Internal reproductive anatomy

Uterus, tubes and ovaries

The uterus is a muscular organ roughly 7–8 cm long in someone who has not been pregnant. Its lining, the endometrium, thickens and sheds across the menstrual cycle. The cervix is its lower opening into the vagina; it changes position, firmness and mucus consistency across the cycle, sitting higher and softer around ovulation.

The fallopian (uterine) tubes carry eggs toward the uterus. Fertilisation, when it occurs, usually happens in the ampulla of the tube, not the uterus.

The ovaries hold a finite follicle pool set before birth — roughly 1–2 million at birth, about 300,000–400,000 at puberty, of which around 400 ovulate over a lifetime. They produce oestradiol, progesterone and testosterone. Ovaries continue producing androgens after menopause.

Uterine position varies: about 20–25 percent of people have a retroverted (backward-tilting) uterus. This is a normal variant, not a defect, though it can make some positions and cervical contact uncomfortable and can make smear tests trickier.

The cervix

The cervix has few of the fine touch receptors of the vulva but is richly supplied by the hypogastric and vagus pathways. Pressure sensation there is pleasurable for some and painful for others; sharp cervical pain during penetration is a signal to change angle or depth, not to push through. Persistent deep pain warrants investigation for endometriosis, fibroids, ovarian cysts, adenomyosis or pelvic inflammatory disease.

Internal male reproductive structures

Sperm produced in the testes mature in the epididymis, travel via the vas deferens, and mix with fluid from the seminal vesicles (about 65–70 percent of semen volume), prostate (about 25–30 percent) and bulbourethral (Cowper's) glands, which produce pre-ejaculate. Pre-ejaculate can contain viable sperm: studies by Killick et al. (2011) and Kovavisarach et al. (2016) found motile sperm in around 17–41 percent of pre-ejaculate samples. Withdrawal is therefore not a reliable contraceptive.

Pelvic floor

A hammock of muscle — levator ani, coccygeus and associated fascia — supporting bladder, bowel and uterus or prostate. It contracts rhythmically at orgasm. Both underactive and overactive pelvic floors cause sexual problems: weakness contributes to incontinence and reduced orgasmic intensity, while hypertonicity contributes to painful penetration, urinary urgency and pelvic pain. Cochrane reviews of pelvic floor muscle training (Dumoulin et al., latest update) show clear benefit for stress urinary incontinence. Self-directed clenching is the wrong treatment for a tight pelvic floor; assessment by a pelvic health physiotherapist distinguishes the two.

Blood and nerve supply

Pelvic sexual sensation travels by four main routes: the pudendal nerve (clitoris, penis, perineum), the pelvic nerve (vagina, cervix, rectum), the hypogastric nerve (uterus, cervix, prostate) and the vagus nerve. Komisaruk and Whipple's work with women with complete spinal cord injury (2004) demonstrated orgasm via the vagus pathway bypassing the spinal cord entirely — direct evidence that genital sensation is not the only route to orgasm.

Variation

Müllerian variations (septate, bicornuate, unicornuate uterus, or Müllerian agenesis as in MRKH) occur in roughly 4–7 percent of people, often discovered only during fertility investigation. Many have no effect on sexual function. Surgical history — hysterectomy, oophorectomy, prostatectomy, gender-affirming surgery — changes internal anatomy, sensation and lubrication in ways worth discussing explicitly with a partner and clinician.

Sources

• Wallace WH, Kelsey TW. "Human ovarian reserve from conception to the menopause." PLoS ONE, 2010.
• Killick SR et al. "Sperm content of pre-ejaculatory fluid." Human Fertility, 2011.
• Kovavisarach E et al. "Presence of sperm in pre-ejaculatory fluid of healthy males." Journal of the Medical Association of Thailand, 2016.
• Komisaruk BR et al. "Brain activation during vaginocervical self-stimulation and orgasm in women with complete spinal cord injury." Brain Research, 2004.
• Dumoulin C et al. "Pelvic floor muscle training versus no treatment for urinary incontinence in women." Cochrane Database of Systematic Reviews, latest update.
• Chan YY et al. "The prevalence of congenital uterine anomalies in unselected and high-risk populations: a systematic review." Human Reproduction Update, 2011.

Last reviewed: August 2026.