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Physiology: Kidney > Micturition > Flashcards

Micturition Flashcards

1
Q

What is micturition?

A

The act of urination (emptying the bladder)

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2
Q

Basic process

A

Urine made in kidneys (1 ml.min-1)
Urine stored in the bladder
Urine released from bladder

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3
Q

Kidney to bladder

A

Urine from al collecting ducts of al nephrons
Emptying into the renal pelvis
Urine enters ureter

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4
Q

Peristaltic waves

A

~1-6 contractions/min

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5
Q

What is the pressure in the ureters

A

10-20 mmHg

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6
Q

What control are ureters under?

A

Myogenic in origin not under CNS

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7
Q

Kidney stones

A

Crystals that separate from the urine within the urinary tract
Normal urine contains citrate to prevent this

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8
Q

What is present in most kidney stones?

A

Calcium (80%) as calcium oxalate or less often as calcium phosphate.
Then uric acid (<10%)
Struvite (<10%)
Cystine (<5%)

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9
Q

What causes kidney stones?

A

Poor urine output/ obstruction, altered urinary pH, infections, excess dietary intake, low concentration of inhibitors

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10
Q

Whos is more likely to have kidney stones

A

Men due to testosterone

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11
Q

Symptoms of kidney stones

A

Dysuria (painful urination)

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12
Q

How much can the bladder store?

A

400 ml w/o much increase in pressure - spherical structure

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13
Q

Female bladder

A

Short urethra - only carries urine

External sphincter poorly developed - more prone to incontinence particularly after childbirth

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14
Q

Male bladder

A

Carries urine and semen

Urine elimination aided by contraction of bulbocavernosus muscle in the penis

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15
Q

Summary of bladder

A

Lining - transitional epithelium
Bladder muscle - detrusor
Impermeable to salt & water
Permeable to lipophilic molecules

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16
Q

Internal sphincter

A

Smooth muscle, involuntary control

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17
Q

External sphincter

A

Striated muscle, voluntary control

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18
Q

Bladder innervation 1

A

Neural circuits in brain & SC coordinate activity of bladder & sphincters circuits act as an on-off switch to alternate between storage & elimination

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19
Q

Bladder innervation 2

A

3 peripheral nerves

  • Parasympathetic (pelvic nerve)
  • Sympathetic (hypogastric nerves)
  • The somatic nervous system (pudendal nerve)
20
Q

Bladder innervation 3

A
  • Sensory: gives sensation (awareness) of fullness and also pain from disease
  • Motor: causes contraction and relaxation of the detrusor muscle and external sphincter to control micturition
21
Q

What do ACh and ATP do the Detrusor

A

Causes detrusor to contract

22
Q

What does NA do the detrusor

A

Inhibits transmission at parasympathetic ganglia - indirectly causes detrusor to relax
Also directly via B-Rs (also in trigone area) causes detrusor to relax

23
Q

What does NO and ACh do the internal sphincter?

A

Relaxes

24
Q

What does Noradrenaline (NA) do to the internal sphincter?

A

Contracts

25
Q

What does the ACh to the internal sphincter?

A

Tonic activity holds external sphincter closed

26
Q

Parasympathetic neurons

A

Contract detrusor - via ACh (muscarinic) + ATP (Purigenic R)
-Relax internal sphincter - via NO (cGMP) & ACh (nictotinic)
Encourage micturition

27
Q

Sympathetic neurons

A

RELAX detrusor- Indirectly via NA (a-R) & directly via NA (beta receptors)
CONTRACTS internal sphincter - NA (alpha R)
Inhibits Micturition

28
Q

Somatic neuron

A

Contract external sphincter - ACh (nicotinic R)

Inhibit micturition

29
Q

Afferent innervation

A

The main afferent pathway is via pelvic nerve (parasympathetic):
Small myelinated A/delta fibers - micturition reflex
Stretch receptor - signal wall tension
Volume receptors - signal bladder filling

30
Q

A fibres

A

Sense tension in detrusor
Filling of bladder
Detrusor contraction
BLADDER FULLNESS, discomfort

31
Q

C fibres

A

Respond to damage & inflammatory mediators

Unmeylinated C fibres - endings in/near epithelium

32
Q

What happens when the bladder is empty?

A

Sphincters closed

Bladder pressure is low

33
Q

What happens when urine arrives?

A

Detrusor relaxes progressively
Little increase in pressure
Sphincters still closed

34
Q

How is micturition modified?

A

Voluntary controlled
The act is an autonomic reflex
However, is inhibited by higher centers in the brain

35
Q

What do disease and injury do to the nervous system?

A

Disrupts voluntary control of micturition

  • Bladder hyperactivity & urge incontinence
  • Stress incontinence
36
Q

Retained urine

A

Clinical infection UTI

37
Q

Bladder infection

A

Called Cystitis or a bladder infection

38
Q

Kidney infection

A

One or both kidney - called pyelonephritis

39
Q

Ureter infection

A

Rarely the site of infection

40
Q

Urethra infection

A

Urethritis

41
Q

How is micturition aided?

A

Reflex contraction of peri-urethral striated muscles also helps compress the urethra

42
Q

How can higher centers modify micturition?

A

Contract external sphincter & levator muscle consiously

43
Q

What are some risk factors of UTIs

A 
Diabetes 
Long term catheter 
Pregnancy 
Prolonged immobility
Kidney stones
Bowel incontinence 
Older age
44
Q

Problems with an ageing bladder

A

Slow urine stream - lead to incomplete emptying and an infection
Incontinence

45
Q

Treatment for ageing bladder

A

Surgery - bladder neck suspension

Bo

Physiology: Kidney (14 decks)

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