DSA - Physiology of Urinary Tract - Micturition

Question 1

3 anatomic divisions of urinary tract

Answer 1

1. upper urinary tract (calycx, pelvis, ureters)
2. Bladder
3. urethra

Question 2

Internal sphincter

Answer 2

involuntary
smooth muscle
PNS innervation
wall of bladder as it narrows toward urethra

Question 3

External sphincter

Answer 3

voluntary
skeletal muscle wraps around exterior of urethra where it joins bladder
somatic innervation

Question 4

Afferent pathway for conscious bladder sensation

Answer 4

Pelvic splanchnic nerve or hypogastric plexus
S2-S4
Posterior column = bladder fullness
Anterolateral column = bladder pain

Question 5

Reflex arc for micturition reflex

Answer 5

From bladder => sacral detrsorr nucleus => to bladder

From urethra => sacral pudendal nucleus/sacral micturition center => to voluntary sphincter

Question 6

Sensory fibers

Answer 6

bladder wall/posterior urethra

activated by stretch

Question 7

Parasympathetic fibers

Answer 7

• from sacral micturition center
• S2-S4 (pelvic n)
• stimulate detrusor muscles
• inhibits contraction of internal urethral sphincter

Question 8

Sympathetic fibers

Answer 8

• hypogastric nerve
• inhibits detrusor constriction
• constricts internal urethral sphincter
• T10-L2

Question 9

Somatic motor neurons

Answer 9

• voluntary
• pudendal nerve
• constricts external urethral sphincter
• S2-S4

Question 10

Pontine micturition center

Answer 10

• CNS control of micturition
• Barrington’s center
• location: locus coeruleus of pons
• descending impulses control sacral micturition center and throracolumbar sympathetic outflow
• coordinates activity of bladder and urinary sphincters

Question 11

Urine moves in ureters via ______

Answer 11

Peristalis

Question 12

Parasympathetic stimulation of ureters

Answer 12

increase peristaltic contraction of ureter

increase deliver of urine to bladder

Question 13

Sympathetic stimulation of ureters

Answer 13

decrease peristaltic contraction of ureters

decrease urine delivery to bladder

Question 14

Early bladder filling

Answer 14

inc bladder radius = inc wall tension

Question 15

LaPlace’s Law:

Answer 15

T = Pr/2

Question 16

Early bladder filling Activation of bladder stretch receptors

Answer 16

Sensory info sent to:

• sacral micturition center => activates PNS
• centers in brainstem and cerebral cortex => suppress PNS impulses

Question 17

Later Bladder Filling

Answer 17

1. inc wall tension => inc frequency of afferent impulses form stretch receptors
2. overrides inhibition of scaral micturition center by higher centers in brain (disinhibition)
3. PNS impulse from sacral cord
   - stimulates bladder contraction
   - inhibit contraction of internal urethral sphincter
4. Urine enters posterior urethra

Question 18

After urine enters the urethra:

Answer 18

1. Sensory impulse from urethra to sacral cord inhibit somatic nerves responsible for constriction of the external sphincter
2. Bladder continues to fill and contraction intensifies
3. Sensory impulses from bladder and urethra become more powerful
4. At right time, external sphincter relaxes
5. urine is voided

Question 19

Passive emptying of Bladder

Answer 19

1. tension of bladder wall decline as urine voided (T = Pr/2)
2. dec radius maintians intravesical pressure (P=2T/r) so as R dec P inc
3. lets bladder empty to residual volume (<25% of capacity)

Question 20

Steps of Micturition (10 steps)

Answer 20

1. Bladder filling begins
2. Stretch activates sensory inputs
3. PNS: bladder contracts, internal sphincter relaxes
4. Brainstem suppresses PNS
5. Somatic motor constrictions external sphincter
6. Bladder continues filling
7. Urine enters urethra, activates stretch receptors
8. Sensory impulses intensify
9. External sphincter relaxes
10. Voiding

Question 21

Types of neuropathic (abnormal) bladders

Answer 21

1. Atonic bladder
2. Denervated bladder
3. Automatic bladder
4. Uninhibited neurogenic bladder

Question 22

Atonic Bladder

Answer 22

• flaccid neuropathic bladder
• cause: destruction of sensory inputs from bladder to sacral cord (diabetes, crush injury, syphilis, MS)
• stretch info no longer transmitted, bladder contractions not initiated
• bladder becomes flaccid and filled to capacity, called “overflow incontinence”, eventually distend, thin walled

Question 23

Denervated Bladder

Answer 23

• hypertrophic areflexic
• Cause: destruction of both afferent and efferent fibers between bladder and cord
• Initially: detrusor contractions cease; bladder becomes flaccid, distended
• Later: detrusor regains spontaneous activity; bladder shrinks, muscle wall hypertrophries

Question 24

Automatic bladder

Answer 24

• spastic neuropathic
• Cause: injury or severing of spinal cord above sacral region: cuts off communication with brain
• Acute phase: ‘spinal shock’: temporarily suppresses micturition relfex => flaccid neuropathic bladder
• Micturition reflex can gradually recover and become exaggerated, resulting in spasticity- control by brain lost

Question 25

Uninhibited Neurogenic Bladder

Answer 25

• autonomic dysreflexia
• Cause: destruction of tracts carrying inhibitory impulses from brain
• Facilitatory inputs remain intact; micturition center is continually stimulated
• Micturition is activated by small amounts of urine
• Detrusor hypertrophies, bladder capacity reduced

Question 26

UTI

Answer 26

• urinary tract infection
• bladder and urethral irritation due to infection
• uninhibited contraction of detrusor muscle with facilitation of the micturition reflex
• leads to urinary frequency and leakage