the lower urinary tract Flashcards
1
Q
describe urine transport, storage and elimination? 2
A
- Passage of tubular fluid out of the kidneys and body via the urinary tract (ureters, urinary bladder urethra)
- Control of bladder function (normal function, problems, therapies)
2
Q
describe the exit of urine out of the kidneys from the collecting duct? 4
A
- Tubular fluid generated within the nephron by processes of filtration, reabsorption and secretion
- Final modifications of tubular fluid occurs in collecting duct under influence of antidiuretic hormone (ADH)
- Tubular fluid travels through common collecting duct deep into the inner medulla of the kidney
- Tubular fluid exits the collecting duct at the tip of the renal pyramid- also known as the renal papilla
3
Q
describe the exit of urine out of the kidneys into the renal pelvis and ureter? 5
A
- Minor and major calyces lead to the renal pelvis
- Fluid deposition into the renal pelvis stretches smooth muscle
- Distension triggers peristaltic contractions at hilus
- Fluid moves down the ureter in pulses towards the bladder for storage and controlled release
- There is no further major modification of the tubular fluid in the lower urinary tract after leaving the kidney as the epithelium is impermeable to water and solutes
4
Q
describe the structure of the ureters? 7
A
- Tubes around 30cm long
- Mucosal layer: transitional epithelium- 3-8 cell thick, impermeable to urine
- Supported by layers of smooth muscles:
- Inner: longitudinal muscle
- Outer: circular/ spiral muscle
- Extra outer layer of longitudinal muscle
- Lumen has folds in relaxed state which dilate out when peristaltic wave and pulse of urine passes through
5
Q
describe the function of the ureters? 3
A
- Dilation of renal pelvis generates action potential from pacemaker cells in hilum
- Peristaltic waves generated- between 1-6 per minute
- The number of contractions can be modulated by the nervous system: parasympathetic NS: enhanced, sympathetic NS: inhibited
6
Q
describe the ureters and peristalsis? 4
A
- Peristaltic contractions consist of successive waves of contractions and relaxation of longitudinal and circular smooth muscle
- Longitudinal muscle contracts first followed by circular muscle relaxation
- Longitudinal muscle then starts to relax allowing a bolus to form followed by circular muscle contraction which pushes against the bolus
- Pattern of contraction is repeated resulting in slow and progressive movement of a pulse of urine along the ureter- PERISTALSIS (also known as vermiculation)
7
Q
describe the entrance of urine into the urinary bladder? 4
A
- Ureters attach to the posterior wall of the urinary bladder
- Pass through the bladder wall at an oblique angle for 2-3 cm into the bladder
- Ureteral openings are slit-like rather than rounded
- This helps to prevent the backflow of urine up to the ureters during contraction of the bladder
8
Q
describe the structure of the urinary bladder? 3
A
- A hollow muscular organ, consisting of fundus (body) and neck
- Outer ‘detrusor’ muscle layer consists of longitudinal, circular/spiral muscles
- Inner muscular layer: transitional epithelium, folded into rugae when bladder is empty, highly elastic- expands as the bladder fills
9
Q
what is the trigone?
A
- Triangular area bounded by openings or ureters
- entrance to the urethra acts as aa funnel to channel urine towards the neck of the bladder
10
Q
what is the function of the urinary bladder? 3
A
- Temporary storage of urine
- Up to 1L capacity
- Stimulated to contract by the parasympathetic NS
11
Q
describe the two sphincters that allow the exit of urine? 8
A
- 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 urethral 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
12
Q
describe the elimination of urine in females? 3
A
- Opens via external urethral orifice locate between the clitoris and the vagina
- Shorter urethra in females- more susceptible to UTI
- External sphincter not as well developed- incontinence following childbirth due to injury
13
Q
describe the elimination of urine in males? 5
A
- Urethra passes through prostate gland and through uro-genital diaphragm and penis
- Longer than females- provides more protection against UTI
- Prostate glands enlarge in 50% of males >60 years (along with hypertrophy of detrusor muscle)
- May require surgical or hormone treatment
- Prostate cancer- one of the commons cancers affecting older men
14
Q
describe micturition? 6
A
- Bladder progressively fills until pressure within the bladder reaches a threshold level
- This elicits the micturition reflex which produces a conscious desire to urinate or eventual emptying of the bladder
- This reflex is an autonomic reflex which is inhibited by higher centres in the brain and facilitated by cortical centres in the brain
- 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
15
Q
describe the filling of the urinary bladder? 4
A
- 1mL/min
- As bladder fills, pressure increases
- Partially full bladder: contractions relax spontaneously after a few seconds
- Increasingly full bladder: contractions more frequent, intense and last longer
16
Q
describe the bladder and sphincter innervation? 4
A
- hypogastric nerve (sympathetic involuntary control)
- Pelvic nerve (parasympathetic involuntary control)
