Gross Anatomy of Urethra

This note briefly describes about the gross anatomy of male and female  urethra along with its blood supply, lymphatic drainage and innervation.

General Consideration
Urethra is the terminal part of the urinary tract and conducts urine from bladder to exterior.
Male urethra and female urethra are considered separately below.

         Muscular tube
         18-20 cm long
         Extends from internal urethral orifice of the urinary bladder to the external urethral orifice at the tip of the glans penis
         also acts as the part of genital tract by providing a passageway for semen during ejaculation.

         Divided into four parts
      •         Preprostatic urethra
      •         Prostatic urethra
  •         Membranous urethra
      •         Spongy urethra

Preprostatic Urethra or Intramural part of urthra
         1-1.5 cm long
         Extends vertically from bladder neck to the superior aspect of prostate
         Associated with internal urethral sphincter
     –        Prevents retrograde movement of semen to the bladder

Prostatic urethra
         4 cm long – widest and most dilatable part
         Descends through the anterior part of the prostate
         Forms a gentle curvature with anterior concavity

Internal features
         Posterior wall presents
        Urethral crest
        Prostatic sinus on each side of the crest
        Seminal colliculus in middle part of the crest
      •         Presents slitlike orifice which leads to Prostatic Utricle
      •         Ejaculatory duct open on/within prostatic utricle

Membranous part
         Shortest and narrowest part, 1-2 cm long
         Lies in the perineal region
         Begins at the apex of prostate and ends at the bulb of the penis
         Traverses the deep perineal pouch and passes through the external urethral sphincter and perineal membrane
         Associated with the external urethral sphincter
         Posterolaterally related with Bulbourethral or Cowper’s gland

Spongy urethra
         The longest part (15-16 cm and 5 mm in diameter)
         Passes through the bulb (Bulbar part of spongy urethra) and corpus spongium of the penis (Penile part of spongy urethra)
         Ends at the external urethral orifice
     •         in the bulb of penis – intrabulbar fossa and
     •         In the glans penis – navicular fossa
         Proximal part receives opening of ducts of bulbourethral glands
         Also receives openings of urethral glands

Arteries, veins, lymph nodes and nerves
         Proximal two parts
        Arterial supply by Prostatic branches of inferior vesical and middle rectal arteries
        Veins follow the arteries and have same name
        Lymph drains mostly to internal iliac lymph nodes
        Nerves are derived from pudendal nerves and prostatic plexus

         Distal two parts
        Artery: Branches of internal pudendal artery
        Vein: Internal pudendal veins
        Lymph nodes: Membranous urethra drains to internal iliac lymph nodes and most of spongy urethra drains to deep inguinal lymph nodes
        Nerves: are branches of pudendal nerve
        Also derived from prostatic plexus
        Afferent fibers passes through pelvic splanchnic nerves

         4 cm long and 6 mm in diameter
         Begins at the bladder neck and passes anteroinferiorly from the internal urethral orifice
         Ends at external urethral orifice in the vestibule of vagina
       –        Lies anterior to the orifice of vagina
         Lies anterior to the vagina
         Its axis is parallel to that of vagina
         Receives the openings of urethral and paraurethral galnds

Arteries, veins, lymph nodes and innervation
         Arteries – internal pudendal and vaginal arteries
         Veins – follow the arteries and have similar names
         Lymph nodes – sacral and internal iliac
         Innervation – pudendal nerve

Following resources are used while preparing this post (readers are strongly recommended to go through them for more details):
Gray's Anatomy for Students
K. L. Moore's Clinically Oriented Anatomy
R. Snell's Clinical Anatomy