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Urinary > 8.1 Micturation > Flashcards

8.1 Micturation Flashcards

1
Q

what is micuration?

A

the intermittent void of urine stored in bladder

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2
Q

how is the bladder able to increase in volume without a significant increase in pressure?

A

as bladder has rugae and transitional epithelium

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3
Q

how much urine can the bladder hold?

A

400-600ml of urine in healthy adults.

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4
Q

what causes the urge to urinate?

A

increase in intravesical pressure

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5
Q

how is micturation controlled in infants?

A

involuntary local spinal reflex where the bladder empties upon reaching a critical pressure.

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6
Q

describe the action of muscles during micturation

A
  1. pelvic diaphragm relaxes
  2. bladder neck mover down stretching the bladder wall stimulating stretch receptors
  3. perineal muscles and the internal and external urethral sphincter relaxes
  4. bladder detrusor muscle contracts
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7
Q

what is the neural innervation of the voiding reflex?

A
  1. bladder stretch receptors stimulates afferent parasympathetic fibres of the bladder.
  2. somatic control via the pudendal nerve innervated the external urethral sphincter, keeping it closed until it is an appropriate time to urinate.
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8
Q

how might a stroke affect micturation?

A

lesion to the frontal gyrus causes:

  • reduced desire to urinate
  • difficulty stopping micturation once started.
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9
Q

how might a lesion of the afferent nerves affect micturation?

A

prevent reflex contractions of the bladder. Bladder becomes distended, thin walled and hypotonic

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10
Q

how might a lesion of the afferent and efferent nerves affect the bladder?

A

shrunken bladder with hypertrophied bladder wall

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11
Q

what conditions may result in bladder dysfunction?

A

spina bifida
diabetes mellitus
multiple sclerosis

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12
Q

what is spina bifida?

A

developmental neural tube defect. Posterior arches of the spine fail to develop, part of the spinal cord and its arches are exposed.

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13
Q

how does diabetes mellitus affect micturation?

A

neuropathy. patient voids infrequently. Leads to bladder distension and overflow incontinence. Presence of residual urine increases risk of infection

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14
Q

how does spinal shock affect continence?

A

overflow incontinence due to flaccid and unresponsive bladder. Overfill and dribbling

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15
Q

After an episode of spinal shock caused by a spinal lesion, what happens to the voiding reflex?

A

voiding reflex returns but has no control from higher centres, patient has no voluntary control over voiding

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16
Q

What is spastic neurgenic bladder?

A

occurs after a spinal lesion. The detrusor and urethral sphincter do not work together and are usually tightly contracted at the same time. Bladder capacity falls and the wall hypertrophies

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17
Q

what is the muscle of the bladder?

A

detrusor muscle

18
Q

describe the structure of the detrusor muscle

A

smooth muscle that surrounds the bladder, lying beneath the submucosa. fibres run in different directions, allowing affective expulsion of urine during voiding phase.

19
Q

what is the function of the internal urethral sphincter?

A

to prevent retrograde ejaculation (only found in men)

has a small role in continence aswell

20
Q

where is the IUS located?

A

in the bladder neck

21
Q

describe the structure of the external urethral sphincter?

A

skeletal muscle under voluntary control that lies in the pelvic diaphragm

22
Q

what is urodynamics?

A

measurement of the changes in bladder pressure in comparison to the increase in bladder volume

23
Q

how is urodynamics measured?

A
  1. insert catheter into the bladder with a manometer on the end
  2. Rectal probe inserted to assess intra-abdominal pressure
  3. work out detrusor muscle pressure
  4. infuse fluid into the bladder, until patient feels the urge to void
  5. Record volume infused and relative pressures.
24
Q

what occurs in the storage phase?

A

bladder increasing in volume but little increase in pressure. As bladder volume increase, the detrusor muscle actively relaxes.

25
Q

what happens in the voiding phase?

A

waves of contraction of the detrusor muscle to void urine

26
Q

what is the main innervation in the storage phase?

A

sympathetics (T10-L2) act to inhibit the contraction of the detrusor muscle and excite the internal urethral sphincter.

27
Q

how does the sensory afferent neurone of the bladder communicate with sympathetic fibres?

A

occurs in the storage phase. Sensory afferent nerve detects bladder wall stretch and enters the spinal cord at S2-S4. Must ascend up the spinal cord to synapse with sympathetic fibres in the T10-L2 level

28
Q

how do we have a conscious appreciation of bladder fullness?

A

as the sensory neurone reports to the cerebral cortex.

29
Q

describe the innervation of the external urethral sphincter in the storage phase

A

needs to remain closed. Excitatory innervation on the sphincter by somatic motor neurones carried in the pudendal nerve. Neurones from the L centre in the brain travel down the spinal cord to innervate the pudendal nerve

30
Q

what spinal nerves control micturition?

A

S2, S3, S4

31
Q

how do the storage phase and voiding phase communicate with each other?

A

M centre communicates with the L centre in the brain. M centre inhibits the L centre when strongly stimulated via the sensory receptor and the paracentral lobules. Pudendal nerve innervation to the EUS is inhibited.

32
Q

what is the main innervation of the detrusor during voiding phase?

A

Parasympathetics (S2-S4) having an excitatory innervation

33
Q

how are parasympathetic nerves stimulates in the voiding phase

A
  1. Sensory afferent nerve detects bladder stretch and communicates directly with the parasympathetic nervous system at S2- S4
  2. sensory afferent nerves detecting high load of bladder stretch stimulate the M centre of the brain. M centre sends excitatory input down to the bladder.
34
Q

what is the positive feedback mechanism used in micturition?

A

stretch receptors detect increased pressure and fire.
causes positive stimulation of the parasympathetic fibres and motor neurones stop firing. Contraction of the detrusor muscle increases the pressure in the bladder further.

35
Q

what gives us voluntary control over micturition?

A

paracentral lobules allow us to have conscious control over the M centre in the brain. We can consciously send positive and negative signals sent to the Micturition centres in the brain.

36
Q

describe the micturition reflex

A

stretch receptors fire after detecting high amounts of bladder stretch

  1. parasympathetics innervated to contract detrusor muscle
  2. M centres innervated. inhibits the L centre and therefore the pudendal nerve supplying somatic motor innervation to the EUS. EUS relaxes.
37
Q

what are micturition cystourethrograms used for?

A

to demonstrate vesicouretic reflux from the bladderinto the uretes and potentially kidneys during the emptying of the bladder.

38
Q

what are the different grades for vesicouretic reflux?

A

grade 1 : contrast medium enters ureter only
grade 2 : contrast fills pelvicalycael system
grade 3: dilation of the calycaes and ureter

39
Q

why are urodynamics useful?

A

help distinguish between UUI and SUI

40
Q

how can the detrusor muscle pressure be measured?

A

by using urodynamic studies, subtract the bladder pressure from the intra-abdominal pressure measured by the rectal probe

41
Q

what is SUI

A

when an increase in intra abdominal pressure leads to involuntary urine leakage with no detrusor muscle contraction

42
Q

what is UUI?

A

detrusor contraction spontaneously or with increased abdominal pressure, and patient feels overwhelming urge to immediately urinate

Urinary (18 decks)

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