Is it odd to be able to urinate while having a full erection? I have heard there is a valve in the urethra which closes off to prevent urination while the penis is errect, and if this valve becomes weak, it can cause retrograde ejaculation and bring about the ability to urinate while still having an errection. Is this true?
Yes, there is a value that shuts off the urinary tract during erections, to allow semen to flow out. If the valve is weak, it can fail to prevent this flow of semen, and the semen will thus flow up into the bladder. This valve makes it difficult to urinate with an erection.
While most men can urinate with an erection, they will be able to do so only with varying degrees of difficulty.