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Equine Urinary System - Horse Anatomy (view source)
Revision as of 16:25, 28 November 2012
, 16:25, 28 November 2012no edit summary
===Innervation===
===Innervation===
The bladder receives sympathetic and parasympathetic nerve supply.
The bladder receives sympathetic and parasympathetic nerve supply.
*Parasympathetic supply: This comes from S1-S3, synapses within the '''pelvic plexus''', continues as the '''pudendal nerve''' and is excitatory to the destrusor muscle. Parasympathetic dominance allows emptying of the bladder.
*'''Parasympathetic supply''': This comes from S1-S3, synapses within the '''pelvic plexus''', continues as the '''pudendal nerve''' and is excitatory to the destrusor muscle via release of Acetylcholine which binds muscarinic acetylcholine receptors. Parasympathetic dominance allows emptying of the bladder.
*Sympathetic Supply: This comes from L1-L4, synapses within the '''caudal mesenteric ganglion''' before entering the '''pelvic plexus. It then continues as the '''hypogastric nerves''' which terminate on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.
*'''Sympathetic Supply''': This comes from L1-L4, synapses within the '''caudal mesenteric ganglion''' before entering the '''pelvic plexus'''. Postganglionic fibres continue as the '''hypogastric nerves''', which terminate on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.
==Urethra==
==Urethra==
This muscular tube is the connection between the bladder and the external environment and plays a vital role in conscious urinary continence.
===The Layers of the Urethra===
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.
===Female===
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.
===Male===
[[Image:maleluttri.jpg|right|thumb|250px|<small><center>A schematic overview of the path of the male urethra</center></small>]]
[[Image:sumbsbladurtri.jpg|right|thumb|250px|<small><center>A schematic overview of the blood supply to the bladder and urethra</center></small>]]
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:
*Pre-prostatic - bladder neck to seminal hillock
*Prostatic portion - openings of deferant, vesicular and prostatic ducts
*Penile portion - ischial arch to penile tip
The combination of the pre-prostatic and prostatic portions 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 [[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.
===Innervation of the External Urethral Sphincter===
The ''urethralis'' muscle receives somatic innervation originating from S1-S3 and continuing via the '''pudendal nerve'''. This releases the neurotransmitter Acetylcholine, which binds to nicotinic Acetylcholine receptors and mediates skeletal muscle contraction of the external urethral sphincter. This is important in urine retention.
===Vascular 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'''.
[[Category:To Do - AP Review]]