Although the small bodies, or endocrine glands, are not physically connected to each other, many of them interact because they all work by releasing hormones into the bloodstream. Blood also carries the hormones to every living cell in the body, allowing the endocrine system to work with the nervous system in regulating all the main functions of the body - reproduction, growth, and production of energy.
Some hormones are necessary for life.
The rest are necessary in proper amounts for good health. If you are told that your condition is hypothyroidism, you have low thyroid function, or not enough thyroid hormones. But hyperthyroidism is high, or too much, thyroid hormone. To a limited degree one can guess that a set of symptoms is caused by hypersecretion or hyposecretion of a particular hormone. The only way to be certain in most instances comes from blood or urine tests.