LUT Structure and Function

Question 1

describe sympathetic innervation to the bladder

Answer 1

L1-L4 in dogs, L2-L5 in cats (FYI)

1. hypogastric nerve: adrenergic
   -noradrenaline/norepinephrine
2. detrusor muscle:
   -smooth muscle
   -beta receptors
   -RELAX muscle to aid in urine storage
3. internal urethral sphincter:
   -smooth muscle
   -alpha receptors
   -CONSTRICT bladder neck

Question 2

describe parasympathetic innervation to the bladder

Answer 2

S1-S3

1. PELVIC NERVE: cholinergic
   -acetylcholine
2. detrusor muscle:
   -smooth muscle
   -muscarinic cholinergic receptors
   -CONTRACT muscle to expel urine

note: no innervation to urethra!
-internal urethral sphincter ONLY innervated by sympathetic!!

Question 3

describe somatic innervation to the bladder

Answer 3

S1-S3

1. PUDENDAL nerve: nicotinic cholinergic receptors
2. external urethral sphincter: striated muscle
3. CONTRACTION of muscle causes constriction of sphincter

micturition is a consciously controlled reflex!!

Question 4

describe the detrusor reflex

Answer 4

1. afferent (GVA) sensory input via pelvic nerve
2. at the sacral segments:
   -interneurons to GVE
   -back out via the pelvic nerve (parasympathetic)
3. detrusor contraction

“the bladder is like the 3rd hindleg”

Question 5

describe the filling/storage and voiding phases

Answer 5

filling/storage phase: sympathetic tone is higher than parasympathetic tone: relax bladder, contract sphincter

voiding phase: parasympathetic tone is higher, decreases sympathetic tone, relaxes smooth muscle urethra and causes bladder contraction, parasympathetic also goes up to pontine micturition center where you consciously sense that you have to pee!!
-then bring signal back to pudendal nerve to inhibit peeing if not in a position to pee

bladder and urethra work opposite to each other

-parasympathetic = peeing
-sympathetic = storage

Question 6

describe the T3-L3 bladder/UMN bladder

Answer 6

1. UMN bladder: C1-L7
2. loss of inhibition to hypogastric and pudendal nerves
3. reflex intact for limbs: hyper-reflexive
4. sphincter contracted
5. voluntary input impaired
6. decreased to no urination causes retention of urine so increases post void residual volume (retaining urine post pee)
7. difficult to express

Question 7

describe lumbosacral/LMN bladder

Answer 7

1. loss of innervation to external sphincter (pudendal)
2. reflexes decreased to absent
   -perineal reflex decreased to absent
3. flaccid sphincter
4. reduced to absent voluntary involvement
5. INCONTINENCE
6. easy to express (no increased pressure at an level of urethra)

Question 8

describe host defense mechanisms of the urinary tract

Answer 8

1. normal bacteria flora inhibits colonization by pathogenic bacteria
2. mucosal defense barriers: glycosaminoglycan layer, IgA, exfoliation of epi cells
3. urethral peristalsis, length, prostatic antibacterial fraction
4. ureteral peristalsis
5. mechanical washout by urine flow
6. urine characteristics that inhibit growth:
   -high osmolality
   -high urea concentration
   -low pH
   -organic acids

Question 9

how do you work up an animal with LUT issues?

Answer 9

1. observe micturition (can be tough)
   -try to gather info about behavior (describe what he does when he pees)
   -multiple cats in litter box? use a camera
2. examine external genitalia
   -extrude penis if male will let you
   -easy in dogs, not in cats
3. rectal exam!!
   -prostate in males
   -pelvic urethra in everyone “piece of spaghetti right over pelvic rim”: feel for tumors, stones, etc.
4. contrast studies to further eval urethra
   -contrat urethrography
   -retrograde vaginourethrography
5. cystoscopy: very useful to see inside!

Question 10

describe initial diagnostics for micturition disorders

Answer 10

1. history:
   -thorough
   -water intake
   -urine output
   -urination description
2. physical exam
   -thorough
   -rectal palpation
   -thorough neuro exam
   -post-void residual volume: measure length, width, height of bladder in cm to get ml/kg
   >3ml/kg = urine retention
   1-3 ml/kg: grey zone
   <1ml/kg = normal