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Renal/Urology > Lecture 11 - Renal Assessment and Micturition > Flashcards

Lecture 11 - Renal Assessment and Micturition Flashcards

1
Q

When are the two situations where is it particularly useful to be able to measure GFR?

A
  1. Patients with renal disease - progression of disease –> nephron destruction + reduced nephron function
  2. For drugs eliminated by the kidney, fall in GFR –> increase in plasma drug levels –> toxicity (therefore may req. dose adjustment in reduced renal function)
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2
Q

What tests are used to measure GFR?

A

Plasma clearance tests (measuring ability of kidneys to clear plasma of various substances)

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3
Q

What formula is used to measure plasma clearance of a substance X?

A 
Cx = [Ux]V/[Px]
Units are mls/min
Ux = urine concentration of x
V = urine flow rate
Px = plasma concentration of x
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4
Q

What is the gold standard plasma clearance test?

A

Insulin clearance

Insulin freely filtered at glomerulus + neither reabsorbed nor secreted
Not metabolised by kidney and doesn’t interfere with normal kidney function

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5
Q

What is the GFR of a normal man?

A

125mls/min

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6
Q

How much does GFR decline per year after 30 years?

A

1ml/min/year

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7
Q

How is GFR clinically measured now as insulin is no longer used?

A

51Cr-EDTA (a radioactive substance that is handled in the kidney in the same way as insulin)

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8
Q

What is routinely used to estimate eGFR?

A

Plasma creatinine

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9
Q

What is creatinine?

A

Breakdown production of muscle creatine

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10
Q

Why can we use creatinine clearance to estimate GFR?

A

As it correlates well with insulin clearance

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11
Q

What is the big caution with using creatinine clearance to estimate GFR?

A

GFR can half before elevation of the plasma creatinine

SO there are formulae using serum cr that take into account confounding variables

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12
Q

What factors affect GFR?

A

Muscle mass
Dietary intake, e.g. creatine supplements vs vegetarians
Drugs

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13
Q

What is normal eGFR approximately?

A

100mls/min/1.73m2

This is usually expressed as a percentage of normal as normal value varies for age/sex etc.

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14
Q

What is the normal clearance of glucose and urea?

A

Glucose - 0 (usually all reabsorbed)

Urea - less than insulin (some reabsorbed)

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15
Q

Clearance of what substance can be used to measure renal plasma flow?

A

The organic anion para-amino-hippuric acid (PAH)

PAH freely filtered at glomerulus and then the PAH remaining in the plasma is actively secreted into the tubule so>90% of plasma is cleared of PAH in one transit to the kidney

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16
Q

What is the average renal plasma flow?

A

660mls/min

17
Q

Contractions of which muscle are responsible for emptying the bladder during micturition?

A

Detrusor

18
Q

Describe the composition of the two urethral sphincters

A

Internal - not a true sphincter, is where smooth muscle at start of urethra acts as sphincter when it is relaxed

External - true sphincter, skeletal muscle under voluntary somatic control

19
Q

What kind of muscle is the detrusor?

A

Smooth

20
Q

What makes up the trigone?

A

2 vesicoureteric openings

Urethral opening

21
Q

What kinds of problems do urethral obstructions lead to?

A

Bilateral renal problems

22
Q

What kind of problems do ureteric obstructions lead to?

A

Unilateral renal problems

23
Q

What is the appearance of the pressure-volume curve of the bladder?

A

Long, flat segment as initial urine enters bladder, sudden sharp rise as micturition reflex triggered

24
Q

What is the normal urine production?

A

750-2500mls

25
Q

What is the effect of parasympathetic innervation to the bladder?

A

Increased contraction of detrusor –> increased pressure in bladder (S2-4)

26
Q

what is the effect of sympathetic innervation to the bladder?

A

Inhibits bladder contraction
Closes internal urethral sphincter
(hypogastric nerves)

27
Q

What is the main function of the sympathetic innervation to the bladder (regarding nerve roots L1-3)?

A

Prevent reflux of semen into bladder during ejaculation

28
Q

What somatic nerves are responsible for keeping the external urethral sphincter closed?

A

Pundenal nerve

29
Q

Describe the sensory innervation of the bladder

A

Stretch receptor afferents from bladder wall, as bladder fills –> increased discharge in afferent nerves to spinal cord –>

a) excitation of PNS
b) inhibition of SNS
c) inhibition of somatic motoneurons to external sphincter
d) pathways to sensory cortex –> sensation of fullness

30
Q

Describe the operation of the local spinal reflex of micturition

A

As bladder fills + becomes distended, stretch receptors are stimulated until their output is great enough to cause bladder contraction via stimulation of PNS and relaxing the EUS via somatic motoneurons

In babies, the micturition reflex operates at this level because higher brain connections have yet to be established

31
Q

Delay in micturition is accomplished by what?

A

Descending pathways from many brain centres which inhibit PNS and stimulate somatic nerves to EUS overriding the bladder stretch receptors

32
Q

What is involved in voluntary initiation of micturition?

A

Descending pathways that stimulate the PNS and inhibit somatic motorneurons thus summating with stretch receptor effects

33
Q

What is one of the initial events in voluntary urination?

A

Relaxation of pelvic floor muscles, which creates a downward tug on detrusor to initiate its contraction

34
Q

How can urine flow be stopped after urination begins?

A

Perineal muscles + external sphincter can be contracted voluntarily

35
Q

How does the urethra empty after urination?

A

Female - by gravity

Male - contractions of bulbocavernosus muscle

36
Q

What 3 major neural lesions may lead to abnormalities of micturition?

A
  1. Interruption of afferent nerves
  2. Interruption of afferent and efferent nerves
  3. Interruption of facilitatory and inhibitory descending pathways from the brain
37
Q

How do some paraplegic patients train themselves to initiate voiding?

A

Pinching/stroking on thighs - mildly noxious stimuli may irridate to autonomic centres and evoke bladder/rectal voiding

Renal/Urology (29 decks)

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