Vagina

The vagina is the female organ of copulation. It is also the lower end of the “birth canal”, and it serves as the excretory duct for products of menstruation. The cavity of the vagina communicates with that of the uterus above, and it opens into the vestibule of the vagina below. The vagina extends downward and forward in a plane parallel to that of the pelvic inlet. This plane is approximately 60 degrees from the horizontal. In the adult, when the urinary bladder is empty, the axis of the vagina forms an angle of a little more than 90 degrees with the axis of the uterus. However, this angle increases as the urinary bladder fills and pushes the fundus of the uterus upward and backward.

The vagina is highly dilatable, especially in the part above the pelvic diaphragm. When the cavity is empty, it is H-shaped in transverse section in most of its extent. Its anterior and posterior walls are in contact with each other below the entrance of the cervix. The anterior wall, which is pierced by the cervix, is about seven and a half centimeters long; the posterior wall is about 9 cm long. These walls are especially distensible. The lateral walls are attached above to the lateral cervical ligament and , below this, to the pelvic diaphragm. They are, therefore, more rigid.

The recess between the vaginal part of the cervix and the walls of the vagina is termed the fornix of the vagina. Although it is continuous around the cervix, it is often subdivided into anterior, posterior, and lateral fornices. The posterior fornix is the deepest, and its wall is related to the peritoneum of the rectouterine pouch.

In most virgins, the opening of the vagina into the vestibule is partially closed by a fold, called the hymen. This fold is variable in size and shape, but is often annular or crescentic. It usually has one opening, but it may be cribriform. When an opening is lacking, the fold is called an imperforate hymen. After the hymen has been torn or ruptured, small rounded fragments remain at the site of its attached margin. These are termed the carunculae hymen.

   

Relations

Anteriorly, the upper part of the vagina is related to the cervix. Just below this, it is separated from the urinary bladder and ureters by loose connective tissue. Because the uterus is usually twisted and the upper part of the vagina is correspondingly deviated ( usually to the left ), much more of one ureter than the other situated in front of the vagina. The urethra is fused with the lower two-thirds of the anterior wall of the vagina.

Posteriorly, the upper part of the vagina is related to the rectouterine pouch, and below this, it is separated from the rectum by relatively avascular connective tissue. The lower part of the vagina is fused with the tendinous center of the perineum.

Laterally, the upper part of the vagina is attached to the parametrium forming the lateral cervical ligament and the two layers of the broad ligament on either side of this. The ureter and uterine artery are also related to this part of the vagina. The pubococcygeal portions of the levatores ani embrace the vagina about 3 cm above its opening and act as a sphincter.

Below the pelvic diaphragm, the vagina is related laterally to the greater vestibular gland, the bulb of the vestibule, and the bulbospongiosus muscle.

   

Structure

The vagina has three layers, a mucosa, a muscular coat, and a fibrous coat, details of which are covered in histology.

   

Blood supply

The upper of the vagina is supplied by branches of the uterine artery. The vaginal artery, sometimes arising as two or three branches from the internal iliac, divides into numerous branches, which are distributed to the front and back of the vagina. These branches may anastomose in the median plane to form two longitudinal trunks, called the anterior and posterior azygos arteries of the vagina. A few branches from the artery of the bulb of the vestibule reach the lower part of the vagina.

The blood from the vagina drains into the vaginal venous plexus, which communicates with the uterine and vesicle plexuses.

   

Blood supply

The labia majora and minora are supplied by the anterior labial branches of the external pudendal arteries and by the posterior labial branches of the internal pudendal arteries. The crura and corpora cavernosa of the clitoris are supplied by the deep arteries of the clitoris. The glans is supplied by the dorsal arteries of the clitoris. The bulb of the vestibule and the greater vestubular gland receive their blood supply from the artery of the bulb of the vestibule and form the anterior vaginal artery.

   

Lymphatic drainage

The lymphatic vessels from the external genital organs drain into the superficial inguinal nodes.
The lymphatic vessels from the upper part of the vagina pass along the uterine artery and drainage into the external and internal iliac nodes. Those from the middle part pass with the vaginal artery and drain into the internal iliac nodes, whereas from the lower part pass to the sacral and common iliac nodes. Lymphatic vessels from the part of the vagina adjacent to the hymen pass to the superficial inguinal nodes.

   

Nerve Supply

The labia majora and minora are supplied by the anterior labial nerve ( from the ilio-inguinal nerve ) and the posterior labial nerves ( from the pudendal nerve ). The bulb of the vestibule is supplied by hte uterovaginal plexus, which is continued as the cavernous nerves of the clitoris. The clitoris is also supplied by the dorsal nerves of the clitoris.

These various nerve include

1) sensory fibres, some of which conduct pain and others of which arise from a variety of special receptors,

2) autonomic fibres, which supply the numerous blood vessels, and

3) autonomic fobres, which supply the various glands.

[Except for its lowermost part, which is supplied by the pudendal nerve, the vagina is supplied by the uterovaginal plexus. The plexus contains autonomic fibres for the supply of smooth muscle as well as vasomotor fibres. There is little sensation in the vagina, except in its lowermost part. ]

   

Examination of pelvic organs

Digital examinations per vaginam are made by placing one or two fingers in the vagina. In bimanual examinations, pelvic structures are palpated between these fingers in the vagina and the other hand placed on the anterior abdominal wall.

The following structures are palpable:

In front, the urethra and the vaginal part of the cervix, the urinary bladder when distended, and the body of the uterus (bimanually).

Behind, the rectum and any masses present in the rectouterine pouch, which is readily accessible. An abscess in this pouch may be drained by an incision in the wall of the vagina behind the posterior fornix. When the sacral promontory is felt, the diagonal conjugate can be measured.

Laterally, the ureters, displaced or enlarged broad ligaments and lymphatic nodes, and displaced or enlarged ovaries and uterine tubes (bimanually).

A speculum introduced into the vagina permits visualization of the vagina and cervix, performance of certain minor operations on the cervix, and under anesthesia, removal of the uterus.

   

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Chapter 36: Female Reproductive System and the Contents of the Female Pelvis