The function of the prostate is simple to sum up: it makes the fluid that feeds and protects your sperm. The prostate is the size of a walnut, about 20 to 25 grams, and sits below your bladder. Where is the prostate exactly, what does it do, and how does it change with age? You will read that below. We think every man should know the basic anatomy of his prostate, because it makes later choices about screening much easier.
One gland, three zones, and a lot of confusion. Time to make it clear.
Where is the prostate?
The prostate sits below your bladder, in front of your rectum and around the upper part of your urethra. It lies deep in your pelvis, in a spot a doctor can feel through the rectum. Because of this position, an enlarged prostate quickly presses on the urethra, which explains urinary symptoms.
The position map in words:
- Below the bladder: the prostate sits right under the bladder outlet, like a ring around the start of your urethra.
- In front of the rectum: the back of the gland borders your rectum. That is why a doctor can feel the prostate with a finger during a rectal exam.
- Around the urethra: the upper part of your urethra runs straight through the prostate. When the gland grows, it squeezes the urethra.
- Walnut-sized: roughly 20 to 25 grams in a young man, which can grow over the years.
That position explains almost everything that can go wrong later. A gland that wraps around your urethra and can grow over a lifetime will, sooner or later, affect the flow.
What does the prostate do?
The prostate makes prostatic fluid, a milky liquid that forms about a third of your semen. This fluid feeds and protects your sperm and helps them stay mobile after ejaculation. Without healthy prostatic fluid, the fertilising ability of sperm would drop.
The fluid contains enzymes, zinc and a protein called PSA. PSA makes semen liquid again after ejaculation. A small amount of this PSA leaks into your blood, and that exact amount is measurable in a blood test.
The prostate also has a muscle function. During ejaculation the gland contracts and pushes the fluid into the urethra. At the same time it closes off the route to the bladder, so semen does not go the wrong way.
In short: the prostate is a fluid factory with a pump built in.
How big is the prostate?
A healthy prostate in a young adult man weighs about 20 to 25 grams, comparable to a walnut. The size of the prostate is not fixed: from age 40 the gland can slowly grow, sometimes to the size of a tangerine or larger. That is a normal part of ageing.
Prostate anatomy consists of three zones, described by pathologist John McNeal (McNeal, 1981). Each zone has its own position and its own clinical meaning. This layout explains why different prostate problems start in different places.
| Zone | Position | Clinically relevant for |
|---|---|---|
| Peripheral zone | Back and lower part, close to the rectum | Most prostate tumours start here; easy to feel during a rectal exam |
| Central zone | Around the ejaculatory ducts, upper part of the gland | Rarely involved in disease; relatively stable over the years |
| Transition zone | Around the urethra, in the middle of the gland | Benign enlargement (BPH); squeezes the urethra and causes urinary symptoms |
This zonal layout is the basis of almost every prostate story. Urinary symptoms usually come from the transition zone, while most tumours start in the peripheral zone.
How does the prostate change with age?
From around age 40, the transition zone of the prostate slowly starts to grow. This benign enlargement is called BPH and is so common that most older men deal with it to some degree. According to the NHG guideline on male urinary symptoms (2024), urinary complaints clearly increase with age.
Because the transition zone sits around the urethra, this growth can hinder the flow. It can show up as urinating more often, a weaker stream, or the feeling that your bladder is not fully empty. These symptoms say little about cancer on their own; they usually fit benign enlargement.
The growth is slow and varies greatly between men. One man notices little by 70, another already around 50.
A baseline measurement of your PSA around age 40 can give a personal reference point, so later changes are easier to read. For the broader context, see our complete guide to prostate health, screening and prevention.
Which symptoms relate to the prostate?
Prostate symptoms usually centre on urinating, because the gland sits around the urethra. Think of needing to urinate more often, a weak or hesitant stream, trouble getting started, or the feeling that your bladder will not empty. These can fit benign enlargement, but they need explanation from a doctor.
Three common patterns, each with its own possible cause:
- Gradual urinary symptoms later in life: often fit benign enlargement (BPH) from the transition zone.
- Sudden pain, fever or burning when urinating: can point to inflammation. Read more in our piece on prostatitis, symptoms and causes.
- An abnormal PSA value without clear symptoms: needs context. What is normal per age you can read in PSA levels by age.
Important: symptoms alone do not tell you what is going on. Many urinary symptoms are benign, but only a doctor can confirm the cause. A PSA blood test here is data, not a diagnosis.
If you have persistent urinary symptoms, pain or a changing stream, see your GP.
Frequently asked questions
Where is your prostate exactly?
Your prostate sits below your bladder, in front of your rectum and around the upper part of your urethra. It lies deep in the pelvis and is roughly the size of a walnut. Because it sits against the rectum, a doctor can feel the prostate with a finger during a rectal exam.
What is the main function of the prostate?
The main function of the prostate is to make prostatic fluid, which forms about a third of your semen. This fluid feeds and protects your sperm. The gland also contracts during ejaculation to push the fluid outward.
Can you live without a prostate?
Yes, you can live without a prostate. For some conditions the gland is removed surgically. This can affect ejaculation and sometimes erections, but it is not needed for survival. Always discuss the consequences with your doctor beforehand.
Getting started
Now that you know where your prostate sits and what it does, a concrete next step is to map your PSA. The Prostate Health Check measures your PSA, so you can go into the conversation with your GP well informed.
References
- McNeal JE. The zonal anatomy of the prostate. The Prostate. 1981;2(1):35-49. PMID: 7279811.
- NHG guideline on male urinary symptoms (Mictieklachten bij mannen). Dutch College of General Practitioners. 2024.
- EAU Guidelines on the Management of Non-neurogenic Male Lower Urinary Tract Symptoms. European Association of Urology. 2024.
Disclaimer
Caliberhealth works with BIG-registered doctors who review your blood results. This article provides general information and is not a substitute for medical advice from a GP or specialist. A blood test is a tool to inform your conversation with your doctor, not a diagnosis on its own. For severe symptoms or concerns about your health: contact your GP, or call 112 in an emergency.
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