the lower urinary tract

Question 1

describe urine transport, storage and elimination? 2

Answer 1

• 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)

Question 2

describe the exit of urine out of the kidneys from the collecting duct? 4

Answer 2

• 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

Question 3

describe the exit of urine out of the kidneys into the renal pelvis and ureter? 5

Answer 3

• 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

Question 4

describe the structure of the ureters? 7

Answer 4

• 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

Question 5

describe the function of the ureters? 3

Answer 5

• 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

Question 6

describe the ureters and peristalsis? 4

Answer 6

• 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)

Question 7

describe the entrance of urine into the urinary bladder? 4

Answer 7

• 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

Question 8

describe the structure of the urinary bladder? 3

Answer 8

• 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

Question 9

what is the trigone?

Answer 9

• Triangular area bounded by openings or ureters

- entrance to the urethra acts as aa funnel to channel urine towards the neck of the bladder

Question 10

what is the function of the urinary bladder? 3

Answer 10

• Temporary storage of urine
• Up to 1L capacity
• Stimulated to contract by the parasympathetic NS

Question 11

describe the two sphincters that allow the exit of urine? 8

Answer 11

• 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

Question 12

describe the elimination of urine in females? 3

Answer 12

• 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

Question 13

describe the elimination of urine in males? 5

Answer 13

• 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

Question 14

describe micturition? 6

Answer 14

• 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

Question 15

describe the filling of the urinary bladder? 4

Answer 15

• 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

Question 16

describe the bladder and sphincter innervation? 4

Answer 16

• 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

Question 17

describe the guarding reflex? 5

Answer 17

• 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

Question 18

describe the micturition reflex? 6

Answer 18

• 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

Question 19

describe neural disruption of micturition? 4

Answer 19

• 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

Question 20

describe the problems with the micturition reflex? 3

Answer 20

• 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

Question 21

describe the urinary incontinence? 12

Answer 21

• 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

Question 22

what promotes micturition?

Answer 22

Ach

Question 23

describe the different drugs for urinary incontinence? 6

Answer 23

• anticholinergics
• tricyclic antidepressants
• desmopressin
• mirabegron
• duloxetine
• purified bovine collagen implants

Question 24

describe anticholinergics? 4

Answer 24

• 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
• .

Question 25

describe tricyclic antidepressants? 3

Answer 25

• Tricyclic antidepressants
• Can be used at low doses for short term treatment for nocturnal enuresis in children under 10
• Imipramine
• Behavioural problems on withdrawal

Question 26

describe desmopressin? 2

Answer 26

• Desmopressin (ADH analogue)

- For children with nocturnal bed wetting

Question 27

describe mirabcgron? 2

Answer 27

• mirabegron (selective beta3 receptor agonist)

- Overactive bladder syndrome

Question 28

describe duloxetine? 3

Answer 28

• Duloxetine
• Increases serotonin and noradrenaline levels
• Moderate to severe stress urinary incontinence

Question 29

what are the treatments for urinary retention? 2

Answer 29

• Acute= catheterisation, surgery

- Chronic= pharmacological intervention, surgery

Question 30

what reduces micturition?

Answer 30

noradrenaline

Question 31

what drugs are used in urinary retention? 2

Answer 31

• alpha adrenergic blocking drugs

- parasympathomimetic (choline ester)

Question 32

describe alpha adrenergic blocking drugs? 5

Answer 32

• 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

Question 33

describe parasympathomimetic (choline esters)? 4

Answer 33

• 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