Is the Prostate a Muscle? What It’s Actually Made Of

The prostate is not a muscle. It is a gland, roughly the size of a walnut, that sits below the bladder and wraps around the urethra. But calling it “just a gland” undersells its complexity, because smooth muscle makes up a meaningful fraction of the organ’s tissue and gives the prostate abilities that pure glandular tissue could never have. That muscular component is central to how the prostate works during urination and ejaculation, why it causes problems as men age, and how some of the most common prostate medications do their job.

What the Prostate Is Actually Made Of

If you sliced a healthy prostate open and looked at it under a microscope, you would find a mix of four main tissue types. One careful imaging study broke down the area occupied by each: smooth muscle accounted for about 22%, fibrous connective tissue made up roughly 54%, glandular epithelium (the cells that produce prostatic fluid) was around 16%, and glandular lumina (the hollow spaces inside those glands) filled the remaining 9%.¹ So the largest single component is fibrous tissue, not muscle. The prostate is predominantly a stroma-heavy organ, where “stroma” refers to the structural scaffolding of smooth muscle fibers and connective tissue that surrounds the secretory glands.

Those proportions shift when the prostate enlarges. In men with benign prostatic hyperplasia (BPH), the stromal compartment tends to balloon. One study of tissue specimens from men with BPH found smooth muscle and fibrous tissue together occupying about 66% of the gland, with epithelium and glandular lumen making up the rest.² The ratio of stroma to epithelium turns out to matter clinically, a point we will return to when discussing urinary symptoms.

What the Smooth Muscle Actually Does

The smooth muscle fibers woven through the prostate are not decorative. They contract and relax in ways that directly affect two things you use your prostate for every day: urinating and ejaculating.

During urination, something surprising happens. Real-time MRI studies have shown that the front portion of the prostate contracts vertically just before the bladder neck opens, helping to funnel the prostatic urethra open so urine can flow through.³ In other words, the prostate’s muscular tissue actively participates in getting urination started. It is not just a passive tube that urine passes through.

During ejaculation, the smooth muscle contracts in a coordinated squeeze that expels prostatic fluid into the urethra, where it mixes with sperm and other secretions. Prostatic fluid is produced continuously, and its drainage from the gland depends on these muscular contractions during both urination and ejaculation.⁴ Without the smooth muscle component, the gland would have no way to push its secretions out.

The Anterior Fibromuscular Stroma

Not all parts of the prostate contain the same proportions of tissue. The front (anterior) surface of the gland is covered by a thick sheet of tissue called the anterior fibromuscular stroma, or AFMS, which is almost entirely smooth muscle and dense connective tissue with very few glands. This is the most “muscular” part of the prostate, and it behaves differently from the rest of the organ.

Ultrasound studies in healthy men have shown that the AFMS changes thickness dynamically during urination, suggesting it actively contracts and relaxes during voiding.⁵ That same research group found the AFMS may contribute to age-related voiding problems, since its function changes as men get older.

How much does this muscular sheet matter? In an experiment using human prostate specimens, surgically dividing the AFMS reduced bladder pressure by about 15% at a given flow rate. When the tissue was reapproximated (stitched back together), the pressure returned to baseline or higher.⁶ This tells us the AFMS plays a real role in maintaining urethral resistance. It is essentially a muscular clamp around the urethra, and its tone matters for both continence and voiding.

Histological studies have also revealed that the anterior prostate lacks the typical glandular structure seen elsewhere in the organ. Instead, striated muscle fibers from the external urethral sphincter extend into the prostate in this region, creating an intricate interface between the voluntary sphincter muscle and the prostate’s own smooth muscle.⁷ This boundary is surgically important: damaging it during prostate surgery can affect urinary continence.

How Nerve Signals Control Prostatic Smooth Muscle

The smooth muscle in the prostate is under involuntary nervous control, meaning you cannot consciously squeeze or relax it the way you can flex a bicep. The prostate’s smooth muscle receives a rich supply of sympathetic nerve fibers that release noradrenaline. When those nerves fire, the noradrenaline binds to alpha-1 adrenergic receptors on the smooth muscle cells, causing them to contract.⁸

The specific receptor subtype responsible was identified as the alpha-1c (now called alpha-1A) adrenergic receptor.⁹ This detail matters more than it sounds, because it opened the door to drugs that specifically target prostatic smooth muscle tone, one of the most prescribed classes of medication for older men.

