Which system in the body is made up of a series of glands?

The answer is the endocrine system because this system is fundamentally composed of a network of glands that produce and secrete hormones directly into the bloodstream. These hormones play critical roles in a variety of bodily functions, including metabolism, growth and development, tissue function, and mood regulation. The glands in the endocrine system, such as the pituitary, thyroid, adrenal glands, and pancreas, release hormones that help maintain homeostasis and regulate various physiological processes throughout the body.

The endocrine system operates in contrast to other systems that may involve glands but are not primarily defined by them. For example, the nervous system relies on a network of neurons and synapses to transmit signals and does not focus on glands as its primary component. Similarly, the circulatory system is defined by its network of blood vessels and the heart, while the muscular system centers around muscle tissues that facilitate movement, rather than hormone production and secretion. Thus, the distinction lies in the unique role of glands within the endocrine system, making it the correct choice in the context of the question.