Urinary Tract Physiology Flashcards
Nice stimulatory feature of the detrusor muscle
Single units are electrically coupled, so stimulation causes a synchronous contraction
Epithelium of the bladder wall
Transitional epithelium (urothelium)
Main urinary sphincters in the bladder (involuntary or voluntary)
Internal sphincter (involuntary)
External sphincter (voluntary)
Internal sphincter
Narrow area at the base of the detrusor m. (near urethra)
Closes when detrusor contracts
External sphincter
Voluntary skeletal m. that wraps around the urethra at bladder junction
Afferent (outgoing) innervation from the bladder goes through which nerves?
Pelvic splanchnic n.
Hypogastric plexus
3 things that causes the bladder to send out afferent signals via the pelvic splanchnic n.
Where does each signal go?
Wall stretch –> dorsal columns of cord
Imminent voiding –> dorsal columns of cord
Bladder pain –> anterolateral columns of cord
From where are afferent signals for bladder wall stretch sent out?
Stretch receptors in walls
From where are afferent imminent voiding signals sent out?
Periurethral striated m.
A patient has chronic bladder pain. What is a surgical way to relieve this?
Why can you do this?
Anterolateral cordotomy
Still maintain sensations for bladder fullness and imminent voiding
Sympathetic efferent innervation to the bladder comes from where?
What nerves?
T10-L2 intermediolateral gray horn
Hypogastric nn.
Sympathetic innervation to the bladder/urethra causes what?
Detrusor/internal sphincter inhibition
External sphincter excitement
Parasympathetic innervation to the bladder/urethra causes what?
Comes from where?
Excite detrusor and internal sphincter
Inhibit external sphincter (relax)
S2-S4 (SMC) –> pelvic splanchnic n. –> ganglia near bladder/urethra
Somatic (voluntary) innervation of bladder/urethra
Perineal branch of pudendal n.
External sphincter relaxation
A patient loses afferent stretch receptors from the bladder. What is the result?
Loss of micturition reflex
Bladder fills until urine leaks out
“Overflow incontinence”
With the previous patient (no micturition reflex), how is each affected:
Bladder fullness
Residual urine volume
Intravesicular pressure
Bladder wall thickness
Always full
High residual (no emptying)
Low intravesicular (no detrusor contraction)
Wall thin and distended
A patient loses afferent stretch receptors AND efferent innervatioin from/to the bladder. What is the result?
Overflow incontinence
With the previous patient (no afferent OR efferent), how is each affected:
Bladder fullness
Residual urine volume
Intravesicular pressure
Bladder wall thickness
Always full, and quicker
Low residual (small lumen)
Low intravesicular
Hypertrophic wall (causes first 2)
Why does the previous patient (no afferent or efferent) have a hypertrophic bladder wall?
Initial denervation hypersensitivity due to efferent injury causes constant contractions –> hypertrophy
A patient sustains a spinal injury above the sacral region. What is the result for the bladder?
Loss of parasympathetic inhibition from brain
Exaggerated micturition reflex –> spastic bladder
Detrusor hypertrophy, high voiding pressure
A patient has a UTI. What happens to urination?
Irritation from infection causes uninhibited contraction of detrusor
Urinary leakage and frequency
A patient sustains damage to their pudendal nerve. What is the result?
Urinary incontinence - can’t close external sphincter
How do sympathetics and parasympathetics affect filling of the bladder?
How?
PSNS - increased ureter peristalsis - increased filling
SNS - decreased ureter peristalsis - decreased filling
During the filling phase of the bladder, what allows for afferent stretch receptors signals to be low-frequency?
Result?
Tension (T) in wall is directly related to pressure (P) and radius (R), so pressure decreases as radius increases (tension maintained)
SLOW pressure increase in filling phase
What allows for full filling to occur (low-frequency afferent signals)?
High centers in stem/cortex can suppress PSNS
How does the pressure in the bladder change as emptying occurs?
Why?
Stays constant
P = T/R, so as it falls in on itself, R decreases while T increases, so P remains constant
Does the bladder usually empty all the way?
NO - 25% residual (125 ml)
First 5 steps of bladder filling
- Begins to fill
- Stretch receptors
- PSNS activated (bladder contraction, I.S. relaxation)
- PSNS suppressed (block above)
- Somatics constrict E.S. all along
As bladder continues to fill, final 5 steps…
- Urine leaks into urethra
- Urethra stretch receptors
- Sensory impulses get intense
- Voluntary E.S. relaxation
- Urine voiding
