Micturition

Question 1

What is micturition?

Answer 1

The process by which the urinary bladder empties when it becomes filled.

Question 2

What transports urine from the kidneys to the bladder and how long is this?

Answer 2

The ureters.

25-35 cm long

Question 3

Where does the ureter enter into the bladder wall?

Answer 3

It enters through the bladder wall through the detrusor muscle at the trigone.

Question 4

What pushes the urine through the ureters? When enhances this action?

Answer 4

Smooth muscle contractions propel urine to the bladder.

Enhanced by parasympathetics and inhibited by sympathetic stimulation.

Question 5

Where are the possible constrictions where kidney stones or other things can clog the ureters?

Answer 5

1) Ureteropelvic junction at ureter and bladder.
2) Behind testicular or ovarian a or v.
3) Pelvic brim (over external iliac a and v)
4) Where the ureter traverses the bladder wall

Question 6

What is the vesicoureteral reflux?

What does it increase the risk of?

Answer 6

Urine goes back into ureter during micturition.

Pyelonephritis

Question 7

What does the detrusor muscle do?

Answer 7

Smooth muscle of the bladder > contracts in micturition

Question 8

What does the trigone do?

Answer 8

Mucosa on posterior wall of bladder above the bladder neck. Where ureters enter bladder and where the bladder neck opens into the posterior urethra.

Question 9

What does the internal sphincter do?

Answer 9

Smooth muscle located in bladder neck > holds in urine when contracted (involuntary)

Question 10

What does the external sphincter do?

Answer 10

Skeletal muscle located in urogenital diaphragm > holds in urine when contracted (voluntary)

Question 11

What part of the spinal cord innervates the bladder?

Answer 11

S2-S4

Question 12

What type of fibers detect bladder FULLNESS?

Answer 12

A(delta) fibers (myelinated) > wall tension (fullness)

Question 13

What type of fibers detect bladder PAIN?

Answer 13

C fibers (unmyelinated) are “silent” and respond to noxious stimuli (chemical irritation and cooling)

Question 14

What system is responsible for bladder emptying? Via what nerve? Via what neurotransmitter and receptor?

Answer 14

The parasympathetics.
Pelvic splanchnic nerve
ACh
Muscarinic (M3)

Question 15

What systems work to stop micturition?

Answer 15

Sympathetics and somatic muscle innervation

Question 16

What does the pontine micturition center (PMC) do?

Answer 16

Controls and coordinates activity of sacral micturition center
Activates external urethral relaxation and sacral parasympathetic outflow > micturition

Question 17

What does the Periaqueductal gray (PAG) do?

Answer 17

Receives afferent bladder signals and passes on to higher brain centers > conscious sensation.
Primary excitatory input to the PMC

Question 18

What can overturn the PAG?

Answer 18

The higher brain center (cortex)

Prevent incontinence

Question 19

What happens if afferent or efferent fibers between bladder and cord are destroyed?

Answer 19

No detrusor contractions.

Urinary retention > overflow incontinence

Question 20

If there is spinal cord damage above the sacrum what happens?

Answer 20

Destrusor does not work, urinary retention occurs.
Eventually micturition reflexes return, detrusor is overactive and sphincter dyssynergia presents.
Periodic incomplete urination.

Question 21

What if there is damage above the pons? (from stroke, tumor, or brain trauma)

Answer 21

Interrupts all inhibitory signals from the brain > continuous stimulation of micturition center > overactive detrusor
Result: frequent, unpredictable urination (complete)

Question 22

Describe urination in an infant.

Answer 22

There is involuntary start/stop.

Though detrusor and sphincter still work in coordination.

Question 23

Describe urination in an adult.

Answer 23

Voluntary start/stop

Detrusor and sphincter work in coordination.

Question 24

Describe urination in a paraplegic patient (spinal cord damage above sacrum).

Answer 24

Void occurs at lower bladder volumes.
Involuntary start/stop
Detrusor and sphincter are uncoordinated (dyssynergia)