Reach deep into the vagina and the fingertip meets a round, knob-like mass. It is the entrance to the uterus, called in anatomy the portio vaginalis, the vaginal portion of the cervix. In Japanese AV and sex-education discourse, the convention is settled of calling this “portio,” using only the head of the Latin word, and discussing it as a specific deep internal erogenous zone.

Portio (Japanese: ポルチオ; borrowed from the front of Latin portio vaginalis uteri) is a medical term for the part of the cervix that protrudes into the vagina (the portio vaginalis), transferred into Japanese sexual discourse. This article covers its anatomical position, the way it is discussed as an erogenous zone, the portio-orgasm discourse, and its treatment in AV and sex education.

Anatomy

The portio vaginalis is the part of the cylindrical cervix that protrudes into the vagina. It is a round convex surface 2–3 cm in diameter, with the cervical os opening at its centre. Its junction with the vaginal wall forms the vaginal fornices (anterior, posterior, left, right lateral); the posterior fornix (near the pouch of Douglas) is deepest and is the end point of penetration in intercourse. Histologically the cervix has a transition zone between stratified squamous epithelium (vaginal side) and columnar epithelium (uterine side). Pain sense is generally dull, and mechanical stimulation is perceived as deep pressure. This is the neural basis for the experience described as “having the uterus pushed.”

Status as an erogenous zone

In Japanese sex-education and AV discourse, there is a convention of discussing the portio as a deep internal erogenous zone where “the uterus is directly stimulated.” Concretely, the sense of collision at the deepest point of penetration, the pressure stimulus described as “thrusting up against the uterus,” and a whole-body response from the autonomic activity around the cervix are called “portio stimulation.” Orgasm by portio stimulation is often described as an independent category alongside clitoral, G-spot, and A-spot orgasm, though whether these have clearly distinct neural mechanisms medically is debated.

Examining the portio-orgasm discourse

The concept of “portio orgasm” has been examined in Western sexology since the 1980s as a response to cervical stimulation. In Komisaruk’s research, cervical stimulation is shown to be transmitted to the centre by neural pathways (mainly the pelvic and vagus nerves) different from those of clitoral stimulation. In Japan, “portio development” and “portio sensation” came to be widely discussed from the 2000s in sensual-massage discourse, and as an AV genre “portio teasing” and “uterine climax” became standardised. Yet the capacity for orgasm by portio stimulation alone varies greatly between individuals and depends strongly on degree of arousal, partnership, and psychological factors.

Treatment in AV and sex education

In AV, “portio teasing” and “portio development” are used as titles and genres, and works explain positions that reach the portio, such as deep thrusting, the standing carry, and the rear-entry position. For viewers it is advertised in connection with “the pleasure of the uterus being thrust” and “deep climax.” In sex education and counselling, careful handling is recommended before discussing the portio as a standalone erogenous zone: raising whole-body arousal first, adequate foreplay, a relationship of trust with the partner, and attention to physical strain, since strong collision against the cervix can be painful.

Related terms

• G-spot
• A-spot
• Clitoris
• Types of orgasm
• Internal climax
• Erogenous zone