The internal lining of the intestines (the intestinal mucosa) has a large amount of small tubular exocrine glands that execute both the secretory and excretory functions. In most exocrine glands, however, these portions are distinct structures, although the excretory portion may be often partially or entirely embedded within the secretory one.
Secretory portion
The gland may be formed by one or more cell types whose characteristics and arrangements are specific to the various gland types.
The cells of the secretory portions of most exocrine glands gather around central space: its lumen into which the secretory product of each cell is released. This lumen is continuous with the lumen of the excretory ducts.
Excretory portion
The wall of the excretory ducts is formed by a lining epithelium arranged as a hollow tube with a central lumen.
The epithelium that forms the wall of the initial part of the ducts is often a simple cuboidal epithelium. In small glands having a short duct this structure is maintained throughout its entire course.
Longer and bigger ducts of more complex glands enlarge, blend with other ducts of the gland, and form even larger and wider ducts. The epithelial wall of these larger ducts may be a simple columnar epithelium and in even larger ducts a stratified epithelium (click to view an excretory duct whose wall is a stratified epithelium).
In this page: the image of a section containing an entire small gland. Its secretory portion is formed by several groups of secretory cells and is seen in light blue color after placing the mouse over the image or clicking on the image.
The excretory duct (highligted in dark blue) consists of a layer of simple cuboidal epitlelium. This, however, can not be easily seen here due to the small magnification of the image.
The gland and its duct are embedded in connective tissue that is part of the wall of the esophagus. Small areas of smooth muscle are present in this connective tissue.
The cavity (lumen) of the esophagus is lined by a stratified squamous epithelium (highlighted in red).
Small gland in the wall of the esophagus. Hematoxylin and eosin. Very small magnification.
