Physiology of Micturition Flashcards
(44 cards)
1
Q
Definition of Micturition:
A
- the process of emptying the urinary bladder
- occurs through a complexity of reflexes
- occurs in a response to an increase in intravesicular (bladder) pressure
2
Q
Brain centers with a role in bladder function:
A
- Pontine Micturition Center (PMC)
- Midbrain periaqueductal gray (PAG)
- Frontal lobes of the cortex
3
Q
Pontine Micturition Center
A
- located in the brainstem
- coordinates micturition with other brain centers
- directs excitatory and inhibitory efferent nerves
- Acted on by a suprapontine centers which allows “switch” from storage to voiding phases
- direct pathways from the PMC project to S2-S4 and determine parasympathetic outflow to the detrusor and reciprocal activity of the motor neurons to the striated urethral sphincter
4
Q
Midbrain periaqueductal gray (PAG)
A
- where ascending afferents synapse during bladder storage
- relays the impulse via the hypothalamus and thalamus to the dorsal anterior cingulate cortex, the right insula,, and the lateral prefrontal cortex
5
Q
Frontal lobes of the cortex:
A
- decisions to void or not is made here
- if decision is to delay voiding: inhibition of the PAG occurs, this suppresses the PMC
- if decision is made to void: prefrontal cortex releases its inhibition on the PAG, the hypothalamus provides a “safe” signal
- PAG excites the PMC, which sends a signal to the sacral spinal cord, leading to relaxation of the urethral sphincter and contraction of the detrusor
6
Q
Peripheral innervation to the lower LUT includes:
A
- hypogastric nerve
- pelvic nerve
- pudendal nerve
7
Q
Hypogastric nerve:
A
- T11-L2
- sympathetic nervous system
- storage of urine
- detrusor relaxes as bladder fills
- bladder relaxation, sphincter contraction
8
Q
Pelvic Nerves:
A
- S2-S4
- parasympathetic nervous system
- sacral dorsal root to pelvic nerve to pelvic plexus to postganglionic nerve at the detrusor
- pelvic sphlanic nerves
- stimulate detrusor to contract
- stimulated by stretch receptors in the bladder wall
- inhibit sympathetic which causes bladder contraction –> sphincter relaxation
9
Q
pudendal nerve
A
- S2-S4
- somatic innervation
cell bodies of nerve originate in Onuf’’s nucleus which is located in the ventral horn of S2-4 - perineal branch innervates the external urethral sphincter which is composed of striated muscle
- inferior rectal branch innervates the anal sphincters
- the striated urethral sphincter (external urethral spinchter or EUS) is the only part of the LUT to receive somatic innervation
10
Q
T/F neural pathways important for bladder function begin at thoracic spine and traverse down to end of spinal cord
A
False. The neural pathways important for bladder function traverse the entire length of the spinal cord
11
Q
Bladder sensation
A
- mechanoreceptors in the bladder wall signal distention and filling of the bladder via A-delta afferent fibers
- small, myelinated A-delta fibers travel from the mechanoreceptor through the pelvic nerve to the sacral micturition center –> inhibiting the parasympathetic innervation to the detrusor
- sympathetic nervous system stores urine
- sensory signals continue through the ascending spinal cord pathways to the PMC in the brainstem resulting in increased activity of the EUS
12
Q
Storage phase
A
- detrusor pressure stays constant with filing until the threshold for micturition is reached (Klausner 2011)
13
Q
Storage phase: bladder compliance is a function of…
A
- viscoelasticity
- the ability of the detrusor muscle cells to elongate while maintaining contractility
- the neurally mediated suppression of signals that promote detrusor contraction
- compliance is determined by urodynamic evaluation
14
Q
what is bladder compliance determined by?
A
urodynamic evaluation
15
Q
storage phase: what are parasympathetic nerves inhibited by?
A
activation of hypogastric nerves
16
Q
storage phase: urethral smooth muscles remain ________ during filling
A
contracted
17
Q
storage phase: outlet press ______ detrusor pressure
A
exceeds
18
Q
storage phase: outlet pressure > detrusor pressure
A
- pressure rises from 0-5 to 10 cm of H20 rapidly upon initial filling
- remains at less than 10 cm until almost capacity
- strong sensation of distension is produced at about 400ml
- in response to this strong sensation a rapid rise in pressure occurs and is referred to as the “desire to void”
19
Q
Storage phase: EUS activity continues to increase as the bladder fills
A
- occurs under the influence of the pudendal nerve (somatic)
- EUS activity peaks just before micturition
20
Q
Micturition reflex can be aborted at any time by:
A
inhibition of higher cortical centers
- damage to the cerebral cortex can reduce the inhibition and may result in urinary frequency, urgency, or urge incontinence
21
Q
Pre-requisites for normal storage phase (carriere, 2006):
A
- good bladder distensibility
- stable detrusor muscle
- absence of obstruction
- urethral closure present at present at rest and under stress.
