Exam 4: Micturition Flashcards
What is micturition?
2 stage process that results in the passage of urine out of the body
What are the 2 stage of micturition?
Passive storage phase
Active voiding phase
What is the detrusor muscle?
Smooth muscle that is essential for voiding
What happens when the detrusor muscle contracts?
It increases pressure in the bladder to 40-60 mmHg
Describe the bladder wall layers
Transitional cell epithelium that maintains a barrier despite expansion and contraction of the bladder
Describe urine transport in the kidney
Urine leaving the collecting ducts is the final product and undergoes no further changes as it is transported to the bladder
Urine flow stretches calyces which increases their inherent pacemaker
Peristaltic contractions result
What is the ureter composed of?
Smooth muscle and a plexus of neurons that coordinate peristalsis
Where do the ureters enter the bladder?
At the trigone, coursing obliquely through the detrusor muscle
What does the normal detrusor tone do?
Prevents the back flow of urine
What is the vesicoureteral reflex?
Inappropriate backflow of urine into the ureter
What is the micturition reflex?
Autonomic spinal cord reflex that can be inhibited or facilitated by centers in the brain
Describe storage for micturition
Detrusor muscle: relax
Urethral sphincter: contract
Describe voiding
Detrusor muscle: contract
Urethral sphincter: relax
What are the nerves involved in micturition?
Hypogastric
Pelvic
Pudendal
What is the hypogastric nerve responsible for?
Sympathetic stimulation
What does the hypogastric nerve go to?
Detrusor muscle
Internal urethral sphincter
What does the hypogastric nerve to the detrusor muscle do?
Causes relaxation via beta 3 adrenergic receptors
What does the hypogastric nerve to the internal urethral sphincter do?
Causes tightening via alpha 2 adrenergic receptors
What is the pelvic nerve responsible for?
Parasympathetic stimulation
Sensory
Forms a reflex arc
What does the parasympathetic stimulation of the pelvic nerve go to?
Detrusor muscle
What does the pelvic nerve to the detrusor muscle do?
Causes contraction via muscarinic cholinergic receptors
What does the pelvic nerve do for sensory?
From the detrusor muscle
Detects stretching
What does the pudendal nerve do?
Somatic to the external urethral sphincter and pelvic floor
What does the pudendal nerve do to the external urethral sphincter and pelvic floor?
Causes contraction via nicotinic cholinergic receptors
What happens in the storage phase?
Stretch receptors in the bladder wall send afferent signals along the pelvic nerve
Activates a reflex arc through the hypogastric nerve, which relaxes the detrusor muscle and increases urethral tone
Voluntary contraction of the external sphincter
What is the micturition reflex a complete cycle of?
Progressive and rapid increases in bladder pressure
Period of sustained maximal pressure
Return of pressure to baseline
What are the 2 possible outcomes for the micturition reflex?
Unsuccessful (no pee)
Successful (pee)
What happens to cause an unsuccessful micturition reflex?
Reflex wasn’t strong enough to overcome control of the external sphincter
Period of inhibition ensues
Cycle starts over but increases in strength
What happens to cause a successful micturition reflex?
Once the reflex is strong enough, it sends a reflex via the pudendal nerve to inhibit the external sphincter
What happens in the voiding phase?
Micturition reflex takes over
Bladder completely empties
What happens when the micturition reflex takes over in the voiding phase?
Detrusor muscle contracts via pelvic nerve stimulation
Urethral sphincters relax through blockage of the hypogastric and pudendal nerve
What can the micturition reflex be inhibited or facilitated by?
The brain stem and cerebral cortex
What is the inhibitory voluntary control achieved by?
Increasing tone in the external urethral sphincter
