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Physio II > Control of Extracellular Osmolarity/[Na+]-Exam 4 > Flashcards

Control of Extracellular Osmolarity/[Na+]-Exam 4 Flashcards

1
Q

What is the most abundant ion in extracellular fluid?

A

Sodium

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2
Q

What is the range in concentrations of sodium?

A

140-145 mEq/L

Avg: 142 mEq/L

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3
Q

What is average osmolarity?

A

300 mOsm/L

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4
Q

What is average osmolarity corrected for interionic attraction?

A

282 mOsm/L

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5
Q

What is the range in osmolarity?

A

291-309 mOsm/L [+/- 3%]

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6
Q

Why is precise control of osmolarity and sodium important?

A

They both control distribution of water between intracellular and extracellular compartments

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7
Q

Sodium and associated anions account for what percent of extracellular solute? What are the associated ions?

A

94%; chloride and bicarbonate

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8
Q

Glucose and urea contribute what percent of total osmolarity?

A

3 to 5%

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9
Q

Why does urea exert little effective osmotic force?

A

Able to permeate cells easily

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10
Q

Why does sodium have a big effect on fluid movement between extracellular and intracellular compartments?

A

Not very permeable

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11
Q

Equation for Plasma Osmolarity

A

(2.1) x (Plasma concentration sodium)

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12
Q

How do you calculate the plasma osmolarity of sodium?

A

Psm= (2.1) x (142 mEq/L) = 298 mOsm/L

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13
Q

What two systems control/regulate extracellular osmolarity and sodium concentration?

A
  1. Osmoreceptor - ADH system

2. Thirst mechanism

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14
Q

Where are osmoreceptor cells located?

A

Anterior hypothalamus

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15
Q

When would osmoreceptor cells shrink?

A

In response to increased ECF [Na+] (i.e. increased osmolarity)

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16
Q

What happens with impulses as osmoreceptor cells shrink? Where are impulses passed?

A

Number of impulses sent to other nerve cells in supraoptic nuclei; impulses passed to posterior pituitary

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17
Q

What do impulses from shrunken osmoreceptor cells stimulate?

A

Release of ADH stored in secretory granules within nerve endings

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18
Q

Water deficit leads to _________(increase/decerease) in extracellular osmolarity.

A

Increase

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19
Q

Increased Extracellular osmolarity leads to increased secretion of what?

A

ADH secretion (posterior pituitary)

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20
Q

ADH secretion leads to increased water reabsorption leading to ____________(increase/decrease) in water excreted.

A

Decrease

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21
Q

ADH is tied to what reflexes?

A

Arterial baroreceptor reflexes and cardiopulmonary reflexes

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22
Q

What do arterial baroreceptor reflexes response to?

A

Changes in blood pressure

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23
Q

What do cardiopulmonary reflexes response to?

A

Changes in blood volume

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24
Q

Reflex pathways tied to ________________ (2) that control ADH production and release.

A

Hypothalamic nuclei

25
Q

Decreased blood pressure and/or decreased blood volume results in ____________ (increased/decreased) ADH release.

A

Increased

26
Q

Small increase of what percent of osmolarity will trigger increase [ADH]?

A

1%

27
Q

Circulating volume must decrease by what percent before appreciable change in [ADH]?

A

10%

28
Q

What percent reduction in circulating volume produces a HUGE increase in [ADH]?

A

15-20%

29
Q

What causes increased ADH release?

A 
Increased plasma osmolarity
Decreased blood pressure
Decreased blood volume
Nausea
Hypoxia
30
Q

What drugs cause increased ADH release?

A

Morphine, Nicotine, Cyclophophamide

31
Q

What causes decrease in ADH release?

A

Decreased plasma osmolarity
Increased blood volume
Increased blood pressure

32
Q

What drugs cause decreased ADH release?

A

Alcohol, Clonidine (Antihypertensive) Haloperidol (dopamine blocker)

33
Q

What mechanism controls fluid intake?

A

Thirst

34
Q

Why is the thirst mechanism important?

A

needed to replace fluid loss via sweating, breathing GI tract

35
Q

Where is the thirst center?

A

Anteroventricular region of third cerebral ventricle (AV3V region); anterolaterally in preoptic nucleus

36
Q

What does the thirst cneter also do?

A

Promotes ADH release

37
Q

Upper portion of thirst center contains what region?

A

Subfornical organ

38
Q

INferior portion of thirst center contains what?

A

Organum vasculosum of the lamina terminalis

39
Q

How long does the drive to drink continue?

A

As long as thirst center is stimulated

40
Q

Neurons within thirst center respond to changes in what? They function like what?

A

Osmolarity; function like osmoreceptors

41
Q

What is the thirst mechanism stimulated by? (threshold for drinking)

A

Sodium concentration 2mEq/L higher than normal

42
Q

What causes increased thirst?

A 
Increased plasma osmolarity
Decreased bp
Decreased blood volume
Increased angiotensin II
dryness of mouth
43
Q

What causes decreased thirst?

A 
Decreased plasma osmolarity
Increased bp
increased blood volume
Decreased angiotensin II
gastic distension
44
Q

What does increased angiotensin II probably act on?

A

Organum vasculosum of lamina terminalis

45
Q

How long does it take to absorb and distribute digested fluid?

A

30-60 minutes

46
Q

Why would we get overhydrated if thirst drive wasn’t suppressed?

A

We would be driven to continue drinking until osmolarity was returned to normal

47
Q

With our regulatory systems, we’re able to prevent large changes in sodium concentration even though sodium intake increases how much?

A

6-fold

48
Q

What would happen if one system of sodium regulation wasn’t functional?

A

Other systems would still maintain the sodium concentration

49
Q

If both sodium regulation methods fail, what happens?

A

There is no other system that can regulate sodium concentration so sodium concentration will show large swings depending on sodium intake

50
Q

What two hormones play an important role in controlling sodium reabsorption?

A

Angiotensin II and aldosterone

51
Q

Angiotensin II and aldosterone do not play a role in controlling what?

A

Sodium Concentartion

52
Q

Increased levels of angiotensin II and aldosterone will result in what?

A

INcreased sodium reabsorption and water reabsorption

53
Q

How would you block the aldosterone system?

A

Removing adrenal glands and infusing aldosterone to maintain plasma concentration

54
Q

Extremely high levels of aldosterone will only produce an increase in sodium of what?

A

3 to 5 mEq/L

55
Q

Complete loss of aldosterone secretion can lead to what?

A

Significant decrease in sodium concentration

56
Q

Sodium depletion leads to ________ depletion.

A

Volume

57
Q

Sodium depletion leads to decreased _____________ (2), which activates the thirst reflex and cardiopulmonary reflex.

A

Blood pressure

58
Q

Increase reflex stimulation results in further decrease in _____________ (2) as volume is ingested and/or reabsorbed.

A

Sodium concentration

Physio II (14 decks)

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