MCAT Bio/Biochem practice questionEndocrine system

The answer

Correct answer: B. The adrenal medulla releases epinephrine and norepinephrine, leading to increased heart rate, bronchodilation, and glucose mobilization.

Tested concept: Adrenal hormones: cortisol and epinephrine

Explanation

The correct answer describes the acute stress response mediated by the adrenal medulla. Upon sudden stress, the sympathetic nervous system stimulates the adrenal medulla to release catecholamines, primarily epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones rapidly increase heart rate, dilate bronchioles to improve oxygen intake, and promote glycogenolysis and gluconeogenesis to mobilize glucose for immediate energy, all characteristic of the 'fight or flight' response. The option stating that the adrenal cortex secretes cortisol is incorrect because cortisol is released from the adrenal cortex, and while it's a stress hormone, its effects (immune suppression, protein catabolism) are more associated with chronic stress rather than the immediate 'fight or flight' response. The option claiming that the adrenal medulla releases aldosterone is incorrect because aldosterone is a mineralocorticoid released from the adrenal cortex, primarily involved in blood pressure regulation through sodium and water balance, not the immediate acute stress response involving the medulla. The option stating that the adrenal cortex secretes insulin is incorrect because insulin is secreted by the pancreas, not the adrenal cortex, and its primary role is to lower blood glucose, which is contrary to the glucose-mobilizing effects needed during acute stress.