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Equine Urinary System - Horse Anatomy (view source)
Revision as of 14:16, 28 November 2012
, 14:16, 28 November 2012→Bladder
==Bladder==
==Bladder==
The bladder is where urine is stored before being expelled by the body through the [[Micturition - Anatomy & Physiology| micturition reflex]]. Without a bladder urinary continence would be impossible.
The bladder is a hollow, muscular organ. It is divided for descriptive purposes into three parts:
*Cranial Pole
*Intermediate body
*Caudal neck
Its wall comprises a muscle layer covered in '''transitional epithelium'''. Its size and posistion are determined by how full it is. When empty the bladder wall is wrinkled and thicker. It rests on the pubic bones, entirely within the pelvis and is largely retroperitoneal. When full and distended, the folds disappear and the wall appears thinner, it then becomes intraperitoneal.
The '''trigone''' of the bladder gets its name as it looks like a triangle without a base. It is of clinical importance and is formed by the paired '''ureteric folds''', which are comprised of the orifice of the ureters. The trigone is visible even when the bladder is full. Ureteral folds extend from the urethral opening to the neck of the bladder, where they merge to form the '''urethral crest'''. It is believed to have increased sensitivty and is of different embryological origin to the rest of tissue. More details can be found [[Kidney and Urinary Tract Development - Anatomy & Physiology#The Bladder|here]].
===Muscles of the Bladder===
[[Image:sumlutshcemtri.jpg|right|thumb|275px|<small><center>A schematic overview of the lower urinary tract showing the innervation and muscles of the bladder</center></small>]]
The three muscular components of the bladder described below play a pivotal part in the [[Micturition - Anatomy & Physiology| micturition reflex.]]
====Detrusor Muscle====
This network of smooth muscle fibres lie in three sheets within the bladder wall and are supplied by both parasympathetic and sympathetic nerves. It is responsible for storage and expression of urine from the bladder.
*Parasympathetic supply: This comes from S1-S3, synapses within the pelvic plexus, continues as the pelvic nerves and is excitatory to the destrusor muscle. Parasympathetic dominance allows emptying of the bladder.
*Sympathetic Supply: This comes from L1-L4, synapses within the caudal mesenteric ganglion in the bladder wall, continues as the hypogastric nerve and ends on beta 2 receptors within the detrusor muscle. It has inhibitory action on muscular contraction, therefore enabling bladder filling.
==Urethra==
==Urethra==