous system: instead of releasing its messengers into a narrow synapse, it dumps them straight into the bloodstream so the whole body responds at once.
ONE GLAND, TWO ORGANS
outer rim ──► ADRENAL CORTEX (from embryonic mesoderm)
makes STEROIDS from cholesterol
• cortisol (glucocorticoid) -> stress, sugar
• aldosterone (mineralocorticoid) -> salt, BP
• DHEA (androgen) -> sex-hormone pool
slow, sustained, hours-to-days
inner core ─► ADRENAL MEDULLA (from neural crest)
makes CATECHOLAMINES from tyrosine
• epinephrine / norepinephrine
fast, brief, seconds-to-minutes