Distribution Of Body Fluids

Question 1

What is the major regulator of electrolyte and fluid balance?

Answer 1

Kidneys are the major regulator of fluid & electrolyte balance. They regulate it via Reabsorption or secretion through the tubules. This occurs under the influence of hormonal control:

ADH & aldosterone

Question 2

What is total body water?

Answer 2

Total body water (TBW)= 50%-60% body weight

Male TBW: 60% weight in kg
Female TBW: 50% weight in kg

Varies with age, fat, content

Question 3

What are the main components of ICF?

Answer 3

2/3rds TBW
Major cations: K+, Mg+
Major anions: proteins & organic PO4^-

Question 4

How can blood volume be calculated?

Answer 4

BV= PV/(1-Hct)

Question 5

What are the components of ECF?

Answer 5

1/3rds TBW

Major cations= Na+
Major anions= CL- &HCO3^

ECF= interstitial fluid(IF)+ plasma volume

ISF= 75% ECF Plasma= 25% ECF

Question 6

What are the Dye techniques to measure TBWand fluids in other compounds?

Answer 6

Volumes can also be measured by using dilution technique
Basic principle that the marker substance will be distributed in various compartments based on its physical characteristics

Isotopic water(D2O), titrated water(THO),Antipyrine- Distributes across all body compartments useful for measuring TBW

-Rafioactive albumin, evans blue- remain in plasma to large to cross capillary walls. Useful fir measuring plasma volume (PV)

Sulfate, mannitol, & Inulin- remain in ECF & can’t cross cell membranes useful for measuring ECF

Question 7

What are Dye techniques to measured in?

Answer 7

The marker substance is measured in
-millimoles(mmol)
-milligrams(mg)
-units of radioactivity-millicuries(mCi)
A known quantity dye is injected & allowed to equilibrate.
Then the concentration of dye is measured in plasma
Then the volumes are calculated

Question 8

How can we calculate compartment volume?

Answer 8

Amount injected-amount excreted/ concentration in plasma

V=Q/C
Or
V-compartment volume, Q=quantity injected-excreted

C=concentrated in plasma after equilibrium

Question 9

How do you calculate plasma osmolarity & TBW osmoles?

Answer 9

In normal healthy 70kg male

TBW= ICF + ECF= 42L (0.6 X 70)
ICF= 28L(0.66 X 42)
ECF= 14L (0.33 X 42)

Plasma osmolarity- 300 mOsmols

Total body osmoles= 300 x 42= 12,600mOsm
ICF osmoles= 300 x 28= 8400 mOsm
ECF osmoles= 300 x 14= 4200 mOsm

Add 4 liters of water of plasma after what is the plasma osmolarity?
TBW= 46L, ICF=30.6L. ECF= 15.3L
Plasma osmolarity= 12600/46= 273.9 or 274 mOsm/Kg

Question 10

What is ECF & ICF at physiological state?

Answer 10

ECF & ICF osmolarity is 290 mOsm/Kg (round it off to 300 mOsm/Kg for calculation purpose)

• This can be altered if by changing either
• Solute concentration or water content
• Plasma osmolarity = 2xNa+ + glucose/18 + BUN/2.8

Question 11

Do changes in ECF affect ICF?

Answer 11

Any changes in the volume will 1st affect the ECF volume, which may or may not alter the ICF volume

The change in volume of ICF occurs only by changes in ECF osmolarity

At equilibrium (steady state) the ICF and ECF osmolarity will be the same

Question 12

What are the types of compartment of fluid imbalance?

Answer 12

There are 6 major disturbances due to alteration in electrolyte or water balance

There are 2 types that can occur-either volume expansion or contraction

Types of volume expansion- can be 3 types

Isosmotic

Hyperosmotic

Hyposmotic