Kidney: Fluid Balance Flashcards

1
Q

What can the kidneys control (5)?

A

Extracellular, specifically plasma, fluid volume- Effective circulating volume (ECV)

Body fluid osmolality by H2O and electrolyte control

The amount of ultrafiltrate produced in the glomeruli

The amount of H2O and electrolytes reabsorbed in the nephron and tubules

Fluid, electrolyte and H+ and HCO3- balance i.e. the amount gained minus the amount lost each day

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2
Q

Where is ultrafiltrate formed?

A

glomerulus

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3
Q

What rate is the ultrafiltrate formed at?

A

80-120ml/min

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4
Q

The countercurrent mechanism in the loop of Henle allows the nephron to control what features of urine?

A
  • osmolality
  • volume
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5
Q

ECV

A

Effective Circulating Volume

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6
Q

A decrease in ECV is combated by renal

A

Na+ retention

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7
Q

Renal Control of ECV:
- changes in ECV trigger 4 pathways
acting upon the kidney:

  • effect
A

1) RAAS
2) Sympathetic Nervous System
3) Antidiuretic Hormone Release
(ADH)
4) ANP (atrial natriuretic peptide)
release

Together, these change renal haemodyanmics and Na+ transport by renal tubule cells

Apart from ADH, most pathways use changes in NA+ excretion to change ECV

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8
Q

Macula Densa sense

A

sodium delivery to the distal tubule

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9
Q

ECV regulation: RAAS:

A

insert diagram

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10
Q

2 types of baroreceptors are:

A
  • central vascular sensors
  • peripheral stretch receptors
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11
Q

Central vascular receptors are locates (3):

A
  • large systemic veins
  • cardiac atria
  • pulmonary vasculature
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12
Q

Peripheral stretch receptors are located (3):

A
  • carotid sinus
  • aortic arch
  • renal afferent arteriole
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13
Q

ECV Regulation: ADH:
- in response to
- receptors involved

A
  • released by the posterior pituitary
    gland in response to
    ***hyperosmolality and volume
    depletion
  • *** antidiuretic effect tmediated by
    V2 receptors acting on renal
    collecting ducts (more permeable to
    H2O)
  • also increases vascular resistance
    mediated by V1 receptor
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14
Q

ECV Regulation: ADH:

A

insert

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15
Q

ECV Regulation: ANP: action:

A
  • actions of ANP are all designed to
    lower ECV
  • Atrial myocytes synthesize and store
    ANP
  • increased ECV causes atrial stretch
    which leads to ANP release into
    blood
  • ANP promotes natriuresis (
    increased Na+ and H2O excretion
    from kidney)
  • causes renal vasodilatation so
    increased blood flow leads to an
    increase in GFR so more Na+
  • more Na+ reaches the macula densa
    so renin release by JGA is reduced,
    hence effects of angiotensin II is
    reduced
  • overall effect: inhibits actions of
    renin and opposes effects of
    Angiotensin II
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16
Q

Hormonal Regulation of Salt and Water Balance:

A

insert table

17
Q

countercurrent mechanism is a predominantly passive process allowing

A

energy efficient way of producing diluted or concentrated urine

18
Q

What is the main solute that governs plasma osmolality?

A

Sodium

19
Q

Water follows sodium across an osmotic gradient

A

low osmalality to high osmolality

20
Q

Osmolality vs tonicity

A

number of particles in solution vs number of osmotically active particles in solution

21
Q

Large molecules contribute to plasma osmotic pressure (tonicity).

True or False?

A

False
not significantly
f.d

22
Q

Osmolar Gap

A
  • difference between the measured
    and calculated osmolality
  • identifies alcohol poisoning that
    might be ingested
23
Q

Rule of thirds: water distribution across body compartments:

A

ICF = 2/3
ECF = 1/3
ISF = 2/3 of ECF
Plasma = 1/3 of ECF`

24
Q

If ECF osmolality increases,

A

cells shrink (ICF decreases)

25
Q

IF ECF osmolality decreases,

A

cells swell (ICF increases)

26
Q

Categorise the following ions as intracellular or extracellular

A

Intra: K+, PO4-, Mg2+
Extra: Na+, Cl-, Ca2+, HCO3-

27
Q

effect of adding NaCl/loosing salt, water, isotonic saline, salt loss

A

insert table

28
Q

Causes of hyponatremia

A

insert

29
Q

Severe hyponatremia leads to

A

cerebral oedema
because excess extracellular volume

30
Q

most hyponetremia occurs from

A

defect in renal water excretion

31
Q

Diagnosis of hyponatremia:

A
  • low serum sodium
  • simultaneous measurement of
    plasma and urine osmolality for
    diagnosis of SIADH (unable to
    produce dilute large volume of urine
    as kidney keeps absorbing)
32
Q

Treatment of hyponatremia:

A
  • salt replacement
  • water restriction
  • treatment of the underlying cause
33
Q

Rapid correction of chronic hyponatremia can lead to

A

central pontine myelinosis
Water from larger ICF volume into ECF

34
Q

Hypernatremia Causes:

A
  • dehydration
  • drugs: Lithium
  • diabetes insipidus: deficiency or
    renal tubular resistance to ADH