Anatomy of the Penis: How An Erection Works

January 25, 2021

4 mins

The penis is a unique organ made up of tissue that's responsible for reproductive and urinary functions. While the outside appearance of the penis may seem straightforward, many complex processes occur within the parts of the penis.

Understanding how different parts of the penis function can help you take better health of your reproductive health.

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What Are the Parts of the Penis?

The main parts of the penis are the glans (head) and shaft. Below the shaft is a separate organ known as the scrotum. The testes in the scrotum are the primary male sexual organs. Sperm is produced in the testes. 

Head

The penis head is also known as the glans penis or glans. The penis head is a cone-shaped organ made of the corpus spongiosum — spongy tissue. Blood vessels within the corpus spongiosum. The head of the penis consists of sensitive nerve endings that are often stimulated during sexual arousal.

The head of the penis is covered by the prepuce or foreskin at the tip. Uncircumcised men have a double roll of excess skin and blood vessels that cover the glans to protect the head. It can be pulled back manually or during an erection to reveal the full glans. Around 85% of men in the U.S. are circumcised at birth.

Shaft

The shaft consists of the urethra — the tube that urine and semen exit the penis from. Also known as the corpus, the shaft is made up of corpora cavernosa and corpus spongiosum.

What is the function of the corpora cavernosa?

Corpora cavernosa is the spongy tissue that expands during an erection. The corpus cavernosa is two columns of tissue that run through both sides of the shaft. An artery runs through the center of each corpus cavernosum as well. In between and along the top of the shaft are two arteries and veins that help to transport blood.

What is the function of the corpus spongiosum?

The remainder of the erectile tissue can be found in the corpus spongiusum. Like the corpora cavernosa, it fills with blood rapidly when you have an erection. The corpus spongiusum prevents the urethra from getting compressed during an erection.

What is the function of the urethra?

The urethra is the tube that runs through the penis and releases urine and semen from the body. It runs through the center of the penis shaft up into the abdomen where it connects to the bladder, but it's also connected to the ejaculatory ducts below the bladder.

Base

The bulbospongiosus muscle and the ischiocavernosus muscle ie at the base of the penis. Muscles at the base of the penis help maintain blood flow to the penis and empty residual semen or urine from the urethra. The suspensory ligament and the fundiform ligament at the base support the structure of the penis.

Scrotum

The scrotum houses the testicles (testes), epididymis, and vas deferens. This is where sperm is held in the body before ejaculation.

The testes

The testes produce hormones like testosterone and sperm through a process called spermatogenesis. These are the male sex cells that fertilize the egg to create a fetus.

The epididymis

The epididymis are tubes located on the back side of the testes. It's a tightly coiled tube about 20 feet in length. They connect the testes to the vas deferens, which are the ducts responsible for transporting sperm up to the urethra for ejaculation.

The epididymides are where the middle stages of sperm maturation take place. Final maturation doesn't take place until the sperm is in the female reproductive tract.

Other Internal Organs in the Penis

The following organs are smaller, but play a big role in the overall reproductive health of a man.

Seminal vesicle

The seminal vesicle is located further along the reproductive tract inside the abdomen. It contributes seminal fluid to the ejaculate fluids, a mixture of proteins and supportive secretions for the sperm during their reproductive travels. Seminal fluids account for about 80% of ejaculate fluid.

Cowper's gland (bulbourethral gland)

The Cowper's Gland or bulbourethral gland is a pea-sized organ in the abdomen. It helps create pre-ejaculate fluid that helps to lubricate the urethra before ejaculation.

Prostate

The prostate surrounds the urethra and produces fluid the body expels during ejaculation. It's a walnut-sized gland that may change as men age.

Older men often experience complications with the prostate. Men over the age of 50 are more likely to experience infection and inflammation in the prostate. Some men can achieve orgasm by prostate massage manually through the anus.

How Does the Size of the Penis Change?

Penis size varies among men. While there is no standard penis size, participants in one study helped health experts estimate an average size.

While the following sizes are not the same for all men, they give a general estimate for most adult men:

• Flaccid penis length: 3.6 inches (in)

• Stretched penis length: 5.2 in

• Erect length 5.16 in

• Flaccid circumference: 3.66 in

• Erect circumference: 4.59 in

How Does an Erection Happen?

The nervous system, neurological system, and circulatory system are all involved in maintaining an erection. The first step to having an erection is being sexually aroused.

When the brain gets the proper signal, the arteries in the penis relax and dilate. Increased blood flow to the penis helps you maintain an erection and ejaculate afterward.

How Does Viagra® Help With Erectile Function?

Viagra® and the other popular erectile dysfunction (ED) medications like Cialis® and Levitra® all work similarly. They inhibit the PDE5 enzyme to strengthen blood flow to the penis. PDE5 is a natural part of the erection process that typically slows down blood flow.

How Rex MD Can Help

Rex MD offers generic versions of Viagra and other ED medications to help improve erectile function. If you're experiencing ED, don't hesitate to find the medication that may work for you.

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