That same male urethra is the passage for sperm-containing semen during copulation. Although the penis normally is soft and flexible, it needs to be hard and stiff to enter a woman's vagina during copulation. To achieve this transformation, called erection, the penis is made from three different masses of spongy tissue filled with many blood vessels.
Fluid pressure produces the erection.
During copulation muscular contractions at the end of the process expel about a teaspoonful or two of semen, which can contain as many as 500 million sperm. Conditions that affect the penis Inability to achieve erection is termed impotence or erectile dysfunction. Certain sexually transmitted diseases, especially syphilis and genital herpes , often have a sore on the exterior of the penis as an early symptom. Warts may be sexually transmitted or may simply develop on the penis. Cancer of the penis is rare, but it does occur and can spread into the lymphatic system.