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==Introduction==

|linkpage =Urinary System - Anatomy & Physiology

[[Image:sumlutshcemtri.jpg|right|thumb|350px|<small><center>A schematic overview of the lower urinary tract showing the nerves and muscles involved in micturition</center></small>]]

|linktext =URINARY SYSTEM

'''Micturition is the normal process of the passive storage and active voiding of urine.'''

|maplink = Urinary System (Content Map) - Anatomy & Physiology

|pagetype =Anatomy

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Micturition is the normal process of the passive storage and active voiding of urine.

After entering the renal pelvis the modification of the urine is over in all domestic species other than the horse where mucin is added.  The urine passes along the [[Ureters - Anatomy & Physiology| ureters]] and enters the [[Urinary Bladder - Anatomy & Physiology|bladder]].  It is here that the urine is stored until it is to be voided.  Urine is not constantly excreted and it is only when there is a significant amount present in the bladder that the process of voiding occurs.  Both the [[Urinary Bladder - Anatomy & Physiology| Bladder]] and the [[Urethra - Anatomy & Physiology| Urethra]] have smooth muscle and thus receive autonomic influence with regard to their activity.  However the urethra also has an element of skeletal muscle giving the animal some degree of conscious control over the voiding of urine.

After entering the renal pelvis the modification of the urine is over in all domestic species other than the horse where mucin is added.  The urine passes along the [[Ureters - Anatomy & Physiology| ureters]] and enters the [[Bladder - Anatomy & Physiology|bladder]].  It is here that the urine is stored until it is to be voided.  Urine is not constantly excreted and it is only when there is a significant amount present in the bladder that the process of voiding occurs.  Both the [[Bladder - Anatomy & Physiology| Bladder]] and the [[Urethra - Anatomy & Physiology| Urethra]] have smooth muscle and thus receive autonomic influence with regard to their activity.  However the urethra also has an element of skeletal muscle giving the animal some degree of conscious control over the voiding of urine.

===Sensory Innervation===

===Sensory Innervation===

The bladder has stretch receptors (alpha receptors in the neck and trigone, and beta receptors in the body) which detect fullness of the bladder. These impulse to the pelvic nerves and so to the sacral spinal cord. The urethra has afferents detecting flow, distension and pain that go via the pudendal nerve to the sacral cord.

The bladder has stretch receptors (alpha receptors in the neck and trigone, and beta receptors in the body) which detect fullness of the bladder. These impulse to the pelvic nerves and so to the sacral spinal cord. The urethra has afferents detecting flow, distension and pain that go via the pudendal nerve to the sacral cord.

===The Muscles===

===The Muscles===

The motor components of the reflex are the [[Bladder - Anatomy & Physiology #Detrusor Muscle| Detrusor Muscle]], [[Bladder - Anatomy & Physiology #Internal Urethral Sphincter| Internal Urethral Sphincter]] and the [[Bladder - Anatomy & Physiology #External Urethral Sphincter| External Urethral Sphincter]].  The former two are supplied by the autonomic nervous system with the latter being of somatic innervation.

The motor components of the reflex are the [[Urinary Bladder - Anatomy & Physiology#Detrusor Muscle| Detrusor Muscle]], [[Urinary Bladder - Anatomy & Physiology#Internal Urethral Sphincter| Internal Urethral Sphincter]] and the [[Urinary Bladder - Anatomy & Physiology#External Urethral Sphincter| External Urethral Sphincter]].  The former two are supplied by the autonomic nervous system with the latter being of somatic innervation.

==The Reflex==

==The Reflex==

This co-ordinated detrusor contraction and sphincter relaxation leads to complete voiding of the bladder and at the same time prevents pressure build up with in the bladder.

This co-ordinated detrusor contraction and sphincter relaxation leads to complete voiding of the bladder and at the same time prevents pressure build up with in the bladder.