1. Shape
   1. The shape is somewhat variable, determined by the integrity of attachments to the pelvic wall.
      
      
   2. The anterior vaginal wall is shorter than the posterior vaginal wall by approximately 3 centimeters. The cervix fills the 3 centimeter difference in the anterior wall.
      
      
   3. The middle of the front and back walls is normally in apposition, resulting in an ìHî shape in cross-section of the vagina.
      
      
   4. The lower portion of the vagina is constricted by the levator ani muscles. Thus, the upper portion has a greater diameter.
      
      
   5. Fixation of the lower third of the vagina by the levator muscles results in a 120 degree angle between the axis of the lower third and the axis of the upper two thirds (posterior tilt).
      
      
   6. Vaginal rugal folds contribute to elasticity.
      
      
2. Size
   1. There is a significant variation in size, based upon age, estrogen effect, parity, and genetics.
      
      
   2. The vaginal length typically ranges from 7 to 10 cm.
      
      
3. Landmarks
   1. The cervix is in the upper portion of anterior vaginal wall.
      
      
   2. The midline ridge that extends the length of both walls is called the anterior or posterior column. The anterior column is identified as the urethral carina in the area of the bladder.
      
      
   3. There is variation in how far externally the urethral meatus is located. Typically, the urethral meatus is directed outward at the level of the hymen, but in possibly 40% of women the urethral meatus is directed into the outermost portion of the vagina.
      
      
   4. The space in front of or behind the cervix is the anterior or posterior fornix.
      
      
   5. The longitudinal folds along the vaginal sidewalls are the anterior and posterior lateral vaginal sulci.

SUPPORT

1. The lower third of the vagina is supported by the levator muscles in the pelvic diaphragm, and by the fibers of Luschka (fibers of the pubococcygeus muscle).
   
   
2. The middle third is supported laterally by a fibrous attachment to the arcuate line, or arcus tendineus that has importance in the paravaginal suspension surgical procedure.
   
   
3. The rectum supports the middle of the posterior vaginal wall, upon which the middle of the anterior vaginal wall rests. The anterior vaginal wall supports the mid portion of the bladder.
   
   
4. Endopelvic fascia in the adventitia layer of the upper third of the vagina is confluent with the fascia of the cervix, so the cardinal and uterosacral ligaments that support the cervix provide significant support for the upper third of the vagina as well. This fascial layer also blends with the rectal and vesical fascia.

BLOOD SUPPLY

1. The vaginal vascular supply courses laterally from the Cardinal ligaments through the paravaginal suspensory ligaments to the vagina.
   
   
2. The main arterial supply (especially to the anterior vagina) is the vaginal branch of the internal pudendal artery, typically with anastomoses from the uterine, inferior vesical, and middle rectal arteries. A second vaginal artery that mainly supplies the posterior vaginal wall may arise from the internal iliac artery, proximal to the uterine artery.
   
   
3. A vaginal arterial plexus extends to a midline vaginal artery in the anterior and in the posterior vaginal walls.
   
   
4. The venous plexus of Santorini is present in the fibrous layer of the vagina and communicates through the cardinal ligaments with the venous system of the bladder, rectum, and paravaginal tissues (the vesicovaginal plexus).

NERVES

1. The vagina has several parallel nerve systems. The most important nerve groups are the pudendal nerve which has chiefly S2-4 derivation and the inferior hypogastric plexus (also S2-4).
   
   
2. There are two main categories of nerves (ie, somatic and visceral), both with afferent and efferent fibers.
   1. Somatic supply is mainly to the lower portion of the vagina.
      
      1. Afferent, or sensory supply to the skin and subcutaneous tissue of the lower 2/3 of the vagina is the pudendal nerve. This distribution corresponds with the embryological origin of this portion of the vagina from the urogenital sinus.
         
         
      2. Parietal peritoneum in the pouch of Douglas (cul-de-sac) is sensitive to trauma and inflammation in a manner characteristic of a peritoneal somatic afferent nerve response, but it is supplied by the visceral afferent nerves of the uterovaginal plexus and also demonstrates characteristic visceral sensitivity to stretch and spasm.
         
         
      3. Efferent (motor) somatic supply is not significant in the vaginal wall since there is no striated muscle, but efferent supply largely from the pudendal nerve controls the levator muscles that provide support, and influence function of the lower third of the vagina.
         
