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Renal > L 4: Physiology and Terminology of Body Fluid spaces > Flashcards

L 4: Physiology and Terminology of Body Fluid spaces Flashcards

1
Q

2 important parameters discussed that the body and kidney spend a lot of time regulating

A
  1. effective vascular volume 2. tonicity
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2
Q

3 Main contributors to effective vascular volume

A
  1. CO 2. SVR 3. Plasma volume which is derived from ECF volume (determined by kidney)
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3
Q

What is effective vascular volume?

A

-hard to define and no single clinical test for it -refers to how well the arterial space is being loaded with blood in such a way that there is adequate end-organ perfusion

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4
Q

2 main body fluid compartments, their proportions and composition

A

Total body water= 1/3 ECF (Na+) and 2/3 ICF (K+) -ECF: 1/4 plasma, 3/4 interstitial fluid

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5
Q

ECF volume is the major determinant of ______. Why do we care?

A

-plasma volume -changes in ECF generally lead to proportional changes in plasma volume -inadequate plasma volume leads to inadequate organ perfusion (low effect vascular volume)

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6
Q

T/F: plasma volume= total blood volume

A

-false; plasma does not include RBCs/hematocrit

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7
Q

Osmolality vs Tonicity

A

-O: ratio of particles/water; usually 290mOsm; can be measured directly in lab

T: tonically active osmoles are CONFINED and osmotically aftive to 1 side of cell membrane (aka effective osmoles–cause fluid shifts); cannot be measured directly by lab

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8
Q

Effective vs ineffective osmoles

A
  • effective: Na, K, Cl, mannitol
  • ineffective: urea, ethanol (spread everywhere)
  • glucose: either depending on insulin; it is effective in absence of insulin bc not allowed to be transported across cell membranes!
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9
Q

Calculation of osmolality and tonicity

A
  • osmo: 2 [Na] + glucose/18 + urea/2.8
  • tonicity: 2[Na] + glucose/18
  • dropped urea from tonicity because it is an ineffective osmol
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10
Q

Why do we care about tonicity?

A
  • it dictates water distribution
  • K+ restricted to ICF and Na to ECF
  • water moves across ICF and ECF to maintain equal tonicity across both compartments
  • changes cause fluid shifts: shrink/swell
  • hypotonic solution= brain swelling; hypertonic: brain shrinking (subdural hematoma)
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11
Q
A
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12
Q

In the intact organism, alterations in tonicity affect which tissue first?

A

-brain >>> RBCs

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13
Q

How are effective vascular volume and tonicity usually maintained in simple terms?

A
  • independently, and body will sacrifice tonicity for EVV every time!
  • EVV: Na in/out via RAAS
  • tonicity:water in/out via hypothalamus/ADH/thirst
  • 2 systems overlap is >10% EVV depleted
  • in other words: we fix volume problems with salt, and tonicity with water
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14
Q

What determines ECF volume?

A
  • TOTAL BODY Na CONTENT
  • Na is major osmole in ECF and is restricted here
  • stable hemodynamics depend on stable ECF volume which is maintained by Na balance
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15
Q

How does our body regulate Na content in body?

A
  • renal excretion of Na
  • extrarenal loss can outpace Na intake under certain conditions (burns, diarrhea, blood loss) leading to total body Na loss and abnormally low ECF volume (hypovolemia)
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16
Q

How do we evaluate volume and tonicity?

A
  • EVV: labs are unreliabled, but clinically determined by history and PE
  • tonicity: clinical exam unreliable (remember it can effect the brain first), but lab evaluation of serum Na and osmolality works!
17
Q

PE tricks for EVV evaluation

A
  • JVP
  • crackles in lung exam
  • peripheral edema
  • acute weight change
  • axillary sweat
18
Q

T/F Serum sodium concentration assess total body sodium

A

-false!!

–[Na]= tonicity level, total body Na determines EVV

-clinical correlate: edematous patient is EVV overloaded yet will have low [Na] and normal total body Na

19
Q

Volume disorder= abnormal ___________.

A
  • total body Na content
  • normal=euvolemia
  • too much Na= volume overload
  • too little Na: volume depletion (NOT the same as dehydration)
20
Q

T/F: Volume depletion = dehydration

A
  • FALSE: they are not the same
  • dehydration implies too little water for the amount of solute in the body (hypernatremia)
  • volume depletion= too little Na
21
Q

Tonicity disorder= abnormal __________.

A
  • RATIO of water to solute
  • in gernal normal T= normal serum sodium (eunatremia)
  • low T: too much water:Na (hyponatremia/hyperaquemia)
  • high T: too little water relative to solume: hypernatremia/hypoaquemia
22
Q

Summarize ECF V disorder vs Osmolar disorders

A
23
Q

2 types of IV fluids

A
  1. IVF used to give NaCl: isotonic saline aka normal saline where tonicity is comparable to portion of blood
  2. IVF used to give water: 5 mg/dl dextrose called D5W: give pure water IV would locally lyse red cells, adding the D5 is close to iso-osmolar initially but dextrose is eventually metabolized leaving behind the pure water addition
24
Q

State what will happen to tonicity, ICF and ECF if 1.5 L of normal saline is added.

A
  • tonicity = the same (isotonic!!)
  • ICF: same (isotonic=no fluid shift)
  • ECF: increase!! how we handle low EVV
25
Q

State what happens to tonicity, ICF and ECF with addition of dry NaCl

A
  • increase tonicity
  • decrease ICF
  • increase ECF
26
Q

State effect of 1.5 L D5W on tonicity, ICF, and ECF

A
  • tonicity: decreases (decrease [Na])
  • ICF increases
  • ECF increases still but slightly (1/3 to ECF, 2/3 to ICF)
27
Q

Give examples of how adding D5W, normal saline, and/or NaCl proves the ECF does not equal [Na]

A
  • giving NaCl increased ECF, and inc [Na]
  • giving D5W: increases ECF, decreased [Na]
  • giving normal saline: increased ECF: no change on [Na]
  • ECF increased in all 3 exmaples independently on plasma Na CONCENTRATION!
28
Q

Effects attenuated in normal people from adding saline, D5W, or NaCl

A
  1. saline: normal eurvolemic person would pee the salt and water out in urine
  2. normal person will pee out extra water
  3. drink water and/or pee out extra Na
29
Q

Take homes: body’s primary goal is to defend adequate circulation and _____ is critical for this. An important secondary goal is to defend ______, _______ is critical fro this.

A
  • Na handling
  • tonicity: water handling
  • water and Na handling are typically independent

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