1. Defintion
Glandular epithelium is a type of epithelial tissue that is specialized for the production and secretion of substances such as enzymes, hormones, mucus, or sweat. It forms the functional tissue of glands (both endocrine and exocrine) and is responsible for synthesizing and releasing products either directly into the bloodstream (endocrine glands) or onto a body surface or into a body cavity (exocrine glands).
2. Classification
2.1. By Method of Secretion
- Endocrine Glands: These glands secrete hormones directly into the bloodstream. They lack ducts.
- Exocrine Glands: These glands secrete their products onto body surfaces or into body cavities through ducts. Examples include sweat glands, salivary glands, and the pancreas (exocrine part).
2.2. By Number of Cells
- Unicellular Glands: Consist of a single cell that secretes its product. An example is the goblet cell.
- Multicellular Glands: Consist of multiple cells organized to form a gland. These glands can have complex structures and include both endocrine and exocrine glands.
2.3. By Type of Secretion
- Merocrine Glands: Secrete their products by exocytosis without any loss of cellular material. An example is the sweat gland.
- Apocrine Glands: A portion of the cell’s cytoplasm and membrane is pinched off during secretion. An example is the scent gland.
- Holocrine Glands: The entire cell disintegrates to release its product, and new cells replace the lost ones. An example is the sebaceous gland of the skin.
2.4. By the Nature of Secretion
- Serous Glands: Secrete watery, enzyme-rich fluids.
- Mucous Glands: Secrete mucus, a thick and viscous substance.
- Mixed Glands: Produce both serous and mucous secretions.