Mechanism of Micturition, Voiding Dysfunction
Functions of Bladder
Collection, Storage of Urine
(↓ Pressure)
Expulsion of Urine
(at appropriate Time, Place)
Bladder Wall able to
Stretch, Rearrange itself to
allow ↑ Bladder Volume
(without significant ↑ in Pressure)
Synchronous Activation of all
Smooth Muscles
(if only part of wall contracted, the
uncontracted compliant areas would
Stretch, Prevent ↑ in Pressure
necessary for urine expelled through
urethra)
Extremely Compliant
Histology
Outer Middle Innermost
Adventitial Connective
Tissue Layer
Smooth Muscle Coat
(Detrusor)
Transitional Cell
Epithelium
Functional Syncytium of
Interlacing Muscle
Bundles
Elastic Barrier that is
Impervious to Urine
Functional Features of Bladder
Normal Capacity 400 – 500 ml
Sensation of Fullness
Accommodate various Volumes
(without change in Intraluminal Pressure)
Initiate, Sustain a Contraction until Bladder is Empty
Voluntary Initiation, Inhibition of Voiding
(despite Involuntary Nature of Organ)
Anatomy
Urethral Sphincter (Male, Female)
Internal External
Involuntary Smooth Muscle Voluntary Striated-Muscle
Bladder Neck Male Female
Prostate ↓
Membranous
Urethra
Mid Urethra
Internal Sphincter (Bladder Neck Sphi ncter)
Condensation of Smooth Muscle of Detrusor
Rich in Sympathetic Innervation
Closed Open
Filling Phase Spontaneous Contraction
Provide Continence Mechanism Contraction Induced by Stimulation of
Pelvic Nerve
External Sphincter
Slow-Twitch, Small Muscle Fibers
Located between Fascial Layers of Urogenital Diaphragm
Voluntary Sphincter Mechanism
• Maintain constant Tonus
• 1° Continence Mechanism
Levator Muscles
• Contribute to Continence (support of Bladder Base)
Relaxation of Sphincter – Voluntary Act
(without which Voiding is Normally Inhibited)
Urethra
Male
Female
Striated Muscular Sphincter
(Invests Distal 2/3 of Urethra)
• Complete Ring of Muscle Proximally
• Fibres passes onto Posterior,
Lateral Vaginal Walls
• At Vestibule, Fibres encompasses
both Urethral, Vaginal Opening
(Urethrovaginal Sphincter)
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Pelvic Diaphragm
Formed by
Coccygeus
Levator Ani (Iliococcygeus, Pubococcygeus, Pubore ctalis)
Fibers
Type I Type II
Tonic Support to Pelvic Structures For Sudden ↑ in
Intra-Abdominal Pressure
In Females
Peritoneum on Superior Surface of Bladder is
• Reflected over the Uterus (Vesicouterine Pouch)
• Continuous Posteriorly over the Uterus (Rectouterine Pouch)
Contraction of Pelvic Diaphragm
Elevates Bladder Neck
Draws it Anteriorly
In Women with Stress Urinary Incontinence
Bladder Neck Drops below Pubic Symphysis
Micturition Innervations
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Micturition Cycle
Bladder Filling (Urine Storage)
Require
Accommodation of ↑ Volumes of Urine at ↓ Intravesical Pressure
(Normal Compliance) with appropriate Sensation
Bladder Outlet that is Closed
• At Rest
• Remains during ↑ Intra-Abdominal Pressure
Absence of Involuntary Bladder Contractions (Detrusor Overactivity)
Pathway (Urine Storage)
Cerebral Cortex Facilitation, Inhibition ↙
Pons Lateral PMC ↓
Thoracolumbar Cord Stimulate Sympathetic ↓
Sacral Cord Inhibit Parasympathetic
Neurons
Stimulate Somatic
Neurons ↓ ↓
Bladder Detrusor Relax Sphincter Contract ↓ ↓
Closed Bladder Neck, Proximal Sphincter
Bladder Response (during Filling)
