Difference between revisions of "Urinary Bladder - Anatomy & Physiology"

Revision as of 09:44, 11 August 2008

()Map URINARY SYSTEM (Map)

The bladder is where urine is stored before being expelled by the body through the micturition reflex.
Without a bladder urinary continence would be impossible.

Anatomy

It is a hollow, muscular organ
It is divided for descriptive purposes into three parts
- Cranial Pole
- Intermediate body
- Caudal neck
Its size and posistion are determined by how full it is.
- When empty the bladder wall is wrinkled and thicker
- When full and distended the folds dissapear and the wall appears thinner
The paired uteric folds are visible even when the bladder is full.
- They extend from the ureteral opening to the neck of the bladder
- Here they merge
- Forms the urethral crest - continues into the urethra

Muscles of the Bladder

The three muscular components of the bladder described below play a pivotal part in the micturition reflex.

Detrusor Muscle

Network of smooth muscle fibres within the bladder wall which are supplied by both parasympathetic and sympathetic nerves.

Internal Urethral Sphincter

Its a thickening of the bladder musculature which is continous with the detrusor and therefore is smooth muscle. However unlike the detrusor its innervation is purely from sympathetic fibres.

External Urethral Sphincter

Unlike the internal sphincter the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system

The Ligaments of the Bladder

Two lateral ligaments
- Insert in the dorsal abdominal wall
- Within them are the residual umbilical vessels

Median ligament
- Connects the bladder to pelvic floor and linea alba

Blood Supply, Innervation and Lymphatic Drainage

Blood Supply - Caudal vesicular artery

Sympathetic Innervation - Via hypogastric nerve from the caudal mesenteric ganglion

