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==Urethra==
==Urethra==
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This muscular tube is the connection between the bladder and the external environment and plays a vital role in conscious urinary continence.
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===The Layers of the Urethra===
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The layers of the walls of the urethra are largely similar to those of the 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.
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===Female===
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The urethra empties at the external urethral orifice on the ventral wall of the [[Female Reproductive Tract - Horse Anatomy#Vagina and Vestibule|vagina]]. This is often at the vestibulo-vaginal junction. Only urine passes through the female urethra. In the horse, the urethra is short and wide.
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===Male===
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[[Image:maleluttri.jpg|right|thumb|250px|<small><center>A schematic overview of the path of the male urethra</center></small>]]
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[[Image:sumbsbladurtri.jpg|right|thumb|250px|<small><center>A schematic overview of the blood supply to the bladder and urethra</center></small>]]
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The urethra empties at tip of penis. The male urethra carries urine, semen and seminal secretions from the [[Male Reproductive Tract - Horse Anatomy#Accessory Sex Glands|accessory sex glands]]. The uretha is divided into 3 parts:
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*Pre-prostatic - bladder neck to seminal hillock
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*Prostatic portion - openings of deferant, vesicular and prostatic ducts
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*Penile portion - ischial arch to penile tip
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The combination of the pre-prostatic and prostatic portions are called the pelvic portion.
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===Muscles of the Urethra===
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The '''''urethralis''''' muscle runs the entire length of the urethra and forms the '''external urethral sphincter'''. Unlike the [[Urinary Bladder - Anatomy & Physiology#Internal Urethral Sphincter|internal sphincter]], the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system.
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=====Somatic Motor Supply - External Urethral Sphincter=====
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* S1-S2
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* Pudendal Nerve
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* No synapse
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* Innervates the urethral skeletal muscle - external urethral sphincter
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* Function is to contract and retain urine
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===Vascular Supply===
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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'''.