VM8054 Veterinary Histology

Shell Gland

Author: Dr. Thomas Caceci
The shell gland is the last of the secretory portions of the oviduct. It makes the hard calcareous shell of the egg, and obviously it has to be pretty big to pass it along to the outside.

Here's about half of it, with the mucosa and submucosa thrown up into extensive folds, but obviously with a large and unobstructed lumen.

The tunica muscularis (TM) is well-developed in this part of the tract. It's required to push the egg the final few centimeters to the vagina; and by this time the eggs is a large and relatively solid structure.

 

This is the deeper region of the shell gland, showing the secretory area. The crypts are lined with stratified cuboidal epithelium (Ep) and the secretory portions are neither so extensive nor so basophilic as those in the magnum and isthmus. This is what you'd expect to be the case, given the different nature of the secretions they produce.

Birds have an exceptionally high level of circulating calcium compared to mammals, thanks to the need to make the shell. The shell is composed mainly of calcium carbonate. Anything which interferes with the pathways in the cells of this gland will cause problems.

Decades ago, the use of DDT as a pesticide produced severe mortality in some birds, mainly those high up in the food chain, such as eagles. Bioconcentration of the DDT caused derangement of the pathways for shell manufacture and suppression of the activity of the shell gland. The result was very thin and fragile shells, that broke too easily; this translated into unusually high losses of chicks in the nest, long before hatching.

Oviduct, chicken; H&E stain, paraffin section, 20x and 400x


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