Final answer:
The endocrine system, controlled by the hypothalamus, is responsible for secreting hormones that regulate almost all other systems via glands like the pituitary, which is known as the master gland.
Step-by-step explanation:
The system responsible for secreting hormones that regulate almost all other systems is the endocrine system. This system comprises a network of glands that produce and secrete hormones into the bloodstream, which carries these chemical messengers throughout the body to regulate various bodily functions, such as metabolism, growth, and sexual development. The pituitary gland, often referred to as the "master gland," plays a pivotal role in this system. It produces hormones that command other endocrine glands, like the thyroid and the pancreas, to secrete their respective hormones. The functioning of the endocrine system is largely under the control of the hypothalamus, a part of the brain that also secretes hormones influencing the pituitary gland.