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PSL301 > PSL301: Water 5 > Flashcards

PSL301: Water 5 Flashcards

1
Q

Water balance is mostly regulated by…

A

ADH

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2
Q

What are ways of water intake?

A
  • food
  • drink
  • metabolism
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3
Q

What are the ways of water loss?

A
  • skin
  • lungs
  • urine
  • feces
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4
Q

Insensible water loss

A

Water loss through breathing and sweat

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5
Q

Why does urine volume not equal water intake?

A

Insensible water loss

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6
Q

The body regulates which aspect of water loss?

A

Urine output

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7
Q

Net water movement in body:

A

Intake (2.5L) - Outtake (2.5L) = 0

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8
Q

Difference between water & sodium regulation

A

Water is tightly regulated

  • respond rapidly to changes
  • maintain Na concentration
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9
Q

Sweating causes rapid reduction in ____

A

urine volume

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10
Q

Do we need to drink 8 glasses of water/day?

A

No, the body will just excrete any excess. There is almost no health benefits.

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11
Q

How is water balance regulated?

A
  • osmoreceptor in hypothalamus detects serum Na concentration
  • swell/shrink depending on stimuli -> send info to hypothalamus
  • change water excretion using ADH
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12
Q

What happens to the osmoreceptor when there is increased intake of water?

A

swell

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13
Q

What happens to the osmoreceptor when there is decreased water?

A

shrink

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14
Q

When does the osmoreceptor swell?

A

diluted serum Na

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15
Q

When does the osmoreceptor shrink?

A

concentrated serum Na

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16
Q

What happens when osmoreceptors sense there is concentrated serum Na?

A

Send 2 diff signals to diff parts of hypothalamus

  1. Increase ADH secretion
  2. Increase thirst & water drinking
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17
Q

2 ways in which vasopressin is secreted

A
  1. osmotic - osmoreceptor initiated

2. non-osmotic

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18
Q

Where is ADH produced?

A

large cell bodies on a few hypothalamic nuclei

  • PVN
  • SON
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19
Q

Where is ADH stored?

A

posterior pituitary

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20
Q

How does ADH get from hypothalamus to posterior pituitary?

A

vesicle

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21
Q

PVN

A

paraventricular nucleus

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22
Q

SON

A

supraoptic nucleus

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23
Q

Where is the SON?

A

above the optic chiasm (where optic nerves cross)

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24
Q

OR

A

osmoreceptor

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25
Q

br

A

baroreceptor

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26
Q

baroreceptors are located at…

A

carotid sinus

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27
Q

baroreceptors react to…

A
  • BP

- CO

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28
Q

baroreceptors are connected to…

What is the implication of this?

A

SON

Circulation also influences ADH secretion

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29
Q

Where is the hypothalamic osmoreceptor located?

A

anterior hypothalamus (OVLT)

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30
Q

what happens when osmoreceptors shrink?

A
  1. cation channels open
  2. cations enter cell (depolarize)
  3. AP lead to increased ADH secretion & thirst
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31
Q

OVLT have ___ cation channels

A

stretch-inhibited

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32
Q

When are the ion channels on osmoreceptors open/closed?

A

closed: diluted Na (stretched)
open: concentrated Na (shrunk)

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33
Q

Vasopressin has a threshold. This means….

A

Below plasma osmolarity of 280 mOsM, there is no effect (no ADH can be found in blood)

34
Q

Relationship between ADH and plasma osmolarity

A

As plasma osmolarity increases, so does plasma ADH -> LINEAR relationship

35
Q

What happens when plasma osmolarity gets higher than 290?

A

You start to feel thirsty

36
Q

When vasopressin is signalled to be released, where does it get released to?

A

venous system

37
Q

secretion of ADH is regulated by…

A

summation of stimulatory & inhibitory signals to SON and PVN

38
Q

serum sodium ____ stimulates thirst

A

> 145

39
Q

serum sodium ____ stimulates vasopressin

A

> 135

40
Q

humans can excrete ___ mL of urine per hour if they wanted to (upper limit). What is the urine osmolality?

A

> 1000

Low osmolality: 50 - 100 mOsM/L

41
Q

humans can excrete ___ mL of urine per hour if they wanted to (lower limit). What is the urine osmolality?

A

< 20

High osmolality: 800 - 1200 mOsM/kg

42
Q

When there is water excess, vasopressin is…

A

suppressed

43
Q

when there is water depletion, vasopressin is…

A

high

44
Q

Urine concentration and dilution

A
  1. isotonic in proximal tubule
  2. very concentrated in descending limb
  3. very dilute in ascending limb (hyposmotic)
  4. depends on ADH/hormone action at collecting duct
45
Q

Which transporters are found on the lumenal side of the ascending limb?

