Urethra - Anatomy & Physiology

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Introduction

This muscular tube is the connection between the bladder and the external environment and plays a vital role in concious urinary continence.

The Layers of the Urethra

The layers of the walls of the urethra are largely similar to those of the urinary bladder apart from one significant difference; in both the male and the female the urethral submucosa has a network of veins which may contribute to continence by forming a kind of erectile tissue.

Female

  • Empties at the external urethral orifice on the ventral wall of the vagina
  • This is often at the vestibulo vaginal junction
  • Only urine passes through it
  • Length and diameter is species specific
    • Short and wide - mare
    • 2 fossa - bitch
    • Suburethral diverticulum - cow and sow

Male

A schematic overview of the path of the male urethra
A schematic overview of the blood supply to the bladder and urethra
  • Empties at tip of penis
  • Divided into 3 parts
    • Pre-prostatic - bladder neck to seminal hillock
    • Prostatic portion - openings of deferant, vesicular and prostatic ducts
    • Penile portion - ischial arch to penile tip
    • Note the first 2 combined are called the pelvic portion

Muscles of the Urethra

The urethralis muscle runs the entire length of the urethra and forms the external urethral sphincter.

Unlike the internal sphincter the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system.

Somatic Motor Supply - External Urethral Sphincter
  • S1-S2
  • Pudendal Nerve
  • No synapse
  • Innervates the urethral skeletal muscle - external urethral sphincter
  • Function is to contract and retain urine

Blood Supply

Blood Supply comes from the Urethral Artery which is a branch of the vaginal artery which in turn is a branch of the internal pudendal which is a branch of the internal iliac.

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