A specialized structures on epithelia are glands and ducts.  A gland consists usually of cuboidal or columnar epithelial cells which make and secrete substances.  Glands are classified as endocrine (if secreted directly into the blood) or exocrine if secreting into a duct.  A duct is a passageway which delivers the secretions to the surface of the epithelia.

Since endocrine glands secrete directly into blood, these glands would most likely be cuboidal cells near a blood vessel.  Common endocrine glands are the pancreas (Islets of Langerhans secrete insulin & glucagon), hypothalamus and  anterior pituitary (not an exhaustive list!!)  You will come across these tissues in other chapters.

For the purpose of this appendix, we will focus on exocrine glands and their ducts as they are a tricky structure to identify, as a first time learner.

Exocrine glands

Just like your home with its many rooms, hallways, and doors, exocrine glands and ducts can vary in length, distribution, and complexity.

Simple Tubular Exocrine Gland

As the name implies, simple tubular is a single layer of epithelial tissue which has deep folds or invagination which form its duct.

Simple Branched tubular

Simple branched tubular is an exocrine gland where there is a single duct but multiple pockets of glandular tissue.  Because of this branching, it is often difficult to capture all of these 3D branches in a 2D section of tissue!

Figure 4 shows branched tubular glands marked out in yellow and blue. The yellow box shows an interesting sample which could be mistaken for two simple tubular glands, but this would be due to the cut of this stomach section.

The possible cut made is visualized below:

It takes time and practice to recognize simple tubular branched glands compared to simple.  When you have a section with lumens of different circumferences, around prominent tubular shaped lumens – yet the secretory cuboidal/columnar cell looks the same around each lumen space, this is highly suggestive of branched tubular gland. [note the yellow box]

Coiled tubular

Coiled tubular is similar to simple tubular, except that the curve of the coiled tubule might not get fully captured in the sectioned plane.  If a coiled tubular gland was presented as a cross-section one can imagine a nest of squirmy things, each surrounding a “hole”.

Here’s a helpful analogy:  imagine a garden hose coiled on the ground.  IF you look at the coil from above, it will look like a lot of circles which may (or may not) lie neatly on top of each other.  OR, if the hose is in a tangled mass, the sectional plane would shows cut sections of  small round to oval profiles of varying sizes. If you’re lucky, the plane might go along the length of the hose allowing for a  dominant tube to be seen with lots of coils nearby.

Again, it takes time and practice to pick up the visual clues that help determine which gland you are looking at.  But using some of the analogies provided, we hope that this process will be easier for you.