Male Reproductive System: Anatomy, Function & Health Guide

What Are the Parts of the Male Reproductive System?

The male reproductive system consists of external organs (the penis and scrotum containing the testicles) and internal organs (the epididymis, vas deferens, seminal vesicles, prostate gland, and Cowper's glands). Together, these structures produce sperm and testosterone, enable sexual intercourse, and facilitate reproduction.

The male reproductive system is a complex network of organs that work together to perform three essential functions: producing sperm cells (spermatogenesis), producing the male sex hormone testosterone, and delivering sperm to the female reproductive tract during sexual intercourse. Unlike many organ systems in the body, the male reproductive system includes structures located both inside and outside the body cavity, each playing a crucial role in reproductive health.

The external structures include the penis and the scrotum, which houses the testicles. These organs are visible outside the body and are directly involved in sexual intercourse and temperature regulation for sperm production. The internal structures, while not visible externally, are equally essential. They include the epididymis where sperm mature, the vas deferens that transport sperm, and the accessory glands (seminal vesicles, prostate, and Cowper's glands) that produce the fluids making up semen.

Understanding the anatomy and function of each component helps individuals recognize normal variations, identify potential health concerns, and make informed decisions about their reproductive health. The male reproductive system also shares some structures with the urinary system, most notably the urethra, which serves as a common pathway for both urine and semen.

External vs. Internal Organs

The division between external and internal reproductive organs reflects both anatomical location and functional requirements. External organs are directly involved in sexual intercourse and must be accessible, while internal organs focus on sperm production, storage, and the creation of seminal fluid. The testicles, while located externally in the scrotum, function more like internal organs in terms of their role in hormone and sperm production.

How Does the Penis Work?

The penis consists of three cylindrical bodies of erectile tissue - two corpora cavernosa and one corpus spongiosum - that fill with blood during arousal to create an erection. The penis serves three functions: delivering sperm during ejaculation, enabling urination, and providing sexual pleasure through the sensitive nerve endings concentrated in the glans (head).

The penis is the primary male sexual organ, serving multiple essential functions in both the urinary and reproductive systems. Anatomically, it consists of three main parts: the root (which attaches to the pelvic bones), the shaft (the main body), and the glans (the sensitive tip). The structure of the penis is uniquely designed to enable both flaccid and erect states, allowing it to function in urination when relaxed and in sexual intercourse when erect.

The erectile tissue of the penis is organized into three cylindrical bodies that run the length of the organ. The two corpora cavernosa lie side by side along the upper portion of the penis and are primarily responsible for rigidity during erection. The corpus spongiosum runs along the underside, surrounds the urethra, and expands at the tip to form the glans penis. This arrangement protects the urethra during erection, keeping it open for ejaculation while the corpora cavernosa become rigid.

Unlike muscles, the penis cannot be strengthened through exercise because erection depends on blood flow, not muscular contraction. The erectile tissue contains smooth muscle and a network of blood vessels. During arousal, nerve signals cause these smooth muscles to relax, allowing blood to rush into the erectile tissue. Simultaneously, veins that normally drain blood from the penis become compressed, trapping blood inside and creating an erection. The firmness of an erection depends on how effectively blood fills and remains trapped in the erectile tissue.

The Glans (Head of the Penis)

The glans, or head of the penis, is the cone-shaped structure at the tip. It contains the highest concentration of nerve endings, making it extremely sensitive to touch and the primary source of sexual pleasure. The urethral opening (meatus) is located at the tip of the glans, serving as the exit point for both urine and semen.

During puberty, small bumps called pearly penile papules may develop around the edge of the glans (the corona). These are completely normal variations consisting of harmless skin cells. They do not spread, are not sexually transmitted, and typically become less noticeable over time. Many males have these papules, and they require no treatment.

The Foreskin

The foreskin (prepuce) is a double-layered fold of skin that covers and protects the glans in uncircumcised males. The inner layer contains glands that produce smegma, a natural lubricant that keeps the glans moist and protects against friction and infection. The foreskin is highly sensitive and contains numerous nerve endings that contribute to sexual pleasure.

The amount of foreskin varies naturally between individuals - some have foreskins that fully cover the glans, while others have partial coverage even when flaccid. In most males, the foreskin can be fully retracted by late childhood or adolescence. If the foreskin cannot be retracted by ages 8-10, or if there are recurrent infections, medical evaluation may be beneficial. Circumcision, the surgical removal of the foreskin, is performed in some cultures for religious, cultural, or medical reasons.

Proper hygiene involves gently retracting the foreskin and cleaning the area with warm water during bathing. This removes accumulated smegma and bacteria that can cause odor or infection if left to build up.

Why Are the Testicles Located Outside the Body?

