Micturition and Incontinence

Question 1

What are the 2 phases of micturition?

Answer 1

1. Continence

2. Voiding

Question 2

What is unique about the trigone muscle, and what does the neck of the bladder do?

Answer 2

Trigone: particularly distensible smooth muscle

Neck: connects bladder to urethra

Question 3

How is the detrusor muscle orientated? What is the benefit of its transitional epithelia? What feature enables it to distend?

Answer 3

3 directions (strength)

Expansion, tight junctions/impermeable barrier deals with toxins and urine is hypertonic (prevents water following)

Question 4

What is the average capacity of the bladder and how long does it take to fill?

Answer 4

Averagely around 550 mL and takes 9 hours to fill (sleeping time)

Question 5

How is the brain informed that the bladder is being filled/in pain?

Answer 5

Stretch receptors

*also sense pain from bladder irritation and temp

Question 6

What are the 3 responses the brain can initiate to voiding, and which nerve coincides with each response?

Answer 6

PS: Pelvic N contracts detrusor

S: Hypogastric N relaxes detrusor muscle and contracts the internal sphincter

Somatic: Pudendal N stimulates external sphincter via pontine micturition centre and cerebral cortex

Question 7

Which region in the brain controls the bladder?

Answer 7

The pontine micturition centre

Question 8

What does the lateral region of the PMC control? What will stimulation to this area result in?

Answer 8

Continence and storage -> stimulation contracts urethral sphincter (keeps urine in)

Question 9

What can a bilateral lesion to the PMC lead to

Answer 9

Reduced bladder capacity, excess detrusor muscle activity, premature voiding/leaky bladder

Question 10

What does the medial region of the PMC control?

What 3 things result from stimulation to this area?

Answer 10

Micturition centre:

decreased urethral pressure, silencing of pelvic floor muscles (EMG signal), Rise in detrusor pressure

-> voiding

Question 11

What does a lesion to the micturition centre lead to?

Answer 11

Severe urinary retention

Question 12

Name a specific part of the brain that is active during voiding

Answer 12

Dorsomedial pontine tegmentum

Question 13

What mechanically happens as the bladder fills?

Answer 13

Rugae flatten, internal urethral sphincter tightens

Question 14

What is the stress-relaxation phenomenon?

Answer 14

As rugae continually flatten the capacity of the bladder can increase up to 700 mL

Question 15

What happens once the bladder reaches about 200 mL?

Answer 15

Micturition Reflex

1. (+) Stretch receptors
   - > afferent to spinal cord
2. PS response to bladder
   * PS MN responses transmitted to thalamus, PMC and cerebral cortex: decide whether you want to pee

Question 16

What happens when you ignore the first signal to pee?

Answer 16

Brain inhibits micturition reflex: Sympathetic: relaxes detrusor
Somatic: pudendal contracts external sphincter

Question 17

Why do children have less of an ability to control micturition?

Answer 17

Underdeveloped corticospinal connections

Question 18

Name 5 things that could cause Incontinence:

Answer 18

1. UTIs
2. Women: stress and urge incontinence
3. Detrusor overactivity: (elderly)
4. Damage to PMC (lose somatic control of external sphincter)
5. Damage to pelvic nerves (lose micturition reflex)

Question 19

Difference between stress and urge incontinence

Answer 19

Stress: weak pelvic floor
*pee when cough, sneeze, laugh, etc

Urge: constant urge (need to retrain bladder)

Question 20

What happens over time if the micturition reflex is continually ignored?

Answer 20

Stretch receptors produce more extreme stimulation -> activates ganglionic neurons in bladder to contract detrusor -> int sphincter opens -> if ext. sphincter doesn’t relax an increase in bladder volume re-initiates the cycle

Question 21

Name 2 causes for pathological urinary retention?

Answer 21

Enlarged prostate, kidney stones

Question 22

What replaces an internal sphincter in females?

Answer 22

The bladder neck and proximal urethra