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Theme 3: The Excretory System and Renal Function > The lower urinary tract > Flashcards

The lower urinary tract Flashcards

1
Q

Passage of tubular fluid out of the kidneys and body via the urinary tract

A

Ureters

Urinary bladder

Urethra

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2
Q

Exit of urine out of the kidneys 1: out of the end of the collecting duct

A

Tubular fluid generated within the nephron by filtration, reabsorption, secretion

Final modification in collecting duct under influence of ADH

Fluid travels through common collecting duct deep into inner medulla

Fluid exits collecting duct at tip of renal pyramid (renal papilla)

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3
Q

Exit of urine out of the kidneys 2: into the renal pelvis and ureter

A

Minor and major calyces lead to renal pelvis

Fluid deposition into renal pelvis stretches smooth muscle

Distension triggers peristaltic contraction at hilus

Fluid moves down ureter in pulses towards bladder for storage and controlled release

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4
Q

Structure of ureter

A

Tubes approximately 30cm long

Mucosal layer: transitional epithelium
- 3-8 cells thick, impermeable to urine

Supported by laters of smooth muscle

  • inner: longitudinal
  • outer: circular/ spiral
  • extra outer layer of longitudinal
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5
Q

Function of ureters

A

Dilation of renal pelvis generates action potential from pacemaker cells in hilum

Peristaltic waves generated between 1 to 6 per minute

Number of contractions modulated by nervous system

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6
Q

Ureters and peristalsis

A

Consist of successive waves of contractions and relaxation of longitudinal and circular

L contracts first followed by C relaxation

L starts to relax allowing bolus to form followed by C contraction which pushes against the bolus

Pattern repeated resulting in slow progressive movement of a pulse of urine along the ureter

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7
Q

The urinary bladder: entrance of urine

A

Ureters attach to posterior wall of urinary bladder

Pass through bladder wall at oblique angle for 2-3cm into bladder

Ureter opening are slit like

This helps prevent backflow of urine up ureters during contraction of bladder

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8
Q

Structure of the bladder

A

A hollow muscular organ, consisting of fundus and neck

Outer ‘detrusor’ muscle layer
- consists of longitudinal and circular/ spinal muscle

Inner mucosal layer

  • transitional epithelium
  • folded into ‘rugae’ when bladder empty
  • highly elastic- expands as bladder fills
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9
Q

The trigone

A

Triangular area bounded by openings of ureters and entrance to urethra

Acts as funnel to channel urine towards neck of bladder

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10
Q

Function of bladder

A

Temporary storage of urine

Up to 1L capacity

Stimulated to contract by parasympathetic nervous system

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11
Q

Internal urethral sphincter

A

Loop of smooth muscle

Convergence of detrusor muscle

Under involuntary control

Normal tone keeps neck of bladder and urethra free of urine

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12
Q

External urethral sphincter

A

Circular band of skeletal muscle where urethra passes through urogenic diaphragm

Acts as a valve with resting muscle tone

Under voluntary control

Voluntary relaxation permits micturition

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13
Q

Elimination of urine: females

A

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)

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14
Q

Elimination of urine: males

A

Urethra passes through prostate gland and through uro-genital diaphragm and penis

Longer than females provides some protection to UTIs

Prostate gland enlarges in 50% males >60 (may require surgical or hormone treatment)

Prostate cancer - one of the most common in older men

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15
Q

Micturition

A

Two stages

  1. bladder progressively fills until pressure within bladder reaches a threshold level
  2. This elicits the micturition reflex which produces conscious desire to urinate
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16
Q

Inhibition of micturition by higher centres in the brain

A

Higher centres keep the micturition reflex under inhibition

Prevents micturition by stimulating continual tonic contraction of external sphincter