22
Q
Storage dysfunction happens with:
A
- detrusor overactivity
- underactive pelvic floor muscles
23
Q
Micturition phase details:
A
- strong urge to urinate signaled from detrusor stretch receptors
- decision is made to void and patient positions over toilet
- striated muscle and sphincteric relaxation results in bladder neck descent and obliteration of the urethrovesical angle
- trigone contracts to close the ureters and open the urethra
- EUS is voluntarily relaxed resulting in increased pelvic nerve activity
- detrusor contraction occurs creating an average of 60-100 cm of H20 pressure to empty the bladder
24
Q
Bladder empties at a rate of
A
25 ml/sec
25
Normal post residual volume
30-100ml
26
What happens after urination is complete?
- detrusor relaxes
- urethra is closed
- ureters are open with the return of the urethrovesical angle and striated muscle activation
27
Pre-requisites for normal micturition phase
- intact neural control
- adequate detrusor functioning
- absence of obstruction
- pelvic floor muscle relaxation
28
Micturition dysfunction:
- non-relaxing pelvic floor muscles.
- poor or absent detrusor contraction
- Mechanical obstruction
29
Storage reflexes:
- Detrusor-sphincter reflex
- guarding reflex
- central coordination of storage reflexes
- Reflex control of bladder compliance
- reflex inhibition of efferent pathways
- Bradley's 4 neurological control loops (Bradley 1974)
30
Detrusor-sphincter reflex:
- sympathetics "on", parasympathetics "off"
- distention of detrusor produces afferent firing of pelvic nerve which stimulates preganglionics in the hypogastric nerve
- maintains greater outlet pressure
31
guarding reflex:
- bladder distention fires afferent discharges
- leads to stimulation of Onulf's nucleus in the sacral cord
- reflex activation of the urethral sphincter causes stronger contraction
32
Central coordination of storage reflexes
- lateral pontine micturition center (PMC) acts to coordinate urine storage with cortical influences to override the spinal reflexes
33
Reflex control of bladder compliance
- viscoelastic tissues of the 3 layer detrusor maintain low intravesical pressure
- allows bladder to fill until appropriate filling level
34
Reflex inhibition of efferent pathways
- parasympathetic efferent inhibition to allow sympathetic and somatic maintenance of storage mechanisms
- Voluntary Urinary Inhibition Reflex (VUIR): aides voluntary control of continence through Bradley's loop 3:
- -contraction of the striated pelvic floor muscles including the striated external sphincter occludes the urethra
- -promotes continence and reflexively relaxes the detrusor muscle,
- -prevents internal urethral sphincter from relaxing, can be taught as part of a home program to defer the urge to void
35
What can be taught as part of a HEP to defer the urge to void?
Voluntary Urinary Inhibition Reflex
uses somatic and parasympathetic system override
36
Describe Bradley's 4 neurological control loops:
Loop 1) connects the CNS and the PMC
Loop 2) connects the detrusor to the PMC (afferent) and the sacral spinal cord (efferent
Loop 3) is described above and connects sensory axon pathways from the detrusor and the striated urethral sphincter to the sacral spinal cord
Loop 4) connects the suprasacral and segmental innervation of the periurethral striated muscles.
37
Normal values: renal input into the bladder is:
1-14ml/min
38
Normal values: bladder capacity:
400-600cc
39
Normal values: Normal frequency of voiding:
4-8x/day (carriere, 2006)
40
Normal values: First sensation to void is at about:
40% of capacity (Fowler, 2006)
41
Normal values: first desire to void is about
60% capacity
- can be delayed if necessary
42
Normal values: strong desire to void at
> 90% capacity
43
Perception of bladder fullness can be affected by state of mind (fowler, 2006)
- anxiety increases the level of desire to void
| - distraction can decrease awareness of bladder sensation
44
Bladder habits leading to dysfunction (CAPP decisions)
- delaying toileting too long can overstretch bladder leading to atonic (low tone) bladder
- hovering over the toilet does not allow adequate relaxation of the pelvic floor muscles
- bearing down to initiate stream or complete urination
- not allowing time for full bladder emptying
- preventative voiding/ voiding just in case
- failing to wipe front to back after bowel movement may lead to UTI
