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
