Sex and the human female reproductive tract--what really happens during and after coitus.

The scientific study of the interaction of human genitals during coitus and after ejaculation with and without female orgasm has always been difficult and controversial with ethical, technical and social problems. The present brief review examines critically the results from these studies. Early observations utilised changes induced in sexually self-aroused subjects or by coitus with artificial (transparent) penes with few objective measurements. These culminated in the synthesis of the useful unitary descriptive, EPOR (excitation, plateau, orgasm, resolution)-model by Masters and Johnson (1966). Later investigations by other workers developed or employed instrumentation to record objectively the changes induced in the motility and pressures of genital muscles, in genital blood flow, in the ion and fluid movements creating the neurogenic transudate of vaginal lubrication, in its pH and pO2 and in the disposition of the ordered spurting ejaculate with subsequent sperm transport. More recently, studies have begun to use endoscopy and ultrasound imaging to picture what really happens especially during penile thrusting. While the newer techniques have often confirmed selected features of the original EPOR model they have also shown that the characterisation of the coital changes just by a unitary model is inappropriate. New observations suggest a plurality in the changes that can occur. Coital mechanisms are dynamic and our investigations and descriptions of them should match their dynamism. The knowledge gained will be more than helpful in the treatment of infertility, genital dysfunctions and disease transmission.