The accessory glands are the three glands that make almost all of the fluid in semen: the seminal vesicles, the prostate, and the bulbourethral glands. Sperm make up only a small fraction of semen, and around two-thirds of its volume comes from the seminal vesicles alone.
That matters more than it sounds. Several lines on a semen analysis report, including volume, pH, fructose, and liquefaction time, are really a report on these glands rather than on sperm. A man who knows which gland each line belongs to can read his own report with far less worry and far more accuracy.
This guide explains where each gland sits, what it adds to semen, the order in which the glands empty, how their output shows up on a semen report, what each related test costs, and when a gland contributes to a fertility problem.
What the Accessory Glands Are
The male accessory glands are three sets of glands that sit along the route sperm take out of the body. Each one adds its own fluid, and together those fluids form the seminal plasma (the liquid part of semen that carries sperm). The table below is a quick map of all three before the detail that follows.
Table 1. The three accessory glands at a glance
Where each gland sits, how big it is and what it contributes to semen.
Gland
Where it sits
Approximate size
What it adds to semen
Seminal vesicles (a pair)
Behind the bladder and in front of the rectum
About 5 cm long each
Most of the fluid volume, plus fructose and clotting proteins
Prostate gland (single)
Directly below the bladder, wrapped around the urethra
About the size of a walnut
A thin, slightly acidic fluid carrying enzymes that later thin semen
Bulbourethral glands, also called Cowper's glands (a pair)
Below the prostate, at the base of the penis
About the size of a pea
A small amount of clear fluid that lubricates the urethra
A small amount of fluid also comes from the ampulla (the widened final stretch of each vas deferens, the tube that carries sperm up from the testicle). The division of labour is simple: the testicles make sperm, and the accessory glands make the fluid that carries, feeds and protects them. For how these glands fit into the rest of the tract, see our guide to how the male reproductive system works.
The Seminal Vesicles: What They Make and Why It Matters
Despite the name, the seminal vesicles do not store sperm
No, the seminal vesicles do not store sperm. They are glands that make fluid. Sperm are stored in the epididymis, the coiled tube that sits against the back of each testicle, and they only meet seminal vesicle fluid at the moment of ejaculation. The word vesicle means a small sac, which is where the confusion starts.
Where are the seminal vesicles?
The seminal vesicles are two coiled, pouch-like glands that sit behind the bladder and in front of the rectum, one on each side. Each is about 5 centimetres long. The duct of each gland joins the end of the vas deferens to form an ejaculatory duct, which empties into the urethra inside the prostate.
What seminal vesicle fluid contains
Seminal vesicle fluid makes up about 60 to 75 percent of semen volume, which is why it is often described as around two-thirds. It is thick, slightly yellowish, and alkaline, and each of its main components has a specific job to do for sperm.
Table 2. What seminal vesicle fluid contains and what each part does for sperm
The five main components of seminal vesicle fluid, read from the sperm's point of view.
Component of seminal vesicle fluid
What it does for sperm
Fructose (a simple sugar)
Supplies the energy sperm use to swim
Alkaline fluid
Helps neutralise the acidity of the male urethra and the vagina, which would otherwise harm sperm
Clotting proteins, mainly semenogelin
Hold semen together as a gel for the first few minutes after ejaculation
Prostaglandins (hormone-like fatty substances)
Thought to act on the female reproductive tract, including its muscle and immune response
Other proteins
Help protect sperm and support their movement
The amount of fluid the seminal vesicles make depends on testosterone, the main male hormone. The glands' growth and output follow the testosterone supply to their lining, not the food you eat. That point matters later on this page because it explains why a common belief about sugar and semen is wrong.
The Prostate and the Bulbourethral Glands
The prostate's role in reproduction
The prostate adds a thin, milky fluid that makes up about 20 to 30 percent of semen. That fluid carries enzymes, including prostate-specific antigen (PSA), which break down the clot formed by seminal vesicle proteins, along with zinc and citric acid. Muscle in the prostate also contracts at ejaculation to push semen into the urethra.
What are the three reproductive functions of the prostate?
Adds fluid to semen: about 20 to 30 percent of the volume, carrying enzymes, zinc, and citric acid.
Thins semen after ejaculation: its enzymes turn the gel formed by seminal vesicle proteins back into liquid so sperm can swim freely.
Helps move semen: its muscle contracts at ejaculation, pushing semen into and along the urethra.
Prostate fluid is slightly acidic, not alkaline
Prostate fluid is not what makes semen alkaline. Many summaries describe it as alkaline, but prostate fluid is in fact slightly acidic. The alkalinity of semen comes mainly from the seminal vesicles. This detail is exactly why an acidic semen sample can be a clue that seminal vesicle fluid is missing. The prostate is important for fertility, but it does not make sperm, and this page covers its reproductive role only.
