This image shows some of the various possible glandular arrangements. These are the simple tubular, simple branched tubular, simple coiled tubular, simple acinar, and simple branched acinar glands.
This image shows some of the various possible glandular arrangements. These are the compound tubular, compound acinar, and compound tubulo-acinar glands.
Every gland is formed by an ingrowth from an epithelial surface. This ingrowth may in the beginning possess a tubular structure, but in other instances glands may start as a solid column of cells which subsequently becomes tubulated.
As growth proceeds, the column of cells may divide or give off offshoots, in which case a compound gland is formed. In many glands the number of branches is limited, in others (salivary, pancreas) a very large structure is finally formed by repeated growth and sub-division. As a rule, the branches do not unite with one another, but in one instance, the liver, this does occur when a reticulated compound gland is produced. In compound glands the more typical or secretory epithelium is found forming the terminal portion of each branch, and the uniting portions form ducts and are lined with a less modified type of epithelial cell.
Glands are classified according to their shape.
If the gland retains its shape as a tube throughout it is termed a tubular gland.
In the second main variety of gland the secretory portion is enlarged and the lumen variously increased in size. These are termed alveolar or saccular glands.
Exocrine glands secrete their products through a duct onto an outer surface of the body, such as the skin or the human gastrointestinal tract. Secretion is directly onto the apical surface. The glands in this group can be divided into three groups:
Apocrine glands a portion of the secreting cell's body is lost during secretion. Apocrine gland is often used to refer to the apocrine sweat glands, however it is thought that apocrine sweat glands may not be true apocrine glands as they may not use the apocrine method of secretion.
Holocrine glands the entire cell disintegrates to secrete its substances (e.g., sebaceous glands)