Urinary Tract Physiology

Question 1

Nice stimulatory feature of the detrusor muscle

Answer 1

Single units are electrically coupled, so stimulation causes a synchronous contraction

Question 2

Epithelium of the bladder wall

Answer 2

Transitional epithelium (urothelium)

Question 3

Main urinary sphincters in the bladder (involuntary or voluntary)

Answer 3

Internal sphincter (involuntary)

External sphincter (voluntary)

Question 4

Internal sphincter

Answer 4

Narrow area at the base of the detrusor m. (near urethra)

Closes when detrusor contracts

Question 5

External sphincter

Answer 5

Voluntary skeletal m. that wraps around the urethra at bladder junction

Question 6

Afferent (outgoing) innervation from the bladder goes through which nerves?

Answer 6

Pelvic splanchnic n.

Hypogastric plexus

Question 7

3 things that causes the bladder to send out afferent signals via the pelvic splanchnic n.

Where does each signal go?

Answer 7

Wall stretch –> dorsal columns of cord

Imminent voiding –> dorsal columns of cord

Bladder pain –> anterolateral columns of cord

Question 8

From where are afferent signals for bladder wall stretch sent out?

Answer 8

Stretch receptors in walls

Question 9

From where are afferent imminent voiding signals sent out?

Answer 9

Periurethral striated m.

Question 10

A patient has chronic bladder pain. What is a surgical way to relieve this?

Why can you do this?

Answer 10

Anterolateral cordotomy

Still maintain sensations for bladder fullness and imminent voiding

Question 11

Sympathetic efferent innervation to the bladder comes from where?

What nerves?

Answer 11

T10-L2 intermediolateral gray horn

Hypogastric nn.

Question 12

Sympathetic innervation to the bladder/urethra causes what?

Answer 12

Detrusor/internal sphincter inhibition

External sphincter excitement

Question 13

Parasympathetic innervation to the bladder/urethra causes what?

Comes from where?

Answer 13

Excite detrusor and internal sphincter
Inhibit external sphincter (relax)

S2-S4 (SMC) –> pelvic splanchnic n. –> ganglia near bladder/urethra

Question 14

Somatic (voluntary) innervation of bladder/urethra

Answer 14

Perineal branch of pudendal n.

External sphincter relaxation

Question 15

A patient loses afferent stretch receptors from the bladder. What is the result?

Answer 15

Loss of micturition reflex

Bladder fills until urine leaks out
“Overflow incontinence”

Question 16

With the previous patient (no micturition reflex), how is each affected:

Bladder fullness
Residual urine volume
Intravesicular pressure
Bladder wall thickness

Answer 16

Always full

High residual (no emptying)

Low intravesicular (no detrusor contraction)

Wall thin and distended

Question 17

A patient loses afferent stretch receptors AND efferent innervatioin from/to the bladder. What is the result?

Answer 17

Overflow incontinence

Question 18

With the previous patient (no afferent OR efferent), how is each affected:

Bladder fullness
Residual urine volume
Intravesicular pressure
Bladder wall thickness

Answer 18

Always full, and quicker

Low residual (small lumen)

Low intravesicular

Hypertrophic wall (causes first 2)

Question 19

Why does the previous patient (no afferent or efferent) have a hypertrophic bladder wall?

Answer 19

Initial denervation hypersensitivity due to efferent injury causes constant contractions –> hypertrophy

Question 20

A patient sustains a spinal injury above the sacral region. What is the result for the bladder?

Answer 20

Loss of parasympathetic inhibition from brain

Exaggerated micturition reflex –> spastic bladder

Detrusor hypertrophy, high voiding pressure

Question 21

A patient has a UTI. What happens to urination?

Answer 21

Irritation from infection causes uninhibited contraction of detrusor

Urinary leakage and frequency

Question 22

A patient sustains damage to their pudendal nerve. What is the result?

Answer 22

Urinary incontinence - can’t close external sphincter

Question 23

How do sympathetics and parasympathetics affect filling of the bladder?

How?

Answer 23

PSNS - increased ureter peristalsis - increased filling

SNS - decreased ureter peristalsis - decreased filling

Question 24

During the filling phase of the bladder, what allows for afferent stretch receptors signals to be low-frequency?

Result?

Answer 24

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

Question 25

What allows for full filling to occur (low-frequency afferent signals)?

Answer 25

High centers in stem/cortex can suppress PSNS

Question 26

How does the pressure in the bladder change as emptying occurs?

Why?

Answer 26

Stays constant

P = T/R, so as it falls in on itself, R decreases while T increases, so P remains constant

Question 27

Does the bladder usually empty all the way?

Answer 27

NO - 25% residual (125 ml)

Question 28

First 5 steps of bladder filling

Answer 28

1. Begins to fill
2. Stretch receptors
3. PSNS activated (bladder contraction, I.S. relaxation)
4. PSNS suppressed (block above)
5. Somatics constrict E.S. all along

Question 29

As bladder continues to fill, final 5 steps…

Answer 29

6. Urine leaks into urethra
7. Urethra stretch receptors
8. Sensory impulses get intense
9. Voluntary E.S. relaxation
10. Urine voiding