The bulbourethral glands and the clear fluid before ejaculation
The small amount of clear fluid released before ejaculation is not made by the testicles. It comes from the bulbourethral glands, two pea-sized glands below the prostate. This fluid lubricates the urethra and neutralises any acidity left in it from urine, preparing the passage for semen. Whether pre-ejaculate can carry sperm is a separate question, answered in our guide to the physical signs that you are fertile.
How the Glands Work Together at Ejaculation
The accessory glands do not empty all at once. They release their fluid in a set order, and that order has a practical consequence for semen testing: different parts of a single sample carry very different contents. Knowing the sequence explains why a partly lost sample can give a misleading result.
Table 3. The order in which the glands empty, with share of volume and what each adds
Read from top to bottom as the sequence of a single ejaculation. Shares are approximate and vary between men and between samples.
Order
Source
Approximate share of semen volume
What it adds
Before ejaculation
Bulbourethral glands
A very small amount
Clear fluid that lubricates and neutralises the urethra
First
Sperm from the vas deferens, mixed with prostate fluid
Sperm and testicular fluid: only a few per cent
Most of the sperm in the sample
Then
Prostate (main contribution)
About 20 to 30 percent
Enzymes, zinc and citric acid in a slightly acidic fluid
Last
Seminal vesicles
About 60 to 75 percent
Fructose, alkaline fluid and clotting proteins
Why losing part of a semen sample matters
Because the first part of the ejaculate carries most of the sperm, losing that first portion during collection can make a sperm count look far lower than it really is. If any part of a sample is spilled or missed, tell the laboratory, even if it feels awkward, because the test may need to be repeated. For collection guidance, see our page on the importance of the semen analysis report.
Why semen clots and then turns liquid
Semen that is thick and jelly-like at first and turns watery a little later is not a sign of a problem. Proteins from the seminal vesicles, mainly semenogelin, make it clot on purpose, which holds sperm together at first. Enzymes from the prostate, including prostate-specific antigen, then break down that clot, usually within 15 to 30 minutes, so sperm can swim freely. Two glands work in sequence, and the laboratory records this change as the liquefaction time.
Reading a Semen Report Through the Glands
Four lines on a routine semen analysis report describe the fluid rather than the sperm: volume, pH, fructose and liquefaction time. Each one is, in effect, a gland reporting in. The table below links each line to the gland it mostly reflects, without giving reference values, because your doctor interprets the numbers in context.
Table 4. Which gland each semen report line reflects, and what an unusual result can point to
Where each fluid result comes from. It does not tell you whether your own number is normal.
Report line
Which gland it mostly reflects
What an unusual result can point to
Volume
Seminal vesicles and prostate
Low volume can mean fluid is not arriving from the glands, or that part of the sample was not collected
pH (how acidic or alkaline the sample is)
The balance between alkaline seminal vesicle fluid and slightly acidic prostate fluid
An acidic sample can mean seminal vesicle fluid is missing from the ejaculate
Fructose
Seminal vesicles
Low or absent fructose can mean their fluid is blocked, or the glands are absent or underdeveloped
Liquefaction time
Prostate
Slow liquefaction can mean the prostate's enzymes are not breaking the clot down as expected
No. Low semen volume does not mean the testicles are making fewer sperm. Sperm make up only a few percent of semen, and most of the volume is fluid from the seminal vesicles and the prostate. So low volume points first to the fluid pathway, or to an incomplete sample. The reverse is also true: a normal-looking amount of semen says nothing about how many sperm it contains.
The pattern doctors look for
Doctors read these lines together, not one at a time. A sample that is low in volume, acidic, low in or missing fructose, and contains no sperm is a recognised sign that fluid from above the prostate is not getting through. That pattern usually points to a blockage in the ejaculatory ducts, or to seminal vesicles and vas deferens that did not develop, and it is confirmed with further tests, typically a scan. It usually causes no symptoms, which is why the report is often the first place it shows up.
Two Things People Get Wrong About the Accessory Glands
The sugar in semen does not come from the sugar you eat
Fructose in semen is made by the seminal vesicles, and how much they make is driven by testosterone, not by diet. Eating more sugar does not raise the fructose in semen, and cutting sugar does not lower it. A low fructose result on a report points to the glands or their ducts, not to what you ate.
You cannot check these glands yourself
Self-check cannot tell you how your accessory glands are working. The seminal vesicles sit deep in the pelvis and cannot be felt from outside. A doctor can feel the prostate during an examination, but touch says nothing about the fluid it makes. A problem with these glands usually causes no symptoms, and shows up in the semen report.
When the Accessory Glands are Part of a Fertility Problem
The accessory glands can be involved in male infertility in a few specific ways. The table below is a map, not a diagnosis: each row names where the problem sits and points to the page that explains it in full.
