The Bladder

Question 1

PASSAGE OF URINE INTO THE URETER

Urine formation is continuous (≥ 1 mL per min)

—–> Peristaltic contractions of the walls of the ureter facilitate the movement of urine into the bladder.

Question 2

URINE TRAVELS DOWN THE URETERS TO THE BLADDER

Question 3

THE URINARY BLADDER

•A muscular sac

–Capacity between 600 and 800 mL

–Collapsed and relaxed when empty

•The main muscle of bladder wall is the detrusor

–composed of three layers of smooth muscle fibres

–fibres arranged differently in each (spiral, longitudinal, circular)

• Stored urine is voided to the exterior via the urethra
• Two muscular rings (sphincters) control urethral opening

–Internal sphincter (involuntary)

•smooth muscle - normally closed (passive contraction)

–External sphincter (voluntary)

•skeletal muscle - normally closed (tonic contraction)

Question 4

WHAT IS THE MAIN MUSCLE OF THE BLADDER WALL?

Answer 4

Detrusor

Question 5

WHICH TWO MUSCULAR RINGS (SPHINCTERS) CONTROL URETHRAL OPENING?

Answer 5

Internal sphincter (involuntary)

External sphincter (voluntary)

Question 6

THE URETERS EMPTY INTO THE URINARY BLADDER

Question 7

CONTROL OF MICTURITION (PASSING OR VOIDING OF URINE)

•Neural regulation of bladder function involves PNS & CNS:

–an involuntary spinal micturition reflex arc (MR)

•present from birth in continent individuals

1. stretch receptors in the wall of the urinary bladder
2. afferent sensory nerve fibres - convey impulses to the spinal chord
3. efferent PS nerve fibres - convey impulses to detrusor and internal sphincter

–voluntary nervous control exercised by the CNS (‘+’ and ‘-’)

• cortex, cerebellum and the micturition centre located in the pons (PMC)
• develops in early childhood; full control normally present at 3 to 5 years

Question 8

NEURAL PATHWAYS CONTROLLING MICTURITION

Question 9

DETRUSOR PRESSURE AND ELECTRICAL ACTIVITY OF THE EXTERNAL SPHINCTER DURING FILLING AND VOIDING