Page 336 - Veterinary Histology of Domestic Mammals and Birds, 5th Edition

318 Veterinary Histology of Domestic Mammals and Birds

The mucosa-submucosa is thrown into primary folds Tunica mucosa
VetBooks.ir with secondary and tertiary folds. The arrangement of the The tunica mucosa is mostly non-glandular and has flat
connective tissue fibres in the folds allows them to flatten longitudinal folds that quickly disappear when the mucosa
out during parturition. In addition, the folds enlarge the is distended. The epithelium is stratified squamous and,
secretory surface area and reinforce the seal formed by depending on species, may be keratinised.
the closed cervix (refer to Veterinary Anatomy of Domestic
Mammals: Textbook and Colour Atlas). Species variation
The mucosal epithelium is simple columnar. It con- Ox: Columnar mucus-producing cells are present in the
tains cells that produce mucus composed of acid and mucosal folds, particularly near the cervix.
neutral proteoglycans. Ciliated cells also occur in isolated Dog: Solitary intra-epithelial secretory cells may be
areas in the cow. The mucus-secreting cells are con- present during oestrus.
centrated on the sides and ridges of the mucosal folds In the bitch, cyclic changes in the vaginal epithelium
(Figure 14.24). In the presence of high progesterone levels can be used to determine the stage of the oestrous
(dioestrus), the mucus thickens to form a seal. Under the cycle. During pro-oestrus and oestrus the epithe-
influence of oestrogen it becomes thin. lium thickens, surface cells become keratinised and
In actively secreting cells, the supranuclear region bulges the cell nuclei become pyknotic and gradually disap-
towards the lumen. During oestrus the cells become smaller. pear. Erythrocytes from the underlying connective
The lamina propria mucosae consists of loose connective tissue traverse the epithelium via diapedesis and enter
tissue that becomes highly oedematous under the influence the vaginal lumen. During oestrus the epithelial cells
of oestrogen. Lattices of dense connective tissue fibre bundles become completely keratinised and anuclear, and the
form the core of the cervical folds. Networks of branching number of free erythrocytes decreases. The epithelial
fibres extend between the externally adjacent muscle cells. lining becomes disrupted and superficial cells disinte-
grate. In the subsequent, longer phase of the oestrous
Species variation
cycle, metoestrus, the epithelium continues to thin
Cat and goat: While the lamina propria contains no through desquamation and new, non-keratinised cells
glands in most species, tubular cervical glands may be form the surface layer. Neutrophils enter the epithe-
present in the queen and doe. lium, and erythrocytes and cell fragments disappear.

The tunica muscularis consists of a thick inner circular The connective tissue framework of the lamina pro-
layer and a thinner outer longitudinal layer. The circular pria mucosae consists of an array of collagen fibres. With
layer incorporates elastic fibres that aid in closing the cer- the aid of elastic fibre bundles, this arrangement of fibres
vix after passage of the fetus. allows the vagina to expand and contract during and after
parturition. Depending on the stage of the cycle, this
Vagina subepithelial tissue contains leucocytes and plasma cells.
The vagina and vestibule form the female copulatory organ. Particularly during pro-oestrus and oestrus these are found
In ruminants, the ejaculate is deposited in the vagina. In in the cervical mucus.
other species the seminal plasma and spermatozoa are
ejaculated into the uterus (horse, dog) or cervix (pig). Tunica muscularis
The structure of the vaginal wall varies with species and, The inner layer of the tunica muscularis consists of
in some instances, exhibits marked cyclic changes. Except smooth muscle cells in a circular orientation. This layer is
during mating and parturition, the lumen of this musculo- surrounded by longitudinal muscle fibres. The muscle cell
membranous tubular organ is reduced to a potential space. layers are connected by a network of collagen and elastic
fibres that supports the mechanical strength, plasticity and
Structure of the vagina contractility of the vaginal wall.
The vagina has a typical layered structure comprised of the:
Tunica serosa and tunica adventitia
· tunica mucosa: Within the peritoneal cavity, the vagina is surrounded by
− stratified squamous epithelium, a loose tunica serosa. This is replaced by a tunica adven-
− lamina propria mucosae with loose connective titia over the retroperitoneal portion of the organ (Figure
tissue, 14.25).
· tunica muscularis incorporating:
− smooth muscle cells,
− elastic fibres and
· tunica adventitia or tunica serosa.

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