Internal

Vagina

In sexual quiescence this is a potential space with an H-shaped cross-section and an elongated S-shaped longitudinal section culminating in a cul-de-sac, the anterior wall of which is penetrated by the cervix. The anterior and posterior walls touch but their film of basal vaginal fluid prevents adhesion. This basal fluid is a mixture of fluids from the vagina itself (basal transudate) with uterine and cervical secretions. The squamous epithelial lining of the vagina actively transports sodium ions from the vaginal fluid back into the blood. As fluid follows this ion movement osmotically the vagina is continually producing and reabsorbing its own fluid. (30)

On sexual arousal, the blood supply to the vaginal walls is increased by the liberation of VIP from the vipergic neural innervation while the venous vessels are probably constricted by the release of the vasoconstrictor neuropeptide Y. (3 d4 Within seconds this creates blood-vessel engorgement and a plasma transudate leaks out of the capillaries and percolates between the cells of the epithelium saturating its small reabsorptive capacity. The newly formed vaginal fluid creates a lubricating film on the vaginal surface which is essential for painless penile penetration. Poor or inadequate lubrication can lead to dyspareunia and subsequent sexual dysfunction. On cessation of sexual arousal or after orgasm the blood flow returns to the basal level and the fluid is reabsorbed back into the blood following the continuous absorption of sodium ions by the epithelial cells.

Coitus and the vagina

The cul-de-sac of the vagina is expanded during sexual arousal and the cervix is lifted clear of its posterior wall (vaginal tenting). (20) In the ventral-ventral ('missionary') coital position, penile penetration and thrusting stretches and stimulates the structures of the anterior vaginal wall which include the urethra, the 'G spot' (see below), and Halban's fascia. All these are thought to be capable of creating erotic excitement when so stimulated, giving rise to a significant part of the sexual pleasure experienced by most women during coitus.

The erotic structures of the anterior vaginal wall: urethra, 'G spot', and Halban's fascia

The urethra, approximately 4 cm long, is invested with erectile tissue which becomes engorged on sexual arousal. (3 d2 Ultrasound imaging during coitus has shown that the thrusting penis stretches the urethra. d5) There is an area a few centimetres from the introitus, at or around the junction of the urethra with the bladder, that becomes swollen and on maintained pressure stimulation can induce orgasm. This urethral area was first identified by Grafenberg (46) but the observation was overlooked until its rediscovery by Ladas et al.^l7 who named it the 'G spot' in recognition of the original discoverer. Anatomically, it probably represents the 'paraurethral' or 'periurethral' glands often refered to as the 'female prostate'. In some women these produce at orgasm a small amount of fluid secretion loosely referred to as the 'female ejaculate' (see Levin(30) for references). These glands are in the space between the bladder trigone and the neck of the urethra (48) which is filled with fibroelastic mesenchymal lamina rich in vascular lacunae and contains nerve fibres and pseudocorpuscular terminals. (49) This area is known as Halban's fascia^9 and when stimulated by pressure (penile or digital) creates intense sexual pleasurable feelings. (48d9)

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Break Free From Passive Aggression

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