- Pudendal nerve (somatic voluntary control)
- Micturition is inhibited by activity in the hypogastric and pudendal nerves and is facilitated by pelvic nerve
17
Q
describe the guarding reflex? 5
A
- promotes continence
- Progressive bladder distension stimulates the pelvic nerve via activation of the stretch receptors in the bladder wall and internal sphincter
- Activation of the pelvic nerve leads to stimulation of the hypogastric nerve
- This causes relaxation and reduced excitability of the bladder detrusor muscle and constriction of the internal sphincter
- The external sphincter is also held closed by the pudendal nerve
18
Q
describe the micturition reflex? 6
A
- promotes the process of micturition
- Stretch receptors in the bladder continue to stimulate the pelvic nerve
- This causes contraction of the detrusor muscle and relaxation of the internal sphincter
- Periodic reflex micturition contractions are also stimulated above 200mL, these relax spontaneously after a few seconds and continue until 300mL where bladder contractions begin to predominate
- Full bladder sensation conveyed to thalamus and then to cerebral cortex which increases the desire to urinate
- At an appropriate time, the voluntary relaxation of the external sphincter via the pudendal nerve- micturition occurs aided by lowering of the diaphragm, contraction of the abdominal muscles and opening of internal sphincter
19
Q
describe neural disruption of micturition? 4
A
- Paraplegia: complete severing of nerve inputs from cerebral cortex- micturition reflex’s return but without cortial control, periodic but unannounced bladder emptying- automatic bladder
- Partial spinal cord damage with loss of inhibitory descending signals- frequent urination as excitory impulses from cerebral cortex remain unopposed- known as uninhibited bladder
- Crush injury of dorsal roots- afferent nerve destruction- micturition reflexes are lost despite the complex efferent system, so bladder fills to capacity and overflows dropwise- atonic bladder
- Infants lack voluntary control over urination until corticospinal connections are established
20
Q
describe the problems with the micturition reflex? 3
A
- Control of micturition can be lost due to stroke injury, Alzheimer’s disease, problems affecting cerebral cortex of the hypothalamus
- Bladder sphincter muscles can lose tone- leading to urinary incontinence
- Urinary retention may develop in males if enlarged prostate gland compresses the urethra and restricts urine flow
21
Q
describe the urinary incontinence? 12
A
- Loss of sensory nerves- due to injury:
- Bladder fills to capacity
- No signals from stretch receptors in the bladder
- Overflow incontinence occurs- atonic bladder
- .
- Involuntary bladder contractions- due to injury:
- Urge incontinence of increased frequency
- .
- Heightened urge incontinence- sensitive bladder:
- Spicy food
- Caffeine/chocolate
- Citrus fruits
- Carbonated beverages
- Excitement of laughter
22
Q
what promotes micturition?
A
Ach
23
Q
describe the different drugs for urinary incontinence? 6
A
- anticholinergics
- tricyclic antidepressants
- desmopressin
- mirabegron
- duloxetine
- purified bovine collagen implants
24
Q
describe anticholinergics? 4
A
- Anticholinergics (muscarinic Ach receptor antagonists)
- inhibit bladder contractions and facilitate involuntary contraction of internal bladder sphincter
- Oxybutynin
- Dry mouth, blurred vision, palpitations, drowsiness, facial flushing
- .
25
describe tricyclic antidepressants? 3
- Tricyclic antidepressants
- Can be used at low doses for short term treatment for nocturnal enuresis in children under 10
- Imipramine
- Behavioural problems on withdrawal
26
describe desmopressin? 2
- Desmopressin (ADH analogue)
| - For children with nocturnal bed wetting
27
describe mirabcgron? 2
- mirabegron (selective beta3 receptor agonist)
| - Overactive bladder syndrome
28
describe duloxetine? 3
- Duloxetine
- Increases serotonin and noradrenaline levels
- Moderate to severe stress urinary incontinence
29
what are the treatments for urinary retention? 2
- Acute= catheterisation, surgery
| - Chronic= pharmacological intervention, surgery
30
what reduces micturition?
noradrenaline
31
what drugs are used in urinary retention? 2
- alpha adrenergic blocking drugs
| - parasympathomimetic (choline ester)
32
describe alpha adrenergic blocking drugs? 5
- Antagonist action at alpha 1A adrenoceptor in bladder neck, relaxes smooth muscle at bladder neck and increases urine flow rate
- Alfuzosin
- Can reduce blood pressure so careful when dosing is required in patients already receiving antihypertensive treatments
- Should be avoided in patients with postural hypotension
- Hypotension, drowsiness, depression, headache, dry mouth, GI disturbances
33
describe parasympathomimetic (choline esters)? 4
- Bethanechol
- Agonist action at muscarinic Ach receptors, increases contraction of the bladder detrusor muscle- limited role in relief of urinary retention- now superseded by catheterisation
- Use with care of avoid using in patient with cardiac disorders- avoid cases involving GI ulceration, asthma, hypotension, epilepsy, Parkinsonism, pregnancy
- Nausea, vomiting, intestinal colic, bradycardic, blurred vision, sweating
