The lower urinary tract Flashcards
Where does urine travel once its been produced by the kidney?
- Tubular fluid travels through common collecting duct deep into inner medulla of kidney
- Tubular fluid exits collecting duct at tip of renal pyramid - also known as the renal papilla
- Minor and major calyces lead to renal pelvis
- Fluid deposition into renal pelvis stretches smooth muscle
- Distension triggers peristaltic contractions at hilus
- Fluid moves down ureter in pulses towards bladder for storage and controlled release
What is A site of drug-induced nephrotoxicity?
renal papilla
A site of drug-induced nephrotoxicity – “renal papillary necrosis”
Why is there no further modification to urine once it leaves the collecting duct?
Note: The is no further major modification of the tubular fluid in the lower urinary tract after leaving the kidney…
…the epithelium is impermeable to water and solutes
What is the structure of the ureters?
- Tubes approximately 30 cm long
- Mucosal layer: transitional epithelium
– 3-8 cells thick, impermeable to urine
What are the 3 layers of smooth muscle that make up ureters?
•Supported by layers of smooth muscle:
- inner: longitudinal muscle (L)
- outer: circular/spiral muscle (C)
- extra outer layer of longitudinal muscle
What is the function of ureters?
- Dilation of renal pelvis generates action potential from pacemaker cells in hilum
- Peristaltic waves generated – between 1 to 6 per minute…
Is the number of contractions of the ureter enhanced or inhibited by the autonomic nervous system?
- parasympathetic NS: enhanced
- sympathetic NS: inhibited
What state is this ureter in?
Lumen shown above in relaxed state with folds…
…these dilate out when peristaltic wave and pulse of urine passes through ureter
How do peristaltic contractions in the ureter work?
- Consist of successive waves of contractions and relaxation of longitudinal and circular smooth muscle:
- Longitudinal muscle contracts first followed by circular muscle relaxation (1)
- Longitudinal muscle then starts to relax allowing a bolus to form followed by circular muscle contraction which pushes against the bolus (2)
- Pattern of contraction is repeated resulting in slow but progressive movement of a pulse of urine along the ureter = PERISTALSIS
What is peristalsis in ureters also known as?
•…also known as “vermiculation” like what earthworms do
How do ureters enter the bladder?
- Ureters attach to posterior wall of urinary bladder
- Pass through bladder wall at oblique angle for 2-3 cm into bladder…
…ureteral openings are slit-like rather than rounded
- together this helps prevent backflow of urine up ureters during contraction of bladder
What is the bladder?
•A hollow muscular organ, consisting of fundus (body) and neck
What are the 2 layers of the bladder?
- Outer “Detrusor” Muscle layer - consists of longitudinal, circular/spiral muscles
- Inner Mucosal layer:
- transitional epithelium
- folded into “rugae” when bladder empty
- highly elastic – expands as bladder fills
What is the trigone?
•Triangular area bounded by openings of ureters and entrance to urethra…
…acts as a funnel to channel urine towards neck of bladder
What is the function of the bladder?
- Temporary storage of urine
- Up to 1 L capacity
- Stimulated to contract by parasympathetic NS
The urinary bladder is guarded by which two sphincters?
Internal urethral sphincter
- Loop of smooth muscle
- Convergence of detrusor muscle
- Under involuntary control
- Normal tone keeps neck of bladder and urethra free of urine
External uretheral sphincter
- Circular band of skeletal muscle where urethra passes through urogenital diaphragm
- Acts as a valve with resting muscle tone
- Under voluntary control
- Voluntary relaxation permits micturition
The _____ in both sexes marks the end of the urinary tract:
The urethra in both sexes marks the end of the urinary tract:
What are the features of the female urethra?
- Opens via external urethral orifice located between clitoris and vagina
- Shorter urethra in females - more susceptible to UTIs
- External sphincter not as well developed - incontinence following childbirth due to injury
What are the features of the male urethra?
- Urethra passes through prostrate gland and through uro-genital diaphragm and penis
- Longer urethra compared to females provide some protection against UTIs
Name 2 pathologies of the prostate
-Prostate gland enlarges in
50% of males >60 yrs
(along with hypertrophy of detrusor muscle)
- may require surgical or hormone treatment
- Prostate cancer – one of the commonest cancers affecting older men (death rate ~ 3%)
What are the 2 stages of emptying the bladder?
(1) Bladder progressively fills until pressure within bladder reaches a threshold level…
(2) …this elicits the “micturition reflex” which produces a conscious desire to urinate or eventual emptying of the bladder
What does Micturition mean?
Urination
The micturition reflex is an _________ reflex which is
(i) inhibited by what
(ii) facilitated by what
The micturition reflex is an autonomic reflex which is
(i) inhibited by higher centres in the brain and
(ii) facilitated by cortical centres in the brain:
What are the 3 steps in the micturition reflex?
Higher centres keep the micturition reflex under inhibition - prevents micturition by stimulating continual tonic contraction of the external sphincter
Cortical centres facilitate urination by initiating the micturition reflex and relaxing the external sphincter
Internal sphincter relaxes at the same time and urination occurs
What happens to micturition reflexes as the bladder fills?
- Bladder fills at 1 mL/min at normal levels of hydration
- As bladder fills, (intravesical) pressure increases
- Partially full bladder: contractions relax spontaneously after a few seconds
- Increasingly full bladder: contractions more frequent, intense and last longer
What are micturition contractions?
– these are periodic reflex contractions of short duration which occur above approximately 200 mL urine volume
What does this graph show?
Red solid line -
Red broken lines -
- Red solid line = normal intrinsic tone of bladder wall (detrusor muscle)
- Red broken lines = pressure peaks (micturition contractions or waves)
What sensations would you feel at each arrow?
