Lesson 2: Voiding Physiology Flashcards
Brain - Cerebral Cortex
- Overall control and direction
- Provide social continence
- Bladder fills → midbrain → cortex
- Decides initiate voiding vs delay
Brain - Pontine Storage Center
- In control when bladder in storage mode
- Bladder wall is relaxed
- Sphincters are closed
Brain - Pontine Micturition Center
Activates when cortex signals to initiate voiding
Causes sphincter relaxation and bladder contraction
Brainstem - Pontine Storage Center (PSC)
Active during storage phase
Nerve cells in sacral spinal cord → pudendal nerve → contraction of external urethral sphincter → contraction of internal sphincter → relaxation of bladder wall
Brainstem - Pontine Micturition Center (PMC)
- Active during emptying phase
- sympathetic systems + Onuf’s Nucleus
Relaxation of internal/external sphincters → parasympathetic system → detrusor contraction
Spinal Cord - Sympathetic System
- Exits cord at T10 - L2
- Stimulates releases of epinephrine and norepinephrine
- Cause bladder neck to tighten and bladder wall to relax
Spinal Cord - Parasympathetic System
- Exits cord at S2 - S4
- Stimulates release of acetylcholine
- Causes bladder to contract
Spinal Cord - Pudendal Nerve
- Exits cord at S2 - S4
- Activate by Onuf’s Nucleus
- Causes contraction of external urethral sphincter
- Provides voluntary control of pelvic floor muscles
Bladder - Urothelium
- Lining of the bladder
- Contains receptors sensitive to thermal, mechanical and chemical stimuli
- Responds to stimuli by secreting signal molecules
- Intensity of signaling increases with distension
- Surface protected by mucin and glycosaminoglycans
Bladder - Lamina Propria
Comprised of
- Interstitial cells
- Fibroblasts
- Nerve cells
- Blood vessel
Bladder - Detrusor
Single unit of smooth muscle
- each cell individually innervated
Muscle cells stretch slowly
- Does not contract until capacity reached OR decision to void
Progressive filling signals are relayed to brain
Bladder - Stretch/Compliance
- Bladder stretches readily to store urine at low pressure
- Permits ongoing delivery of urine from kidneys
- Ureters are low pressure and cannot overcome high bladder pressures
- Reduced compliance + severe urgency at low volumes
- Reduced stretch = impaired urine delivery from kidneys
— Hydronephrosis causes renal damage
Bladder - Contractility
- Allows for complete bladder emptying
- Prevents stasis of urine
- Loss of contractility = impaired emptying +/- urinary retention
Bladder - Infection + Irritants
- Pathogens + irritants increase signaling by urothelium
- Causes urgency + frequency at low volumes
- Can cause bladder spasms d/t mechanical irritants
Factors maintaining urethral closure
Urethral length
Urethral curvature
Prostate gland
Urethral Sphincter - Submucosal Vascular Cushion
- Surrounds proximal urethra
- Acts as non-compressible sponge
- Supports compression of urethra by sphincter
- Estrogen-sensitive tissue
Urethral Sphincter - Urethral Coaptation
Urethral walls stick together to maintain closure
Estrogen-sensitive tissue
Urethral Sphincter Muscles - Internal Sphincter
- Smooth muscle fibers
- Located in proximal urethra + bladder neck
- Contract in response to sympathetic stimulation and increased urethral resistance
Urethral Sphincter Muscles - External Urethral Sphincter
- Urethral sphincter muscle and periurethral muscles
- Contain slow twitch + fast muscle fibers
- Innervated by pudendal nerve + autonomic pathways
Urethral Sphincter Muscles - Pelvic Floor
Supports bladder and urethra in correct anatomical position
Effects of Aging
- increased production of urine overnight
- Changes in bladder wall = decreased bladder capacity
increased urinary frequency - Reduced bladder contractility = higher PVR and increased frequency
- Increased bladder irritability = increased urgency + risk of leakage
- Delayed recognition of bladder filling = less response time
Genders-specific issues
- Men = prostate hypertrophy
- Women = loss of estrogen
Alpha-Adrenergic Agonists
- Mimics effects of sympathetic stimulation on bladder + sphincter function
- Increases urethral resistance by increasing tone in
proximal urethra
Eg. pseudoephedrine and duloxetine
Alpha-Adrenergic Antagonists
- Block effects of sympathetic stimulation of receptors in proximal urethra and bladder neck
- Reduces urethral resistance
Eg. tamsulosin and alfuzosin
Cholinergics
- Mimic effects of acetylcholine
- Causes bladder contraction
Eg. bethanechol
Anticholinergics
- Block the effects of acetylcholine
- Relaxes bladder wall
- Reduces frequency and urgency
Eg. oxybutynin and tolterodine
