Final answer:
In a negative feedback loop, the upstream endocrine gland is regulated via receptors for the downstream hormone, which help maintain hormone levels within an appropriate range, thereby preserving homeostasis.
Step-by-step explanation:
In a negative feedback loop, the upstream endocrine gland is given feedback predominantly via receptors on the gland for the downstream hormone. This mechanism serves to maintain homeostasis by adjusting the production and release of hormones accordingly. Substances in the blood, such as the downstream hormones, signal to the upstream glands when to reduce or stop hormone synthesis and secretion, thus completing the feedback loop.
For example, the anterior pituitary gland releases thyroid-stimulating hormone (TSH) which signals the thyroid to produce thyroid hormones. As the levels of thyroid hormones increase in the blood, they provide feedback to the hypothalamus and anterior pituitary to reduce the further release of TSH, keeping the hormone levels within a narrow range. This process is directed by hormonal stimuli, one of the three mechanisms by which endocrine glands are stimulated, the other two being humoral and neural stimuli.