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Table 37-1. Phases of the erection process

Table 37-1. Phases of the erection process.a
Flaccid phase (1)
Minimal arterial and venous flow; blood gas values equal those of venous blood. Flow rate: 2.5-8 mL/100 g/min (Wagner and Uhrenholdt, 1980); 0.5-6.5 mL/100 g/min (Shirai et al, 1978).b
Latent (filling) phase (2)
Increased flow in the internal pudendal artery during both systolic and diastolic phases. Decreased pressure in the internal pudendal artery; unchanged intracavernous pressure. Some elongation of the penis.
Tumescent phase (3)
Rising intracavernous pressure until full erection is achieved. Penis shows more expansion and elongation with pulsation. The arterial flow rate decreases as the pressure rises. When intracavernous pressure rises above diastolic pressure, flow occurs only in the systolic phases.
Full erection phase (4)
Intracavernous pressure can rise to as much as 80-90% of the systolic pressure. Pressure in the internal pudendal artery increases but remains slightly below systemic pressure. Arterial flow is much less than in the initial filling phase but is still higher than in the flaccid phase. Although the venous channels are mostly compressed, the venous flow rate is slightly higher than during the flaccid phase. Blood gas values approach those of arterial blood.
Skeletal or rigid erection phase (5)
As a result of contraction of the ischiocavernous muscle, the intracavernous pressure rises well above the systolic pressure, resulting in rigid erection. During this phase, almost no blood flows through the cavernous artery; however, the short duration prevents the development of ischemia or tissue damage.
Detumescent phase (6)
After ejaculation or cessation of erotic stimuli, sympathetic tonic discharge resumes, resulting in contraction of the smooth muscles around the sinusoids and arterioles. This effectively diminishes the arterial flow to flaccid levels, expels a large portion of blood from the sinusoidal spaces, and reopens the venous channels. The penis returns to its flaccid length and girth.
aNumbers 1-6 correspond to phases shown in Fig 37-2.
bWagner G, Uhrenhold A: Blood flow measurement by the clearance method in the human corpus cavernosum in the flaccid and erect states. In: Zogniotti AW, Rossi G (editors): Vasculogenic Impotence. (Proceedings of the First International Conference on Corpus Cavernosum Revascularization.) Thomas, 1980. Shirai M et al: Hemodynamic mechanism of erection in the human penis. Arch Androl 1978;1:345.