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CRR > A. Lecture 26 - regulation of water balance > Flashcards

A. Lecture 26 - regulation of water balance Flashcards

1
Q

what is the value of plasma osmolality?

A

280-290 mosmol/Kg H2O (± 3)

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2
Q

what is diuresis?

A

increased production of urine.

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3
Q

what does ADH increase H2O permeability of?

A

Cortical collecting duct (2/3 reabsorption)

Medullary collecting duct (1/3 reabsorption)

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4
Q

how much hypotonic fluid reaches collecting ducts daily?

A

23 litres

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5
Q

in the absence of ADH how much dilute urine can be produced?

A

approx 20 litres.

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6
Q

in the presence of ADH how much concentrated urine can be produced?

A

300 ml

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7
Q

what is ADH?

A

Vasopressin

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8
Q

where is ADH produced?

A

Synthesised in the supraoptic (SON) and paraventricular nuclei (PVN)

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9
Q

where are the SON and the PVN found?

A

in the hypothalamus.

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10
Q

what is the half life of ADH?

A

15 minutes

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11
Q

where is ADH degraded?

A

liver and kidney

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12
Q

what happens to ADH after synthesis?

A

moves to neurohypophysis

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13
Q

how does ADH travel to neurohypophysis?

A

in axons of hypothalamophypophyseal tract

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14
Q

what happens to ADH during the movement?

A

progressively cleaved.

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15
Q

how is ADH stored in nerve terminals?

A

with neurophysin.

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16
Q

what causes ADH release?

A

primary stimulus is plasma osmolality.

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17
Q

how is plasma osmolality sensed?

A

osmoreceptors.

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18
Q

where are osmoreceptors found?

A

located near SON

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19
Q

what is the activation threshold for osmoreceptors?

A

280 mosmol/kg H2O

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20
Q

what happens when osmoreceptors are activated?

A

small amount of tonic ADH release

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21
Q

how sensitive are osmoreceptors?

A

Very sensitive (small increase osmolality = big increase in plasma ADH)

22
Q

how can osmoreceptor thresholds be reset?

A

hypovolaemia

23
Q

what is another stimulus for ADH release?

A

haemodynamics - blood pressure and or volume

24
Q

how is haemodynamics monitored?

A

via baroreceptors

25
Q

how sensitive are baroreceptors compared to osmoreceptors?

A

less sensitive

26
Q

how does nausea impact plasma ADH?

A

plasma ADH increases 100 to 1000 fold

27
Q

what are 3 other stimuli for ADH release?

A

Hypoglycaemia (only modest changes)
Hypoxia (via carotid chemoreceptors)
Angiotensin (↑ osmotic response)

28
Q

what receptor does ADH interact with?

A

V2

29
Q

How does ADH activate adenylate cyclase?

A

via Gs protein

30
Q

what does the activation of adenylate cyclase produce?

A

cyclic AMP (cAMP)

31
Q

what does cAMP activate?

A

protein kinase A (PKA)

32
Q

what happens to PKA?

A

PKA phosphorylates and activates non-functional aquaporin-2 water channels

33
Q

where does active aquaporin-2 channels insert?

A

apical (luminal) membrane.

34
Q

what does the insertion of aquaporin-2 do?

A

causes water permeability to increase. water is reabsorbed and urine is concentrated.

35
Q

true or false - concentrating ability of kidney is limited?

A

true

36
Q

what is the maximum urine osmolality?

A

1400 mosmol/kg H2O

37
Q

what does volume of urine excreted depend on?

A

Level of circulating ADH

Amount of solute to be excreted

38
Q

how much solute to be excreted?

A

800 mosmol/kg H2O solute to be excreted

39
Q

how do you work out the minimum volume of urine which can be excreted?

A

solute/max urine

this is over 24 hours

40
Q

what is micturition?

A

Micturition = urination (voiding of urine)

41
Q

how is urine conveyed?

A

Urine is conveyed from renal pelvis to bladder via ureters

42
Q

what do ureters do?

A

Ureters encourage urine flow by peristalsis

43
Q

how is peristalsis initiated?

A

by pacemaker cells in the renal pelvis

44
Q

what happens to the rugae as bladder initially fills?

A

rugae unfold causing little change in pressure

45
Q

what happens to pressure as volume of urine increases?

A

pressure rises

46
Q

what happens to the stretch receptors in bladder?

A

activate pelvic nerve afferents

47
Q

what do the pelvic nerve efferents do?

A

Pelvic nerve efferents relax internal urethral sphincter

48
Q

is the micturition reflex under voluntary control?

A

not in babies (0-2) but in children and adults.

49
Q

how is the micturition reflex achieved?

A

Achieved by integration with higher centres (pons) via pudendal nerves

50
Q

what happens when the pudendal nerves are tonically active?

A

keep external urethral sphincter closed

51
Q

what happens with voluntary inhibition of pudendal nerve activity?

A

relaxes external sphincter.

52
Q

what does the relaxation of sphincter allowed?

A

micturition.

CRR (3 decks)

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