Glands secreting substances through ducts are _____ glands.

Glands that secrete substances through ducts are classified as exocrine glands. These glands produce and release their secretions onto epithelial surfaces, either directly or through ducts. Common examples include sweat glands, salivary glands, and the pancreas when it releases digestive enzymes.

In contrast, endocrine glands release their hormones directly into the bloodstream without using ducts, affecting distant target organs. Autocrine glands secrete substances that act on the same cells that produce them, while paracrine glands release signaling molecules that act on nearby cells. The defining characteristic of exocrine glands is their duct system, which facilitates the transportation of their secretions to specific sites, distinguishing them from the other types of glands.