Parasympathetic Innervation - Pudendal nerve

Lymphatic Drainage - Iliosacral lymph nodes

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-{{OpenPagesTop}}
+{{toplink
-==Introduction==
+|backcolour = C1F0F6
-* The bladder is where urine is stored before being expelled by the body through the [[Micturition - Anatomy & Physiology| micturition reflex]].
+|linkpage =Urinary System - Anatomy & Physiology
+|linktext =URINARY SYSTEM
+|maplink = Urinary System (Content Map) - Anatomy & Physiology
+|pagetype =Anatomy
+}}
+<br>
+* The bladder is where urine is stored before being expelled by the body through the [[Process of Micturition | micturition reflex]].
 * Without a bladder urinary continence would be impossible.
 ==Anatomy==
-[[Image:bladhistoanat1.jpg|right|thumb|275px|<small><center>Histology cross section of a normal guinea pig bladder (© RVC 2008)</center></small>]]
-[[Image:bladhistoanat2.jpg|right|thumb|275px|<small><center>Histology cross section of a normal guinea pig bladder (© RVC 2008)</center></small>]]
 * It is a hollow, muscular organ
 * It is divided for descriptive purposes into three parts
@@ Line 12: / Line 19: @@
 ** 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
+** When full and distended the folds dissapear and the wall appears thinner
-*** It is entirely in the pelvis of the large species but partly enters the abdomen of the carnivores
+* The paired uteric folds are visible even when the bladder is full.
-*** It is largely retroperitoneal in the larger species
+** They extend from the ureteral opening to the neck of the bladder
-** When full and distended the folds disappear and the wall appears thinner
+** Here they merge
-*** It then becomes intraperitoneal in the larger species
+** Forms the urethral crest - continues into the urethra
-* 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 uteric folds
-** These form by the orifice of the ureters
-** It is visible even when the bladder is full
-** The 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 differant 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==
+===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 [[Process of Micturition | micturition reflex.]]
-The three muscular components of the bladder described below play a pivotal part in the [[Micturition - Anatomy & Physiology| micturition reflex.]]
-====Detrusor Muscle====
+=====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.
+Network of smooth muscle fibres within the bladder wall which are supplied by both parasympathetic and sympathetic nerves.
-=====Parasympathetic Supply - Detrusor Muscle=====
-* S1-S3
-* Synapse in pelvic plexus or bladder wall
-* Pelvic nerves
-* Innvervate the detrusor muscle
-* Action - excitatory
-* Function - empty bladder
-=====Sympathetic Supply - Detrusor Muscle=====
+=====Internal Urethral Sphincter=====
-* L1-L4
+Its a thickening of the bladder musculature which is continous with the detrusor and therefore is smooth muscle.  However unlike the detrusor its innervation is purely from sympathetic fibres.
-* Syanpse in caudal mesenteric ganglion - bladder wall
-* Hypogastric nerve
-* Receptor - beta 2
-* Inhibitory action
-* Allows bladder filling
-====Internal Urethral Sphincter====
+=====External Urethral Sphincter=====
-A thickening of the bladder musculature found at the neck of the bladder which is continuous with the detrusor and is therefore smooth muscle.  However, unlike the detrusor its innervation is purely from sympathetic fibres.
+Unlike the internal sphincter the external sphincter is composed of striated muscle fibres which are under the voluntary control of the somatic nervous system
-=====Sympathetic Supply - Internal Urethral Sphincter=====
-* L1-L4
-* Synapse in caudal mesenteric ganglion
-* Hypogastric nerve
-* Receptor - alpha 1
-* Excitatory action
-* Function - retain urine through increased urethral tone
-====External Urethral Sphincter====
-This third component is more appropriately included in the anatomy section of the [[Urethra - Anatomy & Physiology#Muscles of the Urethra|urethra]].
 ==The Ligaments of the Bladder==
@@ Line 68: / Line 44: @@
 * Two lateral ligaments
 ** Insert in the dorsal abdominal wall
-** Within them are the residual umbilical vessels which still have some patency and convey small amounts of blood to the cranial bladder
+** Within them are the residual umbilical vessels
-** They attach onto the bladder wall at the lateral vesical folds.
 * Median ligament
 ** Connects the bladder to pelvic floor and linea alba
-** Attaches into the bladder at the median vesical fold
-** In the foetus this ligament supports the urachus.
 ==Blood Supply, Innervation and Lymphatic Drainage==
-[[Image:sumbsbladurtri.jpg|right|thumb|275px|<small><center>A schematic overview of the blood supply to the bladder and urethra</center></small>]]
-===Blood Supply===
-The bladder is supplied by cranial and a caudal vesical arteries.
-=====Cranial Vesicular Artery=====
-* Branch of the umbilical artery which branches directly off the internal iliac a.
-* Often not present in the dog thanks to a great reduction of the umbilical artery after birth
-* In cattle it is weak
-* In pigs and horses it is relatively strong
-=====Caudal Vesicular Artery=====
-* Branch of the vaginal or prostatic artery
-** These in turn are branches of the internal pudendal artery which in turn is a branch of the internal iliac.
-* Main supply to the bladder
-=====Species Differences in the Origin of the Vaginal Artery=====
-The description above relates to the bitch.  However the vaginal artery branches directly off the internal iliac in some species.  This is because the level of the division of the internal iliac a. into the internal pudendal a. and caudal gluteal a. varies.  The division is more cranial in the dog and the horse so you have a short internal iliac and a long internal pudendal and the vaginal artery branches off the latter in these species.  In the cow and pig however the reverse is true and division is far more caudal resulting in the vaginal artery actually being a branch of the internal iliac.
-===Lymphatic Drainage===
+'''Blood Supply''' - Caudal vesicular artery
-*Iliosacral lymph nodes
+'''Sympathetic Innervation''' - Via hypogastric nerve from the caudal mesenteric ganglion
-==Alternative Anatomical Thinking==
-Some people now think that rather than an internal sphincter which contracts to resist urine outflow there is an actual structure which is opened when its muscle bundles contract.  This would mean in these species that urinary continence relies on the external sphincter.  It is not certain as yet which structure is correct but this idea does concur with the recent demonstration that the proximal urethra plays a role in urine storage in the dog and goat.
-{{Learning
-|flashcards = [[Bladder Anatomy & Physiology Flashcards|Bladder Anatomy Flashcards]]
-}}
-==Webinars==
+'''Parasympathetic Innervation''' - Pudendal nerve
-<rss max="10" highlight="none">https://www.thewebinarvet.com/urogenital-and-reproduction/webinars/feed</rss>
-[[Category:Lower Urinary Tract - Anatomy & Physiology]][[Category:Bullet Points]]
+'''Lymphatic Drainage''' - Iliosacral lymph nodes