T3 L12 Function of lower urinary tract Flashcards
What structures are involved in the passage of tubular fluid out of the kidneys & body via the urinary tract?
Ureters
Urinary bladder
Urethra
What processes are used to generate tubular fluid within the nephron?
Filtration
Reabsorption
Secretion
Where does the tubular fluid exit the collecting duct at?
At the tip of the renal pyramid (pelvis)
What leads to the renal pelvis?
Minor & major calyxes
Wha triggers peristaltic contractions at the hilus?
Distention
Pacemaker cells are activated by stretch
Describe the structure of the ureters
30cm long tubes
Mucosal layer
Supported by layers of smooth muscle
Lumen has folds in the relaxed state which dilate out when the peristaltic wave & pulse of urine pass through ureter
Describe the mucosal layer of the ureters
Transitional epithelium
3-8 cells thick
Impermeable to urine
What layers of smooth muscle are present in the ureter?
Inner: longitudinal muscles
Outer: circular/spiral muscles
Extra outer layer of longitudinal muscle
What is the function of the ureters?
Dilation of renal pelvis generates an action potential from the pacemaker cells in the hilum
Peristaltic waves are generated at 1-6 per minute
What modulates the rate of peristaltic contractions?
Parasympathetic nervous system enhances 5-6 waves per min
Sympathetic nervous system inhibits to slow waves in times of stress
What are peristaltic contractions?
Similar to those in GI tract 1) Longitudinal muscle contracts 2) Circular muscle relaxes 3) Longitudinal muscle relaxes 4) Bolus can form 5) Circular muscle contraction 6) Pushes against bolus Pattern of contraction results in slow, progressive movement of a pulse of urine
Describe the entrance of ureters into the bladder
Ureters attach to posterior wall & pass through at an oblique angle for 2-3 cm into bladder
Ureter openings are slit like
What is the structure of the urinary bladder
Hollow muscular organ with funds & neck
Outer detrusor muscle layer
Inner mucosal layer
Trigone
What is the trigone?
Triangular sheet of muscle bounded by the openings of the ureters & entrance to urethra
Acts as a funnel
Describe the inner mucosal layer of the urinary bladder
Transitional epithelium
Folded into rugae when bladder is empty
Highly elastic
What is the function of the urinary bladder?
Temporary store of urine - holds up to 1L
Stimulated to contract by parasympathetic nervous system
What are the 2 sphincters controlling the exit of urine?
Internal urethral sphincter
External urethral sphincter
What is the internal urethral sphincter?
Loop of smooth muscle Convergence of detrusor muscle Under involuntary control Normal tone keeps neck of bladder &. urethra free from urine Impacted in incontinence
What is the external urethral sphincter?
Circular band of skeletal muscle where urethra passes through urogenital diaphragm
Acts as a valve with resting muscle control
Under voluntary control
Voluntary relaxation permits micturition
Damaged in childbirth
Describe the urethra in females
Opens via external urethral orifice between clitoris & vagina
Shorter urethra - higher risk of UTIs
External sphincter is not as well developed
Describe the urethra in males
Passes through prostate gland & through urogenital diaphragm & penis
Longer urethra
Describe prostate gland enlargement
Occurs in 50% of males above 60
Occurs along with hypertrophy of detrusor muscle
May require surgical or hormonal treatment
What are the 2 stages in emptying the bladder?
1) Bladder fills until pressure within bladder reaches a threshold level
2) Elicits micturition reflex which produces a conscious desire to urinate
What inhibits the autonomic reflex?
Higher centres in the brain inhibit the micturition reflex
Prevents micturition be stimulating continual tonic contraction of external sphincter
What facilitates the autonomic reflex?
Cortical centres in the brain facilitate urination by initiating micturition reflex & relaxing external sphincter.
Internal sphincter relaxes at same time & urination occurs
When do periodic reflex contractions of a short duration occur?
Above 200ml or urine
In a partially full bladder the contractions spontaneously relax after a few seconds
Increasingly full bladder = contractions more frequent, intense & last longer.
What nerves inhibit micturition?
Hypogastric
Pudenal nerve
What nerves facilitate micturition?
Pelvic nerve
What is the guarding reflex?
Promotes continence
During bladder filling there is progressive bladder distention which stimulates the pelvic nerve via activation of stretch receptors in bladder wall & internal sphincter
Activation of pelvic nerve stimulates hypogastric nerve
External sphincter is held closed by the pudenal nerve
What does stimulation of the hypogastric nerve cause?
