Penis Anatomy

You’re with your penis all day long, but how much do you know about penis anatomy?

While you may be familiar with what you can see on the outside, your penis has many more important structures just below the surface. When one of these structures doesn’t work as it should, you may experience problems getting an erection, ejaculating, or urinating.

In this article, we’re taking you back to biology class to learn all about the internal and external parts of a penis. You’ll also learn about the vascular features and nerves that help your penis work properly and what to do when something goes wrong.

There are three external male reproductive organs: the testicles (testes), the scrotum, and the penis. In terms of reproduction, the testicles produce sperm and testosterone, the scrotum protects the testicles, and the penis delivers sperm during ejaculation.

The external anatomy of the penis includes these visible parts:

• Glans penis. Also known as the head or tip of the penis, this rounded area at the end of your penis is highly sensitive due to an abundance of free nerve endings.

• Penis shaft. Resembling a tube, the shaft of the penis (or body of the penis) extends from the lower belly to the glans penis. Many men are concerned about the length and girth of their penis shaft. The average penis size in its flaccid state is around 3.6 inches (5.2 inches erect), with an average girth of around 3.7 inches (4.6 inches).

• Prepuce (foreskin). If you’re uncircumcised, your prepuce or foreskin is the loose fold of skin that covers your glans penis. When you have an erection, the prepuce slides back to expose the glans. During circumcision, the foreskin is removed.

• Frenulum. Shaped like a small V, the frenulum is a small piece of penile skin that connects the foreskin to the glans. It’s located on the underside of the penis near the tip.

• Urethral meatus. The urethral meatus refers to the slit-like hole at the tip of the penis from which urine and semen come out.

Nearby, the scrotum, which is the sac of skin that houses your testicles, is located just below your penis. And the perineum refers to the space between your scrotum and anus.

The internal structure of the penis consists of erectile tissues, connective tissues, muscles, and ligaments. If you’ve ever looked at a penis diagram, you might have seen the following key players:

• Root of the penis. The root is the fixed part of the penis attached to the body. It contains the bulb of the penis and crura (which house the erectile tissues) and the ischiocavernosus and bulbospongiosus muscles.

• Erectile tissues. The erectile tissues start at the root of the penis and extend into the shaft and tip of the penis. The corpus cavernosum is one of two cylindrical bodies of spongy tissues and smooth muscle that fill with blood during sexual arousal, enabling penetration. The other is the corpus spongiosum, a cylindrical body of erectile tissue that surrounds the urethra ventrally. It remains less rigid during erection to keep the urethra open for ejaculation.

• Connective tissues. The connective tissues in the penis help you maintain an erection and protect the erectile tissues. These tissues include the tunica albuginea, a fibrous layer surrounding the internal penile structures that contracts during an erection, and Buck’s fascia, which surrounds the tunica albuginea. The septum of the penis, which separates the two corpora cavernosa, is also made of connective tissues.

• Muscles. The ischiocavernosus and bulbospongiosus muscles compress the deep dorsal veins in the penis to prevent blood from draining out of the corpora cavernosa.

• Ligaments. Two suspensory ligaments help support the penis at its base, keeping it close to the pelvic bone.

• Urethra. The urethra is the tube that carries urine and semen out of your penis through the urethral meatus.

In addition to the internal and external parts of the penis, there is a network of arteries and blood vessels that play a crucial role in the erectile process. The vascular supply of the penis refers to the parts that control the blood flow required for erectile function.

Here are the vascular components that enable blood supply to the penis:

• Iliac artery. The iliac artery supplies blood to the lower part of the body, including the pelvis and lower extremities.

• Internal pudendal arteries. The internal pudendal arteries branch off from the iliac artery and are the main blood suppliers to the corpus cavernosum.

• Dorsal arteries. The dorsal arteries, which run along the deep dorsal vein between the corpora cavernosa, supply blood to the fibrous layer surrounding the erectile tissues.

• Deep dorsal vein. While the superficial dorsal vein drains blood from the penile skin and foreskin, the deepdorsal vein drains it from the erectile tissue to help your erection go down.

The nerve supply (or innervation) of the penis plays a role in sensory input and regulates the vascular changes that enable erectile function.

The main nerves in and around the penis consist of:

• Pudendal nerve. The pudendal nerve is the main nerve of the perineum and genitals. It controls movement and sensation for various structures in your penis and branches off into other nerves.

• Dorsal nerve. Branching off the pudendal nerve is the dorsal nerve, which relays sensory information to the central nervous system, which is required to obtain and maintain an erection.

• Cavernous nerves. The cavernous nerves contain sympathetic and parasympathetic fibers that supply the erectile tissues and help induce and relieve erections.

• Nerve endings. The abundance of free nerve endings in the glans penis is what makes it one of the most sensitive parts of the body.

Accessory glands secrete fluids that help facilitate reproduction. These fluids exit the body through the penis.

The main accessory glands of the male reproductive system include:

• The bulbourethral glands. Also known as the Cowper’s glands, the bulbourethral glands are located near the base of the penis. In response to sexual stimulation, they secrete pre-ejaculate fluid, also known as pre-cum, to lubricate the tip of the penis and neutralize acids in the urethra and vagina.

• Seminal vesicles. Located behind the bladder, the seminal vesicles secrete fluid containing fructose, protein, and prostaglandins that make up the bulk of semen and help support sperm as they make their way through the reproductive tract.

