Glands

Compund Multicellular Glands

Compund multicellular glands have a branched duct. Compound tubular glands are found as the duodenal glands of the small intestine. Mammary glands are compound alveolar.

Multicellular Exocrine Glands

Each muticellular exocrine gland has two basic parts: an epithelium-walled duct and a secretory unit consisting of the secretory epithelium. Most multicellular exocrine glands have supportive connective tissue surrounding the secretory unit, carrying with it blood vessels and nerve fibers. Multicellular glands are classified according to the structure of their ducts, and further categorized depending on wherther their secretory units are tubular, alveolar or tubuloalveolar..

Endocrine Glands

Endocrine glands lack ducts - they are often referred to as "ductless glands." Endocrine glands secrete directly into the tissue fluid that surrounds them. The product of endocrine glands are hormones, which they release into the extracellular space. Released hormones enter nearby capillaries and travel through the bloodstream to their target organs, which will respond in a specific way to the hormone signal.

Glands

Epithelial cells that make and secrete a product form glands. The products of glands are aqueous fluids that usually contain proteins.

Exocrine Glands

Exocrine glands are numerous. They secrete their products onto the body surface (skin) or into body cavities (eg. the digestive tube). The activity of exocrine secretion is local. There are two types of exocrine glands: unicellular and multicellular.

Alveolar Multicellular Glands

Glands are categorized as alveolar if their secretory cells form spherical sacs. Sebaceous glands are an example of a simple branched alveolar gland.

Tubular Multicellular Glands

Glands are categorized as tubular if their secretory cells form tubes.

Classification of Glands

Glands are classified as endocrine (internal seceretion) or exocrine (external secretion) depending on where they release their product and unicellular or multicellular based on the number of cells in the gland. Unicellular glands are scattered throughout epithelial sheets, whereas most multicellular glands develop by invagination of an epithelial sheet into the underlying connective tissue.

Tubuloalveolar Multicellular Glands

Glands are tubuloalveolar of they contain both tubular and alveolar units. Salivary glands are an example of compound tubuloalveolar glands.

Secretion

Secretion is the process whereby gland cells obtain needed substances from the blood and transform them chemically into a product that is discharged from the cell. The protein product is made in the rough ER, then packaged into secretory granules by the Golgi apparatus and released by the cell through exocytosis.

Simple Multicellular Glands

Simple multicellular glands have an unbranched duct. Simple tubular glands are found in the intestine. Simple branched tubular glands are found in the stomach.

Unicellular Exocrine Glands

The only important example of a one-celled exocrine gland is the goblet cell. As its name indicates, the goblet cell is shaped like a drinking glass with a stem. Goblet cells are found scattered among the epithelial lining of organs, such as the intestinal and respiratory tracts. They are found inside the trachea, bronchus, and larger bronchioles in respiratory tract, small intestines, the colon, and conjunctiva in the upper eyelid Goblet cells produce mucin, a glycoprotein that dissolves in water when secreted, resulting in mucus. Mucus covers, protects and lubricates many internal body surfaces.