The testicles hang outside the body in the scrotum to maintain a temperature 2-4°C (3-7°F) lower than core body temperature, which is essential for optimal sperm production. The cremaster muscle automatically adjusts testicular position - raising them closer to the body in cold conditions and lowering them when warm - to maintain this critical temperature range.

The scrotum is the pouch of skin hanging behind the penis that contains and protects the testicles, epididymis, and lower portions of the spermatic cords. This external location serves a vital purpose: temperature regulation. Sperm production (spermatogenesis) requires a temperature approximately 2-4°C lower than normal body temperature. If the testicles remained inside the body cavity, the higher temperature would impair or halt sperm production entirely.

The scrotum has several mechanisms for temperature regulation. Its skin is thin and contains sweat glands for cooling. More importantly, the cremaster muscle can contract to pull the testicles closer to the body when cold (conserving heat) or relax to let them hang lower when warm (promoting heat dissipation). This is why testicles appear to "shrink" in cold water and hang lower after a hot shower. The dartos muscle in the scrotal skin also contracts in cold conditions, making the scrotum appear wrinkled and smaller.

It is normal and common for one testicle (usually the left) to hang slightly lower than the other and for one to be slightly larger. This asymmetry prevents the testicles from being compressed against each other during physical activity. The average testicle is roughly the size of a small plum, measuring about 4-5 cm in length and 2-3 cm in width.

The Testicles (Testes)

The testicles are the primary male reproductive glands, performing two essential functions: producing sperm and synthesizing testosterone. Each testicle contains approximately 800 tightly coiled seminiferous tubules where sperm are produced. Between these tubules are Leydig cells, which produce testosterone in response to hormonal signals from the pituitary gland.

Sperm production begins at puberty and continues throughout life, though it may decline somewhat with age. The testicles produce approximately 100 million sperm per day. The entire process of spermatogenesis - from stem cell to mature sperm - takes about 74 days. Specialized cells called Sertoli cells within the seminiferous tubules nurture developing sperm and help regulate the process.

Testosterone, produced by the Leydig cells, is responsible for male sexual characteristics including facial hair, deeper voice, muscle development, and sex drive. It also stimulates sperm production and maintains bone density and red blood cell production. Testosterone levels are highest in the morning and naturally decline with age, though significant decreases may warrant medical evaluation.

Factors Affecting Sperm Production

Several factors can affect the testicles' ability to produce healthy sperm. Temperature is paramount - tight underwear that holds the testicles close to the body, prolonged hot baths, or frequent sauna use can temporarily reduce sperm production. Regular showering and brief sauna visits do not typically cause problems, and production usually returns to normal when the heat exposure stops.

Other factors affecting fertility include certain medications, smoking, excessive alcohol consumption, obesity, and various medical conditions. Fever can temporarily reduce sperm counts for up to three months, as sperm take that long to fully develop. Environmental toxins and radiation exposure can also impair testicular function.

How Do Sperm Travel Through the Reproductive Tract?

After being produced in the testicles, sperm travel through the epididymis (where they mature over 2-3 weeks), then through the vas deferens (during ejaculation), past the seminal vesicles and prostate (where they mix with fluids), and finally through the urethra to exit the body. This journey transforms immature sperm into fully functional cells capable of fertilization.

The journey of sperm from production to ejaculation involves several specialized structures, each playing a critical role in sperm maturation and transport. Understanding this pathway helps explain male fertility and the basis for certain contraceptive methods like vasectomy.

The Epididymis

The epididymis is a long, tightly coiled tube (about 6 meters if uncoiled) attached to the back of each testicle. Despite its compact appearance, it provides an extensive pathway where sperm undergo essential maturation. Sperm leaving the testicles are immature and incapable of fertilization - they cannot swim and cannot penetrate an egg.

During the approximately 2-3 weeks sperm spend traveling through the epididymis, they undergo crucial changes. They develop the ability to swim (motility) and acquire proteins on their surface that will eventually enable them to recognize and bind to an egg. The epididymis also stores mature sperm until ejaculation. Old sperm that are not ejaculated are broken down and reabsorbed by the body or expelled with urine.

The Vas Deferens

The vas deferens (also called ductus deferens) is a muscular tube about 45 cm long that connects the epididymis to the ejaculatory duct. During ejaculation, powerful contractions of the muscular walls propel sperm from the epididymis toward the urethra. Each vas deferens passes from the scrotum through the inguinal canal into the pelvic cavity, where it loops over the bladder before joining with a duct from the seminal vesicle.

Vasectomy, a common male contraceptive procedure, involves cutting and sealing the vas deferens to prevent sperm from reaching the ejaculate. After vasectomy, sperm continue to be produced but are reabsorbed by the body. The procedure does not affect hormone production, sexual function, or ejaculation - only the presence of sperm in the semen.

