Vagina vaginal epithelium

Vaginal Rings. Vaginal epithelium is readily permeable to contraceptive steroids. Since the vascular drainage of the vagina bypasses the Hver, this route of adrninistration potentially permits utilisation of dmgs that have low oral activity. 

In postmenopausal women, the incidence of mitosis in the basal and parabasal layers and the number of small blood vessels decreases. The vaginal epithelium becomes extremely thin, cell boundaries in the surface are less distinct, the micro-ridges of the cells are dramatically reduced, and the vagina is often invaded with leukocytes. Naturally, this thinning of the epithelium leads to a substantial increase in the permeability of this tissue. 

Although, as described above, the vagina is permeable to many peptides and proteins, in most cases the bioavailability is insufficient for systemic therapy and is also highly variable. Penetration enhancers may be used to promote peptide absorption across the vaginal epithelium. However, less extensive investigations on the use of penetration enhancers for the vaginal route have been carried out in comparison to other routes, such as intranasal and transdermal (see Sections 9.7.1 and 8.6.1). 

Dry vagina the bioadhesive gel can hydrate vaginal tissue for 3-4 days after a single application. Tissue hydration is caused by an increased blood flow, thus increasing transudation of vaginal fluid though the intercellular channels of the vaginal epithelium. 

The human vagina, a fibromuscular tube 10-15 cm long, extends upwards and backwards from the vulva to the lower uterine cervix. Blood is supplied to the vagina via the uterine and pudendal arteries, and is drained from the vagina by a rich plexus, which flows into the internal iliac veins. The surface of the vaginal epithelium is kept moist by cervical secretions. The pH of vaginal fluid is 4-5. 

The vagina offers a substantial area for drug absorption because numerous folds in the epithelium increase the total surface area. A rich vascular network surrounds the vagina whereas the vaginal epithelium is covered by a film of moisture consisting mainly of cervical mucus and fluid secreted from the vaginal wall. 

Unlike other tissues, the vagina is greatly affected by steroid replacement therapy. Estrogen replacement therapy is often used to treat menopausal symptoms. The postmenopausal state of the vaginal epithelium, with its thinner epithelium and increased permeability, is an important consideration in drug delivery. The minimization of epithelial fluctuation will result in less fluctuation in absorption, affecting both systemic and local drug deliveries. 

The fluid within the lower reproductive tract originates from variety of sources. The vaginal epithelium produces a small amount of fluid, which is bacteriostatic because of its high acidity (pH 3 ). This acidic fluid mixes with mucus, which is produced at the cervix, to create an overall acidic environment (pH 5-7) within the lumen of the vagina. The cervix produces 20-60 mg of mucus per day, with as much as 1 g/day during mid-cycle. The overall volume of vaginal fluid appears to be 2 to 8 mL/day [40]. 

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