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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 (see reproduction). Erection can also occur to some extent in the [[clitoris]] and the nipples of the female.<ref>{{REFweb