Download MBBS Physiology of Micturition Lecture PPT

Physiology Of Micturition

And

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Bladder Dysfunctions
Gross Anatomy

? External features :Bladder is a hollow

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muscular viscous organ .

?pyramidal in shape having apex base & 3

surfaces.

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?Neck- lowest part, continues as urethra.
? Interior of bladder : mucosa shows irregular

folds, & smooth trigone.

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Urinary Bladder

? Urinary bladder is a sac like structure in the

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pelvic cavity.

? It is a distensible organ made up of smooth

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muscle called detrusor muscle , depicting the

Latin word "pushes down".

? Smooth muscles are arranged in three

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bundles: spiral, longitudnal, and circular.

? The bladder epithelium has superficial layer of

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flat cells and deep layer of cuboidal cells.

Urethral Sphincters

? There are 2 sphincters

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?Internal sphincter :located at the neck of the

bladder ,made up of bundle of smooth muscle

(sphincter vesicae) ,and innervated by

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sympathetic (hypogastric) and

parasympathetic(pelvic) nerves. Therefore, it is

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under autonomic control.

?External sphincter : present around urethra in its

proximal part ,made up of skeletal

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muscle(sphincter urethrae) ,innervated by

somatic (pudendal) nerves . Therefore under

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voluntary control.

? Male urethra -20cm,3 parts ?
? Female urethra -4cm ,traverses external sphincter,

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lies in front of vagina.

INNERVATION OF URINARY BLADDER

Parasympathetic(S2,3,4) Sympathetic T11-L2

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via pelvic nerves via hypogastric nerves
Somatic fibres(S2,3,4)

? Via pudendal nerves

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? Innervates external sphincter


Transport of urine from kidney

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Urine from collecting ducts flows into renal

calyces

Stretches calyces & es pacemaker activity

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Initiates peristaltic contraction in renal pelvis &

along the length of ureter

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Urine enters bladder
? In adults ureter is 25-35cm long.
? Peristaltic activity in ureter are enhanced by

parasympathetic stimulation and inhibited by

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sympathetic stimulation.

? There is no significant change in composition of

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urine as it flows from renal calyces and ureter to

the bladder.

? Trigone of bladder

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? Vesicouretric reflux ?
? Uretrorenal reflex (explain)
Micturition reflex

? Micturition is the process by which urinary

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bladder empties when it becomes filled.

? It is a reflex phenomenon, integrated in spinal

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cord.

? This spinal reflex is influenced by activities of the

higher center.

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? Urine enters the bladder without producing much

increase in intravesical pressure untill well filled,

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because smooth muscle exhibit property of

plasticity

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Mechanism Of Micturition

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Filling of the bladder stimulates its stretch

receptors

Impulses travel in afferent(pelvic) nerve

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Reaches S2,3,4 spinal segment (center)

Parasympathetic fibers form efferent limb which

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travel in pelvic nerves
Parasympathetic stimulation causes contraction of

detrusor and relaxation of internal sphincter

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Urine passes into the urethra

Also external sphincter relaxes due to cortical

influences

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Urine finally comes out of urethra and is completely

emptied by effect of gravity in females

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And by contraction of bulbocavernous muscle in

males

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? Contraction of abdominal muscle and descent of

diaphragm es intra-abdominal pressure which

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helps in expulsion if urine.

? Pelvic , perineal, and levator ani muscle relaxes

which causes downward pull of detrusor muscle

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and aids in initiation of contraction.

? Voluntary control of micturition is influenced by

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cortical activities and by learning to contract the

external sphincter.
Control Of Micturition

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? Micturition reflex is controlled by centers in the

brainstem.

? Facilitatory area is present pons and inhibitory

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area is in midbrain.

? What is the effect of neurexis above 1. pons

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2.midbrain on micturition ?

? Posterior hypothalamus also contain facilitatory

area for micturition.

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? Cortex has voluntary inhibitory control on

micturition.

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? Control of urination starts to develop at about

2yrs

Bladder Dysfunctions

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? 3 major types of bladder dysfunctions are due to

neural lesions:

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1. Interruption of the afferent nerve.

2. Interruption of both afferent & efferent nerves.

3. Interruption of facilitatory & inhibitory pathways

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descending from brain.

? In all 3 types the bladder contracts , but

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contractions are not sufficient so residual urine

is left .
Deafferentation

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When sacral dorsal roots are cut in

experimental animals or interrupted by

disease of dorsal root , such as tabes dorsalis .

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? All reflex contraction of bladder are abolished.
? Bladder is distended, thin walled,and

hypotonic.

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? Some contractions occurs because of intrinsic

response of smooth muscle to stretch.

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? Overflow incontinence occurs.
Denervation

When both afferent and efferent fibers are

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destroyed as in tumor of cauda equina or filum

terminale.

? Bladder is flaccid and distended for a while.

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? Gradually the muscle of `decentralised bladder'

become active ,with many contraction waves that

expel dribbles of urine.

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? Bladder is shrunken and its wall is hypertrophied .
? This hyperactive bladder is due to denervation

hypersensitivity.

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.
Spinal cord transection

? During spinal shock bladder is flaccid and

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unresponsive , there is overflow incontinence .

? In recovery phase , voiding reflex returns but

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there is no voluntary control and no inhibition

or facilitation from higher center.

? How Mass reflex helps paraplegic patients ?

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? Sometimes voiding reflex is hyperactive

leading to spastic neurogenic bladder

? Reflex hyperactivity is worsen by infection .

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? Nocturnal enuresis/Bed wetting : Involuntary

micturition during sleep, normal phenomenon

in children below 3yrs ,due to incomplete

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myelination of motor nerve fiber of bladder.

? It may be primary or secondary type .
? If present beyond 5yrs need proper evaluation

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and treatment.
Urinary incontinence : is any

involuntary leakage of urine

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