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Chapter 2: Pathophysiology of Erectile Dysfunction

Chirag N. Dave; Arthur L. Burnett; Amin S. Herati

INTRODUCTION

Erectile dysfunction (ED) refers to the inability to achieve or maintain an erection that is sufficient for satisfactory intercourse. It is multidimensional and can arise from organic, relational, and/or psychogenic causes.1 The Massachusetts Male Aging Study (MMAS) reported a 52% prevalence of mild to moderate ED in men aged 40 to 70, and ED was found to be associated with age, health status, and emotional function.2,3 ED has detrimental effects on partner satisfaction and the couple’s quality of life. It was previously believed that most ED was psychogenic; however, more recent evidence shows that roughly 80% of ED is organic.3 ED may be a manifestation of endothelial dysfunction. Cardiovascular disease, poor general health status, diabetes, smoking, medications, and socioeconomic status are well-established risk factors for ED. Identification of these comorbid conditions offers the men’s health provider an opportunity to diagnose and intervene on conditions that may otherwise be asymptomatic. This chapter includes a brief discussion of the physiology of erection as it relates to a more complex discussion of the pathophysiology of ED.

PHYSIOLOGY OF ERECTILE FUNCTION

Key Points: Physiology of Erection

  • Erections are the result of neural activation, cavernosal smooth muscle relaxation, increased penile blood flow, and venous occlusion.

  • Nitric oxide (NO) activates guanylate cyclase to generate cyclic guanosine monophosphate (cGMP), leading to sequestration of calcium and smooth muscle relaxation

  • Phosphodiesterase type 5 (PDE5) inhibitors act by inhibiting PDE5 and increasing cGMP concentrations

The penis is composed of 3 cylindrical bodies, the paired communicating corpora cavernosa dorsally, and the corpus spongiosum ventrally. The corpus spongiosum surrounds the urethra and is continuous with the glans penis. These cylinders are encased by the dense, bilayered tunica albuginea, which is relaxed in the flaccid state and stretched in the erect state. All 3 corporal bodies are surrounded by Bucks (deep) and Dartos (superficial) fascia. The bulbospongiosus and ischiocavernosus muscles surround the base of the penis and contribute to erection and ejaculation (Fig. 2-1).4

FIGURE 2-1

Pelvic and penile anatomy. Top: Relations of the bladder, prostate, seminal vesicles, penis, urethra, and scrotal contents. Lower left: Transverse section through the penis. The paired upper structures are the corpora cavernosa. The single lower body surrounding the urethra is the corpus spongiosum. Lower right: Fascial planes of the lower genitourinary tract.

Three illustrations show the pelvic and penile anatomy. Three illustrations show the pelvic and penile anatomy. The first illustration shows the cross section of the pelvis which shows bladder in the front followed by rectovesical pouch. Below the bladder lies the prostate behind which the rectum is located. Pubic symphysis lies below the bladder below which the suspensory ligament of penis is located. Just below suspensory ligament of penis has a top layer of corpus cavernosum followed by corpus spongiosum and then the urethra followed by another layer of corpus spongiosum. The tip of the penis has glans penis and fossa navicularis. Behind the penis lies the scrotal septum. The second illustration on the lower left shows a transverse section of the penis. Two round structures at the upper portion are corpora cavernosa below which a single lower body surrounding the urethra is corpus spongiosum. Corpora cavernosa is covered by tunica albuginea. The corpora cavernosa and corpus spongiosum are covered by Buck’s facia followed by Colles’ fascia, and then finally by the skin. The third illustration on the lower right shows the fascial planes of the lower genitourinary tract and identifies the Denovilliers is behind the prostrate, Scarpa’s fascia is along the Pubic symphysis, Buck’s fascia is along the penile structure, Colles’ fascia is along the corpus spongiosum above the scrotum, and Dartos fascia is along the bottom penile and scrotal surface.
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The arterial supply to the penis is derived from the internal pudendal artery, which is a branch of the internal iliac artery. The internal pudendal artery traverses Alcock canal before dividing into the bulbourethral, dorsal, and cavernosal arteries. The venous drainage of the penis is via the deep and superficial veins.

The penis is basally in a flaccid state, which is mediated by smooth muscle contraction as a result of sympathetic stimulation, myogenic control, and endothelium-derived contracting factors such as ...

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