Here's why:

* Epithelium: This tissue type is specialized for covering surfaces and lining cavities. It's characterized by tightly packed cells with minimal intercellular space. This structure makes it ideal for secreting substances.

* Glandular Epithelium: This is a specific type of epithelial tissue that forms glands. Glands are structures that produce and release substances, often hormones or enzymes, into the bloodstream, body cavities, or onto a surface.

Types of Glandular Epithelium:

* Exocrine glands: These glands secrete their products through ducts onto a surface. Examples include sweat glands, salivary glands, and mammary glands.

* Endocrine glands: These glands release their products (hormones) directly into the bloodstream. Examples include the thyroid gland, pituitary gland, and adrenal glands.

Important Note: While epithelial tissue is the primary tissue of glands, they also contain other tissues to support their function, such as connective tissue for structural support and blood vessels for nutrient supply.