Difference between revisions of "Micturition - Anatomy & Physiology"

Revision as of 16:41, 18 August 2008

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

Introduction

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 and enters the 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 and the 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 concsious control over the voiding of urine.

Innervation Involved in the Reflex

Sensory

The fullness of the bladder is detected by stretch sensitive nerve endings in the bladder wall

Motor

The motor components of the reflex are the Detrusor Muscle, Internal Urethral Sphincter and the External Urethral Sphincter. They former two are supplied by the autonomic nervous system with the latter being of somatic innvervation.

The general aim for the sympathetic and somatic systems is to retain urine
The general aim for the parasympathetic system is to void urine

Parasympathetic Supply - Bladder Detrusor Muscle

S1-S3
Synapse in pelvice plexus or bladder wall
Innvervate the detrusor muscle
Action - excitatory
Function - empty bladder

Sympathetic Supply - Bladder Detrusor Muscle

L1-L4
Syanpse in caudal mesenteric ganglion - bladder wall
Receptor - beta
Inhibitory action
Allows bladder filling

Sympathetic Supply - Internal Urethral Sphincter

L1-L4
Synapse in caudal mesenteric ganglion
Receptor - alpha
Excitatory action
Function - retain urine through increased urethral tone

Somatic Motor Supply - External Urethral Sphincter

S1-S2
Pudendal Nerve
No synapse
Innervates the urethral skeletal muscle - external urethral sphincter
Function is to retain urine

Central Connections

There is aspects of control by the Pons and the Cerebral Cortex with possible influences from the cerebellum.

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-{{OpenPagesTop}}
+{{toplink
+|backcolour = C1F0F6
+|linkpage =Urinary System - Anatomy & Physiology
+|linktext =URINARY SYSTEM
+|maplink = Urinary System (Content Map) - Anatomy & Physiology
+|pagetype =Anatomy
+}}
+<br>
+Micturition is the normal process of the passive stoage and active voiding of urine.
 ==Introduction==
-[[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>]]
+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 concsious control over the voiding of urine.
-'''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.
+==Innervation Involved in the Reflex==
-===Sensory Innervation===
+===Sensory===
-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 fullness of the bladder is detected by stretch sensitive nerve endings in the bladder wall
-===Central Intregration===
+===Motor===
-The co-ordination of the urethralis and detrusor muscles from information recieved from the stretch receptors occurs in the '''pons'''. This micturition centre also branches to the thalamus, cerebellum and cerebral cortex. It is the cerebral cortex that is responsible for voluntary control of micturition.
+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]].  They former two are supplied by the autonomic nervous system with the latter being of somatic innvervation.
-===The Muscles===
+* The general aim for the '''sympathetic and somatic systems''' is to '''retain urine'''
-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 general aim for the '''parasympathetic system''' is to '''void urine'''
-==The Reflex==
+===Parasympathetic Supply - Bladder Detrusor Muscle===
+* S1-S3
+* Synapse in pelvice plexus or bladder wall
+* Innvervate the detrusor muscle
+* Action - excitatory
+* Function - empty bladder
-===Storage phase - Sympathetic system dominant===
+===Sympathetic Supply - Bladder Detrusor Muscle===
+* L1-L4
+* Syanpse in caudal mesenteric ganglion - bladder wall
+* Receptor - beta
+* Inhibitory action
+* Allows bladder filling
-* This involves contraction of the urethral sphincters to prevent leakage of urine
+===Sympathetic Supply - Internal Urethral Sphincter===
-* Alpha-adenergic stimulation causes constriction of the bladder neck
+* L1-L4
-* Beta-adenergic stimulation causes relaxation of the detrusor muscle and so promotes low pressure filling of the bladder
+* Synapse in caudal mesenteric ganglion
-* Direct inhibition of the pelvic nerves is provided by the hypogastric nerve
+* Receptor - alpha
-* The main barrier to urine outflow though is the constriction of the '''urethralis''' muscle being provided with constant tone by the pudendal nerve.
+* Excitatory action
+* Function - retain urine through increased urethral tone
-Once bladder capacity is reached the stretch receptors are stimulated which send impulses via the pelvic nerve to the sacral spinal cord and finally to the pons. Here integration occurs and there is concious acknowledgement of the need to urinate.
+===Somatic Motor Supply - External Urethral Sphincter===
+* S1-S2
+* Pudendal Nerve
-===Emptying phase - Parasympathetic system dominant===
+* No synapse
+* Innervates the urethral skeletal muscle - external urethral sphincter
-The efferent impulses from the pons travel to the sacral region and simultaneously:
+* Function is to retain urine
-* Inhibition of the pudendal nerve, thus causing relaxation of the urethralis muscle.
-* Stimulation of the parasymphathetic neurons, inhibiting adrenergic tone to the neck thus leading to relaxation of the internal urethral sphincter. This increased input also leads to contraction of the detrusor muscle.
-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.
-{{Learning
-|flashcards = [[The Process of Micturition - Renal Flash Cards - Anatomy & Physiology|Micturition Flashcards]]
-}}
-{{OpenPages}}
+===Central Connections===
-[[Category:Lower Urinary Tract - Anatomy & Physiology]]
+There is aspects of control by the Pons and the Cerebral Cortex with possible influences from the cerebellum.