Label the nerve
Which nerves inhibit and stimulate micturition?
Micturition is inhibited by activity in the hypogastric and pudendal nerves
It is facilitated by activity in the pelvic nerves
How does the guarding reflex promote continence?
During bladder filling:
- Progressive bladder distension stimulates the pelvic nerve via activation of stretch receptors in bladder wall and internal sphincter (1)
- Activation of the pelvic nerve leads to stimulation of the hypogastric nerve
- Hypogastric nerve stimulation causes:
(i) relaxation and reduced excitability of the bladder detrusor muscle (2)
(ii) constriction of the internal sphincter (3)
•Also, the external sphincter is held closed by pudendal nerve (4)
How does the micturition reflex coordinate the process of micturition?
- Stretch receptors in bladder continue to stimulate the pelvic nerve
- Stimulation of the pelvic nerve also causes:
(i) contraction of the detrusor muscle (1)
(ii) relaxation of the internal sphincter (2)
- Periodic reflex micturition contractions are also stimulated above 200 mL. These relax spontaneously after a few seconds
- These micturition contractions continue to be stimulated and relax but at > 300 mL bladder contractions begin to predominate
- Full bladder sensation conveyed to thalamus and then to cerebral cortex. Desire to urinate starts to increase…
- At appropriate time, voluntary relaxation of external sphincter occurs via pudendal nerve. Micturition occurs, aided by lowering of diaphragm, contraction of abdominal muscles and opening of internal sphincter
What is paraplegia?
•Paraplegia: complete severing of nerve inputs from cerebral cortex (1)
–Mictuiation reflexes return, but without cortical control
–Periodic but unannounced bladder emptying – “Automatic bladder”
What effect would partial spinal cord damage with loss of inhibitory descending signals have on urination?
•Partial spinal cord damage with loss of inhibitory descending signals (2)
–Frequent urination as excitatory impulses from cerebral cortex remain unopposed
–Known as “Uninhibited bladder”
What effect would crush injury of the dorsal route have on urination?
•Crush injury of dorsal roots (3)
–Afferent nerve destruction - micturition reflexes lost despite complete efferent system
–Bladder fills to capacity and overflows dropwise - “overflow incontinence”
Known as “Atonic bladder”
How is urination different in infants?
Infants lack voluntary control over urination until corticospinal connections are established
What are the 3 problems with the micturition reflex?
(1) Control of micturition can be lost due to:
- stroke injury, Alzheimer’s disease, problems affecting cerebral cortex or the hypothalamus (e.g. a brain tumour)
(2) Bladder sphincter muscles can lose tone (e.g. after pregnancy): leading to urinary incontinence
(3) Urinary retention may develop in males if enlarged prostate gland compresses the urethra and restricts urine flow
What are the functional classifications of micturition issues?
Failure to store urine = incontinence
Failure to empty bladder = retention
- Due to bladder dysfunction
- Due to problem with outlet of urine
What are the 3 main types of urinary incontinence?
•Loss of sensory nerves – due to injury
–Bladder fills to capacity
–No signals from stretch receptors in bladder
–Overflow incontinence occurs (Atonic bladder)
•Involuntary bladder contractions – due to injury
–Urge incontinence or increased frequency
•Heightened urge incontinence – sensitive bladder
–Spicy food (capsaicin)
–Caffeine/chocolate (xanthines)
–Citrus fruits (citric acid)
–Carbonated beverages (sugar, sweeteners)
–Excitement or even laughter :-D
_____ released by the Pelvic Nerve promotes micturation (bladder emptying)
ACh released by the Pelvic Nerve
promotes micturation (bladder emptying)
How does ACh promote incontinence?
Detrusor muscle contraction
Involuntary sphincter relaxation
How can anticholinergics be used to promote urinary continence and name an example?
Actions: - inhibit bladder contractions
- facilitates involuntary contraction of internal bladder sphincter
Examples: OXYBUTININ
What are the unwanted effects of anticholinergics?
Unwanted effects: Dry mouth, blurred vision, palpitations, drowsiness, facial flushing (Atropine-like)
How can tricyclic antidepressants be used to promote urinary continence?
Tricyclic antidepressants, e.g. IMIPRAMINE can be used at low doses for short-term treatment for nocturnal enuresis in children > 10 years but can have side effects, e.g. behaviour problems on withdrawal
Mechanisms: - anticholinergic and direct muscle relaxant effects on the bladder but also inhibits re-uptake of noradrenaline and serotonin increasing their levels
Name 3 other drugs which can promote urinary continence?
DULOXETINE also increases serotonin and noradrenaline levels – for moderate to severe stress urinary incontinence
DESMOPRESSIN (ADH analogue) – also useful in children for nocturnal bed-wetting
MIRABEGRON – selective b3 receptor agonist – useful for overactive bladder syndrome
Which bladder drug is possibly linked to dementia?
Oxybutynin
How is acute and chronic urinary retention treated?
•Acute urinary retention
–Catheterisation
–Surgery
•Chronic urinary retention
–Pharmacological intervention
Surgery
_____ released by the Hypogastrc Nerve
reduces micturation (promotes retention)
NA released by the Hypogastrc Nerve
reduces micturation (promotes retention)
Where is the site for urinary retention drugs action?
Name 2 other urinary retention drugs
Neostigmine, Pyridostigmine – inhibit breakdown of acetylcholine – also promote incontinence (bladder emptying)
Finasteride, Dutasteride are inhibitors of androgen synthesis (5α–reductase inhibitors) - useful for relieving urinary retention caused by prostate hyperplasia