Normal Adult Bladder response to Filling (at Physiologic Rate)
(Almost Imperceptible Change in Intravesical Pressure - ↑ Compliant)
1° due to Elastic, Viscoelastic Properties
When Collagen Component ↑, Compliance ↓
(main component of Bladder Stroma)
Occur in
• Chronic Inflammation
• Bladder Outlet Obstruction (BOO)
• Neurologic Decentralisation
Outlet Response (during Filling)
Gradual ↑ in Pressure during Bladder Filling
(contributed at Striated Sphincter Element, Smooth Sphincter Elements)
Guarding Reflex
Bladder Emptying (Voiding)
Require
Coordinated Contraction of Bladder Smooth Musculature
(adequate Magnitude, Duration)
Concomitant ↓ Resistance at level of Smooth, Striated Sphincter
Absence of Anatomic Obstruction (as oppose d to Functional)
Pathway (Afferent)
Cerebral Cortex Sensory Perception ↑
Pons Medial PMC ↑ Thoracolumbar Cord Lateral Spinothalamic ↑ Sacral Cord Sacral Cord ↑
Bladder Receptors in Muscle of Bladder
Wall, Mucosa ↑ Bladder Distended with Urine
Pathway (Micturition)
Cerebral Cortex Facilitation, Inhibition ↓
Pons Medial PMC
Thoracolumbar Cord
Sacral Cord Stimulate
Parasympathetic Neurons
Inhibit Somatic
Neurons ↓ ↓ Bladder Detrusor Contract Sphincter Relax ↘ ↙
Micturition
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Voiding Dysfunction
Filling (Storage) Failure
Bladder Overactivity Outlet Underactivity
Expressed as
• Phasic Involuntary Contractions
• ↓ Compliance
• Combination
Result from
• Damaged Sphincter
(Smooth, Striated, Both)
• Support of Bladder Outlet in
Female
Bladder-related storage failure may also occur in absence of Overactivity
because of ↑ Afferent Input from Inflammation, Irritation, other causes of
Hypersensitivity, Pain
Bladder Overactivity
Involuntary Contractions ↓ Compliance
Neurologic Disease, Injury Neurologic Disease, Injury
• Sacral, Infrasacral Level
• Result from any process that
Destroy Viscoelastic, Elastic
Properties of Bladder Wall
↑ Afferent Input (Inflammation,
Irritation of Bladder, Urethral Wall)
BOO
Stress Urinary Incontinence
Aging
Idiopathic
Outlet Underactivity
May occur with
Neurologic Disease, Injury
Surgical, Mechanical Trauma
Aging
Sphincter Incontinence will Ensue
Genuine Stress Incontinence (GSI) Intrinsic Sphincter Deficiency (ISD)
Associated with
• Hypermobility of Bladder Outlet
• Urethral Hypermobility
Due to Poor Pelvic Support
Nonfunctional at Rest
(Poorly Functional)
• Bladder Neck (BN)
• Proximal Urethra
Outlet that was
• Competent at Rest
• Lost its Competence when
↑ Intra-Abdominal Pressure
Stress-Related Urinary Incontinence
(SUI)
Symptoms that arise 1° from
Damaged to
• Muscles
• Nerves
• Connective Tissues
• Combination within Pelvic Floor
Urethral Support is Important in
Female
Urethral Hypermobility
Weakness of Pelvic Floor supporting structures
During ↑ in Intra-Abdominal Pressure
(Descent of Bladder Ne ck, Proximal Urethra)
If Outlet opens concomitantly, SUI ensues
Emptying (Voiding) Failure
Bladder Underactivity Outlet Overactivity, Obstruction
Result from Temporary, Permanent
Alteration in one of the
Neuromuscular Mechanisms
(necessary to Initiate, Maintain a
Normal Detrusor Contraction)
Men ↑
Due to Anatomical Obstruction
(mostly)
Due to Failure of Relaxation, Active
Contraction of Striated, Smooth
Sphincter during Bladder Contraction
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