Retrograde ejaculation
When semen enters into the bladder instead of flowing through the penis during orgasm, is referred to as retrograde ejaculation. However, it feels like a normal orgasm and doesn't usually affect sexual pleasure. Retrograde ejaculation is also known as dry orgasm.
When male experience orgasm, a tube called vas stops the transportation of sperm to prostate, where it gets mixed with other fluids to generate liquid semen or ejaculation. The muscle at the top end of the bladder presses to stop ejaculation to enter into the bladder, and it passes from the prostate, entering into the tube inside penis. Any factor that disturbs this involuntary movement and inhibits the sphincter muscle contraction, may lead to retrograde passage of semen into the bladder.
Ejaculation is an essential step in normal human reproductivity and its failure leads to chances of infertility. Although, retrograde ejaculation isn't that much harmful for fertility.