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Physiology > Micturition > Flashcards

Micturition Flashcards

1
Q

Micturition

A

2 stage process that results in the passage of urine out of the body

  • passive storage phase
  • active voiding phase
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2
Q

Anatomy of the bladder

A
  • detrusor musle
  • apex
  • body
  • neck
  • trigone (smooth portion)
  • urethra: internal sphincter (smooth extension of detrusor), external sphincter (skeletal)
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3
Q

Detrusor muscle

A

Smooth muscle essential for voiding

  • cells fuse with each other creating a low-resistance electrical pathways facilitating coordinated contraction
  • when contracts, increases pressure in the bladder 40-60 mmHg
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4
Q

Bladder wall layers

A

Transitional cell epithelium maintains a barrier despite expansion and contraction of the bladder

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5
Q

Urine transport: kidney

A

Urine leaving the collecting ducts is the final product and does not undergo further changes

  • urine flow stretches calyces which increases inherent pacemaker
  • peristaltic contractions result
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6
Q

Urine transport: ureter

A

Composed of smooth muscle and a plexus of neurons that coordinate peristalsis

  • parasympathetic: enhances
  • sympathetic: inhibits
  • pain fibers are present
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7
Q

Pain triggers

A
  • reflex constriction of the ureter

- uretorenal reflex: constricts renal arterioles = reduced urine output

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8
Q

Ureters enter the bladder at the ____

A

Trigone

  • course obliquely thru detrusor muscle
  • normal detrusor tone prevents backflow
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9
Q

Vesicoureteral reflux

A

Inappropriate backflow of urine into the ureter

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10
Q

Micturition reflex

A

Autonomic spinal cord reflex that can be inhibited or facilitated by centers in the brain

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11
Q

Storage

A
  • detrusor muscle: relax
  • urethral sphincter: contract
  • sense when it is time to go
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12
Q

Voiding

A
  • detrusor muscle: contract

- urethral muscle: relax

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13
Q

Nervous system

A
  • brain: cerebral cortex and micturition center
  • autonomic: parasympathetic (void) and sympathetic (store)
  • somatic: sensory, motor
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14
Q

Hypogastric nerve

A

Sympathetic stimulation

  • to the detrusor: causes relaxation via beta 3 adrenergic receptors
  • to the internal urethral sphincter: causes tightening via alpha 1 adrenergic receptors
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15
Q

Pelvic nerve

A

Parasympathetic stimulation

  • to the detrusor: causes contraction via muscarinic cholinergic receptors
  • sensory: from the detrusor, detects stretching
  • forms a reflex arc
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16
Q

Pudendal nerve

A

Somatic

  • to the external urethral sphincter and pelvic floor
  • causes contraction via nicotinic cholinergic receptors
17
Q

Functions when blocked

A
  • pelvic: detrusor relaxation and bladder filling
  • hypogastric (body): detrusor contraction, urination
  • hypogastric (neck): urination
  • pudendal: urination
18
Q

Function when inappropriately stimulated

A
  • pelvic: overactive bladder
  • hypogastric (body): urine retention
  • hypogastric (neck): urine retention
  • pudendal: urine retention
19
Q

Function when inappropriately blocked

A
  • pelvic: bladder atony, urine retention
  • hypogastric (body): decreased bladder compliance and increased filling pressure
  • hypogastric (neck): open urethra, incontinence
  • pudendal: open urethra, incontinence
20
Q

Storage phase

A

Stretch receptors in the bladder wall send afferent signals along pelvic nerve

  • activates reflex arc thru hypogastric nerve relaxing detrusor, increasing urethral tone
  • voluntary contraction of external sphincter
21
Q

Micturition reflex

A

At a certain pressure threshold, reflexes begin and contractions are stimulated by stretch receptors and reflex arc in pelvic nerve

  • initially, contractions are short and self limiting
  • pressure increases with filling causing increased contractions
22
Q

Micturition reflex is self _____

A

Regenerative
- complete cycle of progressive and rapid increases in bladder pressure, period of sustained max pressure, return of pressure to baseline

23
Q

2 outcomes are possible with micturition reflex

A

Unscuccessful
- reflex wasn’t strong enough to overcome control of external sphincter
- period of inhibition
- cycle starts over, but increases in strength
Successful
- once reflex is strong enough, it sends a reflex via pudendal nerve to inhibit external sphincter

24
Q

Voiding phase

A

Micturition reflex takes over

  • detrusor muscle contracts via pelvic nerve stimulation
  • urethral sphincters relax thru blockage of the hypogastric and pudendal nerve
  • bladder empies
25
Q

Voluntary control

A
  • cerebral cortex
  • micturition center in the pons: receives afferent info and provides UMN control
  • cerebellum (mostly inhibitory)
26
Q

Inhibitory control

A

Achieved by increasing tone in external urethral sphincter

27
Q

Initiating micturition

A
  • abdominal muscles are voluntarily contracted
  • increases pressure in bladder and increases stimulation of stretch receptors
  • stimulates micturition reflex and inhibits external urethral sphincter
28
Q

Risk factors for micturition disorders

A
  • underlying disease
  • learned behavior
  • interventions
  • drugs
29
Q

Disorders of storage

A
  • urethral sphincter mechanism incontinence
  • LMN
  • overactive bladder
30
Q

Disorders of voiding

A
  • detrusor atony
  • UMN
  • mechanical obstruction
  • functional obstruction
31
Q

UMN bladder causes inhibitory signals to the ____ and _____

A

Hypogastric and pudendal nerve

Physiology (33 decks)

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