Final answer:
Cortisol secretion from the adrenal cortex is initiated by ACTH, which is released by the pituitary gland in response to HPA axis activation due to stressors.
Step-by-step explanation:
The synthesis and secretion of cortisol from the adrenal cortex are primarily stimulated by the adrenocorticotropic hormone (ACTH). ACTH is produced by the anterior lobe of the pituitary gland as a result of the hypothalamic-pituitary-adrenal (HPA) axis activation. This axis starts when the hypothalamus secretes a neurohormone in response to stress, then the pituitary releases ACTH, which in turn promotes cortisol release from the adrenal cortex. Cortisol helps in regulating the stress response, blood pressure, blood volume, nutrient uptake and storage, fluid and electrolyte balance, and inflammation. Furthermore, cortisol participates in glucose metabolism, especially during long-term stress by promoting gluconeogenesis, the breakdown of fats and proteins for energy, and by interacting with epinephrine to cause vasoconstriction.