Which of the following is a characteristic feature of endocrine glands?

Endocrine glands are a specific type of gland in the body that play a crucial role in hormonal regulation. The characteristic feature of endocrine glands is their method of secretion, which involves directly releasing hormones into the bloodstream. This allows hormones to be transported throughout the body to target tissues and organs, where they exert their effects.

This direct secretion into the blood is what distinguishes endocrine glands from other types of glands, such as exocrine glands, which secrete substances through ducts to specific locations, such as sweat or salivary glands. Hormones can have widespread effects, affecting multiple target organs, which further emphasizes the role of systemic hormone action as opposed to localized effects, characteristic of other signaling mechanisms.

In contrast, the other options refer to traits associated with different types of glands or secretion processes. For instance, secretion through ducts pertains to exocrine glands, localized effects typically describe autocrine or paracrine signaling rather than the broad effects hormones tend to have, and non-hormonal secretion does not align with the function of endocrine glands, as these glands are specifically known for hormone production. Therefore, the direct secretion of hormones into the blood is a defining feature of endocrine glands.