33) Differentiating Between Exocrine & Endocrine Glands and Multicellular & Unicellular Glands

Glands- consist of one or more cells that make and secrete (export) a particular product.

Endocrine Glands- are often called ductless glands. Endocrine glands produce hormones, regulatory chemicals that they secrete by exocytosis directly into the extracellular space. Endocrine glands are structurally diverse, so one description does not fit all. Although most endocrine glands are compact multicellular organs, some individual hormone-producing cells are scattered in the digestive tract mucosa and in the brain, called the diffuse endocrine system. Endocrine gland secretions are also varied, ranging from modified amino acids to peptides, glycoproteins and steriods.

Exocrine Glands- are far more numerous than endocrine systems and may of their products are familiar. All exocrine glands secrete their products onto body surfaces (skin) or into body cavities- the unicellular glands directly by exocytosis and the multicellular glands via an epithelial-walled duct that transports the secretion to the epithelial surface. Exocrine glands are a diverse lot. They include mucous, sweat, oil and salivary glands, the liver which secrets bike, the pancreas which synthesizes digestive enzymes and many others.
-Unicellular Exocrine Glands- an example would be the goblet cell which is shaped like a drinking glass with a stem. Goblet cels are sprinkled in the epithelial lining of the intestinal and respiratory tracts amid columnar cells with other functions. In humans, all such glands produce mucin, a complex glycoprotein that dissolves in water when secreted. Once dissolved, mucin forms mucus, a slimy coating that both protects and lubricates surfaces.
-Multicellular Exocrine Glands- have two basic parts: an epithelium-derived duct and a secretory unit consisting of secretory cells. These glands are structurally more complex and either simple or compound. Simple glands have an unbalanced duct, whereas compound glands have a branched duct. The glands are further categorized by their secretory units as tubular, alveolar or tubuloaveolar. Multicellular exocrine glands secrete their products in different ways. Most are merocrine glands which secrete their products by exocytosis as they are produced, not altering the secretary cells in any way. The pancreas and salivary glands belong to this class. Secretary cells of holocrine glands accumulate their products within them until they rupture and replaced by a division of underlying cells. Holocrine gland secretions include the synthesized product plus dead cell fragments. An example of a holocrine gland are the sebaceous (oil) glands of the skin.