The pituitary gland is a central organ in the endocrine system. This means that it has a superior role to other endocrine glands, i.e. those that secrete active substances directly into the blood. The pituitary gland is called the main motor of the endocrine system because it secretes hormones that direct the 'secretory work' of the other endocrine glands. Among other things, it influences the thyroid gland, mammary glands, adrenal cortex, ovaries and testes, and lipid and carbohydrate metabolism in general.