Micturition Flashcards
What is micturition?
How body gets rid of urine
Upper Urinary Tract (2) describe one of them
Kidney and Ureter
Ureter:
- lined with smooth muscle
- has lots of sensory fibers (exm pain with having kidney stones)
Ureteral peristalsis:
- Sympathetic- inhibit contraction
- parasympathetic- promote contraction
- propel urine down from kidney to lower urinary tract
Lower Urinary Tract (2)
describe both
Urethra and Bladder
Urethra
- external urethral sphincter: lined by skeletal muscle, voluntary control, somatic nervous system
Bladder
- detrusor and internal urethral sphincter: lined smooth muscle, involuntary control
- Trigone (posterior side of bladder)
- sense fullness of bladder
- ureteral opening (2): where urine comes into bladder
- internal urethral opening
Blockade of ureteral outflow
- kidney stone in ureter
- increase hydrostatic pressure
- ureteral dilation
- continued blockade-> increase pressure
- hydronephrosis (swelling of kidney)-> risk of acute renal failure
- body normally does ureteral reflux
- if stone is present-> turn off reflex to lower pain (sensory fibers)
Anatomic Constrictions (4)
1) Urethropelvic junction
2) Testicular/Ovarian artery and vein
3) External iliac artery and vein
4) Bladder wall
Vesicoureteral Reflux
- ureteral opening is not fully closed
- urine travels back up ureter
- cause ureteral dilation
- higher risk of pyelonephritis
Afferent (sensory) bladder signaling
- purpose
- pathway
- types (2)
-sense fullness from bladder -> send signal to brain
Intravesical pressure stretch signals (bladder is stretched) -> sensory nerve fibers (run with pelvic splanchnic nerve and hypogastric plexus) -> S2-S4 (sacral micturition center)
Types of Sensory Fiber
1) Bladder fullness- Alpha delta fibers (myelinated)- normal
2) Bladder Pain - C Fibers (unmyelinated) - Abnormal ( in infection)
- C fibers are always present, but may not always get fired
Efferent (motor) bladder signaling
-Pathways (3)- which NT and receptor
- brain to bladder
1) Parasympathetic S2-S4-> pelvic splanchnic nerve-> detrusor m. contraction -> internal sphincter relaxation => push urine out of body NT: Ach Receptor: mAchR (M3)
2) Sympathetic
L2-> hypogastric n-> detrusor m. relaxation & internal sphincter contraction
NT: NE
R: adrenergic
3) Somatic ( voluntary pathway) S2-S4-> pudendal n. -> external urethral sphincter contraction -> urinary tension - Skeletal muscle Nt: Ach Receptor: nAchR
Storage Reflex
- guarding
- only in spinal cord
- short reflex, will fill but not fully
Activated by bladder filling-> sympathetic & somatic outflow-> detrusor m. relaxation and external sphincter contracted
Voiding Reflex
-Brain
Activated by full bladder-> afferent sensory neurons transmit to spinal cord, brain-> stimulate parasympathetic outflow and inhibit sympathetic/somatic outflow-> detrusor M. contact and external sphincter relaxes
Voiding Reflex Brainstem parts (3)
1) Cerebral Cortex
2) Pons- Pontine Micturition Center (PMC)
3) Midbrain- periaqueductal gray (PAG)
Cerebral Cortex
highest level of processing
- Interprets sensation (fullness/pain)
- Can partially inhibit micturition reflex
Pons
- Aka Barrington’s nucleus
- Receives signals from PAG and higher brain cortex (cerebral cortex)
- Activates external sphincter relaxation and sacral parasympathetic outflow -> micturition
- Control/coordinate S2-S4
Midbrain
- Receives afferent bladder signals
- Primary excitation input to PMC
- Higher brain centers can suppress or stimulate input of PAG to the PMC
Urination in Adult
- voluntary start/stop
- detrusor m and sphincter work in coordination
