Glandular epithelial tissue is a specialized type of epithelial tissue that forms glands, which are structures designed for secretion. A gland can be defined as a single cell or a group of cells that release products into the environment, such as sweat, bile, or hormones. Glands are categorized into two main types: exocrine and endocrine glands.
Exocrine glands secrete their products onto body surfaces or into body cavities, which can be remembered by the prefix "ex-" indicating exit. These glands can be unicellular, consisting of a single cell, or multicellular, which utilize ducts to transport their secretions. Examples of exocrine gland secretions include mucus, sweat, oil, and milk.
In contrast, endocrine glands release their secretions directly into the bloodstream, allowing hormones to travel throughout the body and affect distant organs. The prefix "en-" in endocrine signifies entry into the blood. Endocrine glands are typically multicellular and do not have ducts for secretion. Notably, while most epithelial tissues are adjacent to open spaces, endocrine glands are an exception; they initially form with ducts that later regress, making them appear disconnected from open spaces.
Understanding the distinction between these two types of glands is crucial, as exocrine glands will be the primary focus in upcoming lessons, while endocrine glands will be explored in detail later in the course when discussing the endocrine system.