Why does increased blood flow to the penis make it hard? -

I know that the the penis is spongy tissue so increased blood flow makes it get bigger and that the penis needs to get hard for penetration to occur. So how does spongy tissue and blood together produce a hard penis?

An erection is the stiffening and rising of the penis, which occurs during sexual arousal, though it can also happen in non-sexual situations. The primary physiological mechanism that brings about erection is the autonomic dilation of arteries supplying blood to the penis, which allows more blood to fill the three spongy erectile tissue chambers in the penis, causing it to lengthen and stiffen. The now-engorged erectile tissue presses against and constricts the veins that carry blood away from the penis. More blood enters than leaves the penis until an equilibrium is reached where an equal volume of blood flows into the dilated arteries and out of the constricted veins; a constant erectile size is achieved at this equilibrium.

The above is not really true. If you constrict to outflow of blood from the penis, it would soon die and fall off. What actually happens is the the veins leading into the penis are dilated allowing additional blood to flow into the penis. Since the outflow remains the same, the blood expands the penis and it become erect. Since blood is still flowing in the out ot the penis at the normal rate, it remains healthy and well.

The blood flows in but is constricted flowing out. Fills up the tissues amp; boing, you have wood