8-4 Body Fluid Compartments Flashcards Preview

Kathleen's Renal I > 8-4 Body Fluid Compartments > Flashcards

Flashcards in 8-4 Body Fluid Compartments Deck (24):

What are the body fluid compartments?

 TBW - Total Body Water = 0.6 X body weight, ~42 L

ICF - Intracellular fluid = 0.4 x body weight, ~28 L

ECF - Extracellular fluid = 0.2 x body weight, ~14 L

IF - Interstitial fluid = 3/4 of ECF, ~10.5 L

Plasma = 1/4 of ECF, ~3.5 L


What are the components of ECF? What separates them?

Interstitial fluid


Transcellular fluid


Separated by capillary wall


What makes up transcellular fluid? What space does it occupy?

Small amt of water - epithelial secretions, synovial fluid, CSF

 - o ccupies third space


What are the different constituents of intracellular versus extracellular body fluids?


High in Na+, Cl-, HCO3-

low in K+



High in K+, Mg++, PO4-

Low in Na+


The membrane between the ICF and the ECF compartments is what? What is this permeable to? What is it not permeable to?

Cell membrane

Permeable to water, impermeable to charge/electrolytes


Fluid distribution between ECF and ICF is dependent on what? What drives this fluid distribution?

Osmotic effects - mostly Na+ and Cl-

Distribution of ions determined by ATPase activity


The membrane between ECF compartments separates what? What is it permeable to?

Plasma and interstitial fluid makes up the ECF compartment, and is separated by the capillary wall


Permeable to small ions


What affects fluid distribution in the ECF? What are these a balance of?

Fluid distribution in plasma and interstitial fluid that makes up the ECF is determined by Starling forces

 - balance between hydrostatic pressure and colloid osmotic pressure

 - these are determined by fluid volume and protein concentration in the vasculature and interstitial spaces


An imbalance of fluids between compartments frequently results in what? What are some causes?

Edema - non-pitting or pitting


Causes: loss of plasma proteins, ATPase activity


What is non-pitting edema?

swollen cells due to increased ICF volume; non-responsive to diuretic action

 - difficult to treat


What is pitting edema? What are some causes of it, and what is this treated with?

increased interstitial fluid volume

–Nephrotic syndrome, CHF, pregnancy, cirrhosis

 - can be treated with diuretics, usually less severe than non-pitting


Osmotic equilibriation is established between ECF and ICF. Why?

Cell membranes separate these 2, and are highly permeable to water



Infusion of hypertonic solution into ECF will result in what changes in ICF? What is this called?

Hyperosmotic volume expansion

Initially, ECF will have an increased mOsm/L or concentration, and an increased volume due to saline infusion

Then, water will rush into ECF, leaving ICF with a decreased volume but an increased mOsm/L or concentration

Water will rush into ECF until ICF and ECF are roughly equilibrated as far as mOsm/L or concentration

Results in larger volume for ECF, and a lower volume for ICF, and a higher mOsm/L for both


What would happen if you were to infuse a solution of isotonic saline into ECF? What is this called?

Isosmotic volume expansion 

ECF volume increases

No change in osmolality between ICF and ECF

But! Plasma protein concentration/cell count goes down due to dilution (extra fluid)

Arterial BP goes up, expanded ECF (plasma + third space) happened


What happens to osmotic equilibration with diarrhea? What is this called?

Loss of isotonic fluid - isosmotic volume contraction

ECF volume decreases

No change in osmolality - no water shift between ICF and ECF

Plasma protein concentration, hematocrit increases

Loss of arterial blood pressure

Decrease in ECF volume, no change in osmolality for ICF or ECF



If you were to wander in the desert for 40 days, what would happen to ICF and ECF? What is this called?

Hyperosmotic volume contraction

Sweat is hyposmotic

ECF osmolality is increased

ECF volume is decreased - loss of volume via sweat

Water leaves ICF

ICF osmolality increases until ECF is equivalent

ICF volume decreases


What would happen to ECF and ICF if you had SIADH? What is this called? What about hematocrit and blood protein levels?

Gain of water - hyposmotic volume expansion

Excess water is retained

ECF has more water, increased volume

ECF osmolality decreases

Water goes into cells

ICF osmolality decreases until its equivalent to ECF

ICF volume increases

Plasma protein conc drops, RBCs become bigger so hematocrit stays the same


What would happen to your ECF and ICF if you had adrenal insufficiency? What is this called?

Adrenocortical insufficiency = loss of NaCl, hyposmotic volume contraction

Osmolality of ECF decreases - decreased Na+ reabsorption in kidneys, excrete more NaCl than water

ECF volume decreases

Water shifts into cells

ICF osmolarity decreases until it equilizes with ECF

ICF volume increases

Plasma protein conc increases due to decreased ECF volume

Hematocrit increases - reduced ECF volume, RBCs swollen due to more water

Arterial blood pressure decreases due to decreased ECF volume



What is the response to volume expansion?

Volume expansion

 - decreased SNS activity, decreased renin, decreased aldosterone

 - heart secretes ANP and BNP, causing dilation of afferent arteriole

 - ANP and BNP work on brain, reducing ADH output

 - urodilantin is released, causing increased dilation and volume in collecting ducts

 - Na+, water excretion increased


What is the response to volume contraction?

Volume Contraction

 - increased SNS, constriction of afferent arteriole, increased renin

- decreased pressure on heart, increased ANP and BNP synthesis

 - less ANP and BNP works on brain, increased ADH secreted

 - increased renin causes increased aldosterone

 - increased aldosterone favors reabsorption of water, Na+

 - less water, Na+ excretion

 - less urodilantin, contracted collecting tubule



What does tonicity relate to?

Tonicity of a solution relates to the effect of that extracellular solution on cell volume

Implies 2 entities: cell and the solution its sitting in


What does tonicity rely on?

Depends on the concentration of impermeant solutes in the extracellular vs. intracellular fluid



In regards to tonicity, what is the difference between isotonic, hypotonic, and hypertonic?

–No change in cellular volume = isotonic solution
–Cellular volume increase (swelling) = hypotonic solution
–Cellular volume decrease (shrinking) = hypertonic solution