The endocrine system is a network of glands across the body that secretes chemical messages called hormones. The pituitary gland is sometimes known as the master gland, because the hormones released by the pituitary gland control and stimulate the release of hormones from other glands in the endocrine system. Other examples include: the testes, which release androgens, which include the main hormone testosterone; the ovaries, which release oestrogen that controls the regulation of the female reproductive system, including the menstrual cycle and pregnancy.