What type of gland is responsible for secreting hormones directly into the bloodstream?

Endocrine glands are the type of glands responsible for secreting hormones directly into the bloodstream. They play a crucial role in regulating various physiological processes throughout the body, including growth, metabolism, and mood. Hormones produced by endocrine glands, such as insulin from the pancreas and adrenaline from the adrenal glands, are released directly into the circulatory system, allowing them to travel to target organs and tissues that have specific receptors for those hormones.

In contrast, exocrine glands secrete their substances through ducts to specific locations, such as sweat or salivary glands. Holocrine and merocrine glands are both types of exocrine glands, characterized by their secretion methods; holocrine glands release entire cells filled with product, while merocrine glands secrete by exocytosis, releasing only the product itself without any cell loss. Thus, these options are not related to hormone secretion into the bloodstream, supporting why endocrine glands are the correct choice for this question.