Erection begins with sexual stimulation. Sexual stimulation can be tactile (for example, by touching the penis), or mental (for example, by having sexual fantasies). Sexual stimulation generates electrical impulses along the nerves going to the penis and causes the nerves to release nitric oxide, which in turn increases the production of cyclic GMP (cGMP) in the smooth muscle cells of the corpora cavernosa. The cGMP causes the smooth muscles of the corpora cavernosa to relax, and allow rapid blood flow into the penis. The in-coming blood fills the corpora cavernosa, making the penis expand. If you need viagra now viagra buy online "We found that male workers who had high exposure to BPA in the workplace had a much higher risk of male sexual dysfunction compared to other workers in the same city who were matched for age and other factors," said lead study author Dr. De-Kun Li, a reproductive and perinatal epidemiologist at Kaiser Permanente's Division of Research in Oakland, Calif. "A caveat here is those workers did have a much higher BPA exposure than most Americans or Chinese in the general population." About four percent of participants had RLS (944 of 23,119 men), and about 41 percent (9,433 men) had erectile dysfunction. Men with RLS were older and were more likely to be Caucasian. The prevalence of erectile dysfunction also increased with age.