Functional Significance
The histological structure of the vagina ensures the execution of its essential physiological tasks:
- Reproductive function. The vagina serves as the primary receptacle for sperm and is an integral part of the birth canal. High tissue elasticity allows the organ to stretch significantly during the passage of the fetus.
- Protective function. An acidic environment is maintained within the organ's cavity, serving as a natural barrier and effectively suppressing the proliferation of pathogenic flora.
- Trophic function. The vaginal environment provides nutrition for male gametes.
Biochemical mechanism of protection and nutrition: Superficial epithelial cells of the vagina accumulate large amounts of glycogen in their cytoplasm. Upon natural desquamation into the lumen of the organ, this carbohydrate is released. Local microflora actively metabolize glycogen, converting it into lactate (lactic acid). Lactic acid acidifies the environment, protecting against infections, and simultaneously serves as an excellent nutritional substrate that supports sperm motility and viability.
Mucous Membrane (*Tunica mucosa*)
This is the internal, most functionally active layer of the wall, undergoing regular cyclic changes.
Epithelial Layer Lined by stratified squamous partially keratinized epithelium. Three distinct cell layers are clearly differentiated:
- Basal;
- Intermediate;
- Superficial.
Superficial cells contain keratohyalin granules, although complete cornification (formation of cornified scales) does not occur under normal conditions. Furthermore, these cells are the richest in glycogen.
Cyclic Changes (Desquamation) The epithelium responds sensitively to hormonal fluctuations. The rate of superficial cell desquamation directly depends on blood estrogen concentrations. The peak of desquamation occurs right in the middle of the cycle — at ovulation. In histological smears, this manifests as an increasing number of desquamated cells leading up to ovulation, followed by their decline. The biological purpose of this process is to create an optimal carbohydrate-rich environment for sperm during the period of highest fertilization probability.
Lamina Propria Beneath the epithelium lies the lamina propria composed of loose connective tissue. It forms numerous papillae that deeply interdigitate with the epithelial layer. The tissue is characterized by a high content of elastic fibers, which provides elasticity and stretchability, as well as an abundance of lymphocytes ensuring local immunity.
Muscular and Adventitial Layers
The middle and outer layers of the wall provide mechanical strength, contractility, and organ fixation.
Muscular Layer (Tunica muscularis) Unlike the cervix, where circular muscle bundles predominate, the muscular layer of the vagina is formed primarily by longitudinal bundles of smooth myocytes. This orientation of muscle elements allows the organ to adapt its length.
Adventitial Layer (Tunica adventitia) The outer layer consists of loose connective tissue connecting the vagina to surrounding pelvic structures. A characteristic feature of the adventitia is the presence of robust venous plexuses.