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Flashcards in Micturition Deck (31)
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1

Micturition

2 stage process that results in the passage of urine out of the body
- passive storage phase
- active voiding phase

2

Anatomy of the bladder

- detrusor musle
- apex
- body
- neck
- trigone (smooth portion)
- urethra: internal sphincter (smooth extension of detrusor), external sphincter (skeletal)

3

Detrusor muscle

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

4

Bladder wall layers

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

5

Urine transport: kidney

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

6

Urine transport: ureter

Composed of smooth muscle and a plexus of neurons that coordinate peristalsis
- parasympathetic: enhances
- sympathetic: inhibits
- pain fibers are present

7

Pain triggers

- reflex constriction of the ureter
- uretorenal reflex: constricts renal arterioles = reduced urine output

8

Ureters enter the bladder at the ____

Trigone
- course obliquely thru detrusor muscle
- normal detrusor tone prevents backflow

9

Vesicoureteral reflux

Inappropriate backflow of urine into the ureter

10

Micturition reflex

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

11

Storage

- detrusor muscle: relax
- urethral sphincter: contract
- sense when it is time to go

12

Voiding

- detrusor muscle: contract
- urethral muscle: relax

13

Nervous system

- brain: cerebral cortex and micturition center
- autonomic: parasympathetic (void) and sympathetic (store)
- somatic: sensory, motor

14

Hypogastric nerve

Sympathetic stimulation
- to the detrusor: causes relaxation via beta 3 adrenergic receptors
- to the internal urethral sphincter: causes tightening via alpha 1 adrenergic receptors

15

Pelvic nerve

Parasympathetic stimulation
- to the detrusor: causes contraction via muscarinic cholinergic receptors
- sensory: from the detrusor, detects stretching
- forms a reflex arc

16

Pudendal nerve

Somatic
- to the external urethral sphincter and pelvic floor
- causes contraction via nicotinic cholinergic receptors

17

Functions when blocked

- pelvic: detrusor relaxation and bladder filling
- hypogastric (body): detrusor contraction, urination
- hypogastric (neck): urination
- pudendal: urination

18

Function when inappropriately stimulated

- pelvic: overactive bladder
- hypogastric (body): urine retention
- hypogastric (neck): urine retention
- pudendal: urine retention

19

Function when inappropriately blocked

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

20

Storage phase

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

Micturition reflex

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

Micturition reflex is self _____

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

23

2 outcomes are possible with micturition reflex

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

Voiding phase

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

Voluntary control

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

26

Inhibitory control

Achieved by increasing tone in external urethral sphincter

27

Initiating micturition

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

28

Risk factors for micturition disorders

- underlying disease
- learned behavior
- interventions
- drugs

29

Disorders of storage

- urethral sphincter mechanism incontinence
- LMN
- overactive bladder

30

Disorders of voiding

- detrusor atony
- UMN
- mechanical obstruction
- functional obstruction