The opening of the vagina may be covered by a membrane or surrounded by a fold of connective tissue called the hymen. This tissue is usually replaced by irregular tissue tags after sexual activity and childbirth occur. The lower vagina is somewhat constricted as it passes through the urogenital hiatus in the pelvic diaphragm; the upper vagina is more spacious. The entire vagina is characterized by its distensibility, which is most evident during childbirth.
The vagina is closely applied anteriorly to the urethra, bladder neck and trigonal region, and posterior bladder; posteriorly, the vagina lies in association with the perineal body, anal canal, lower rectum, and posterior cul-de-sac. It is separated from both the lower urinary and gastrointestinal tracts by their investing layers of fibromuscular elements known as the endopelvic fascia.
Figure 5.15 The uterus, fallopian tubes, and ovaries.
The vagina is composed of three layers: 1.
Mucosa—nonkeratinized stratified squamous epithelium, without glands. Vaginal lubrication occurs primarily by transudation, with contributions from cervical and Bartholin gland secretions. The mucosa has a characteristic pattern of transverse ridges and furrows known as rugae. It is hormonally sensitive, responding to stimulation by estrogen with proliferation and maturation. The mucosa is colonized by mixed bacterial ﬂora with lactobacillus predominant; normal pH is 3.5 to 4.5.
2.
Muscularis—connective tissue and smooth muscle, loosely arranged in inner circular and outer longitudinal layers.
3.
Adventitia—endopelvic fascia, adherent to the underlying muscularis.
Blood Supply The blood supply of the vagina includes the vaginal artery and branches from the uterine, middle rectal, and internal pudendal arteries.
Innervation The innervation of the vagina is as follows: the upper vagina—uterovaginal plexus; the distal vagina—pudendal nerve.
Uterus The uterus is a fibromuscular organ usually divided into a lower cervix and an upper corpus or uterine body (Fig. 5.15).
The portion of cervix exposed to the vagina is the exocervix or portio vaginalis. It has a convex round surface with a circular or slitlike opening (the external os) into the endocervical canal. The endocervical canal is about 2 to 3 cm in length and opens proximally into the endometrial cavity at the internal os.
The cervical mucosa contains both stratified squamous epithelium, characteristic of the exocervix, and mucus-secreting columnar epithelium, characteristic of the endocervical canal. The intersection where these two epithelia meet—the squamocolumnar junction—is geographically variable and dependent on hormonal stimulation. It is this dynamic interface, the transformation zone, which is most vulnerable to the development of squamous neoplasia.
In early childhood, during pregnancy, or with oral contraceptive use, columnar epithelium may extend from the endocervical canal onto the exocervix, a condition known as eversion or ectopy. After menopause, the transformation zone usually recedes entirely into the endocervical canal.
Production of cervical mucus is under hormonal inﬂuence. It varies from profuse, clear, and thin mucus around the time of ovulation to scant and thick mucus in the postovulatory phase of the cycle. Deep in the mucosa and submucosa, the cervix is composed of fibrous connective tissue and a small amount of smooth muscle in a circular arrangement.
The body of the uterus varies in size and shape, depending on hormonal and childbearing status.