Endocrine glands secrete hormones into which of the following?

Endocrine glands are specialized organs that play a key role in the endocrine system by producing and releasing hormones directly into the bloodstream. These hormones then travel through the circulatory system to target organs or tissues, where they exert their effects. This process is distinct from exocrine glands, which secrete substances through ducts to the exterior of the body or into body cavities.

When considering the functions and characteristics of endocrine glands, the secretion of hormones into body fluids such as blood is essential for regulating various physiological processes, including metabolism, growth, and mood. This systemic delivery of hormones allows for a coordinated response throughout the body to maintain homeostasis.

In contrast, options like body cavities and surface tissues do not accurately represent the mechanism of hormone secretion by endocrine glands, and excretory ducts pertain to the secretion of substances like enzymes or digestive fluids, rather than hormones. Thus, the correct understanding of endocrine function is clearly captured by the notion that hormones are secreted into body fluids like blood.