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Disease pathwayAndrology / Sexual Medicine

Erectile Dysfunction

An erection is a neurovascular event — ED is usually a vascular warning sign, so treat the penis and screen the heart.

Pathway
NO → cGMP
+
Effect
relax → fill → trap
+
Marker
endothelial health
Orientation

The big picture

Sexual stimulation releases nitric oxide in the cavernosal nerves and endothelium; NO raises cGMP; cGMP relaxes cavernosal smooth muscle; the sinusoids fill, expand, and compress the draining veins (veno-occlusion) — trapping blood and producing rigidity. ED is failure anywhere along inflow, relaxation, or veno-occlusion.

Golden rule

PDE5 inhibitors plus nitrates can kill — that interaction is absolute. And ED is the canary for cardiovascular disease: investigate the man, not just the symptom.

Pathophysiology

Mechanism pathway

Tap any step to see why it happens.

Illustration

The penis — cross-section

The penis — cross-section (layers from outside in)

Read it from the outside inward: skin → dartos/superficial fascia → Buck's (deep) fascia wrapping all three bodies, then a tunica albuginea around each erectile body. The two dorsal corpora cavernosa do the erecting; the ventral corpus spongiosum carries the urethra.

Dorsal neurovascular bundle deep dorsal vein (blue) + paired dorsal arteries (red) + nerves — 12 o'clock Skin thin, hairless, freely mobile Dartos / superficial (Colles') fascia loose subcutaneous layer beneath the skin Buck's (deep) fascia tough layer that encloses ALL THREE bodies together Tunica albuginea thick fibrous sheath around EACH corpus (brown band) Corpora cavernosa (×2) paired dorsal erectile chambers — the erection Cavernosal (deep) artery runs centrally in each corpus cavernosum Corpus spongiosum + urethra ventral; surrounds the urethra, forms the glans distally
Buck's fascia (encloses all 3) Tunica albuginea (around each) Cavernosal erectile tissue Spongiosum (urethra)
The key distinction this figure makes clear: the tunica albuginea is a thick fibrous sheath wrapped around each individual corpus (the brown bands), whereas Buck's fascia is the outer tough layer that binds all three bodies together (the dark band beneath the dartos and skin). The two corpora cavernosa are the dorsal erectile chambers, each with a central cavernosal artery; the ventral corpus spongiosum carries the urethra and expands distally to form the glans. The dorsal neurovascular bundle — deep dorsal vein, paired dorsal arteries, and dorsal nerves — lies at the 12 o'clock position deep to Buck's fascia. Grounded in leading urology references.
Presentation

Symptom sorter

The common presentation.

Gradual difficulty achieving/maintaining erectionsReduced rigidity and loss of spontaneous (morning) erections in organic EDFrequent overlap with diabetes, hypertension, smoking, obesity
Work-up

Diagnostic algorithm

Each step answers one question. Tap to expand.

Management

Treatment ladder

Fix reversible causes, optimise cardiovascular health, then escalate by efficacy and patient preference.

1
Lifestyle + cardiovascular optimisation + drug review
2
PDE5 inhibitor (if no nitrates)
3
Testosterone if hypogonadal
4
Intracavernosal alprostadil or vacuum device
5
Penile prosthesis for refractory cases
Pharmacology

Drug selector

PDE5 inhibitor

First line
Targets
Blocks cGMP breakdown
Onset
30–60 min (tadalafil longer/daily)
Use when
Most ED; needs intact NO signalling and sexual stimulation
Side effects
Headache, flushing, dyspepsia, visual changes
Board trap: Absolutely contraindicated with nitrates and soluble guanylate cyclase stimulators
Procedures

Procedure chooser

Surgical / procedural options
  • Penile prosthesis (inflatable) for refractory ED — durable and high-satisfaction
Safety

Complications

Disease complications
  • Relationship and psychological distress
  • Missed cardiovascular disease or diabetes
  • Missed hypogonadism
Treatment complications
  • PDE5i + nitrate hypotension (can be fatal)
  • Priapism from injection therapy
  • Prosthesis infection/mechanical failure
How to prevent
  • Always ask about nitrates before a PDE5i
  • Counsel injection patients on priapism
  • Screen and treat reversible causes first
How to manage
  • Priapism >4 h: urological emergency (aspirate ± phenylephrine)
  • PDE5i hypotension: supportive, avoid further nitrates
  • Escalate refractory ED to prosthesis
Safety

Red flags

Concurrent nitrate or recreational 'popper' use (PDE5i contraindicated)
Low libido + fatigue + small testes (hypogonadism)
Peyronie's deformity or penile fibrosis
Sudden ED after pelvic surgery/trauma (neurovascular injury)
Reference

Summary tables

Organic vs psychogenic ED

FeatureOrganicPsychogenic
OnsetGradualSudden
Morning erectionsAbsentPreserved
SituationalNo (all settings)Yes (situational)
Risk factorsVascular/diabetesStress/relationship
Recall

Memory hooks

NO → cGMP → relax → fill → trap → rigid.

PDE5i + nitrates = forbidden.

ED = endothelial alarm; screen the heart.

Morning erections preserved → psychogenic.

Fertility wish → no exogenous testosterone.

Exam

Board traps

Man on isosorbide/GTN asking for sildenafil — contraindicated, dangerous hypotension.

ED + low libido + small testes — check testosterone and prolactin.

Young man, sudden ED, intact morning erections — psychogenic.

Erection lasting >4 hours after injection therapy — priapism emergency.

Apply

Clinical cases

Case 1

A 58-year-old smoker with type 2 diabetes requests sildenafil for gradually worsening ED and absent morning erections. He takes isosorbide mononitrate for angina.

What is the key safety issue and the broader implication?

Test yourself

Quiz

Connect

Related topics

Male InfertilityProstate Cancer: Treatment by RiskPeyronie's Disease
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