Which type of glands release their products onto an external surface?

Exocrine glands are specifically designed to release their products onto an external surface or into body cavities. This type of gland typically utilizes ducts to transport secretions to the surface where they are needed. For instance, sweat glands and salivary glands are classic examples of exocrine glands, as they secrete substances that serve specific functions outside of the bloodstream, such as regulating temperature through perspiration or aiding in digestion with saliva.

In contrast, endocrine glands release hormones directly into the bloodstream, making their products available throughout the body rather than on any external surface. Neurotransmitter glands are not a formally recognized type of gland and often refer to the release of neurotransmitters by neurons rather than a glandular function. Secretory glands is a more general term that can describe glands that secrete various substances, but it does not specify the route of secretion as exocrine glands do. Therefore, the uniqueness of exocrine glands in their function of releasing products onto external surfaces is what makes this choice the correct answer.