Why Alpha Blockers Work

If you or someone you know takes tamsulosin (Flomax), alfuzosin, doxazosin, or terazosin for an enlarged prostate, these drugs work precisely because the prostate contains smooth muscle. They are alpha-1 receptor blockers: they bind to the same receptors that noradrenaline uses, but instead of triggering contraction, they block the signal. The smooth muscle relaxes, the urethra opens up a bit wider, and urine flows more easily.¹⁰

This is why alpha blockers can start improving urinary symptoms within days, much faster than drugs that shrink the gland itself (like finasteride, which takes months). Alpha blockers do not change the size of the prostate at all. They change its muscle tone. The gland is the same size but softer, squeezing the urethra less tightly. The first characterization of these receptors in human prostatic tissue was a milestone, because it provided a concrete target for drug development.¹¹

More recently, researchers have explored adding a second pathway. PDE5 inhibitors like tadalafil (the active ingredient in Cialis) promote smooth muscle relaxation through a different chemical route involving a molecule called cGMP. Lab studies have found that tadalafil can enhance the inhibitory effects of tamsulosin on nerve-driven contractions in human prostate tissue.¹² Animal research has shown that testosterone regulates the PDE5 pathway in prostatic smooth muscle, suggesting hormonal status may influence how well these drugs work.¹³ Tadalafil is already approved for both erectile dysfunction and BPH symptoms, in part because of this dual smooth-muscle relaxation mechanism.

The Stroma-to-Epithelium Ratio and BPH Symptoms

Not every man with an enlarged prostate has bothersome urinary symptoms, and the tissue composition may explain why. A study comparing prostate tissue from men with symptomatic versus asymptomatic BPH found a telling difference: men with symptoms had about 62% stromal tissue (which includes smooth muscle and fibrous tissue), compared to 54% in men without symptoms. The ratio of stroma to epithelium was 4.6 in the symptomatic group versus 2.7 in the asymptomatic group.¹⁴

This suggests that when prostate enlargement is driven more by stromal growth (including smooth muscle proliferation) than by glandular growth, symptoms are worse. It makes intuitive sense: more smooth muscle means more tissue that can actively contract around the urethra, and more fibrous tissue means a stiffer, less compliant gland. A prostate that enlarged mainly by growing more glandular tissue might cause less obstruction because that tissue does not squeeze and does not resist compression as forcefully.

This insight also explains why two men with similarly sized prostates can have wildly different symptom levels. Prostate size alone is a poor predictor of urinary bother. What the prostate is made of, not just how big it is, determines how much trouble it causes.

How the Prostate’s Tissue Changes With Age

The prostate does not just get bigger as men age. Its structural composition changes at the molecular level. Studies comparing prostate tissue from young and old animals have found that aged prostates express lower levels of genes encoding key structural collagens, including types I and III. More strikingly, while the total amount of collagen protein may not decrease dramatically, its organization deteriorates. Over 70% of aged prostates examined in one study showed disorganized, swollen, and fragmented collagen fibers, compared to the tightly organized, compact fibrils seen in young tissue.¹⁵

This disorganization matters because the collagen matrix is the scaffolding within which smooth muscle cells and glands sit. When that scaffolding becomes disordered, the mechanical properties of the whole organ change. The prostate becomes stiffer in some areas and less resilient in others. Separate research has shown that hormonal changes with age can drive increased collagen deposition (fibrosis) in specific prostate lobes, particularly when testosterone and estrogen levels shift together.¹⁶

The stiffening of the basement membrane surrounding prostatic glands also appears to be a non-trivial event. Collagen-IV in these membranes accumulates chemical modifications called advanced glycation end-products with age, causing crosslinking and increased rigidity. This mechanical change can trigger cellular responses that promote abnormal cell growth, linking age-related tissue remodeling to the earliest steps in prostate cancer development.¹⁷

How the Prostate’s Stroma Participates in Cancer

In prostate cancer, the stromal tissue surrounding the tumor undergoes a transformation known as reactive stroma. This process begins early in cancer development and intensifies as the disease progresses.¹⁸ The smooth muscle cells and fibroblasts in the vicinity of a tumor are replaced by a different cell type called myofibroblasts, which ramp up production of extracellular matrix proteins and promote new blood vessel growth.¹⁹

Reactive stroma is not a passive bystander. It actively influences tumor behavior, creating a microenvironment that can encourage cancer cells to grow, invade, and spread. Understanding this stromal transformation has become a significant focus in prostate cancer research, because targeting the stromal compartment could complement therapies aimed at the cancer cells themselves. The prostate’s muscular and connective tissue is not just a structural envelope for glands; it is a dynamic participant in both normal function and disease.

