Final answer:
Hormone levels are chiefly regulated by negative feedback, which prevents further secretion of a hormone when levels are adequate. Additional mechanisms include humoral stimuli responding to extracellular fluid changes, hormonal stimuli from other hormones, and neural stimuli from the nervous system.
Step-by-step explanation:
Four control mechanisms exist to regulate hormone availability and potency, ensuring that hormone levels in the body are accurately maintained. The first mechanism is negative feedback, where the hormone's rising levels in the bloodstream inhibit its further release. This is the most common and essential mechanism governing hormonal level control. The remaining mechanisms are humoral, hormonal, and neural stimuli.
The humoral stimuli mechanism responds to changes in extracellular fluid or ion levels, instigating hormone release. For example, low calcium levels in the blood can trigger the release of parathyroid hormone. Hormonal stimuli refer to the release of one hormone in response to the presence of another hormone, such as the thyroid-stimulating hormone from the pituitary gland, which prompts the release of thyroid hormones. Finally, neural stimuli involve the nervous system directly stimulating endocrine glands to release hormones, as occurs in the fight-or-flight response, leading to adrenaline release.