17
Q

Facilitation of micturition by cortical centres in the brain

A

Cortical centres facilitate urination by initiating the micturition reflex

Relaxes external sphincter

18
Q

Filling the urinary bladder

A

Bladder fills at 1ml/min at normal hydration

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

19
Q

Bladder and sphincter innervation

A

Hypogastric nerve

  • sympathetic
  • involuntary control
  • L2

Pelvic nerve

  • parasympathetic
  • involuntary control
  • S2,3

Pudenal nerve

  • somatic
  • voluntary control
  • S2,3
20
Q

The guarding reflex promotes continence: during bladder filling

A

Distension of bladder stimulates pelvic nerve via stretch receptors in bladder wall and internal sphincter

Activation of pelvic nerve leads to stimulation of hypogastric nerve

Hypogastric nerve causes

  • relaxation and reduced excitability of bladder detrusor muscle
  • constriction of internal sphincter

External sphincter held closed by pudendal nerve

21
Q

As bladder continues to fill with urine

A

Stretch receptors continue to stimulate to pelvic nerve

Stimulation of pelvic nerve also causes

  • contraction of detrusor muscle
  • relaxation of the internal sphincter

Periodic reflex micturition contractions also stimulated above 200ml

Micturition contractions continue to be stimulated and relax but at >300ml bladder contractions begin to predominate

Full bladder sensation conserved to thalamus and then to cerebral cortex- desire to urinate increases

Voluntary relaxation of external sphincter via pudendal nerve

Micturition occurs

22
Q

Paraplegia

A

Complete severing of nerve inputs from cerebral cortex

  • micturition reflexes return, but without cortical control
  • periodic but unannounced bladder emptying
  • ‘automatic bladder’
23
Q

Partial spinal cord damage with loss of inhibitory descending signals

A

Frequent urination as excitatory impulses from cerebral cortex remain unopposed

Known as ‘uninhibited bladder’

24
Q

Crush injury of dorsal roouts

A

Afferent nerve destruction- micturition reflexes lost despite complete efferent system

Bladder fills to capacity and overflows dropwise- ‘overflow incontinence’

Known as ‘atonic bladder’

25
Q

Problems with micturition reflex

A
  1. Control of micturition can be lost ( stroke injury, Alzheimer’s, cerebral cortex or hypothalamus problems)
  2. Bladder sphincter muscle lose tone (urinary incontinence)
  3. Urinary retention may develop in males if enlarged prostate gland compresses the urethra and restricts urine flow
26
Q

Functional classifications

A

Failure to store urine- incontinence

Failure to empty- renetion

27
Q

Urinary incontinence

A

Loss of sensory neurones (due to injury)

  • bladder fills to capacity
  • no signals from stretch receptors in bladder
  • overflow incontinence occurs

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)
28
Q

Anticholinergic actions

A

Actions: inhibit bladder contractions

Facilitate involuntary contractions of internal bladder sphincter

e.g. oxybutinin

Unwanted effects

  • dry mouth
  • blurred vision
  • palipitations
  • drowsiness
  • fascial flushin
29
Q

Tricyclic antidepressants

A

Used at low doses short term for nocturnal enuresis in children >10

Muscle relaxant effects on bladder, inhibits re-uptake of noradrenaline and serotonin

Can cause behavioural problems

e.g. impramine

30
Q

Urinary retention

A

Acute urinary retention

  • catheterisation
  • surgery

Chronic urinary retention

  • pharmacological intervention
  • surgery
31
Q

a- adrenergic blocking drugs used in urinary retention

A

Actions

  • antagonist action a1A adrenoreceptors in bladder neck
  • relaxes smooth muscle at bladder neck and increases urine flow

Cautions

  • can reduce blood pressure
  • avoided in patients with postural hypotension

Unwanted effects

  • hypotension
  • drowsiness
  • dpression
  • headache
  • dry mouth
  • GI disturbances
32
Q

Parasympathomimetics (choline esters)

A

Actions

  • agonist action at muscarinic ACh receptors
  • increased contractions of the bladder detrusor muscle

Cautions

  • avoid in patients with cardiac disorders
  • avoid in GI ulceration, asthma, hypotension, epilepsy, parkinsonism, pregnancy

Unwanted effects

  • nausea and vomiting
  • intestinal colic
  • bradycardia
  • blurred vision
  • sweating

e.g. bethanecol

Theme 3: The Excretory System and Renal Function (13 decks)

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