There are two main activities we think of when talking about hormones. The first is intracellular and intercellular communication: this communication’s quality depends on hormones which will interact not only at the level of the cell membrane, but also within the cell. The second is cellular homeostasis, that is, the preservation of a permanent balance of all functions.
Hormones are therefore essentially there to coordinate organ function. They are essential to our metabolic balance, and their concentration is also important. Transported through the blood, they travel deep into cells and activate production chains for cellular components. They build new ones and induce reactions which release the energy necessary for life.
This is all directed, of course, by the brain, specifically by the hypothalamus, which coordinates the activity of all peripheral hormones via two glands: the pituitary and pineal glands. These peripheral hormones will, in turn, influence the glands which emitted them by biofeedback control. Furthermore, a peripheral hormone can influence another by stimulating or inhibiting it.
The levels of certain hormones decrease with age. The thymus, which produces some of our hormones, also disappears around 40 years of age. Some consider this decrease to be a sign of aging, and that the measurement of hormone levels in the organism would be a reliable means of evaluating our biological age, independently of how old we are.