adrenal

Meaning: The adrenals are paired endocrine glands with two distinct parts. The outer cortex makes steroid hormones from cholesterol. Aldosterone (a mineralocorticoid) increases Na⁺ reabsorption and K⁺ secretion in the distal nephron, which raises blood volume and pressure. Cortisol (a glucocorticoid) raises blood glucose, mobilizes energy stores and suppresses inflammation and immune activity. The cortex also makes some androgens. The inner medulla is modified sympathetic tissue: when preganglionic sympathetic neurons stimulate it, it releases epinephrine and norepinephrine, which are amine hormones made from tyrosine, producing fight-or-flight effects.

On the MCAT: The cortisol axis is hypothalamus (CRH) → anterior pituitary (ACTH) → adrenal cortex (cortisol), with negative feedback. Expect questions such as: an ACTH-secreting tumor raises cortisol, while high cortisol from any source lowers CRH and ACTH. Aldosterone release is driven mainly by angiotensin II in the renin–angiotensin–aldosterone system. Passages also contrast mechanisms. Steroids cross the membrane, bind intracellular receptors and change transcription, which is slower and longer lasting. Catecholamines bind cell-surface G protein-coupled receptors and use second messengers such as cAMP, which is fast.

Common confusion: Students swap the products of the layers or assume the pituitary controls the whole gland. ACTH acts on the cortex, not the medulla. The medulla responds to nerve input. Remember: cortex = steroids, medulla = amines.