Relaxation & reduced excitability of bladder detrusor muscle
Constriction of internal sphincter
What is the micturition reflex?
Bladder continues to fill with urine
Stretch receptors continue to stimulate pelvic nerve
Periodic reflex micturition contractions are stimulated above 200ml
Full bladder sensation is conveyed to thalamus –> cerebral cortex –> desire to urinate increases
What does stimulation of the pelvic nerve cause?
Contraction of detrusor muscle
Relaxation of internal sphincter
What aids micturition?
Lowering of diaphragm
Contraction of abdominal muscles
Opening of internal sphincter
What is paraplegia?
Complete severing of nerve inputs from cerebral cortex
Micturition reflexes return without cortical control
Periodic unannounced bladder emptying = automatic bladder
What happens with partial spinal cord damage with loss of inhibitory descending damage?
Frequent urination as excitatory impulse from cerebral cortex remain unopposed
Uninhibited bladder
What happens if there is a crush injury of the dorsal roots?
Afferent nerve destruction –> micturition reflexes lost despite a complete efferent system
Bladder fills to capacity & overflows dropwise leading to overflow incontinence
Atonic bladder
Why do infants lack voluntary control of urination?
The corticospinal connections aren’t established
What can cause control of the micturition reflex to be lost?
Stroke injury
Alzheimer’s disease
Problems affecting cerebral cortex or hypothalamus such as a brain tumour
What happens in urinary retention?
Compresses urethra & restricts urine flow
Bladder fills to capacity & there are no stretch receptors in the bladder leading to overflow incontinence
What is incontinence?
Failure to store urine
What is retention?
Failure to empty bladder
Due to bladder dysfunction or a problem with outlet of urine
What can heighten the incontinence urge?
Spicy foods Caffeine / chocolate Citrus fruits Carbonated beverages Excitement or laughter
How does acetylcholine lead to urinary incontinence?
Leads to detrusor muscle contraction & involuntary sphincter relaation
What is the action of anticholinergics?
Inhibit bladder contractions to relax bladder
Facilitate involuntary contractions of internal bladder sphincter
What is an example of an anticholinergic?
Oxybutinin
What are the unwanted effects of anticholinergics?
Dry mouth Blurred vision Palpitations Drowsiness Facial flushing
What is imipramine?
Tricyclic antidepressant
Used in low doses for the short-term treatment of nocturnal enuresis for children above 10.
Can have side effects on withdrawal
What is the mechanism of anticholinergics?
Anticholinergic & direct muscle relaxant effects on bladder
Inhibits re-uptake of noradrenaline & serotonin which increases their levels
What is duloxetine?
Tricyclic antidepressant
Increases serotonin & noradrenaline levels
Use for moderate to severe stress urinary incontinence
What is desmopressin?
ADH analogue
Useful in children for nocturnal bedwetting
What is mirabegron?
Selective beta 3-receptor agonist
Useful for overactive bladder syndrome
Works through sympathetic nervous system
What are some examples of tricyclic antidepressants?
Imipramine
Duloxetine
Desmopressin
Mirabegron
When are purified bovine collagen implants used?
Useful for urinary incontinence
Surgical procedure
How can acute urinary retention be treated?
Catheterisation
Surgery
How can chronic urinary retention be treated?
Pharmacological intervention
Surgery
What is the action of alpha adrenergic blocking drugs?
Antagonist effect at alpha 1A adrenoreceptor in neck of bladder
Relaxes smooth muscle at neck of bladder to increase urine flow rate
What cautions are indicated for alpha adrenergic blocking drugs?
Can reduce blood pressure so be careful in patients receiving antihypertensives
Avoid in patients with postural hypotension
What are the unwanted effects of alpha adrenergic blocking drugs?
Hypotension Drowsiness Depression Headache Dry mouth Gi disturbances
What is the action of parasympathomimetics (choline esters)?
Agonist action at muscarininc acetylcholine receptors
Increase contraction of bladder detrusor muscle
Limited role in the relief of urinary retention
What is an example of a parasympathomimetic?
Bethanechol
What cautions are there for the use of parasympathomimetics?
Those with cardiac disorders such as arrhythmias GI ulceration asthma Hypotension Epilepsy Parkinsons Pregnancy
What are the unwanted effects of parasympathomimetics?
Nausea Vomiting Intestinal colic Bradycardia Blurred vision Sweating
