Physiology of Micturition Flashcards
What is the pathway of urine from the kidneys
urine flows from the kidneys to the ureters via peristaltic contraction of the smooth muscle from the ureters, they enter the bladder at an oblique angle to prevent reflux of urine, the urine then passes from the bladder into the urethra
What is the sphincters of urethra
The internal urethra spinchter
The external urethral spinchter
why isn’t the internal spinchter a true spinchter
Is located where the smooth muscle at the start of the urethra and acts as a spinchter when the smooth muscle is relaxed, and therefore passive contracts
Why is the external spinchter a true spinchter
is made up of skeletal muscle under voluntary somatic control
What is the arrangement of the bladder
bag of smooth muscle called detrusor muscle, arranged in a spiral, longitudinal and circular bundles
What is the characteristic shape of the preside -volume curve of the bladder
there is a long flat segment as the initial increments of urine enter the bladder and then suffer sharp rise as the micturition reflex is triggered
What is a cytometrogram mesure
A plot of bladder (intravesical) pressure against the depressant of fluid in the bladder
What is the normal daily urine production
varies between 750ml - 2500mls in temperate climates
What is the difference between urethral and ureter obstructions
Urethral obstruction - bilateral renal problems
where ureter obstruction causes unilateral renal problems
Overall how is mictruation controlled
By two controlling pathways learned to override spinal reflex urination
What is the type of motor innervation is involved in the spinal reflex of mictruition
Rich parasympathetic supply (via pelvic nerves)
Spare sympathetic supply (via hypogastric nerves)
Somatic motor neurones (via pudendal nerves)
What is the affect of parasympathetic innervation in motor control of mictrution
increase activity and contraction of detrusor muscle, causing an increase pressure within the bladder
What is the affect of sympathetic innervation in motor control of mictrution
inhibit bladder contraction and closes the internal urethral spinchters
How important is sympathetic supply to bladder function
not very important to bladder function (but cutting the hypogastric nerve causes frequency of micturition)
main function is to prevent the reflux of semen into the bladder during ejaculation
What is the affect of somatic motor neurone innervation in motor control of mictrution
innervate the skeletal muscle that forms the external urethral spinchter, keep the spinchter closed even against strong bladder contractions, (gives a tonic discharge)
What triggers sensory innervation in spinal reflex of mictrution
As the bladder fills, it becomes distended and the stretch receptors in the bladder wall are increasingly stimulated, until their output becomes great enough to cause bladder contraction
How does the sensory innervation cause the bladder to contract
Causes:
Excitation of parasympathetic outflow
Inhibition of sympathetic outflow
Inhibition of motor neurones to external spinchter (so tonic discharge inhibited)
send pathway to sensory cortex to give sensation of fullness
Why do babies wet themselves
the micturition reflex operates at this spinal reflex level because the higher brain connections have to be established to over ride it,
Thats why babies need to lean to potty train, to learn how to hold and delay their pee
What are the two controlling pathway learned to overside spinal reflex
Delay of urination
Voluntary initaition of urination
How is delay of urination achieved
Via the pontine storage area in the brain stem sending descending pathways that inhibit urination :
Inhibit parasympathetic
stimulate the somatic nerves to the eternal spinchters, thus over-ridding the input from the bladder stretch receptors
How is voluntary initiation of urination achieved
Via the pontine mictruition pathway that involves descending pathway, that stimulate urination:
stimulate parasympathetic
inhibit the somatic motor neurones thus summating with the stretch receptor effects
When does pontine mictruition area over ride pontine storage area
Happens when the bladder is full up the stretch receptors trigger the pontine centre as the need to pee is to much so over rides pontine storage area
What happens when individual is consciously ready to urinate
consciously initiates voiding
causing the bladder to contract and the outlet to relax
(the relaxation of the muscles of the pelvic floor may cause a sufficient downward tug on the detrusor muscle to initiate its contraction)
What can control the process of urination once initiated
perineal muscles and external spinchter can be contracted voluntarily, preventing urine flowing down the urethra or interrupting the flow once urination begins
What occurs after urination in males and females
female urethra empties by gravity
urine remaining in the male urethra is expelled by contraction of bulbocavernousus muslce
What are the abnormalities of mictrution due to neural lesion
interuption of afferent nerves
interuption of both afferent and efferent nerves
interruption of facilitatory and inhibitory descending pathways from the brain
What affect does neural lesions have on mictrution
the bladder contracts but the contractions are generally insufficient to empty the bladder completely
How do some paraplegic patients train themselves to initiate void
pinching or stroking their things causing a mild mass reflex
as after spinal section, afferent stimuli irradiate from one reflex to centre to another
so when a relatively minor noxious stimulus is applied to the skin, it may irradiate the autonomic centres to evoke bladder or rectal voiding
basically returning some measure of voluntary control by allowing them to induce an intentional mass reflex
What is the adult volume of urine needed to overside voluntary control and initiate spinal reflex
300-350mls
