Epithelia in which all the cells are specialized for secretion are usually organized as the secretory portions of exocrine glands, which are continuous with the non-secretory epithelia of ducts through which the secreted product is discharged. The secretory cells and ducts constitute the parenchyma or functional portion of the glandular organ, while the connective tissue surrounding these epithelial structures makes up the organ’s stroma.

Glands can be classified structurally based on the structure of both the duct and the secretory portion.

• Ducts can be branched (compound) or unbranched (simple).
• The overall shape of glands’ secretory portions can be tubular, acinar (rounded), or tubuloacinar (tubular with a rounded end).
• The secretory portion may also be described further, as in branched tubular or coiled tubular (i.e., long and not branched).

What exactly is branched or not branched in simple and compound glands respectively?

Try to distinguish the two significant parts of a gland: the secretory unit (acinus or tubule) from the duct.

Study the following examples of glands in some of these structural classifications.

Serous and mucous elements of a gland.