Developmentally, why are secretory glands described as epithelial specialisations?
Prelab Exercise 1 –EPITHELIA 1 Epithelia and Glands Epithelial cells cover or line surfaces and also form ducts and glands. They may be arranged in a single layer (simple epithelium) or in multiple layers (stratified epithelium). Normal epithelium nearly always rests upon or is surrounded by fibrous connective tissue. Other multicellular glands have their secretory portion embedded in the connective tissue underlying the epithelium. The secretion is either discharged directly from the secretory portion onto the epithelium or reaches the epithelium via a duct system that consists of non-secretory cells. Multicellular glands. The simplest form of a multicellular gland is a secretory epithelial sheath-a surface epithelium consisting entirely of secretory cells (e.g. the epithelium lining the inner surface of the stomach, where the mucous secretion protects the stomach wall from the acidic contents of the stomach) . Two types of glands exist: endocrine glands and exocrine glands. Glands are composed of single cells or groups of cells specialized for secretion. All glands arise in early development from lining or covering epithelia. Exocrine glands are those that keep their connection with the epithelium in the form of a duct. Unicellular Glands. consist of a single secretory cell. In mammals the only example of unicellular exocrine glands are goblet cells, which occur in the epithelium of many mucous membranes. Goblet cells secrete the glycoprotein mucin, which by the uptake of water is converted into a slimy substance, mucus. 1 Stratified signifies two or more layers of epithelial cells. 2  By convention, a stratified epithelium is described according to the shape of cells on its free surface. 3  Regardless of whether the surface cells are squamous, cuboidal, or columnar, the underlying cells are usually cuboidal. Stratified cuboidal and columnar epithelia. are not common. A two-layered cuboidal epithelium is, for example, seen in the ducts of the sweat glands. Stratified columnar epithelia are found in the excretory ducts of the mammary gland and the main excretory duct of the large salivary glands. • Serous glands: cells secrete a watery fluid, often containing enzymes or other proteins. Within the cell the secretory product is usually in the form of secretory granules. • Mixed (seromucous) glands: contain both mucous and serous secreting cells. Most glands are of this type. 1 A columnar epithelium is often associated with secretion or absorption.  2 Glandular describes epithelial tissue found in glands and specialized for exocrine or endocrine secretion.  3 Transitional describes a specialized type of epithelium which lines urinary passages. • Serous glands: cells secrete a watery fluid, often containing enzymes or other proteins. Within the cell the secretory product is usually in the form of secretory granules. • Mixed (seromucous) glands: contain both mucous and serous secreting cells.
Multicellular glands