         
   2. Visceral nerve supply is significant for the upper vagina, musculature, and glands. All pelvic visceral nerve fibers course in the endopelvic fascia beneath the pelvic parietal peritoneum. These nerves arise from the Inferior hypogastric plexus, which gives rise to three other divisions. One division is the uterovaginal plexus (Frankenhausen's plexus --mainly consisting of S2-4) around the ureter and uterine artery. Fibers from the uterovaginal plexus accompany the vaginal artery and vein to the vagina.
      1. Afferent fibers transmit interoceptive, noxious stimuli from the peritoneum at the pouch of Douglas, and from the cervix and upper 1/3 of the vagina to nerve roots S2-4, consistent with the Mullerian embryologic origin of these structures.
         
         
      2. Efferent fibers supply smooth muscle and glands.
         
         Autonomic
         
         1. Sympathetic nerves constrict smooth muscle of the arteries and arterioles. Sympathetic nerve fibers from T1-L2 accompany sacral nerves of the hypogastric plexus.
            
            
         2. No parasympathetic fibers have been described in association with the pelvic arteries and arterioles. The chief importance of vaginal parasympathetic efferent fibers (S2-4) is to mediate sexual response in the lower portion of the vagina. Parasympathetic fibers are found in the pudendal nerve and in the inferior hypogastric plexus.
            
            
      3. Visceral motor fibers control vaginal wall smooth muscle and glands.
         
         

LYMPHATICS/IMMUNE

1. Lymphatic drainage is to the para-aortic nodes.
   
   
2. No intraepithelial immune cells are present in the normal state, but Langerhan's cells in the area of the basement membrane migrate to a site of inflammation.
   

EPITHELIUM

1. Layers
   1. The mucosa consists of non-keratinized stratified squamous epithelium.
      
      
   2. The submucosa is equivalent to the dermis at other body sites.
      
      
   3. The muscularis is somewhat interspersed with the submucosa and adventitia.
      
      
   4. The high content of elastin in the adventitia contributes to elasticity of vagina. This layer of variable thickness is an extension of the endopelvic fascia that provides some degree of support for all of the pelvic organs.
      
      
   5. A serosa (peritoneal layer) is only present in the cul-de-sac, or pouch of Douglas behind the uterus.
      
      
2. Glands
   1. Bartholin's glands are identified at 3 and 9 o'clock external to the hymen.
      
      
   2. Skene's glands are in the periurethral area.
      
      
   3. Epithelial glycoprotein coat is an apparent epithelial transudate.
      
      
   4. Cervical mucus from endocervical secretory cells (columnar epithelium) contributes to the vaginal fluid.
      
      
   5. The vagina has no glands but these vestibular glands provide moisture for the vagina.
      

FUNCTION

1. The vagina is an external access to a visceral organ (the uterine cavity) with reproductive and coital functions.
   
   
2. As a microbial interface, the vagina is a barrier to a significant microbial load.
   

CLINICAL CORRELATES

1. The redundant countercurrent vaginal blood supply concentrates chemicals (antibiotics, potential irritants, etc.) in the vagina.
   
   
2. Pain of vaginal origin is vague locally, and can be referred elsewhere in the pelvis. This nerve signal overlap is due to close proximity of numerous poorly myelinated sensory nerve fibers in the extensive pelvic nerve plexus.
   
   
3. Relative to other skin structures, the vagina is not well supplied with nerve endings. Thus, pain response to mechanical stimuli is somewhat blunted, but is intensified by inflammation.
   
   
4. A vaginal urethral meatus may increase risk of post coital UTI.
   
   
5. Disruption of epithelium contributes to symptomatic microbial overgrowth, or increases susceptibility to infection by pathogens.
   

REFERENCES
Burgos MH, Roig de Vargas-Linares CE. Ultrastructure of the Vaginal Mucosa. In: Hafez ESE, Evans ET, eds. The Human Vagina. Amsterdam, Elesvier, 1978;63

Witkin SS. Immunology of the Vagina. In: Summers PR, ed. Vaginitis in 1993. Clin Obstet Gynecol 1993;36:122-7

Rogers RM. Basic Pelvic Neuroanatomy, in Steege JF, Metzger DA, Levy BS, eds. Chronic Pelvic Pain An Integrated Approach. Philadelphia, W. B. Saunders Company, 1996;31-58