What Do the Prostate and Seminal Vesicles Do?

The seminal vesicles contribute about 60-70% of semen volume, providing fructose (sugar) for sperm energy and prostaglandins that stimulate female reproductive tract contractions. The prostate produces about 25-30% of semen, adding enzymes that liquefy semen after ejaculation and zinc that protects sperm. Together, these glands create the optimal environment for sperm survival and transport.

The accessory glands of the male reproductive system - the seminal vesicles, prostate gland, and Cowper's glands - do not produce sperm but create the seminal fluid that nourishes, protects, and transports sperm. Remarkably, sperm cells themselves make up only 2-5% of semen volume; the rest consists of secretions from these glands.

The Seminal Vesicles

The seminal vesicles are two elongated glands, each about 5 cm long, located behind the bladder. They produce a thick, yellowish fluid that constitutes the majority of semen volume. This fluid is rich in fructose, which provides energy for sperm motility after ejaculation. It also contains prostaglandins that may help stimulate contractions in the female reproductive tract, potentially aiding sperm movement toward the egg.

The seminal vesicle fluid also provides proteins that help semen coagulate immediately after ejaculation (forming a gel-like consistency), which may help retain semen in the female reproductive tract. Enzymes from the prostate later liquefy this coagulated semen, releasing sperm to swim freely.

The Prostate Gland

The prostate is a walnut-sized gland located just below the bladder, surrounding the first part of the urethra. It produces a thin, milky fluid that makes up about 25-30% of semen volume. Prostatic fluid contains enzymes (including prostate-specific antigen, or PSA) that liquefy coagulated semen, zinc that has antibacterial properties and protects sperm DNA, and citric acid that provides additional energy for sperm.

The prostate also contains smooth muscle fibers that contract during ejaculation, helping propel semen through the urethra. Because the prostate surrounds the urethra, enlargement of the prostate (common with aging) can affect urination, causing symptoms like weak stream, incomplete emptying, or increased frequency.

Cowper's Glands (Bulbourethral Glands)

The Cowper's glands are two small, pea-sized glands located below the prostate. During sexual arousal, they secrete a clear, slippery fluid called pre-ejaculate or "pre-cum." This fluid neutralizes any acidic urine residue in the urethra, creating a more hospitable environment for sperm passage. It also provides lubrication for the urethra and can contribute minor lubrication during intercourse.

While pre-ejaculate itself does not normally contain sperm, it can pick up residual sperm from a previous ejaculation still present in the urethra. This is one reason why withdrawal is not a reliable contraceptive method.

How Does the Urethra Function in the Male Body?

The male urethra is a 15-20 cm tube that serves dual functions: carrying urine from the bladder and transporting semen during ejaculation. A sphincter mechanism prevents simultaneous passage of both fluids, automatically closing the bladder connection during erection and ejaculation. This is why urinating with an erection is difficult or impossible for most men.

The male urethra is significantly longer than the female urethra (approximately 15-20 cm vs. 4 cm) because it must travel through the penis. This longer pathway provides some protection against urinary tract infections, which are less common in males. The urethra can be divided into three sections: the prostatic urethra (passing through the prostate), the membranous urethra (passing through the pelvic floor), and the spongy or penile urethra (running through the corpus spongiosum of the penis).

The urethral meatus is the external opening at the tip of the glans penis. During embryonic development, the urethra forms by the fusion of tissue along the underside of the penis. Variations in this development can result in hypospadias (opening on the underside) or, rarely, epispadias (opening on the upper side), conditions that can be surgically corrected if needed.

The sphincter mechanism at the bladder neck automatically closes during erection and ejaculation, preventing retrograde ejaculation (semen entering the bladder) and ensuring forward ejection of semen. This same mechanism makes urination during erection difficult, as the bladder outlet is closed. After orgasm and when arousal subsides, normal urinary function resumes.

What Is the Frenulum and Why Is It Sensitive?

The frenulum is a small, elastic band of tissue on the underside of the penis connecting the glans to the shaft, just below the urethral opening. It is one of the most sensitive areas of the male genitalia due to its high concentration of nerve endings. While the frenulum can stretch during intercourse, it occasionally tears, causing bleeding and pain that usually heals without treatment.

The frenulum (sometimes called the "banjo string") is a triangular fold of skin on the underside of the penis where the glans meets the shaft. This small structure plays an important role in sexual sensation because it contains a dense network of nerve endings. For many males, stimulation of the frenulum is particularly pleasurable.

The frenulum is designed to stretch during erection and intercourse. However, if it is naturally short (a condition called frenulum breve) or becomes stretched too quickly, it can tear. A torn frenulum typically causes bleeding and pain but is not dangerous. The wound usually heals on its own within a week or two with proper hygiene. In cases of recurrent tearing or very short frenulum causing discomfort, a minor surgical procedure called frenuloplasty can release the tension.

