Physiology of Micturition

Question 1

Where is urine formed?

Answer 1

In the renal tubules, it is the filtrate that is not reabsorbed

Question 2

What is the path of urine?

Answer 2

Formed in the renal tubules, travels through the calyxes (major and minor) until it drains into the renal pelvis

Question 3

Once the fluid is in the renal pelvis, where does it then drain into?

Answer 3

Ureters

Question 4

What is the path of urine following the ureters?

Answer 4

Urine flows through the ureters to the bladder by being propelled by contractions of the ureter wall smooth muscle

Question 5

What is the bladder?

Answer 5

A balloon-like chamber with walls of smooth muscle collectively termed as the detrusor muscle.

Question 6

What is the effect of contraction of the detrusor?

Answer 6

Squeezes on the urine in the bladder lumen to produce urination

Question 7

Which structure functions as the internal urethral sphincter?

Answer 7

The part of the detrusor muscle at the base (or the neck) of the bladder where the urethra begins

Question 8

What kind of muscle surrounds the urethra? What is it?

Answer 8

A ring of skeletal muscle known as the external urethral sphincter

Question 9

What is the function of the external urethral sphincter?

Answer 9

The contraction of the external urethral sphincter prevents urination even when the detrusor muscle contracts strongly.

Question 10

What is micturition governed by?

Answer 10

The micturition reflex
Voluntary control

Question 11

What initiates micturition?

Answer 11

A nervous reflex which causes the smooth muscle of the bladder walls to contract and expel the urine

Question 12

What is the parasympathetic system like whilst the bladder is filling?

Answer 12

The parasympathetic input to the detrusor is minimal, and a result, the muscle is relaxed

Question 13

How does the arrangement of muscle layers of the detrusor affect the internal urethral sphincter?

Answer 13

The arrangement of smooth muscle fibers, when the detrusor is RELAXED, causes the internal urethral to be passively closed.

Question 14

What is the sympathetic input to the urethral sphincters like during the filling phase, and what is the effect of it on the detrusor muscle?

Answer 14

There is a strong sympathetic input to the internal urethral sphincter and strong input by the somatic neurons to the internal and external urethral sphincters, the detrusor muscle relaxes and both sphincters are closed during filling phase

Question 15

What happens to the pressure inside the bladder as it fills up with urine?

Answer 15

The pressure within the bladder increases, which stimulates the stretch receptors in the bladder walls

Question 16

What volume of urine can the bladder accommodate before e the tension starts to rise?

Answer 16

250 to 400mL before tension starts to rise and activate the stretch receptors of the bladder walls

Question 17

What happens to the AFFERENT neurons of the stretch receptors?

Answer 17

They enter the spinal cord and stimulate the parasympathetic neurons which then cause the detrusor to contract

Question 18

What happens to the shape of the bladder when the detrusor contarcts?

Answer 18

There is a change in the shape of the bladder, which pulls open the internal urethral sphincter

Question 19

What is the effect of the AFFERENT input of stretch receptors on the sympathetic neurons?

Answer 19

Inhibits the sympathetic neuron to the internal urethral sphincter, which further contributes to its opening

Question 20

What is the effect of the AFFERENT neurons of the stretch receptors on the somatic nerons?

Answer 20

They inhibit the somatic motor neurons in the external urethral sphincter, causing it to relax and thus open

Question 21

During the filling phase what is the innervation like?

Answer 21

Parasympathetic: inhibited
Sympathetic: stimulated
Somatic: stimulated

Question 22

During micturition what is the innervation like?

Answer 22

Parasympathetic: stimulated
Sympathetic: inhibited
Somatic: inhibited

Question 23

Other than the local spinal reflex, what other control of micturition is there?

Answer 23

Voluntary control of micturition

Question 24

What is the voluntary control of micturition like?

Answer 24

Descending pathways from the brain influence reflex, determining the ability to prevent or initiate micturition voluntarily

Question 25

What happens if there is a loss of the descending pathways from the brain?

Answer 25

Loss of these descending pathways leads to the elimination of the ability to voluntarily control micturition

Question 26

What can lead to the loss of descending pathways from the brain?

Answer 26

Spinal cord damage

Question 27

What causes the bladder fullness sensation?

Answer 27

As the bladder distends, the input from the blade stretch receptors causes the sensation of fullness and the urge to urinate

Question 28

Which innervation is bladder fullness sensed through?

Answer 28

Ascending pathways to the brain

Question 29

What are the different possible responses to bladder fullness?

Answer 29

Urination can be voluntarily prevented or initiated

Question 30

How can urination be voluntarily prevented?

Answer 30

Activating the descending pathways that stimulate both the sympathetic and somatic motor nerves to the internal and external urethral sphincters

Question 31

How can urination be voluntarily initiated?

Answer 31

Via the descending pathways that stimulate the parasympathetic neurons

Question 32

What controls micturition?

Answer 32

Complex interactions in different areas of the brain

Question 33

What do the areas in the brainstem facilitate?

Answer 33

They can facilitate both initiation and inhibition of urination

Question 34

What is the effect of the area of the midbrain on urination?

Answer 34

It can inhibit it

Question 35

Which area of the brain can help facilitate urination?

Answer 35

The area of the posterior hypothalamus

Question 36

What is the effect of string inhibitory input from the cerebral cortex? When is it taught?

Answer 36

Prevents involuntary urination, and it is taught during toilet training in childhood

Question 37

What is the definition of incontinence?

Answer 37

The involuntary release of urine that occurs commonly in elderly people

Question 38

What are the most common types of incontinence?

Answer 38

Stress incontinence
Urge incontinence

Question 39

What induces stress incontinence?

Answer 39

Sneezing
Coughing
Exercise

Question 40

What is associated with urge incontinence?

Answer 40

Associated with the desire to urinate

Question 41

Which population is stress incontinence most common in?

Answer 41

More common in women due to a loss of urethral support provided by the anterior vagina

Question 42

Which kinds of medications are associated with the relief of stress incontinence?

Answer 42

Estrogen replacement therapy to improve vaginal tone

Question 43

What is the solution in severe cases of stress incontinence?

Answer 43

May require surgery to improve vaginal support of the bladder and urethra

Question 44

What is the cause of urge incontinence?

Answer 44

It is often unknown in individual patients. However, an irritation to the bladder can cause urge incontinence

Question 45

What kind of irritation to the bladder can lead to urge incontinence?

Answer 45

Bacterial infection

Question 46

What can treat urge incontinence?

Answer 46

Drugs such as tolterodine or oxybutynin which antagonize the effect of the parasympathetic nerves on the detrusor muscle

Question 47

What are the side effects of the drugs used to treat urge incontinence and why?

Answer 47

They are anticholinergic, so they can have side effects such as blurred vision, constipation, and increased heart rate