The Urinary Bladder Flashcards
What facilitates movement of urine into the bladder
Peristaltic contractions of the walls of the uereter
capacity of urinary bladder
600-800 mL
what is the urinary bladder
a muscular sac
What is the urinary bladder like when empty
collapsed and relaxed
Detrusor
main muscle of the bladder wall
composed of 3 layers of smooth muscle fibres, arranged differently in each layer (spiral, longitudinal, circular)
How is stored urine moved to the exterior
via urethra
sphincters at urethral opening
2 muscular rings that control the opening
Internal sphincter
Involuntary
smooth muscle- normally closed (passive contraction)
External sphincter
voluntary
skeletal muscle- normally closed (tonic contraction)
trigone muscle
bladder’s stretch receptors
What does neural regulation of bladder function involve (control of Micturition)
PNS and CNS
Involuntary spinal micturition reflex arc (MR)
present from birth
- stretch receptors in wall of urinary bladder
- afferent sensory nerve fibres convey impulses to the spinal cord
- Efferent PS nerve fibres convey impulses to detrusor and internal sphincter
Voluntary nervous control exercised by the CNS (+ and -)
cortex, cerebellum and micturition centre located in the pons (PMC- pontine micturition centre)
Develops in early childhood, full control at age 3-5
micturition
passing/ voiding of urine
ie peeing
neural pathways controlling micturition
- Urine fills bladder and stretches wall
- Stretch receptors send a signal via sensory afferent fibres to sacral portion of spinal cord
- Parasympathetic efferent fibres stimulate detrusor muscle to contract and internal urethral sphincter to relax, causing micturition
- Interneurons in spinal cord communicate the ‘full bladder’ signal to micturition center in the pons
- Cerebral cortex facilitates micturition by allowing external urethral sphincter to relax, urine voided
contraction of detrusor muscle
squeezes on the urine in the bladder lumen to produce urination
What happens when the bladder is filling
parasympathetic input to detrusor muscle is minimal, so the muscle is relaxed. When the detrusor muscle is relaxed, the internal sphincter is passively closed due to how the layers of muscle are arranged.
Also there is strong sympathetic input to the internal urethral sphincter and strong input by somatic motor neurones to the external urethral sphincter.
Hence detrusor relaxed and both sphincters shut
detrusor type of innervation
parasympathetic (causes contraction)
internal sphincter type
sympathetic (causes contraction)
External sphincter type
Somatic motor (causes contraction)
During filling which muscles stimulated
detrusor inhibited
internal and external sphincter stimulated
During micurition which muscles stimulated
only detrusor
Incontinence
Involuntary release of urine
Male urethra surrounded by
penis
sphincters play a role in
holding urine in bladder
What is found between sphincters in males
prostate gland-activates sperm
Female system
doesn’t have internal sphincter
shorter urethra
More likely change of UTI
where is micturition centre
pons
stretching of bladder causes
incr firing of pelvic nerve- fast signals to spinal cord, then to micturition centre. Sends impulses to cause contraction of detrusor
