urinary bladder & micturition

Question 1

how bladder can store urine with only minimal increase in intravesical pressure

Answer 1

bladder wall SM has tonic contractile activity
-urine delivery = expansion bladder
increase volume, so pressure doesnt increase
as bladder increase 75-400 mL, rise in intravesical pressure is minimal
stimulation SNS (innervate internal) and inhibition PSNS (innervate bladder wall, urethra) nerves allow for bladder expansion

Question 2

describe micturition reflex pathway, be sure to differentiate btw automatic spinal component and voluntary component

Answer 2

bladder filling (400 mL) –> activation micturition reflex (initiates by stretch receptor activation)–>bladder wall contraction and internal sphincter relaxation –> micturition (external sphincter relaxation

once micturition reflex initiated, voiding can occur depending on voluntary and supraspinal control

• Barrington’s nucleus facilitates voiding
• inhibitory centers in HTh and cerebrum oppose voiding as intravesical pressure rises

Question 3

delivery urine to bladder

Answer 3

from CD, enters duct of Bellini, passes through minor and major calyces to renal pelvis

• urine collects in pelvis, the increased pressure initiates peristalsis (along ureters)
• peristaltic waves travel at 3 cm/s, occur with frequency btw 1/s to <1/min

Question 4

anatomy bladder

Answer 4

body (fundus)- stores urine

• urine drains from uretal orfices into trigone
• mucosal membrane of epithelial cells
• detrusor muscle (EC smooth muscle) in bladder wall

bladder neck (posterior urethra)
- funnel-shaped region btw fundus and urethra
-walls contains detrusor and elastic fibres
2 sphincters:
internal- smooth, tonic contraction
external-skeletal, voluntary