Micturition Flashcards
- What is the definition of micturition
the periodic discharge of urine from the bladder through the urethra
- what is micturition intiated by?
it is initiated by voluntary relaxation of the sphincter muscle below the bladder
- What maintains micturition
maintained by reflex contraction of the muscles of the bladder
where does urine produced by the kidneys drain into
Drains into urinary bladder via ureters on both sides of body
how much volume does the adult bladder hold?
500ml
what does the internal urethral sphincter guard?
internal urethral sphincter guards outlet to urethra
what is the external urethral sphincter responsible for?
External sphincter (aka external urethral sphincter) responsible for voluntary control
why is female urethra shorter than male urethra
Male urethra travels through penile shaft therefore female urethra is shorter
- What type of organ is the Urinary bladder
hollow organ
- What forms the BODY of the urinary bladder
– formed by detrusor muscle
- What forms the NECK of the urinary bladder?
trigone in its posterior aspect
- What guards the emptying of the bladder?
internal and external sphincters
- What type of muscle is the internal sphincter made of
completely involuntary ( smooth muscle)
- What type of muscle is the external sphincter made of
voluntary. ( skeletal muscle)
- What muscle is responsible for emptying of the bladder
Detrusor muscle
- What is the advantage of the urinary tract being made up of stratified Squamous epithelium
It allows stretching of the bladder
- What nerve fibres supply the urinary bladder and the internal sphincter
supplied by sympathetic and
parasympathetic nerve fibres
- What vertebral levels is the sympathetic supply found and what is the nerve called
- L1/L2
- Hypogastric nerve
- What nerve fibres supply the external sphincter
supplied by somatic nerve fibres
called the Pudendal nerve
what vertebral levels is the sympathetic supply found and what is the nerve called
- S2,S3,S4
- pelvic nerve
- What do sensory fibres in the pelvic nerve do?
carry impulse from the stretch receptors present on the wall of urinary bladder and urethra.
- What does the stimulation of the hypogastric nerve cause?
Relaxation of detrusor muscle and
Constriction of internal sphincter which causes filling of the bladder
- What is another name for the hypogastric nerve
nerve of filling.
- What does stimulation of the pelvic nerve cause
Contraction of detrusor muscle
And relaxation of internal sphincter resulting in the emptying of the bladder
- What is another name for the pelvic nerve
the nerve of micturition.
- What state does the pudendal nerve keep the external sphincter in?
constricted state.
- What happens when the pelvic nerve is blocked
When this nerve is blocked, external sphincter relaxes however can be controlled voluntarily
- What type of smooth muscle does the wall of the ureter contain
spiral, longitudinal and circular bundles of smooth muscle.
- How often do peristaltic contractions occur
occur 1 to 5 times per minute
- When does the first sense of filling occurs
When volume of urine reaches nearly 150ml
- At how many ml of urine does a marked sense of filling occur at?
400ml
- Where are spinal centres of micturition located
Located in sacral and lumbar segments
- What are spinal centres of micturition controlled by
higher centres of brain.
- Where is the facilitatory centre of the higher centres of micturition located
Pontine region, Posterior hypothalamus.
where is the inhibitory centre of the higher centres of micturition located?
mid brain
outline the 10 step process of the micturition reflex
- volume of urine in the bladder reaches near 400ml and intra-vesical pressure increases
- Bladder wall stretches and stretch receptors on the bladder wall are activated
- Sensory signal is given to spinal centres through sensory fibres of parasympathetic (pelvic) nerve and a reflex arc is produced in spinal cord.
- Motor signal is given to urinary bladder through motor fibres of parasympathetic nerve (pelvic nerve), causing detrusor muscle contracts and internal sphincter relaxed.
- Urine passes down into proximal urethra and an afferent impulse is given to the spinal cord
- Afferent impulse reaches the higher centres in brain via the spinethalamic tracts. If the signal from brain stem is to micturate, impulse created from spinal centre block pudendal nerve.
- at the same time the sympathetic efferent are inhibited
- external sphincter relaxes and micturition occurs
- If the signal from brain stem is not to micturate, sympathetic efferents are stimulated and as a result, detrusor expands and internal sphincter constricts
- External sphincter remains constricted. so, urine continues to accumulate in bladder.
- What are 3 types of bladder abnormalities
- Deafferentation
- Denervation
- Absence of regulation by higher centres
- How can deafferentation occur?
Due to injury to afferent sensory nerve fibres
- What are features of deafferentation
- Individual is unaware of distension of bladder
- Voluntary micturition is possible
- If such person fails to micturate at reg intervals, bladder overflows + causes dribbling of urine overflow incontinence.
- Why does bladder wall remain flaccid?
- Because no afferent supply
- What is automatic bladder?
bladder empties automatically and the sphincter relaxes passively by increased intra-vesical pressure seen in Tabes dorsalis ( syphilis)-degeneration of dorsal nerve roots (tabetic bladder).
- What is denervation?
injury to both afferent and efferent nerves.
- What are features of denervation
- Voluntary micturition is completely lost.
- Nerve supply completely lost, so it’s called isolated bladder /decentralized bladder.
- What is denervation also called
called flaccid neurogenic bladder/ hypoactive neurogenic bladder.
what are the 2 higher centres that can regulate micturition
- Lesion of superior frontal gyrus
- Lesion in midbrain
what happens to micturition in there is a lesion of superior frontal gyrus
reduces desire to urinate and difficulty in stopping micturition once it has started
how do paraplegia patients initiate micturition
they pinch or stroke their thighs which provokes a mild mass reflex
what happens to micturition if there is a lesion in the midbrain
causes continuous excitation of spinal micturition centres, resulting in frequent and uncontrollable micturition
