What do glands in the endocrine system primarily secrete?

Glands in the endocrine system primarily secrete hormones, which are biochemical messengers that travel through the bloodstream to target organs or tissues. These hormones play crucial roles in regulating various physiological processes including growth, metabolism, reproduction, and mood. The endocrine system consists of various glands, such as the pituitary, thyroid, adrenals, and pancreas, each responsible for producing specific hormones that have far-reaching impacts throughout the body.

The other options represent substances that are not primarily secreted by endocrine glands. Nutrients are generally obtained through diet rather than secreted by glands. Enzymes are typically secreted by exocrine glands or various cells in the digestive system to facilitate biochemical reactions. Electrolytes, while important for cellular function and included in bodily fluids, are regulated more so by the kidneys and other tissues rather than being secreted as a primary function of endocrine glands. Thus, hormones are the correct answer as they are the key product of the endocrine system and are essential for maintaining homeostasis in the body.