It measures many things including blood sugar level. The hypothalamus is connected to the pituitary gland which is yet another endocrine gland. Negative feedback is the special mechanism for turning the hormones off after they have done their job. So when your blood sugar level drops, the amount of insulin produced also falls, and when your blood sugar level has risen back to normal, the amount of adrenalin and glucocorticoids falls. A hormone is a chemical messenger .
Endocrine organs make hormones .
Almost every organ in the body is affected by one or more hormones. Target organs ar controlled by hormones . The hypothalamus helps to control the pituitary gland. It secretes hormones which control other endocrine glands. Another page in this Web Site to explain it.