Liquidos Corporales

Body Fluids http://cats.med.uvm.edu/physiology/bodyfluids
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The Body's Water
Fluid Compartments
Measuring Volumes
Ionic Composition
Units of Measure
Calculating Osmolarity
The Anion Gap
Clinical Examples
Fluid Movements
Transport Mechanisms
Membrane Transport
Osmosis
ICF-ECF Exchange
Calculating Exchange
Examples
ISF-Plasma Exchange
Capillary PressuresStudy Questions
Answers
Water and its dissolved constituents make up the bulk of your body, and determine
the nature of nearly every physiological process.
In most individuals, approximately 60% of the total weight is water. This percentage
varies between 50% and 70%, with the exact value primarily dependent on a
person's fat content. Since fat has very low water, individuals with more fatwill have
a lower overall percentage of body weight as water.
In the first sections of this document, we'll examine how the body's water is
distributed into several functional compartments, with significant differences in the
ionic composition of each.
© 1999, Joe Patlak
Department of Molecular Physiology and Biophysics
University of Vermont (joe.patlak@uvm.edu)
Body Fluidshttp://cats.med.uvm.edu/physiology/bodyfluids
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Fluid Compartments in the Body
The body's water is effectively compartmentalized into several major divisions.
Intracellular Fluid (ICF) comprises 2/3 of the body's water.
If your body has 60% water, ICF is about 40% of your weight.
The ICF is primarily a solution of potassium and organic anions, proteins etc.
(Cellular Soup!).
The cellmembranes and cellular metabolism control the constituents of this
ICF.
ICF is not homogeneous in your body. It represents a conglomeration of
fluids from all the different cells.
Extracellular Fluid (ECF) is the remaining 1/3 of your body's water.
ECF is about 20% of your weight.
The ECF is primarily a NaCl and NaHCO3 solution.
The ECF is further subdivided into three subcompartments:Interstitial Fluid (ISF) surrounds the cells, but does not circulate. It
comprises about 3/4 of the ECF.
Plasma circulates as the extracellular component of blood. It makes up
about 1/4 of the ECF.
Transcellular fluid is a set of fluids that are outside of the normal
compartments. These 1-2 liters of fluid make up the CSF, Digestive Juices,
Mucus, etc.
40% x 70 kg = 28 L water ISF, 10 LPlasma,
4L
Tr
a
ns,
1L
Intracellular Water =40% Extracellular=20%
Total Body Water = 60% of weight
The 60-40-20 Rule:
60 % of body weight is
water
40% of body weight is
intracellular fluids
20% of body weight is
extracellular fluid
Body Fluids http://cats.med.uvm.edu/physiology/bodyfluids
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Special Notes:
All the body's fluid compartments are in osmoticequilibrium (except
for transient changes).
The ions and small solutes that constitute the ECF are in equilibrium
with similar concentrations in each subcompartment.
The ECF volume is proportional to the total Na content.
Measuring the Volumes of the Body's
Compartments
It is sometimes necessary to know more precisely how water is distributed between
the various compartments in a particularindividual. The volumes of some of the
compartments can be measured by the dilution method.
For the dilution method, one adds an extrinsic, measurable, compound that
distributes fully within the compartment of interest. This method relies on the
formula:
Concentration = Amount / Volume or:
Volume = Amount Added-Amount Lost / Measured Concentration
Directly Measurable volumes:
Total Body Water:Use D20 or radioactive water (tritiated).
Distributes throughout all aqueous solutions.
ECF Volume: Use Inulin (a starch) or Sucrose. These distribute
throughout body, but are excluded from cells.
Plasma Volume: Use radioactive albumin or dye (Evans Blue) that
stay in plasma only.
Indirectly Measurable Volumes:
There is no practical way to measure only the intracellular or the interstitial...