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# 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