Which one of the following is classed as an endocrine gland?

The pancreas is classified as an endocrine gland because it plays a crucial role in regulating blood sugar levels through the secretion of hormones, primarily insulin and glucagon, directly into the bloodstream. This process exemplifies the primary function of endocrine glands: to release hormones that regulate various physiological processes throughout the body.

In contrast, other options listed serve primarily exocrine functions or are not primarily defined as endocrine glands. The gallbladder stores and concentrates bile produced by the liver, while the parotid and sublingual glands are salivary glands that secrete saliva into the oral cavity through ducts. Therefore, while they are important in their respective roles, they do not have the hormone-secreting function characteristic of endocrine glands like the pancreas does. This distinction is critical in understanding the functions of various glands in the body.