A

Na-K-2Cl cotransporter

Allow NaCl to be transported without H2O

46
Q

Which face is always permeable to water: apical or basolateral?

A

basolateral

47
Q

How can permeability to water be blocked at the apical membrane?

A

Block paracellular pathway

48
Q

How does ADH increase water reabsorption?

A
  1. ADH bind to basolateral membrane receptor V2
  2. activate cAMP & secondary messangers
  3. cause vesicles w/ aquaporin 2 to move to apical membrane
49
Q

Besides the presence of ADH, what else is needed for water to move out of the lumen? How is this achieved?

A
  • osmotic gradient

- high solute concentration in ISF because of the solute absorbed out at the ascending limb

50
Q

Which receptor does ADH bind to?

A

V2 on basolateral membrane

51
Q

Where can V2 receptors be found?

A

distal convoluted tubule & collecting duct

52
Q

Where are V1 receptors located?

A

in blood vessels

53
Q

What does V1 receptors do?

A

Vasopressin binds to them

Causes constriction of blood vessels

54
Q

What must be functional in order to have urine excretion?

A
  1. thick ascending limb to generate concentrated ISF

2. cortical & medullary collecting duct (ADH binding site)

55
Q

How does the CD dilute urine when there is too much water?

A
  • ADH is not secreted

- Na channels on CD & DCT still pump Na out of lumen

56
Q

How does the CD prevent urine dilution?

A

countercurrent arrangement of vessels in medulla

57
Q

countercurrent exchange

A
  • arrangement of vasa recta in medulla
  • blood becomes progressively concentrated as vessels enter the inner medulla
  • prevent disturbing the concentrated ISF
  • allow urine to be concentrated
58
Q

Minimum urine osmolality

A

50 mOsM/kg

59
Q

value: concentrated urine

A

> 300 mOsM/kg

60
Q

value: dilute urine

A

< 300 mOsM/kg

61
Q

hyponatremia

A

too much water

62
Q

hypernatremia

A

too little water

63
Q

polyuria

A

high urine flow > 3L/day

64
Q

Is hyper/hyponatremia more common?

A

hyponatremia

65
Q

hyponatremia is usually caused by…

A

Too much ADH; failure to suppress ADH

66
Q

What causes reduced circulating volume?

A
  • heart failure

- volume depletion

67
Q

What might some reasons for too much ADH be?

A
  • decreased circulating volume (baroreceptor stimuli)
  • cancer (make ADH)
  • drugs
  • NOT OSMORECEPTOR
68
Q

hyponatremia is a common symptom of which disease?

A

heart failure

69
Q

rapid onset of hyponatremia causes…

A

swelling of brain cells

  • increased intercranial pressure
  • compression of brain stem in foramen magnum
  • seizure, coma, death
70
Q

slow onset of hyponatremia causes…

why?

A

no symptoms

- brain cells adapt by removing solutes (takes water out with it)

71
Q

hypernatremia indicates a problem with…

A
  • thirst/intake of fluid (thirsty, but can’t get access to water)
  • water loss (less common)
72
Q

consequence of acute hypernatremia

A

brain cells shrink

  • vessels that attach brain to skill breaks -> hemorrhage
  • seizure, coma, death
73
Q

consequence of chronic hypernatremia

A

no symptoms

- brain cells adapt by adding solutes to hold water in

74
Q

Causes of polyuria

A
  1. not enough ADH (central diabetes insipidus)
  2. kidney can’t respond to ADH (nephrogenic DI)
  3. excess water intake
  4. osmotic diuresis / hyperglycemia
75
Q

central diabetes insipidus means…

A 
central = problem with hypothalamus or posterior pituitary
diabetes = too much urine
insipidus = dilute urine
76
Q

nephrogenic DI vs. central DI

A 
nephrogenic = problem at kidney
central = problem at brain
77
Q

genetic causes of neprogenic DI

A
  1. abnormal V2 receptor gene (x-linked)

2. abnormal aquaporin 2 gene

78
Q

why is polyuria commonly seen in diabetics?

A
  • lots of glucose in blood
  • filtered by glomerulus
  • not enough SLGT to reabsorb all back to blood
  • glucose is a solute, so pulls water into lumen
79
Q

DDAVP

A

synthetic vasopressin

80
Q

why is hypernatremia so rare?

A

As long as person is conscious, he/she can drink water to prevent it

81
Q

How do baroreceptors stimulate ADH release?

A

Connected to SON, which produces ADH

PSL301 (29 decks)

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