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Physiology > Integrative Physiology I Regulation of Extracellular Fluid Osmolarity and Na Concentration > Flashcards

Integrative Physiology I Regulation of Extracellular Fluid Osmolarity and Na Concentration Flashcards

1
Q

in what ways can water be lost

A

-insensible loss by skin and lungs
- sweat
-feces
-urine

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2
Q

which does ADH effect: ECF osmolarity or plasma volume

A

both

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3
Q

how does ADH effect changes in ECF osmolarity? for excess water ingested

A
  • excess water ingested -> decreased body fluid osmolarity -> decreased firing by hypothalamic osmoreceptors ->decreased ADH secretion ->decreased plasma ADH -> decreased tubular permeability to water in CD -> decreased water reabsorption in CD -> increased water excretion
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4
Q

how does ADH work with changes in plasma volume? for ex low plasma volume

A
  • low plasma volume -> low venous, atrial, and arterial pressures -> increased ADH secretion -> increased plasma ADH -> increased tubular permeability to water in CD -> increased water reabsorption in CD -> decreased water excretion
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5
Q

is ADH more sensitive to changes in osmolarity or volume

A

osmolarity

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6
Q

what are the factors that increase ADH secretion

A

-increased ECF osmolarity
- decreased blood volume via low ANP
- decreased blood pressure via baroreceptor activity
- nausea
- hypoxia
- nicotine and morphine
- ANG II

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7
Q

what are factors that decrease ADH secretion

A
  • low ECF osmolarity
  • high blood volume via high ANP
  • high BP via high baroreceptor activity and indirectly via decrease in ANG II
    -ethanol
    -cold
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8
Q

what is syndrome of inappropriate ADH (SIADH)

A

-excrete a concentrated urine
- too much ADH function

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9
Q

when is SIADH most often seen

A

neurologic disease, head injury, lung tumors or after major surgery

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10
Q

what does excessive ADH secretion cause

A

-hyponatremia
-decreased plasma osmolarity
-urine hyperosmolarity

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11
Q

what does excessive ADH secretion not cause

A

-sodium handling
- only defect is in water excretion

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12
Q

is there feedback inhibition of ADH

A

no

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13
Q

how is SIADH treated

A

ADH inhibitor drugs like demeclocycline

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14
Q

what happens in DI

A

-excrete a dilute urine
- too little ADH fcuntion

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15
Q

what are the types of DI

A

-hypothalamic or central DI
- nephrogenic DI
- polydipsic DI

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16
Q

what happens in hypothalamic DI

A

-defect in ADH synthesis or release
-decreased [ADH]plasma

17
Q

what happens in nephrogenic DI

A

-defect in ADH action
-failure to maintain hyperosmotic medullary gradient
-elevated [ADH]plasma

18
Q

what happens in polydipsic DI

A

-compulsive water drinking

19
Q

what are the symptoms of DI

A

-polyuria
- nocturia
- polydipsia

20
Q

what is polyuria defined as

A

greater than 3 liters urine/day

21
Q

what are the 2 factors that determine urine volume

A

-amount of solute to be excreted (OUV)
- [ADH]plasma

22
Q

what are the 3 major mechanisms of polyuria

A
  • decrease in Na+ reabsorption (kidney disease, diuretics)
  • reduced ADH secretion
  • ADH resistance
23
Q

what can cause ADH resistance

A

-lithium and tetracyclines
-hypercalcemic nephrogenic DI

24
Q

what are the mechanisms of regulation of [Na+] ECF

A

-osmoreceptor -ADH system
- the thirst mechanism
- aldosterone and ANG II
- salt appetite

25
Q

what are the primary mechanisms that regulate [Na+] ECF

A

-osmoreceptor-ADH system
- the thirst mechanism

26
Q

how do aldosterone and ANG II regulate [Na+]ECF

A

-alter Na+ mass but NOT concentration
- changes in Na+ mass accompanied by volume changes (thirst, ADH)

27
Q

what are the stimuli for thirst

A

-low plasma volume (MAP and ECF volume)
- increased plasma osmolarity
-dry mouth

28
Q

what part of the brain responds to signals that initiate drinking

A

hypothalamic thirst center

29
Q

where does ANG II act to increase thirst

A

centrally

30
Q

what receptors detect low plasma volume for thirst response and what do they do

A

baroreceptors and cause increase in ANG II and directly stimulate thirst

31
Q

what receptors detect high plasma osmolarity for thirst response and what do they do

A

osmoreceptors and directly cause thirst

32
Q

what reduces thirst

A

metering of water intake by GI tract

33
Q

what are stimuli that increase salt appetite

A

-sodium deficits
- decreased blood volume
-decreased blood pressure associated with circulatory insufficiency

34
Q

what Na+ concentration do humans function normally at and what is the average consumption in the US every day

A

-function normally at 20 meq/day
- average: 200 meq/day

35
Q

what is the response to increase in osmolarity but no change in volume

A
  • ADH secreted -> increased renal water reabsorption
    -thirst -> increased water intake -> increased ECF volume and increased BP -> kidneys excrete salt and water and osmolarity and volume returns to normal AND cardiovascular reflexes lower BP to return BP and volume to normal
36
Q

what is the response to decrease in MAP without change in volume or osmolarity

A
  • decreased BP -> decreased GFR -> decreased NaCl transport across macula densa of DT -> paracrines -> granular cells of afferent arteriole -> increase renin secretion
  • decreased BP -> cardiovascular control center -> increase sympathetic activity -> granular cells of afferent arteriole -> increase renin secretion
  • renin makes ANG I -> ANG II ->arterioles to vasocontrict, CV center in medulla increases CV response, hypothalamus increases ADH and thirst, adrenal cortex increases aldosterone which increases Na+ reabsorption -> all of which increase BP and volume to maintain osmolarity
37
Q

what is the response to increased blood volume and no change in osmolarity

A
  • increased BV causes atrial stretch ->atrial myocardial cells stretch and release ANP -> acts on hypothalamus to decrease ADH, kidney to increase GFR and decrease renin, adrenal cortex to decrease aldosterone, and medulla to decrease BP -> all of which increase NaCl and water excretion

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