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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