Penis.howUrgent signs
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Orientation

Anatomy and how it works

A plain-language map of external and internal structures, erections, sensation, urination, and ejaculation.

Evidence checked July 15, 2026 · Editorially reviewed, not clinician-reviewed
Clinical side cutaway of adult penile anatomy showing erectile tissue, urethra, blood vessels, and nerves.
Educational illustration — not a diagnostic image · Medical illustration: NIDDK / NIH
In 20 seconds

The penis is part of both the urinary and reproductive systems. Skin, erectile tissue, blood vessels, nerves, the urethra, and nearby pelvic structures all contribute to what you see and feel.

01

What to know

  • The glans is the sensitive head; the shaft contains erectile tissue that fills with blood during an erection.
  • The urethra carries urine and semen at different times. Burning, discharge, blood, or inability to urinate is not simply an appearance question.
  • Foreskin mobility varies with age and anatomy. It should never be forced, especially in children.
  • Sensation, angle, veins, skin tone, and resting size vary between people and can change with temperature, stress, medication, and age.
What people often get wrong

A similar-looking photo or one matching symptom cannot confirm a cause. Timing, change, examination, and sometimes testing matter.

02

Useful next steps

  • Learn your usual baseline without repeatedly checking or comparing.
  • Describe a change by location, timing, pain, and whether it affects urination or sexual function.

When to get care

Do not rely on guesswork when the pattern changes.

  • Seek care for a new persistent lump, sore, discharge, bleeding, major color change, pain, or loss of function.
Use the Concern Navigator →

03

What a clinician may ask

  1. When did you first notice it, and is it changing?
  2. Is there pain, discharge, bleeding, fever, urinary change, or loss of function?
  3. Were there recent medicines, illness, injury, sexual contact, products, or procedures?
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