Sexuality is a complex concept encompassing far more than the simple sexual act. Sexuality in fact includes the physiological, behavioural and relational aspects of human sexual life, which are variously influenced by psychological factors (e.g. sexual fantasies, desire, arousal, psychosexual orientation, and the choice of the sexual object), as well as social and organic (vascular, nervous, and endocrine) factors.
From a functional point of view, a normal penile erection may be defined as an erection which permits the penetration of a lubricated vagina without additional assistance. Concerning the erectile mechanism, the haemodynamic changes in the penis require a high degree of central and peripheral nervous coordinated control and an unaffected endocrine system.