To understand what makes one curve, you need to understand what the penis is made of. The penis is comprised of three parallel expandable cylinders, or corpora. The two corpora cavernosa make up the top part of the shaft, while the corpora spongiosum is positioned in the groove between and beneath them, wrapping around the urethra and forming the head of the penis. Each of the corpora is surrounded by a thin layer of tissue called the tunica albuginea. When a male is aroused, chemical signals are sent from the brain and spinal cord that increase the blood flow to the penis.
Blood flows into the corpora faster than it can escape, and engorgement occurs.
Normally, the tissue layers surrounding the corpora have enough elasticity to allow for full expansion. When this process occurs symmetrically, a straight erection results. All the Angles Many men have some degree of penile angulation. Rarely are these conditions severe enough to require surgery. Peyronie's disease accounts for some cases of severe penile curvature.