Anatomy of the Penis

Aka: Anatomy of the Penis, Penile Anatomy, Penis, Erection

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II. Anatomy: General

  1. Cross Section
    1. uroMalePenisXsGrayBB588.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    2. uroMalePenisXsGrayBB1155.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  2. Corpus
    1. uroMalePenisMusclesGrayBB1136.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    2. uroMalePenisCorpusGrayBB1154.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)

III. Anatomy: Shaft of Penis

  1. Corpus Cavernosum (two)
    1. Two large columns of erectile tissue on penile dorsum
    2. Columns separated by septum of fibers
  2. Tunica albuginea
    1. Bands together the two columns of corpus cavernosa
  3. Lacunar space (Space of Smith)
    1. Surrounds tunica albuginea
    2. Intralacunar Smooth Muscle found within space
  4. Corpus spongiosum
    1. Located on ventral side (underside) of penis
    2. Does not contribute to penile rigidity
    3. Contains Urethra

IV. Anatomy: Glans (Head) of Penis Innervation

  1. Sensation
    1. Pudendal nerve supplies dorsal nerves to penis
  2. Erectile function
    1. Parasympathetic input (excitatory)
      1. Nervi erigentes runs adjacent to Prostate Gland
      2. Parasympathetic Nerves join at hilum of penis
      3. Nerves course through corpus cavernosa
    2. Sympathetic input (inhibitory)
      1. Sympathetic Nerves supplied by thoracolumbar plexus

V. Anatomy: Vascular Supply of the Penis

  1. Arterial inflow
    1. Supplies glans penis and shaft of penis
    2. Branches of deep internal pudendeal arteries
      1. Common penile artery
      2. Bulbar artery
      3. Dorsal artery
      4. Urethral artery
      5. Cavernosal artery
  2. Venous drainage
    1. Superficial penile veins
      1. Superficial dorsal vein
    2. Intermediate penile veins
      1. Emissary vein
      2. Circumflex vein
      3. Deep dorsal vein
    3. Deep penile veins
      1. Hilar vein (Santorini's Plexus)
      2. Cavernosal vein

VI. Physiology: Erection

  1. Step 1: Flaccid Penis
    1. Intralacunar (cavernosa) Smooth Muscle contracted
    2. Under Alpha adrenergic control (Norepinephrine)
  2. Step 2: Cavernous nerve stimulation (Parasympathetic)
    1. Alpha Adrenergic Receptor blockade
      1. Acetylcholine
      2. Vasoactive intestinal peptide (VIP)
      3. Prostaglandin (Prostacyclin system)
      4. Nitric oxide (nitrergic system)
        1. Released from nerve endings
        2. Activates Guanosine Triphosphate to produce cGMP
    2. cGMP causes Smooth Muscle relaxation
    3. Intralacunar (cavernosa) Smooth Muscle relaxes
  3. Step 3: Arterial Inflow increases
    1. Lacunar space dilates
    2. Helicine artery dilates
  4. Step 4: Venous outflow blocked
    1. Subtunical venules compressed
    2. Emissary veins (in tunica albuginea) compressed
  5. Step 5: Erection as lacunar space pools with blood
    1. Blood fills space rapidly with arterial dilation
    2. Blood trapped due to venous constriction
  6. Step 6: Ejaculation (Sympathetic Stimulation)
    1. Controlled by hypogastric plexus sympathetic impulse
  7. Step 7: Detumescence (Penis flaccid again)
    1. Decreased parasympathetic tone
    2. Baseline sympathetic tone maintained

VII. References

  1. Jordan (1999) Postgrad Med 105(2): 131-47 [PubMed]

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