The bulbourethral glands are small spherical glands located lateral to the membranous urethra. The ducts that convey bulbourethral secretion open into the proximal part of the spongy urethra.
Figure 1: A labeled illustration of a posterior view of the bulbourethral glands, highlighted on the left with the entire male reproductive system, and on the right in more detail.
The bulbourethral glands secrete alkaline mucus in response to sexual stimulation. This mucus can adjust the pH in the urethra so that the environment changes from being acidic due to transporting acidic urine, to more pH neutral. This adjustment of the urethral pH will increase sperm viability because acidic environments kill sperm cells.