How does the endocrine system/glands influence the functions of the cells/organs?

The endocrine system regulates how much of each hormone is released. This can depend on levels of hormones already in the blood, or on levels of other substances in the blood, like calcium. Many things affect hormone levels, such as stress, infection, and changes in the balance of fluid and minerals in blood. Hormones act as catalysts to affect the physiological activities of other cells in the body. A hormone will produce a reaction in the target cells, either stimulating or inhibiting function.