The seminal vesicles are a pair of coiled, tube-like glands that sit behind the bladder and just above the prostate. Each one has a duct that joins the vas deferens, the tube carrying sperm from the testicle, to form an ejaculatory duct. The two ejaculatory ducts pass through the prostate and open into the urethra.
Despite the name, they do not store sperm. Their job is to make fluid, and a lot of it: about 65% of semen volume. That fluid is rich in semenogelins, fibronectin, prostaglandins, cytokines and fructose1.
Seminal vesicle fluid is alkaline, and it dominates the later spurts of an ejaculate, while the first spurts are richer in sperm and prostate fluid4.
What do the seminal vesicles do?
They make the bulk of the fluid in semen and load it with ingredients that fuel, hold and protect sperm. Their output matters for fertility, not just for volume.
Seminal vesicle secretions:
- Supply fructose, a sugar sperm use for energy1.
- Provide semenogelins, which make semen form a gel straight after ejaculation before prostate enzymes break it down1.
- Support sperm motility and the stability of sperm chromatin, the tightly packed DNA in the sperm head2.
- Help suppress immune activity in the female reproductive tract, which may protect sperm2.
Can seminal vesicle problems lower semen volume?
Yes. Because they supply most of the fluid, anything that blocks, damages or underdevelops them can cut semen volume sharply.
Doctors group the causes of low semen volume into three broad types: collection problems, structural problems such as blockages, and functional problems such as nerve or bladder-neck issues3. Seminal vesicle trouble falls mainly into the structural group.
To check the glands, doctors may measure seminal fructose. It is the traditional marker of seminal vesicle function, although it varies with sperm count, so it needs careful interpretation2. Imaging such as an ultrasound scan can also show whether the glands and ducts look normal. These results are read alongside a repeat semen analysis, an examination and, where needed, hormone tests, rather than on their own.
Do the seminal vesicles affect fertility?
Yes. Their secretions do more than add volume, and when the glands underperform, sperm quality can suffer.
A review of seminal vesicle function concluded that when the glands are underactive, sperm motility, the stability of sperm chromatin and the immune protection sperm receive in the female tract may all be affected2. Seminal vesicle proteins are also what make semen clot straight after ejaculation, before prostate enzymes release the sperm again1.
That does not mean a smaller load signals a fertility problem. Volume changes day to day for many ordinary reasons, and only a semen analysis can tell you how your sperm are doing.
When should you see a doctor?
Most men never think about their seminal vesicles, and that is fine. It is worth getting checked if something changes and stays changed.
Talk to your GP if you notice:
- Consistently very low semen volume, or none at all (see hypospermia).
- Blood in your semen or pain when you ejaculate.
- Difficulty conceiving after a year of trying.
Common questions
Do the seminal vesicles store sperm?
No. The name is misleading. Sperm mature and are stored in the epididymis and vas deferens; the seminal vesicles make fluid that only meets the sperm at the moment of ejaculation, in the ejaculatory ducts.
Where are the seminal vesicles?
They sit behind the bladder and just above the prostate, one on each side. Their ducts join the vas deferens to form the ejaculatory ducts, which run through the prostate into the urethra.
What is seminal fructose?
It is a sugar made by the seminal vesicles that gives sperm energy. Labs can measure it, and a low level alongside low semen volume can point doctors towards a problem with the seminal vesicles or the ducts they drain through.
Read more on this
How to increase semen volume: what actually works
Is it normal for semen volume to change day to day?
Sources
- Anamthathmakula P, Winuthayanon W. Mechanism of semen liquefaction and its potential for a novel non-hormonal contraception. Biol Reprod. 2020;103(2):411-426. PubMed
- Gonzales GF. Function of seminal vesicles and their role on male fertility. Asian J Androl. 2001;3(4):251-258. PubMed
- Roberts M, Jarvi K. Steps in the investigation and management of low semen volume in the infertile man. Can Urol Assoc J. 2009;3(6):479-485. PubMed
- Rodriguez-Martinez H, Martinez EA, Calvete JJ, et al. Seminal plasma: relevant for fertility? Int J Mol Sci. 2021;22(9):4368. PubMed
Not medical advice. Written by Eric Stephens from the research cited above; not reviewed by a doctor. If something worries you, see a GP.