Fluid and Electrolyte Study Guide

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  • Topic: Extracellular fluid, Sodium, Interstitial fluid
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Unit 2 – Fluid and Electrolyte Imbalance
A.Homeostasis
a.State of equilibrium in the body
b.Naturally maintained by adaptive responses
c.Body fluids and electrolytes are maintained within narrow limits B.Water content of the body
i.Varies with age, gender, body mass
1.Men have more muscle mass → increased water, fat cells have less water content b.50-60% of the weight in an adult
c.45-55% in older adults
d.70-80% in infants
C.Body Fluid Components
a.ICF
b.ECF
i.Intravascular (plasma)
ii.Interstitial
iii.Transcellular
D.Electrolytes
a.Substances whose molecules dissociate into ions (charged particles) when placed into water i.Ions: charged particles
ii.Cations: positively charged
iii.Anion: Negatively charged (protein carries a negative charge) b.Electrolytes are measured in millimoles per liter
c.US uses milliequivalent (mEq)
d.Composition of Electrolytes
i.ICF
1.Prevalent cation is K+
2.Prevalent anion is PO4 3-
ii.ECF
1.Prevalent cation is Na+
2.Prevalent anion is Cl-
E.Mechanisms controlling fluid and electrolyte movement
a.Diffusion
i.Movement of molecules from high to low concentration
1.Occurs in liquids, solids, gases
2.Membrane separating two areas must be permeable to diffusing substance 3.Requires no energy
b.Facilitated diffusion
i.Movement of molecules from high to low concentration without energy 1.Uses specific carrier molecules to accelerate diffusion
2.Passive and requires no energy
c.Active transport
i.Process in which molecules move against concentration gradient (ie. Sodium-potassium pump) 1.External energy required (ATP)
d.Osmosis
i.Movement of water (not particles) compartments separated by a membrane permeable to water but not to solute ii.Water moves from low solute to high solute concentrations iii.Requires no energy!!

e.Osmotic Pressure
i.Amount of pressure required to stop osmotic flow of water 1.Determined by concentration of solutes in solution
2.Measured in milliosmoles
f.Osmotic movement of fluids
i.Types of solutions
1.Isotonic (osmolality is the same)
2.Hypotonic (hyperosmolar) - less concentrated (less particles), more dilute (lower osmolality) 3.Hypertonic (hyperosmolar) – more concentrated, higher osmolality ii.Normal plasma osmolalit 275-295mOsm/kg

1.Water deficit
2.Water excess
g.Hydrostatic Pressure
i.Force within a fluid compartment
ii.Major force that pushes water out of vascular system at capillary level 1.Example – BP – force against the wall of a vessel
h.Oncotic Pressure (Colloidal osmotic pressure)
i.Osmotic pressure exerted by colloids in a solution
1.Protein is a major colloid*
F.Fluid Movement in Capillaries
a.Amount and direction of movement determined by:
i.Capillary hydrostatic pressure
ii.Plasma oncotic pressure
iii.Interstitial hydrostatic pressure
iv.Interstitial oncotic pressure
G.Fluid shifts
a.Plasma to interstitial fluid shift results in edema
i.Elevation of venous hydrostatic pressure
ii.Decrease in plasma oncotic pressure
iii.Elevation of interstitial oncotic pressure
b.Interstitial fluid to plasma
i.Fluid drawn into plasma space with increase in plasma osmotic or oncotic pressure ii.Compression stockings decrease peripheral edema
c.Fluid movement b/w ECF and ICF
i.Water deficit (increased ECF)
1.Associated with symptoms that result from cell shrinkage as water is pulled into vascular system a.1st change seen is in the CNS w/ level of consciousness
ii.Water excess (decreased ECF)
1.Develops from gain or retention of excess water
d.Fluid Spacing
i.First spacing
1.Normal distribution of fluid in ICF and ECF
ii.Second Spacing
1.Abnormal accumulation of interstitial fluid (edema)
iii.Third Spacing
1.Fluid Accumulation in part of body where it is not easily exchanged with the rest of the ECF 2.Hard to clinically correct, dangerous
a.Examples: transcellular fluid in...
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