Micturition

Question 1

Autonomic control of ureteral peristalsis

Answer 1

Parasympathetic - enhances contractions

Sympathetic - inhibits contractions

Question 2

Ureterorenal reflex

Answer 2

Blocked ureter –> pain –> sympathetic reflex telling kidneys to constrict renal arterioles and decrease renal output

Question 3

Major sites for anatomic constriction of ureters

Answer 3

Ureteropelvic junction

Pelvic brim, where ureter crosses over external iliac a.+v.

Where ureter traverses bladder wall

Question 4

Blockade of ureteral flow can lead to retrograde nephron function known as _____

Answer 4

Vesicoureteral reflux

Question 5

Bladder fullness is detected by myelinated ____ fibers

Answer 5

A-delta

Question 6

Bladder pain is detected by unmyelinated ___ fibers

Answer 6

C-type

Question 7

Parasympathetic innervation to urinary tract

[when does it predominate, what are its effects, receptor, NT?]

Answer 7

Predominates when bladder EMPTYING

S2-S4 –> detrusor contraction + internal sphincter relaxation –> micturition

NT = ACh (cholinergic)

Receptor = muscarinic (M3)

Question 8

Sympathetic innervation to urinary tract

[when does it predominate, what are its effects, receptor, NT?]

Answer 8

Predominates when bladder is FILLING

L2 –> hypogastric nn –> detrusor relaxation + internal sphincter contraction –> retention

NT = NE (adrenergic)

Receptor= alpha 1 in urethra/bladder neck, beta2-3 in detrusor

Question 9

Somatic innervation of urinary tract

[mechanism, NT, receptor]

Answer 9

Under voluntary control:

S2-S4 -> pudendal n. (Somatic) –> external bladder sphincter contraction –> urine retention

NT = ACh

Receptor = nicotinic

Question 10

What part of the brainstem controls and coordinates activity of the sacral micturition center by activating external urethral relaxation and increasing sacral parasympathetic outflow leading to micturition?

Answer 10

Pontine micturition center (PMC) aka “barringtons nucleus”

Question 11

What does the PMC receive input from

Answer 11

PAG (periaqueductal gray) and other higher brain centers

[PAG is the primary excitatory input to the PMC]

Question 12

What part of the brainstem receives afferent sensory signals from the bladder and passes them to the higher brain centers which then allow or suppress its ability to excite the PMC?

Answer 12

PAG

Question 13

What part of the brain interprets sensation of full/empty bladder and can stop urine stream once micturition has begun?

Answer 13

Cerebral cortex

Question 14

Urination in adult vs. infant vs. paraplegic

Answer 14

Adult = voluntary, detrusor and sphincter in coordination

Infant = void at lower bladder volumes, involuntary, detrusor and sphincter in coordination

Paraplegic = void a lower bladder volumes, involuntary, detrusor-sphincter dyssynergia