• Prostate gland. This walnut-sized gland secretes a milky fluid that helps sperm move properly. Muscles in the prostate also ensure that semen is forcefully pushed into the urethra and expelled from the body during ejaculation.

On average, men release around 1.5 to 5.0 milliliters of semen each time they ejaculate. Each milliliter of semen contains 15 to 200 million sperm.

Like the accessory glands, the ducts and tubes of the male reproductive system aren’t necessarily considered penis anatomy, but they do work with the penis to ensure semen makes its way out of the body.

The main ducts of the male reproductive system include:

• Epididymis. The epididymis holds sperm after they leave the testes, where they complete the maturation process.

• Vas deferens. When they’re mature, sperm leave the epididymis and pass through vas deferens, which is a long, narrow tube that connects with the seminal vesicles.

• Ejaculatory duct. From the vas deferens, combined with fluid from the seminal vesicles, sperm travel through the short ejaculatory duct to the urethra, where they are eventually expelled from the body.

The complex machinery you just learned about work together to help the penis accomplish its two main functions:

• Intercourse. When you’re sexually stimulated, your brain sends messages to your vascular and nervous systems, prompting a relaxation of smooth muscle and an increase in blood flow. If everything works as it should, your penile tissues fill with blood and you get an erection, making penetration possible. Intercourse typically ends in orgasm and ejaculation, and your erection subsides as blood exits the penis.

• Urination. The other important job of the penis is urinary function. Urine drains from the bladder into the bladder neck and out through the urethra.

Numerous medical conditions can prevent the anatomical pieces from working as they should, resulting in common male issues like erectile dysfunction (ED), painful erections, ejaculatory disorders, and more.

Some common medical conditions related to the penis include:

• Priapism. Priapism is a non-sexual prolonged erection that occurs when there’s a problem with the inflow or outflow of blood to the penis. Contributing factors include penile injuries, blood disorders, and certain medications. Priapism is a medical emergency. Left untreated, it can result in permanent sexual dysfunction.

• Peyronie’s disease. Peyronie’s disease occurs when scar tissue (or plaque) causes penile curvature, leading to painful erections or erectile dysfunction.

• Hypospadias and epispadias. The urethral opening is usually at the tip of the penis. But if you have one of these congenital conditions, this isn’t the case. Hypospadias causes the urethral opening to be on the underside of the penis, while epispadias causes it to be on the top of the penis. Surgery is typically recommended.

• Phimosis. Phimosis occurs when the foreskin is too tight to pull back and reveal the glans. It can cause painful erections and pain during urination.

• Erectile dysfunction. ED is the inability to get or maintain an erection. There are a number of contributing factors, such as blood vessel issues, nerve damage, low testosterone, medications, and more. Psychological factors can also play a role. Treatment may involve ED prescription medications that help increase blood flow to the penis, therapy, lifestyle changes, or a combined approach.

• Penile fracture. A penile fracture occurs when trauma or forcible bending causes the penile tissues to snap, rupture, or tear. It can lead to bruising, bleeding, loss of erection, and pain. Surgical treatment is typically required.

• Diseases and infections. Various penis diseases and disorders can impact the organ, including sexually transmitted infections (STIs), yeast infections, penile cancer, and inflammation of the penile skin. If you notice pain, discharge, abnormal growths, or discoloration, you should see your healthcare provider immediately so they can diagnose the issue.

• Ejaculatory disorders. Ejaculatory disorders like premature ejaculation (PE) or delayed ejaculation (DE) occur when you either ejaculate too early or have trouble reaching ejaculation. Nerve issues, certain medications, injuries, and mental factors can contribute to either disorder. Treatment for PE may include therapy or medication that helps desensitize the penis.

This list of penile medical conditions is not exhaustive. If you notice something different about how your penis looks or functions, you should reach out to a healthcare provider to figure out what’s going on.

Knowing when to seek professional help can be difficult sometimes. Take this advice from Peter J. Stahl, SVP of Men’s Sexual Health & Urology at Hims & Hers: “A helpful rule of thumb is that one-off or rare and sporadic sexual problems are normal. People should seek help, though, for any sex problems that are persistent, recurrent, result in avoidance of partnered sexual activity, or that are impacting mental health.”

With so many internal and external components supported by complex networks of nerves and blood vessels, the penis is one impressive organ. When it functions as it should, your penis is a major player in helping you have intercourse and reproduce. When it’s not working as it should, it can understandably cause significant distress.

Here are some key takeaways to send you on your way:

• The penis contains numerous internal and external parts. External parts of a penis include the glans, shaft, and foreskin. Internal parts include the erectile tissues, muscles, and ligaments that play crucial roles in sexual function and urination.

• The two main functions of the penis are intercourse and urination. Various arteries and nerves regulate blood flow to the penis to enable you to achieve and maintain an erection. The other main function of the penis is urination.

• Several medical issues can affect penis function. These issues include erectile dysfunction, Peyronie’s disease, and ejaculatory disorders. It’s important to seek medical advice if you notice any changes or problems.

If you’re dealing with an issue like ED or PE, schedule an online consultation to figure out what’s going on and to see if you qualify for prescription medication.

Want more tips on how to keep your penis functioning properly? Read these 13 tips on keeping your penis healthy, find out how to increase blood flow to the penis, and check out these 18 surprising penis facts.