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How does blood flow produce an erection?

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Front view anatomical diagrams of the male and female reproductive systems, with labeled organs including penis, testis, prostate gland, uterus, ovary, and vagina. — human reproductive system Organs and structures of the male and female reproductive systems.

An erection is produced through a complex physiological process involving the human reproductive system and the nervous system.

When physical or psychological stimulation occurs, neural signals trigger the release of nitric oxide in the penis. This chemical promotes the formation of cyclic guanosine monophosphate (cGMP), which causes the smooth muscles of the corpora cavernosa to relax.12

As these muscles relax, the arteries supplying the penis dilate, allowing blood to flow rapidly into the spongelike spaces of the erectile tissue. This influx of blood causes the tissue to expand and distend. Simultaneously, the pressure from the expanding tissue compresses the veins against surrounding fibrous structures, which restricts blood outflow. By trapping the blood within the organ, the penis becomes enlarged and rigid.13

The corpus spongiosum also fills with blood but remains less rigid than the corpora cavernosa, ensuring the urethra remains open for the passage of semen.1