Micturition Flashcards
Type of muscle of the bladder
Smooth muscle (detrusor muscle)
Type of epithelial lining
Transitional epithelium
Shape of pressure-volume curve of bladder
Long flat segment as the initial increments of urine enter the bladder 》a sudden sharp rise as the micturition reflex is triggered.
Normal daily urine production
750ml-2500mls
What volume of urine gives one the first urge to void
100ml
What volume of urine gives one the urgent urge to void
> 450ml
Parasympatheitc, sympathetic and somatic motor innervation of bladder
Parasympatheitc = pelvic nerves S2-S4 Sympathetic = hypogastric nerves L1-L3 Somatic = Pudenal nerves S2-4
Action of Parasympathetic innervation of bladder
Increases contraction of detrusor muscle 》pressure inside bladder
P = piss
Action of Sympathetic innervation of bladder
Inhibit bladder contraction
Close internal “sphincter”
Main function is to prevent reflux of semen into bladder during ejaculation
S = semen
Result of cutting hypogastric nerves
Increased frequency of micturition
Action of Somatic innervation for bladder
Innervates skeletal muscle that forms the external urethral sphincter
Can keep sphincter closed even under strong bladder contractions
What’s responsible for the sensory innervation of bladder
Stretch receptors in the bladder wall
Action of stretch receptors
Bladder fills 》increased discharge of afferent nerves to spinal cord 》excitation of parasympathetic and inhibition of sympathetic outflow 》inhibition of somatic motoneurones 》pathways to sensory cortex => sensation of fullness
What is micturition essentially
A spinal reflex, that may or may not be influenced by higher centres
Volume of urine needed to initiate spinal reflex
~300-350mls
How is delay achieved and what parts of the body are involved in it
By descending pathways from many brain centres, including cortex and brainstem
They inhibit parasympatheitc and stimulate somatic nerves of external sphincter
How is voluntary micturition achieved and what is involved in it
Achieved by descending pathways
Which stimulate parasympathetic and inhibit somatic innervation of external sphincter
After urination how is urine expelled from the urethra in males and females
Females = by gravity Males = contraction of the Bulbocavernosus muscle
3 types of micturition abnormalities due to neural lesions and their effect
Interruption of afferent nerves
Interruption of both afferent and efferent nerves
Interruption of facilitatory and inhibitory descending pathways from the brain.
Bladder contracts but the contractions are insufficient to empty bladder completely 》urine is left in the bladder
How do some paraplegic initiate voluntary voiding and how does this work
Stroke or pinch their thigh 》mild mass reflex
After spinal section, afferent stimuli irradiate from one reflex centre to another.
When a minor noxious stimulus is applied to the skin it may irradiate to autonomic centres, evoking voiding.
