Changes

# especially the swelling and rigidity that occur in the [[Corpus cavernosum penis|two corpora cavernosa and corpus spongiosum]] of the [[penis]] as a result of sexual or other types of stimulation. Impulses received by the nervous system stimulate a flow of blood from the arteries leading to the [[penis]], where the erectile tissue fills with blood, and the penis becomes firm and erect. Erection makes possible the transmission of [[semen ]] into the body of the female. Erection can also occur to some extent in the [[clitoris]] and the nipples of the female.<ref>{{REFweb

[[Circumcised]] males may experience tight and/or painful erections if there is insufficient residual shaft [[skin]] to permit full expansion and extension of the shaft of the [[penis]] during erection. [[Tissue expansion]] may relieve the pain and tightness.