The Surrounding Muscles People Confuse With the Prostate

Part of the confusion about whether the prostate is a muscle comes from its neighbors. The urethra passing through the prostate is surrounded by its own muscular layers: a longitudinal smooth muscle layer, a circular smooth muscle layer, and the external urethral sphincter, which is made of skeletal (voluntary) muscle.²⁰ Beyond those, the pelvic floor muscles form a hammock of voluntary muscle below the prostate.

When men are told to do Kegel exercises, they are contracting their pelvic floor muscles, not their prostate. The prostate sits above that muscular floor and cannot be voluntarily squeezed. Yet the pelvic floor and the prostate are so close together that problems in one area often masquerade as problems in the other.

Chronic Pelvic Pain and Pelvic Floor Spasm

A condition called chronic prostatitis or chronic pelvic pain syndrome (CP/CPPS) illustrates this overlap. Despite the name, the prostate itself is often not infected or inflamed in a traditional sense. A large cohort study found that 51% of men with CP/CPPS had tenderness somewhere in the pelvic region. The prostate was the most commonly tender site (41% of patients versus 5% of controls), but the external and internal pelvic floor muscles were also tender in 13-14% of patients, compared to none of the controls.²¹

Many urologists now believe that a substantial portion of CP/CPPS cases involve chronic tension or spasm in the pelvic floor muscles rather than a problem with the prostate gland itself. Physical therapy targeting the pelvic floor has become a first-line treatment for some of these men, a shift that would make no sense if the prostate were truly the sole source of pain. The alpha-1 blockers used for BPH are also sometimes prescribed for CP/CPPS, on the theory that relaxing the prostate’s smooth muscle may reduce urethral pressure and ease symptoms.⁴

The Prostate’s Stiffness as a Diagnostic Clue

The classic digital rectal exam, where a doctor feels the prostate through the rectal wall, is fundamentally a test of tissue stiffness. What the examiner feels is the combined mechanical properties of smooth muscle, connective tissue, glandular tissue, and any abnormal masses. Laboratory measurements of excised prostate tissue have found a median elastic modulus of about 43 kPa for whole glands, placing the prostate’s stiffness somewhere in the range of soft rubber or dense bread dough. Prostates with palpable abnormalities tended to be stiffer (median around 47 kPa) than those without (around 31 kPa).²²

These numbers help explain why a skilled examiner can sometimes detect a hard nodule suggesting cancer in an otherwise spongy gland. Tumors and areas of fibrosis are stiffer than the surrounding mix of smooth muscle and glandular tissue. The prostate’s normal softness, conferred partly by its glandular content and partly by relaxed smooth muscle, is what makes abnormally firm areas stand out to the touch. Newer imaging techniques like MRI elastography attempt to map these stiffness differences across the whole gland, essentially doing what the examiner’s finger does but with greater spatial resolution and objectivity.

Where the Prostate Comes From in Development

The prostate develops during fetal life from an embryonic structure called the urogenital sinus. Solid buds of epithelial cells push outward from the urogenital sinus lining into the surrounding mesenchyme (a loose embryonic connective tissue), then elongate, branch, hollow out, and eventually differentiate into the secretory glands and ducts of the mature prostate.²³ The smooth muscle and fibrous tissue of the adult prostate derive from that surrounding mesenchyme, while the glandular cells come from the epithelial buds.

This dual origin is one reason the prostate is not simply one thing. It is a composite organ from the start: glandular tissue and stromal tissue developing side by side, influencing each other’s growth through chemical signals that continue to operate throughout life. When doctors and researchers talk about “stromal-epithelial interactions” in the prostate, they are describing a conversation between two tissue types that began before birth and never really stopped. That ongoing dialogue is a major reason the prostate remains so biologically active well into old age, capable of both benign enlargement and malignant transformation in ways that many other organs are not.