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

The endocrine system is composed of a network of ductless glands that produce and secrete hormones directly into the bloodstream. These hormones travel through the circulatory system to target organs and tissues, where they regulate a variety of bodily functions such as metabolism, growth and development, tissue function, and mood.

Unlike the nervous system, which relies on nerve impulses to transmit information quickly, the endocrine system communicates more slowly via hormones, affecting processes over a more extended period. This long-lasting regulation is crucial for maintaining homeostasis in the body.

The circulatory system is involved in transporting blood, nutrients, gases, and hormones but does not specifically consist of glands that produce hormones. The excretory system is focused on the removal of waste products from the body, and while the nervous system transmits signals through neurons, it does not involve hormone secretion. Therefore, the correct answer is the endocrine system, which plays a vital role in hormonal balance and regulation in the body.