THE URINARY BLADDER ANATOMY AND PHYSIOLOGYDr. Ali Kamal M. SamiM.B.Ch.B. M.A.U.A.F.I.B.M.S. M.I.U.A.
A hollow muscular organA reservoir for urineThe adult bladder normally has a capacity of 400–500 ml.
When empty, bladder lies behind the pubicsymphysis &it is a pelvic organ.In infants and children , it is situated higher.When it is full, it rises above the symphysisand can readily be palpated or percussed.When over distended, as in acute or chronicurinary retention, it may cause the lowerabdomen to bulge visibly.
Extending fromthe dome of thebladder to theumbilicusis a fibrouscord, themedianumbilicalligament, whichrepresents theobliteratedurachus .
Ureters enter the bladderposteroinferiorly are about 5 cm apart.The orifices,situated at interuretericridge that forms the proximal borderof the trigone, are about 2.5 cm apart.The trigone occupies the area betweenthe ridge and the bladder neck.
The internal sphincter, orbladder neck, is not a true circular sphincter but a thickening formed by interlaced and converging muscle fibers of the detrusor as they pass distally to become the smooth musculature of the urethra.
RELATIONSIn males, the bladder is relatedposteriorly to the seminalvesicles, vasa deferentia, ureters,and rectum .In females, the uterus andvagina are interposedbetween the bladder andrectum .The dome and posteriorsurfaces are covered byperitoneum.So in this area the bladder isrelated to the small intestineand sigmoid colon.
HistologyThe mucosa of thebladder is composedof transitionalepithelium. Beneath it ,is asubmucosal layerformed of connectiveand elastic tissuesExternal to thesubmucosa is thedetrusor muscle
the detrusor muscle which is made up of amixture of smooth muscle fibers arranged atrandom in a longitudinal, circular, and spiralmanner without any layer formation or specificorientationExcept close to the internal meatus,where the detrusor muscle assumes 3definite layers:Inner longitudinal,middle circular,and outer longitudinal.
A. ARTERIAL1-Superior Vesical,2-Middle Vesical,3-Inferior Vesicalarteries, which arisefromthe anterior trunk ofthe internal iliac(hypogastric)artery,4-The obturatorartery.5-The inferior glutealartery.In females, the 6-uterine and 7-vaginalarteries also send branches to the bladder.
B. VENOUSSurrounding the bladder is a rich plexus of veinsthat ultimately empties into the internal iliac(hypogastric) veins.
LymphaticsThe lymphatics of the bladderdrain into1-the vesical,2-external iliac,3-internal iliac (hypogastric),4-common iliac lymph nodes.
The nerves concerned in micturition are as follows.1-The parasympathetic input; derivedfrom the anterior primary divisions of thesecond, third and fourth sacral segments ( S2,S3,S4). These fibers pass through the pelvicsplanchnic nerves inferior hypo gastricplexus, from which they are distributed to thebladder.The pelvic plexus is easily damaged duringexcisions of the rectum, following whichdisturbances of micturition and sexual function mayoccur.
2-The sympathetic input;These nerves arise in the 11ththoracic to the second lumbarsegments (T11,T12,L1,L2).Pass via the presacral hypogastric nerve and the sympatheticchains to the inferior hypogastric plexus, which is situatedlateral to the rectum, thebladder
3-Somatic innervations; passes to the distal sphincterthrough the Pudendal nerves andthrough the inferior hypo gastricplexus .
The sympathetic nerves convey afferent painfulstimuli following over distension of the fundus , from themucosa where they respond to touch, temperature andpain, and also from the muscle of the detrusor andlamina propria where they convey stretch information. These afferents pass via the inferior hypo gastricplexus .Efferent fibers pass via the pelvic parasympathetics.Normal micturition is coordinated in the Pons in themidbrain where detrusor contraction is timed withinhibition of the distal sphincter mechanism.