8.1 Micturation

Question 1

what is micuration?

Answer 1

the intermittent void of urine stored in bladder

Question 2

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

Answer 2

as bladder has rugae and transitional epithelium

Question 3

how much urine can the bladder hold?

Answer 3

400-600ml of urine in healthy adults.

Question 4

what causes the urge to urinate?

Answer 4

increase in intravesical pressure

Question 5

how is micturation controlled in infants?

Answer 5

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

Question 6

describe the action of muscles during micturation

Answer 6

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

Question 7

what is the neural innervation of the voiding reflex?

Answer 7

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.

Question 8

how might a stroke affect micturation?

Answer 8

lesion to the frontal gyrus causes:

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

Question 9

how might a lesion of the afferent nerves affect micturation?

Answer 9

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

Question 10

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

Answer 10

shrunken bladder with hypertrophied bladder wall

Question 11

what conditions may result in bladder dysfunction?

Answer 11

spina bifida
diabetes mellitus
multiple sclerosis

Question 12

what is spina bifida?

Answer 12

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

Question 13

how does diabetes mellitus affect micturation?

Answer 13

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

Question 14

how does spinal shock affect continence?

Answer 14

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

Question 15

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

Answer 15

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

Question 16

What is spastic neurgenic bladder?

Answer 16

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

Question 17

what is the muscle of the bladder?

Answer 17

detrusor muscle

Question 18

describe the structure of the detrusor muscle

Answer 18

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

Question 19

what is the function of the internal urethral sphincter?

Answer 19

to prevent retrograde ejaculation (only found in men)

has a small role in continence aswell

Question 20

where is the IUS located?

Answer 20

in the bladder neck

Question 21

describe the structure of the external urethral sphincter?

Answer 21

skeletal muscle under voluntary control that lies in the pelvic diaphragm

Question 22

what is urodynamics?

Answer 22

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

Question 23

how is urodynamics measured?

Answer 23

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.

Question 24

what occurs in the storage phase?

Answer 24

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

Question 25

what happens in the voiding phase?

Answer 25

waves of contraction of the detrusor muscle to void urine

Question 26

what is the main innervation in the storage phase?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

how do we have a conscious appreciation of bladder fullness?

Answer 28

as the sensory neurone reports to the cerebral cortex.

Question 29

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

Answer 29

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

Question 30

what spinal nerves control micturition?

Answer 30

S2, S3, S4

Question 31

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

Answer 31

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.

Question 32

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

Answer 32

Parasympathetics (S2-S4) having an excitatory innervation

Question 33

how are parasympathetic nerves stimulates in the voiding phase

Answer 33

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.

Question 34

what is the positive feedback mechanism used in micturition?

Answer 34

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.

Question 35

what gives us voluntary control over micturition?

Answer 35

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.

Question 36

describe the micturition reflex

Answer 36

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.

Question 37

what are micturition cystourethrograms used for?

Answer 37

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

Question 38

what are the different grades for vesicouretic reflux?

Answer 38

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

Question 39

why are urodynamics useful?

Answer 39

help distinguish between UUI and SUI

Question 40

how can the detrusor muscle pressure be measured?

Answer 40

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

Question 41

what is SUI

Answer 41

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

Question 42

what is UUI?

Answer 42

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