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The human penis — it’s a fascinating bit of engineering capable of seemingly countless pleasures, concerns, and complications. If you have one or spend a good amount of time with one, you might think you’re intimately acquainted with its anatomy. Well, we’ll bet you still have a few things to learn.
First things first: The penis is the male sex organ that is used for reproduction and urination. The penis transports urine from the bladder out of the body when you pee. After puberty, the penis carries sperm (which is produced in the testicles) and semen (which is produced in the seminal vesicles, prostate gland, and bulbourethral glands) out of the body during ejaculation.
And besides those two strictly biological functions, the penis is also a source of sexual pleasure.
- The penis is part of the external male reproductive system (which also includes the scrotum and testicles).
- The structure of the penis includes the glans, corpus cavernosum, and corpus spongiosum. All contain erectile tissue that fills with blood to form an erection.
- Anatomical irregularities of the penis can be present from birth or can develop with age.
- These irregularities include micropenis, trapped penis, and Peyronie’s disease.
Anatomy of the penis
The penis is located at the base of the pelvis, above the scrotum, a sac of tissue that contains the testicles.
Most parts of the penis consist of erectile tissue filled with blood vessels. An erection results from a change in blood flow, during which the blood vessels in the penis fill with blood. When that blood drains, the penis becomes flaccid again.
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The structure of the penis includes:
The urethra is a tube that runs down the length of the penis. It transports urine and semen out of the body.
Glans (head of the penis, or glans penis)
The bulb comprises the tip of the penis. In uncircumcised men, the glans is covered by moist tissue called mucosa. (Mucosa, also known as “mucous membrane,” lines many cavities and passages of the body, including the mouth and gastrointestinal tract.) In circumcised men, the foreskin is removed, and the glans becomes keratinized or replaced with dry skin.
The foreskin is a double-layered ring of tissue that covers the glans. It’s composed of smooth muscle tissue, blood vessels, neurons, and mucous membranes. The foreskin is retractable. Cleaning underneath it is necessary to prevent a buildup of smegma, or oils produced by the foreskin, which can cause irritation and infection if not cleared away regularly.
Conventional wisdom holds that the glans of the uncircumcised penis is more sensitive than the circumcised glans, which supposedly becomes hardened and less sensitive from constant exposure and rubbing against clothing.
The shaft of the penis is the area between the glans and the abdomen.
In plural, corpora cavernosa. These two tubes of spongy tissue run down either side of the penis. When this tissue becomes engorged with blood, an erection happens.
This tube of spongy tissue runs down the front of the penis, ending at the glans. The corpus spongiosum also fills with blood during an erection.
This is a fibrous tissue that encircles and contains the corpora cavernosa, providing essential support to that erectile tissue (Brock, 1997).
The frenulum is a flexible band of connective tissue directly under the glans that looks like one spoke of a web and helps the foreskin retract. It may or may not be removed during circumcision.
Anatomical irregularities of the penis
A micropenis is an abnormally small penis that is present from birth. A micropenis is defined as a stretched penile length (SPL) in adult males as 3.66 inches or less. A micropenis is very rare: studies indicate 0.6 percent of men worldwide have the condition (Cleveland Clinic, n.d.)
This is a birth defect in which the opening for urine is on the underside of the penis rather than the tip. This condition can be corrected surgically.
An abnormal curvature of the end of the penis, which is present from birth, chordee may require surgical correction in severe cases.
An extremely rare condition in which a congenital male (meaning, a person possessing XY chromosomes) is born without a visible penis. It occurs in less than 1 in 30 million live births. Fewer than 100 cases have been reported (Berhane, 2019).
This describes a number of issues in which the penis looks smaller than expected. These include micropenis, trapped penis, webbed penis, or a partially hidden penis caused by excessive pubic fat in obese children or adult men (Cimador, 2015).
A trapped penis occurs because of an improperly performed circumcision. If too little or too much of the foreskin is removed, adhesions can cause the penis to retract below the skin of the scrotum (Cimador, 2015).
A webbed penis is a deformity in which the skin of the scrotum extends onto the penile skin (El-Koutby, 2010).
Phimosis (or paraphimosis)
This is a condition in which the foreskin is too tight and can’t be retracted or returned to its normal position over the penis head. (This is common in uncircumcised children and typically resolves naturally by the time the child is three years old. In rare cases, it might require intervention if it causes symptoms like redness, pain, or swelling.)
Balanitis is an inflammation of the glans, usually due to a viral, bacterial, or yeast infection. It’s common—3% to 11% of males experience it during their lifetime—and can be relieved by medication. Posthitis is an inflammation of the foreskin (prepuce), and balanoposthitis involves both the glans and the foreskin (Wray, 2020). Circumcised males have a 68% lower chance of developing balanitis than uncircumcised males (Morris, 2017).
Peyronie’s disease is a condition in which scar tissue builds up in the penis, making it curve. It’s believed a breakdown in the tunica albuginea causes collagen plaques to develop there, resulting in deformity and pain (Herwig, 2015). Peyronie’s disease can cause painful erections and can worsen with time, causing erectile dysfunction (ED).