What system consists of ductless glands secreting hormones into the bloodstream?

The endocrine system is comprised of a network of ductless glands that produce and secrete hormones directly into the bloodstream. These hormones act as chemical messengers that communicate with various cells and organs throughout the body, regulating processes such as metabolism, growth, reproduction, and mood.

Each gland in the endocrine system, such as the pituitary, thyroid, adrenal glands, and pancreas, has specific functions and secretes particular hormones that influence different physiological functions. Because of this direct secretion into the bloodstream, the endocrine system plays a crucial role in maintaining homeostasis and responding to internal and external stimuli.

Other systems, such as the circulatory system, are involved in transporting blood and nutrients but do not primarily function in hormone secretion. Similarly, the nervous system uses nerve impulses for communication rather than chemical messengers like hormones, while the excretory system is focused on the elimination of waste rather than hormone regulation. Hence, the endocrine system is uniquely characterized by its mechanism of hormone secretion into the bloodstream, distinguishing it from the other systems mentioned.