Micturition and Urinary incontinence

Question 1

What are the 2 phases of micturition? What can damaging of these 2 phases lead to?

Answer 1

1. Continence: damage to continence neurones can cause incontinence
2. Voiding; damage to these neurones can cause urinary retention

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 feature enables it to distend?

Answer 3

Muscle is orientated in 3 general directions to give it strength

Does not use peristalsis, uses transitional epithelium for expansion and dealing with toxins (tight junctions form an impermeable barrier)

Question 4

What is the difference between the internal and external urethral sphincter?

Answer 4

Internal is involuntary and only in males

External: formed by pelvic floor muscles and is voluntary, both genders

Question 5

Why is it so important that transitional epithelium forms an impermeable barrier?

Answer 5

The urine is hypertonic, and could draw water out of the body’s cells

Question 6

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

Answer 6

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

Question 7

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

Answer 7

Stretch receptors continually indicate sensation and can also sense pain from bladder irritation and temperature. They send afferent nerves to the brain

Question 8

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

Answer 8

Parasympathetic response: Pelvic N contracts the detrusor

Sympathetic response: Hypogastric N relaxes the detrusor muscle and contracts the internal sphincter

Somatic response: Pudendal N stimulates the external sphincter by communicating with the Pontine Micturition Centre and cerebral cortex - decision of whether to pee or not

Question 9

Which region in the brain controls the bladder?

Answer 9

The pontine micturition centre

Question 10

What does the lateral region of the PMC control?

What will stimulation to this area result in?

Answer 10

Lateral region controls continence and storage:

Stimulation will result in a contraction of the urethral sphincter to keep urine in

Question 11

Name 5 things that a bilateral lesion to the PMC can lead to

Answer 11

1. Inability to store urine
2. Reduction in bladder capacity
3. Excessive detrusor muscle activity
4. premature voiding
5. leaky bladder

Question 12

What does the medial region of the PMC control?

What 3 things result from stimulation to this area?

Answer 12

The medial region is the micturition centre:
Stimulation results in
1. decrease of urethral pressure
2. silencing of pelvic floor muscles (EMG signal)
3. Rise in detrusor pressure

Overall leads to voiding

Question 13

What does a lesion to the micturition centre lead to?

Answer 13

Severe urinary retention

Question 14

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

Answer 14

Dorsomedial pontine tegmentum

Question 15

What happens mechanically for the bladder to begin to fill?

Answer 15

Rugae flatten and the internal urethral sphincter will tighten

Question 16

What is the stress-relaxation phenomenon?

Answer 16

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

Question 17

What happens once the bladder reaches about 200 mL?

Answer 17

Micturition Reflex
1. Stretch receptors stimulated

2. Afferent fibres go to the spinal chord
3. Parasympathetic responses transmitted back to the bladder
4. Parasympathetic motor neurone responses are transmitted to the thalamus, PMC and cerebral cortex: decide whether you want to pee

Question 18

Where is the thalamus and what is its role?

Answer 18

The thalamus is above the brainstem between the cerebral cortex and the midbrain.

It’s function is to relay sensory and motor signals to the cerebral cortex

Question 19

What happens when you ignore the first signal to pee?

Answer 19

1. Brain sends impulses down spinal chord to inhibit the micturition reflex: sympathetic relaxation of the detrusor muscle
2. The pudendal N is stimulated and contracts the external sphincter to prevent urination

Question 20

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

Answer 20

The cortico-spinal connections haven’t been developed in the CNS

Question 21

Can the bladder fully empty?

Answer 21

10 mL of urine is left in the bladder after normal urination

Question 22

Explain how pressure increases over time in the bladder

Answer 22

At first, pressure only increases minorly, but as volume steadily increases the pressure will increase more rapidly

Question 23

Name 5 things that could cause Incontinence:

Answer 23

1. UTIs: chemical stimuli increases bladder activity
2. Women: stress and urge incontinence
3. Detrusor overactivity: common in older individuals
4. Damage to the CNS might lose innervation to the PMC and control of external sphincter (pudendal N)
5. Damage to pelvic nerves can abolish the micturition reflex

Question 24

What’s the difference between stress and urge incontinence and how would you treat them?

Answer 24

Stress: Caused by a weak pelvic floor, urination may occur when someone coughs, sneezes, laughs after childbirth, elderly, etc. Need to do pelvic floor exercises

Urge: Need to urinate constantly, person must retrain their bladder

Question 25

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

Answer 25

1. As the bladder continually fills: stretch receptors will produce more extreme degrees of stimulation that activate ganglionic neurones in the bladder to initiate detrusor muscle contractions until the pressure of the detrusor muscle overcomes the ability to keep the int. sphincter closed
2. If bladder >500 mL int.sphincter opens
3. If external sphincter doesn’t relax at this point an increase in bladder volume will re-initiate the cycle

Question 26

Name 2 causes for pathological urinary retention?

Answer 26

1. Enlarged prostate gland in men, may be due to cancer or inflammation
2. Kidney stones

Question 27

What replaces an internal sphincter in females?

Answer 27

The bladder neck and proximal urethra