Table 5. Where accessory gland problems sit, and where to read more
One row per location. Causes, tests and treatment are covered on the linked pages.
Where
What can go wrong
Read more
Ejaculatory ducts
A blockage that stops seminal vesicle fluid and sperm from reaching the urethra
Doctors assess the accessory glands through tests rather than examining them directly. Most men only ever need a routine semen analysis, which already reports volume, pH and liquefaction. The other two tests below are ordered selectively, usually when the first report shows a pattern that needs explaining.
Table 6. Indicative costs of tests that assess accessory gland function in India
Ranges are indicative for Cloudnine Fertility centres and are confirmed at booking.
Test
What it checks
Indicative cost
When it is usually ordered
Semen analysis
Volume, pH, liquefaction, sperm count, movement and shape
Rs 470 to Rs 1,800 (commonly Rs 1,030 to Rs 1,150)
First test for every man being assessed for fertility
Seminal fructose test
Whether seminal vesicle fluid is reaching the sample
Rs. 800 to 2200
When volume is low, and no sperm are seen
Transrectal ultrasound (a scan through the back passage)
Size of the seminal vesicles and whether the ejaculatory ducts are blocked
Rs. 2500 to Rs.6000
When the report pattern suggests a blockage
Costs vary by city, by centre and by whether tests are bundled into a wider male fertility work-up. A repeat semen analysis is common, because a single sample can be affected by illness, the number of days since last ejaculation, or an incomplete collection. For what the report itself covers, see why the semen analysis report matters.
Seek medical care if
You notice blood in your semen that does not settle or keeps coming back; pain during or after ejaculation; pain or burning when passing urine, especially with a fever; or being unable to pass urine. Sudden severe pain in a testicle can be a twisting of the testicle and needs same-day emergency care.
Most couples do not need to wait for a problem to appear before seeking an assessment. The table below sets out when a check is recommended.
Table 7. When to seek a fertility assessment
Timing guidance for couples trying to conceive. Both partners should be assessed together.
Situation
When to seek an assessment
Trying to conceive, female partner under 35
After 12 months without success
Female partner aged 35 or older
After 6 months without success
A semen report has shown low volume, an acidic pH or no sperm
Now, without waiting
History of surgery in the groin or pelvis
Sooner, without waiting the full 12 months
Both partners should be assessed at the same time, because a delay on one side delays the whole picture. The Cloudnine Fertility team can review an existing semen report and explain which gland each line points to. Learn more about male infertility treatment at Cloudnine Fertility, or book an appointment with a Cloudnine Fertility specialist.
FAQs
Your questions, clearly answered
Find clear, trusted answers to the most common questions about IVF—designed to guide and support you every step of the way.
What do the seminal vesicles do?
They make most of the fluid in semen. The seminal vesicles are two small glands behind the bladder, and their fluid supplies sugar for energy, helps protect sperm from acidity, and makes semen clot briefly after ejaculation. Around two-thirds of the volume of semen comes from them.
Do the seminal vesicles store sperm?
No. Despite the name, the seminal vesicles do not store sperm. They are glands that make fluid. Sperm are stored in the epididymis, next to each testicle, and only mix with seminal vesicle fluid at the moment of ejaculation.
What does the prostate do for fertility?
It adds a thin fluid to semen, about 20 to 30 per cent of the volume. That fluid carries enzymes that turn semen from a gel back into a liquid a short time after ejaculation, which helps sperm move freely.
What is fructose in semen?
Fructose is a sugar produced by the seminal vesicles that provides sperm with energy. It is sometimes measured during a fertility work-up, usually when semen volume is low, because its absence shows that fluid from the seminal vesicles is not reaching the sample.
Why is my semen volume low?
Usually because less fluid is reaching the sample, not because fewer sperm are being made. Most semen volume comes from the seminal vesicles and prostate. A missed part of the sample is common, and a blockage is less common. Your doctor reads volume alongside the rest of the report, using the WHO reference values.
Why is semen thick at first and then watery?
Because two glands work in sequence. Proteins from the seminal vesicles make semen clot as it leaves the body, and enzymes from the prostate break that clot down, usually within 15 to 30 minutes. Both stages are normal.
What do the bulbourethral glands do?
They make a small amount of clear fluid that appears before ejaculation. It lubricates the urethra and neutralises any acidity left in it from urine. This fluid is made by the bulbourethral glands, not by the testicles.
Can a blockage in the ejaculatory ducts cause infertility?
Yes. The ejaculatory ducts carry sperm and seminal vesicle fluid into the urethra. A complete blockage typically shows on a semen report as a low-volume, acidic sample with no fructose and no sperm, and it usually causes no symptoms. A doctor confirms it with a scan, and our azoospermia guide explains what happens next.
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