Each adrenal gland is a steroid factory stacked on a panic switch
Above every kidney sits a yellowish gland the size of a few centimeters yet dense with arteries—up to sixty may enter each one. Outer cortex layers drip aldosterone, cortisol, and androgens; the inner medulla dumps adrenaline when stress hits.
Human adrenals rest in the retroperitoneum, slightly medial atop the kidneys, inside renal fascia beneath the diaphragm and tethered to its crura. The right gland is pyramidal, the left semilunar and a bit larger; together an adult pair weigh about seven to ten grams, roughly five centimeters long, three wide, and up to one thick, yellowish beneath a fatty capsule. A weak connective septum keeps them near but separate from the kidneys they crown.
Cortex zones specialize after cholesterol is taken up from LDL or made locally and shuttled into mitochondria—the rate-limiting step of steroidogenesis. Zona glomerulosa makes aldosterone to retain sodium, excrete potassium, and raise blood pressure, reclaiming about two percent of filtered sodium. Zona fasciculata—nearly eighty percent of cortical volume—builds cortisol and cortisone to mobilize glucose, fat, and amino acids while damping immunity and inflammation. Zona reticularis releases DHEA, DHEA-S, and androstenedione for later conversion to sex hormones. Medullary chromaffin cells, driven by sympathetic fibers from thoracic levels T5–T11, secrete about eighty percent adrenaline and twenty percent noradrenaline straight into blood, like a synapse-free ganglion.
Blood arrives via superior, middle, and inferior suprarenal arteries—up to sixty small vessels per gland—and exits asymmetrically into the vena cava or left renal vein. Cortisol secretion follows ACTH’s circadian rhythm, peaking early morning. Too much cortisol yields Cushing’s syndrome; too little, Addison’s disease; enzyme blocks such as 21-hydroxylase deficiency cause congenital adrenal hyperplasia. The same tiny organs thus throttle salt, sugar, sex steroids, and split-second fight-or-flight.
Source: Adrenal gland
