Prostate Function: What Does the Prostate Do?

Overview – three main functions of the prostate

The prostate gland has three primary functions, all related to male reproduction and sexual health:

• Produces seminal fluid: The prostate secretes a milky, alkaline fluid that makes up 20‑30% of semen volume. This fluid nourishes and protects sperm.
• Facilitates ejaculation: During orgasm, the prostate contracts, pushing prostatic fluid into the urethra and helping to expel semen. It also closes the bladder neck to prevent retrograde ejaculation.
• Hormonal metabolism: The prostate converts testosterone into its more potent form, dihydrotestosterone (DHT), which drives prostate growth and function.

Seminal fluid production – what's in prostatic fluid?

The prostate produces a thin, milky, slightly alkaline (pH ~7.3) fluid that is added to semen just before ejaculation. This fluid contains:

• Prostate-specific antigen (PSA): An enzyme that liquefies semen after ejaculation, allowing sperm to swim freely.
• Prostatic acid phosphatase (PAP): Another enzyme (historically used as a cancer marker, now replaced by PSA).
• Citric acid: A nutrient for sperm (energy source).
• Zinc (Zn²⁺): High concentrations (500‑1000 times higher than in blood). Zinc has antibacterial properties and stabilises sperm chromatin.
• Polyamines (spermine, spermidine): Contribute to the characteristic odour of semen and may protect sperm DNA.
• Calcium and magnesium: Ions important for sperm motility.

Prostatic fluid makes up 20‑30% of semen volume (the rest comes from seminal vesicles [60‑70%] and bulbourethral glands [<5%]).

Role in ejaculation – contraction and bladder neck closure

During ejaculation, the prostate plays two critical mechanical roles:

• Prostatic contraction: Smooth muscle in the prostate contracts, squeezing prostatic fluid into the urethra. This adds to the volume and force of ejaculation.
• Bladder neck closure: The prostate contains smooth muscle fibres that help close the bladder neck during ejaculation. This prevents semen from going backward into the bladder (retrograde ejaculation).

If the bladder neck does not close properly (e.g., after TURP surgery or due to medications like tamsulosin), retrograde ejaculation occurs – semen enters the bladder and is passed with urine later. This is harmless but can affect fertility.

Hormonal function – testosterone to DHT conversion

The prostate contains high levels of the enzyme 5‑alpha reductase type 2. This enzyme converts testosterone into dihydrotestosterone (DHT), which is 5‑10 times more potent than testosterone.

• Why DHT matters: DHT is the primary hormone that stimulates prostate growth and function. It binds to androgen receptors in prostate cells, promoting cell proliferation and secretory activity.
• Clinical relevance: Medications that block 5‑alpha reductase (finasteride, dutasteride) reduce DHT levels, causing the prostate to shrink by 20‑30% – used to treat BPH and male pattern baldness.
• Testosterone source: The prostate does NOT produce testosterone – testosterone comes from the testes (95%) and adrenal glands (5%).

Prostate-specific antigen (PSA) – what it does

PSA (kallikrein‑3, KLK3) is a serine protease produced exclusively by prostate epithelial cells. Its normal function is to liquefy semen after ejaculation.

• Mechanism: After ejaculation, semen forms a gel (from seminal vesicle proteins). PSA breaks down these proteins, allowing sperm to swim freely and reach the egg.
• PSA in blood: Normally, very little PSA enters the bloodstream. Elevated blood PSA can indicate prostate disease (BPH, prostatitis, or cancer).
• PSA as a marker: PSA screening is used for prostate cancer detection, but it is not cancer‑specific – only a biopsy can confirm cancer.

Without PSA, semen would remain clotted, and fertility would be impaired. Men with very low PSA (e.g., after prostatectomy) are usually infertile unless sperm extraction is performed.

What happens without a prostate? (After prostatectomy)

The prostate is not essential for survival, but its removal (radical prostatectomy for cancer) causes several changes:

• Dry ejaculation (anejaculation): No semen is produced (the prostate and seminal vesicles are removed). Orgasms still occur but are "dry" (no fluid).
• Infertility: Natural conception is impossible without sperm in the ejaculate. Sperm can still be extracted from the testes for assisted reproduction (IVF/ICSI).
• Erectile dysfunction (common but not inevitable): If the neurovascular bundles are damaged, erections may be impaired. Nerve‑sparing surgery preserves erectile function in many men.
• Urinary incontinence (usually temporary): The external urethral sphincter can compensate, but some men have stress incontinence.
• No hormonal changes: Testosterone production (from testes) continues normally.

How BPH affects prostate function

Benign Prostatic Hyperplasia (BPH) is non‑cancerous enlargement of the prostate, primarily affecting the transitional zone. How does BPH affect prostate function?

• Seminal fluid production: BPH does NOT impair prostatic fluid production – the prostate continues to secrete fluid normally.
• Fertility: BPH does not cause infertility unless it leads to ejaculatory duct obstruction (rare).
• Ejaculation: BPH does not impair ejaculation, but BPH medications (alpha‑blockers) can cause retrograde ejaculation (semen goes into the bladder). This is harmless but can be distressing.
• Urinary symptoms: BPH obstructs the urethra, causing weak stream, frequency, urgency, and nocturia – but these are not "prostate function" per se; they are due to mechanical obstruction.

In summary, BPH affects urinary function (due to obstruction) but preserves reproductive function. Fertility is usually normal.

How prostate cancer affects function

Prostate cancer affects function in two ways: local invasion and treatment side effects.

• Early cancer (confined to prostate): Usually no effect on prostate function – PSA may be elevated, but the gland still produces fluid, and erections/ejaculation are normal.
• Locally advanced cancer (spread beyond prostate): Can invade the ejaculatory ducts (haematospermia), urethra (haematuria, obstructive symptoms), or neurovascular bundles (erectile dysfunction).
• Treatment side effects:
  • Radical prostatectomy: Dry ejaculation, possible erectile dysfunction and incontinence.
  • Radiation therapy: Can cause erectile dysfunction (over years), urethral strictures, and haematospermia.
  • Hormone therapy (ADT): Reduces libido, erectile dysfunction, but does not affect ejaculation (still dry if prostate removed).

Fertility preservation (sperm banking) is recommended for men with prostate cancer who may undergo treatment, as most treatments cause infertility.

Common myths about prostate function

• Myth: "The prostate produces testosterone."
  ➜ Fact: Testosterone is produced by the testes and adrenal glands. The prostate converts testosterone to DHT.
• Myth: "The prostate controls erections."
  ➜ Fact: Erections are controlled by nerves near the prostate, not the prostate itself. Those nerves can be damaged during prostate surgery.
• Myth: "The prostate produces urine."
  ➜ Fact: No. Urine is produced by the kidneys. The prostate only surrounds the urethra.
• Myth: "An enlarged prostate always causes erectile dysfunction."
  ➜ Fact: BPH does not cause ED. However, some BPH medications (alpha‑blockers) can cause ejaculatory issues.
• Myth: "Without a prostate, you can't have an orgasm."
  ➜ Fact: Orgasms still occur, but they are "dry" (no semen). The sensation may be slightly different but is still pleasurable for most men.

Interactive FAQ – Prostate function

Disclaimer: This information is for educational purposes. If you have concerns about prostate function, fertility, or side effects of prostate treatment, consult a urologist at Vivekananda Hospital.