Flashcards in Urination Deck (79)
How is urine transported from the kidneys to the bladder?
- Via ureters, peristalsis
- Locally regulated smooth muscle
- Low pressure in renal pelvis
- Also passive due to constant pressure from urine produced in kidney
The normal process of passive storage and active voiding of urine
- What happens to the urine after the kidneys
How is retrograde flow back up the ureters prevented?
- Ureters enter at oblique angle to bladder
- As bladder fills, closes off the ureters
- However, retrograde flow can occur while in ureters although is prevented by peristalsis and constant pressure from kidneys
What type of muscle is present in the bladder and urethra?
- Bladder: smooth muscle
- Urethra: smooth and skeletal muscle
What is the main function of sympathetic innervation to the bladder?
- Contracts internal sphincter preventing passage of urine
Where is the detrusor muscle?
- Network of smooth muscle fibres within bladder wall
What is the innervation to the detrusor muscle?
- Sympathetic and parasympathetic
Describe the internal urethal spincter
- Thickening of bladder muscularture
- Smooth muscle
- Sympathetic supply
Describe the external urethral sphincter
- Striated muscle fibres
- Under voluntary control of somatic nervous system
- Also used in storage
Describe the function of the sensory innervation to the bladder
- Stretch sensitive
- Nerve endings in bladder wall
- Indicate level of filling
What types of motor innervation are involved in micturition?
Describe the somatic innervation of micturition (outflow, synapse, what it innervates, function)
- Outflow S1-2 (pudendal nerve)
- No synapse
- Innervates urethral skeletal muscle (external urethral sphincter)
- Function is to retain urine
Describe the parasympathetic supply to the bladder (outflow, synapse, what it innervates, neurotransmitterfunction)
- Outflow S1-3 (pelvic plexus)
- Synapse: pelvic plexus or bladder wall
- Innervates detrusor muscle
- Excitatory, empty bladder
Describe the sympathetic supply to the detrusor muscle (outflow, synapse, neurotransmitter, receptor, function)
- Outflow: L1-4
- Synapse: caudal mesenteric ganglion (or occasionally bladder wall)
- Beta receptor
- Inhibitory, allow bladder filling
Describe the sympathetic supply to the internal sphincter muscle (outflow, synapse, neurotransmitter, receptor, function)
- Outflow: L1-4
- Synapse: caudal mesenteric ganglion
- Excitatory, retains urine and increases urethral tone
What is the significance of the sympathetic outflow to the bladder and internal sphincter?
- Same outflow
- Allows excitation of sphincter and relaxation of detrusor to allow urine storage
Describe the central connections involved in the innervation of the bladder
- Control at pons and cerebral cortex
- Some postulated control from cerebellum
- Some bladder function local (within spinal cord) , some cerebrocortical input
- Cerebral input allows control of all the processes
What is the detrusor reflex?
The reflex contraction of the detrusor muscle in order to expel urine
How is the detrusor reflex stimulated?
- Increase in bladder pressure during filling
- Detrusor stretched
- Once at certain level of stretch = reflex contraction to urinate
- Moderated in local reflex arc (no brain involvement)
- Contraction occurs against urethral sphincter tone
What is the micturition reflex?
The reflex ejection of urine from the bladder, via the urethra
- Combination of detrusor reflex with inhibition of sympathetic, and voluntary motor supply to the bladder and urethra
Describe the micturition reflex
- Voluntary or automatic
- Detrusor contraction (stimulated by increased pressure)
- Inhibits sympathetic and somatic supply to urethral sphincters
- Bladder contracts, sphincters open, urine voided
- Moderated at levels of sacral spinal and lumar spinal cord segments
What ensures complete voiding of the bladder?
- Positive feedback to destrusor
- Will be completed once initiated
Describe the automatic control of micturition
- Once bladder reaches particular pressure
- No control of detrusor muscle, only control over external urethral sphincter
- Reflex pathways, bladder empties spontaneously
Describe the voluntary control of micturition
- Suppression of autonomic reflexes to a degree, but overridden once reaches certain pressure
- Can initiate micturition at appropriate time
- Increase intra-abdominal pressure to increase bladder pressure and initiate detrusor and micturition reflex
What drugs increase sphincter tone?
What drugs decrease sphincter tone?
- Alpha-adrenergic blockers
- Skeletal muscle relaxants
What drugs increase detrusor tone?
Lak of voluntary control of excretory functions (can occur alongside normal micturition as is a lack of voluntary control, not dysfunction of micturition itself)
What do disorders of micturition refer to?
- Abnormalities of detrusor or sphincters
- Normal, increased or decreased activity