Urinary Bladder and Micturition

Question 1

Describe the path of delivery of urine to bladder.

Answer 1

collecting duct → duct of Bellini → minor and major calyces → renal pelvis

Question 2

What happens as urine collects in the pelvis?

Answer 2

increased pressure initiates peristalsis (along ureters)

• even when bladder is really full, peristalsis can push against pressure in bladder to get more urine from kidney to bladder

Question 3

What are the two main parts of the bladder?

Answer 3

body
bladder neck (posterior urethra)

Question 4

Body of Bladder

What does it do?

Answer 4

storage of urine

Question 5

Body of Bladder

Where does urine drain from?

Answer 5

from ureteral orifices into trigone

Question 6

Body of Bladder

What is the mucosal membrane composed of?

Answer 6

transitional epithelial cells

- initially cuboid shaped
- then squamous (stretched out) shaped
bladder expands a lot

Question 7

Body of Bladder

What is the detrusor muscle?

Answer 7

electrically coupled smooth muscle found within bladder wall

Question 8

Bladder Neck (Posterior Urethra)

What is this structure?

Answer 8

funnel-shaped region between fundus and urethra

Question 9

Bladder Neck (Posterior Urethra)

What muscles and fibres does this structure contain?

Answer 9

detrusor muscle

elastic fibres

Question 10

Bladder Neck (Posterior Urethra)

What are the two sphincters?

Answer 10

• internal – smooth muscles, tonic contraction (reflexive pathway)
• external – skeletal muscle, voluntary control

Question 11

Storage of Urine

What type of activity does the bladder wall smooth muscle have?

Answer 11

inherent tonic contractile activity

Question 12

Storage of Urine

Does pressure increase as bladder volume increases?

Answer 12

rise in intravesical pressure is minimal

Question 13

Storage of Urine

What nerves allow for bladder expansion?

Answer 13

• stimulation of sympathetic nerves

- inhibition of parasympathetic nerves

Question 14

Storage of Urine

What gradually empties the bladder?

Answer 14

pressure waves that occur during voluntary voiding

Question 15

What are the three branches of innervation of the bladder?

Answer 15

sympathetic – hypogastric nerves, innervate bladder wall and internal sphincter

parasympathetic – pelvic nerves, innervate bladder wall and posterior urethra

somatic motor nerves – pudendal nerves, innervate external sphincter

Question 16

Micturition Reflex – Mechanism

Answer 16

see notes

Question 17

What are the two phases of micturition?

Answer 17

filling phase

voiding phase

Question 18

What occurs during the filling phase of micturition?

Answer 18

at low pressure (< 20 cm H2O) or volume (< 400 mL), some reflexive detrusor muscle contractions occur – but they are transient, and do not cause voiding

Question 19

What occurs during the voiding phase of micturition?

Answer 19

as intravesical pressure rises ( > 20 cm H2O), micturition reflex occurs

• once micturition reflex has been initiated, voiding can occur depending on voluntary and supraspinal control (Barrington’s nucleus, and inhibitory centres)
• voiding typically empties bladder completely (<5-10 mL of urine remaining)

Question 20

In healthy adults, when does micturition occur?

Answer 20

only when inhibitory cortical control is suppressed

Question 21

Micturition – Voiding Phase

What does Barrington’s nucleus (pons) do?

Answer 21

acts to facilitate voiding

Question 22

Micturition – Voiding Phase

What do inhibitory centres in hypothalamus and cerebrum do?

Answer 22

oppose voiding as intravesical pressures rise up to 100 cm H2O