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Electrolyte Homeostasis Part 1 Cheat Sheet by

NURS601 Week 1 - Fluid shifts & Electrolytes


Electr­olyte homeos­tasis is the interplay of electr­olyte intake and absorp­tion, electr­olyte distri­bution, electr­olyte excretion, and electr­olyte loss through abnormal routes
If electr­olyte excretion or loss through abnormal routes increases, electr­olyte intake also must increase to prevent electr­olyte imbalance
There are many things that may cause an electr­olyte imbalance

Hormones involved in mainta­ining fluid balance

Net effect
ADH (Antid­iuretic hormone)
Blood pressure increases (with fluid intake); blood volume increases (with fluid intake); blood osmolarity decreases
Renin-­ang­iot­ensin system
Blood pressure increases
Blood plasma Na+ mainta­ined, blood plasma K+ decreases. Blood volume and blood pressure maintained (by decreasing urine output)
Atrial natriu­retic peptide (ANP)
Promotes natriu­resis, elevated urinary excretion of Na+ (and Cl-), accomp­anied by water. Increases loss of water in urine


Primary fluid in the body
Most physio­logical processes require water
Water delivers electr­olytes & nutrients, and carried away waste.
Helps regulate body temp. and helps maintain blood volume
Water balance is affected by age, gender, muscle mass (more muscle = more water, more fat = less water)
60% of an adults body weight is water - there is more water in a child and less in an eldery person, placing these popula­tions at increased risk of fluid & electr­olyte imbalances
Daily intake requir­ements is 2000-3­000mL (in ideal condit­ions, changes in situations such as fever, increased metabolism etc.)
1L of water = 1kg weight so daily weighs can be a good indicator of whether a patient is mainta­ining good fluid & electr­olyte balance
Intake sources: Liquids (1500m­L/day), Solid foods (800mL­/day), Metabolism (300mL­/day)
Fluid loss sources: Kidney (1200-­150­0mL­/day), Skin (500-6­00m­L/day), Lungs (400mL­/day), GI Tract (100-2­00m­L/day)
Measur­eable intake sources: Oral fluid, tube feedings, Parenteral fluid, Enemas, Retained irrigation fluid
Measur­eable output sources: Urine, Emesis, Feces, Drainage from body cavities
Not measur­eable intake sources: Solid foods, metabolism
Not measurable output sources: Sweating, vapori­sation through lungs

Regulation of fluid balance

Regulation of F&E movement

Movement of water through a semi-p­erm­eable membrane from an area of low concen­tration to an area of high concen­tration
important in the transport of gases; sometimes requires the assiss­tance of a transport system (facil­itiated diffusion - used in insulin & glucose); similar to filtration but more about movement of particles that movement of fluid (also includes gas transport & electr­olytes)
Differ­ences in water volume, i.e. hydros­tatic pressure. Happens at tissue capillary level from capill­aries to inters­titial fluid, i.e. edema; hydros­tatic pressure pushes fluid through the membranes (cell & vessel walls)
Active Transport
Molecules have to move against a conc. gradient, requiring active energy and a transport system - such as a Na-K pump requiring ATP - which moves 2 substances at the same time in opposite direct­ions, againt conc. gradients.

Fluid Shifts

If intrac­ellular fluid (ICF) becomes hypertonic relative to extrac­ellular fluid (ECF), water moves from ICF to ECF via osmosis, causing cell death
If ECF becomes hypotonic relative to ICF, water moves from ECF into cells, expanding the cell and potenially causing cell to burst


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