What is an Erection?

illustration of sideview of pelvis of a person with a penis. The testicles are in front, at the bottom, within the scrotal sack. The penis is just above that, the bladder above the penis in the center of the pelvic cavity. Rectum is in back, ending in anus. Prostate gland lies between bladder and penis.

What is an erection? It should be a common question, but it isn’t. Here’s a practical explanation of what happens in an erection.