How Does Ejaculation Work?

Ejaculation is a reflex consisting of two phases: emission (where sperm mix with seminal fluid and collect in the prostatic urethra) and expulsion (where rhythmic muscle contractions forcefully propel semen through the urethra). The average ejaculate volume is 2-6 mL containing approximately 200-500 million sperm. Ejaculation is usually accompanied by orgasm, though the two can occur independently.

Ejaculation is the process by which semen is expelled from the body during sexual climax. It is a complex reflex involving coordination between the sympathetic and somatic nervous systems, multiple muscle groups, and the reproductive tract structures. Understanding ejaculation helps clarify male fertility and sexual function.

The emission phase occurs first, controlled by the sympathetic nervous system. The vas deferens contracts to move sperm toward the prostatic urethra. Simultaneously, the seminal vesicles and prostate contract, adding their secretions. The internal urethral sphincter closes to prevent semen from entering the bladder (and urine from mixing with semen). This creates a small reservoir of semen in the prostatic urethra.

The expulsion phase follows immediately. The bulbospongiosus and ischiocavernosus muscles at the base of the penis contract rhythmically (typically 3-15 contractions), propelling semen through the urethra and out of the body. These contractions occur about 0.8 seconds apart and produce the pleasurable sensations associated with orgasm.

Components of Semen

Semen is a complex mixture designed to protect and transport sperm. The composition is released in a specific sequence during ejaculation: prostatic fluid and sperm first, followed by the thicker seminal vesicle secretions. This sequence optimizes sperm delivery and survival.

Fresh semen coagulates within seconds of ejaculation, forming a gel-like consistency. Over the next 15-30 minutes, enzymes (particularly PSA from the prostate) liquefy the semen, allowing sperm to swim freely. Normal semen appearance is whitish-gray and slightly viscous after liquefaction; it has a characteristic odor due to its alkaline pH and specific chemical components.

Volume, color, and consistency of ejaculate can vary based on frequency of ejaculation, hydration status, diet, and overall health. After 3-4 days without ejaculation, volume typically reaches 2-6 mL containing approximately 100 million sperm per milliliter (200-500 million total). More frequent ejaculation results in lower volumes and sperm counts per ejaculation, though this does not indicate reduced fertility.

Sperm Cells

Sperm are the male reproductive cells essential for fertilization. Each sperm has three parts: a head containing the DNA (genetic material), a midpiece packed with mitochondria (providing energy for movement), and a tail (flagellum) that propels the sperm forward. Sperm are microscopic - about 50 micrometers long - and can only be seen under magnification.

While the testicles produce approximately 100 million sperm daily, the continuous renewal of stem cells means sperm production never depletes. Old sperm not ejaculated are broken down and reabsorbed. During fertilization, sperm carry either an X or Y chromosome, determining the biological sex of offspring (XX = female, XY = male).

When Should You See a Doctor About Reproductive Health?

Seek medical evaluation for: any lump or swelling in the testicles, persistent testicular pain, changes in testicle size, difficulty achieving or maintaining erections, blood in urine or semen, painful urination, penile discharge, or fertility concerns. Regular self-examination helps detect changes early when treatment is most effective.

Most changes in the male reproductive system are normal variations or minor issues that resolve on their own. However, certain signs and symptoms warrant medical attention. Knowing when to seek care can help catch serious conditions early and provide peace of mind for benign ones.

Testicular lumps or swelling should always be evaluated by a healthcare provider. While most lumps are benign (such as cysts, spermatoceles, or varicoceles), testicular cancer, though rare, is most common in young men (ages 15-35) and has excellent cure rates when detected early. Any new lump, hardness, or significant change in testicle size should prompt a medical visit.

Persistent testicular pain, especially if associated with swelling, fever, or redness, may indicate epididymitis, orchitis, or testicular torsion. Testicular torsion - where the testicle rotates and cuts off its blood supply - is a medical emergency requiring immediate treatment to save the testicle. Sudden, severe testicular pain should prompt emergency evaluation.

Erectile dysfunction (difficulty achieving or maintaining erections sufficient for intercourse) can have physical causes including cardiovascular disease, diabetes, hormonal imbalances, or medication side effects, as well as psychological causes. Because erectile dysfunction can be an early indicator of cardiovascular disease, medical evaluation is important even if the sexual impact seems minor.

Blood in semen (hematospermia) is often benign and self-limited, especially in younger men, but should be evaluated, particularly if persistent or occurring in men over 40. Blood in urine, painful urination, or penile discharge may indicate infection and require treatment.

Couples who have been unable to conceive after one year of regular unprotected intercourse should seek fertility evaluation. Male factor infertility contributes to approximately 40-50% of couple infertility, and many causes are treatable.