The Lactobacillus acidophilus present within the vagina produce lactic acid from glycogen to maintain the pH at between 4.9 and 3.5 which has a bacteriostatic action. The anterior fornix has the lowest pH, which gradually rises towards the vestibule.
At birth, there is passive transfer of maternal hormones and Lactobacilli which are present for the first 4 weeks of life. Consequently vaginal pH is low and after the concentration of hormones has receded, the pH rises to 7 where it remains until puberty. This high pH is associated with an increased risk of infection1.
In post-puberty women, the pH can be raised during menstruation, but also it can increase after periods of frequent acts of coitus because both vaginal transudate and ejaculate are alkaline. Acidity can also be decreased by alkaline secretion of the cervical glands. During pregnancy the mean vaginal pH isapproximately 4.2.2.
Cervical bacterial flora in sexually active healthy women using oral contraceptives or intrauterine contraceptive devices is rich in anaerobes, however, barrier contraception with a condom prevents this anaerobic shift and maintains a lactobacilli-dominated flora in the cervix3.
The outer cell layers of the vagina contain E-glucuronidase, acid phosphatase, with smaller amounts of a-naphthylesterase, DPNH diaphorase, phosphoamidase and succinic dehydrogenase. Basal cell layers contain E-glucuronidase, succinic dehydrogenase, DPNH diaphorase, small amounts of acid phosphatase and a-naphthylesterase.
Alkaline phosphatase, lactate dehydrogenase, aminopeptidase and esterase activity are all markedly elevated in the follicular phase of the menstrual cycle, but fall immediately prior to ovulation4. Their activity begins to rise again one day after ovulation.
Mucus is secreted by endocervical glands and its production is oestrogen dependent. It is minimal immediately after menstruation, but during the pre-ovulation stage, the raised oestrogen increases mucus production. The mucus also becomes more transparent, viscous and elastic reaching a maximum just before ovulation which lasts approximately 2 days post-ovulation.
The menstrual cycle lasts approximately 28 days and it can be divided into 4 phases: the follicular, ovulatory, luteal and menstrual phases. The phases equate to repair, proliferation, secretion and menstruation. Repair begins even before menstruation has completely ceased. During the follicular or proliferative phase, the oestradiol levels increase, resulting in the uterine epithelium increasing in thickness from 20 layers or 0.2 mm to over 40 layers during the ovulatory phase (Figure 12.4). The major feature of the proliferative phase is the increase in ciliated and microvillus cells. The ciliogenesis begins on day 7-8 of the cycle. The stroma becomes becomes vascular and oedematous and a large number of cells including lymphocytes and macrophages derived from bone marrow are present in the endometrium. Secretion takes place from days 16-28. In this phase the oestrogen levels drop and the levels of progesterone incrase and hence the effects become dominant. The drop in oestrogen can
Coiled Secreting Uterine Glands
Figure 12.4 Effect of the menstrual cycle on the uterine epithelium
Figure 12.4 Effect of the menstrual cycle on the uterine epithelium lead to the thickening of the endometrium being reduced and intermenstrual bleeding occurring. The endometrial glands produce a thick glycogen-rich mucoid secretion. There is an increase in vascularisation and the uterus is ready to receive an embryo. If implantation does not occur, the corpus luteum begins to degenerate, progesterone levels drop which causes the endometrium to breakdown. The coiled arterioles of the superficial layers of the outer endometrium contract thus depriving the superficial layers of oxygen, resulting in menstruation. Menstruation can last for anything up to about a week.
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