Excitement Phase
Fullness of the penis is an early sign of sexual excitement. It results from enlargement of the arteries (blood vessels in) to the penis, so that more blood flows in. Tiny valves in the veins, (blood vessels out) then close so that less blood flows out. This is how the penis gets hard. The size of the soft penis does not relate to its size when hard. In the overweight man it appears smaller than it is, as a pad of fat makes it less easy to see.

Plateau Phase
Later on in arousal, more intense excitement leads to further swelling of the tip of the penis (the glans). Fluids from the glands near the opening of the penis lubricate the opening. The man can usually decide how long to make this phase last. This control is difficult if the man is under pressure or anxious. Premature Ejaculation can occur if control is lost.

Orgasm Phase
The Orgasm in men has two parts.

1. The point of no return, after which control is lost. This moment is marked by muscular spasms in the Prostate Gland and semen stores.
2. The semen is forced out of the penis by rhythmic muscular spasms in the area behind the penis and under the scrotum or balls, and spasms in the tube from the bladder. A muscle at the bladder entrance closes to stop the semen from going into the bladder.

Refractory Phase
Immediately after ejaculation, as the penis is relaxing, further ejaculation is impossible, and the man cannot get excited.

See also