Download MBBS (Bachelor of Medicine and Bachelor of Surgery) Latest Physiology of Micturition Lecture PPT
Physiology Of Micturition
And
Bladder Dysfunctions
Gross Anatomy
? External features :Bladder is a hollow
muscular viscous organ .
?pyramidal in shape having apex base & 3
surfaces.
?Neck- lowest part, continues as urethra.
? Interior of bladder : mucosa shows irregular
folds, & smooth trigone.
Urinary Bladder
? Urinary bladder is a sac like structure in the
pelvic cavity.
? It is a distensible organ made up of smooth
muscle called detrusor muscle , depicting the
Latin word "pushes down".
? Smooth muscles are arranged in three
bundles: spiral, longitudnal, and circular.
? The bladder epithelium has superficial layer of
flat cells and deep layer of cuboidal cells.
Urethral Sphincters
? There are 2 sphincters
?Internal sphincter :located at the neck of the
bladder ,made up of bundle of smooth muscle
(sphincter vesicae) ,and innervated by
sympathetic (hypogastric) and
parasympathetic(pelvic) nerves. Therefore, it is
under autonomic control.
?External sphincter : present around urethra in its
proximal part ,made up of skeletal
muscle(sphincter urethrae) ,innervated by
somatic (pudendal) nerves . Therefore under
voluntary control.
? Male urethra -20cm,3 parts ?
? Female urethra -4cm ,traverses external sphincter,
lies in front of vagina.
INNERVATION OF URINARY BLADDER
Parasympathetic(S2,3,4) Sympathetic T11-L2
via pelvic nerves via hypogastric nerves
Somatic fibres(S2,3,4)
? Via pudendal nerves
? Innervates external sphincter
Transport of urine from kidney
Urine from collecting ducts flows into renal
calyces
Stretches calyces & es pacemaker activity
Initiates peristaltic contraction in renal pelvis &
along the length of ureter
Urine enters bladder
? In adults ureter is 25-35cm long.
? Peristaltic activity in ureter are enhanced by
parasympathetic stimulation and inhibited by
sympathetic stimulation.
? There is no significant change in composition of
urine as it flows from renal calyces and ureter to
the bladder.
? Trigone of bladder
? Vesicouretric reflux ??
? Uretrorenal reflex (explain)
Micturition reflex
? Micturition is the process by which urinary
bladder empties when it becomes filled.
? It is a reflex phenomenon, integrated in spinal
cord.
? This spinal reflex is influenced by activities of the
higher center.
? Urine enters the bladder without producing much
increase in intravesical pressure untill well filled,
because smooth muscle exhibit property of
plasticity
Mechanism Of Micturition
Filling of the bladder stimulates its stretch
receptors
Impulses travel in afferent(pelvic) nerve
Reaches S2,3,4 spinal segment (center)
Parasympathetic fibers form efferent limb which
travel in pelvic nerves
Parasympathetic stimulation causes contraction of
detrusor and relaxation of internal sphincter
Urine passes into the urethra
Also external sphincter relaxes due to cortical
influences
Urine finally comes out of urethra and is completely
emptied by effect of gravity in females
And by contraction of bulbocavernous muscle in
males
? Contraction of abdominal muscle and descent of
diaphragm es intra-abdominal pressure which
helps in expulsion if urine.
? Pelvic , perineal, and levator ani muscle relaxes
which causes downward pull of detrusor muscle
and aids in initiation of contraction.
? Voluntary control of micturition is influenced by
cortical activities and by learning to contract the
external sphincter.
Control Of Micturition
? Micturition reflex is controlled by centers in the
brainstem.
? Facilitatory area is present pons and inhibitory
area is in midbrain.
? What is the effect of neurexis above 1. pons
2.midbrain on micturition ?
? Posterior hypothalamus also contain facilitatory
area for micturition.
? Cortex has voluntary inhibitory control on
micturition.
? Control of urination starts to develop at about
2yrs
Bladder Dysfunctions
? 3 major types of bladder dysfunctions are due to
neural lesions:
1. Interruption of the afferent nerve.
2. Interruption of both afferent & efferent nerves.
3. Interruption of facilitatory & inhibitory pathways
descending from brain.
? In all 3 types the bladder contracts , but
contractions are not sufficient so residual urine
is left .
Deafferentation
When sacral dorsal roots are cut in
experimental animals or interrupted by
disease of dorsal root , such as tabes dorsalis .
? All reflex contraction of bladder are abolished.
? Bladder is distended, thin walled,and
hypotonic.
? Some contractions occurs because of intrinsic
response of smooth muscle to stretch.
? Overflow incontinence occurs.
Denervation
When both afferent and efferent fibers are
destroyed as in tumor of cauda equina or filum
terminale.
? Bladder is flaccid and distended for a while.
? Gradually the muscle of `decentralised bladder'
become active ,with many contraction waves that
expel dribbles of urine.
? Bladder is shrunken and its wall is hypertrophied .
? This hyperactive bladder is due to denervation
hypersensitivity.
.
Spinal cord transection
? During spinal shock bladder is flaccid and
unresponsive , there is overflow incontinence .
? In recovery phase , voiding reflex returns but
there is no voluntary control and no inhibition
or facilitation from higher center.
? How Mass reflex helps paraplegic patients ?
? Sometimes voiding reflex is hyperactive
leading to spastic neurogenic bladder
? Reflex hyperactivity is worsen by infection .
? Nocturnal enuresis/Bed wetting : Involuntary
micturition during sleep, normal phenomenon
in children below 3yrs ,due to incomplete
myelination of motor nerve fiber of bladder.
? It may be primary or secondary type .
? If present beyond 5yrs need proper evaluation
and treatment.
Urinary incontinence : is any
involuntary leakage of urine
This post was last modified on 30 November 2021