The isthmus, like other regions of the oviduct is secretory. It produces
proteins of the soft egg membranes, the papery material that adheres to the inside of the shell when an egg is broken.
The isthmus, like other regions of the oviduct is secretory. It produces
proteins of the soft egg membranes, the papery material that adheres to the inside of the shell when an egg is broken.
The organ has deep crypt-like folds and, like the upper regions of the tube, is designed to expand considerably to permit passage of the egg (which, by the time it reaches this part of the tube, it has grown considerably in size and has received its albumen coat). Strongly basophilic glands (G) are the source of the membranes.
Note the tunica muscularis (TM) around the outside, which is important in propelling the egg further along the tract. It's rather thin at this point.
The epithelium lining this portion of the oviduct (Ep) is a simple columnar type. The nuclei of these cells is basally located.
The protein-secreting nature of the submucosal glands is also fairly obvious, although these are not so heavily stained as those of the magnum. The lumen of the crypt is filled with secretory material that lies on top of the cells.
Oviduct, chicken; H&E stain, paraffin section, 40x and 200x
