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Fluid and Electrolyte Balance Chapter 18
Fluid and Electrolyte Balance
Fluid Balance
relative constancy of body fluid levels
homeostasis
Electrolytes
substances such as salts that dissolve or break apart in water solution.
Body Fluids
Water is the most abundant body compound
Average body water volume is based on a healthy, nonobese 150lb male
Water is 60% of body weight in males, 50% in females
Volume averages 40L in a 150lb male
Body Fluids
Variation in total body water is related to: the total body weight of the individual,
the fat content of the body- the more fat the less water,
gender – female body has about 10% less water than the male body
age – in a newborn infant, water may account for 80% of total body weight. In the elderly, water per pound of weight decreases.
Body Fluid Compartments Intracellular fluids (ICF)
largest fluid compartment
located inside cells
serves as solvent to facilitate intracellular chemical reactions
Body Fluid Compartments
Extracellular fluid (ECF) Plasma, interstitial fluid (IF), lymph, joint fluids, cerebrospinal
fluids, etc..
Called the internal environment of the body
Surrounds cells and transports substances to and from them
Mechanisms that Maintain Fluid Balance
As long as output and intake of water are equal, the total amount of water in the body does not change.
Sources of fluid intake – liquids we drink, water in foods, and water formed by catabolism of foods.
Sources of fluid output – kidneys, lungs, skin, and intestines. Of these the kidney’s change the most day to day.
Mechanisms that Maintain Fluid Balance Factors that act as mechanisms for controlling fluid
balance 1. Concentration of electrolytes in the ECF
2. Capillary blood pressure
3. Concentration of proteins in the blood
The Importance of Electrolytes in Body Fluids
Electrolytes – compounds that break up or dissociate in water solution into separate particles called ions (NaCl)
Ions – the dissociated particles of an electrolyte that carry an electrical charge (Na+)
Nonelectrolytes – organic substances that do not break up or dissociate when placed in water solution (glucose)
Electrolyte Functions
Many ions are considered to be major, or important, “trace” elements in the body.
Examples - Iron – hemoglobin production and iodine – thyroid hormone
Electrolyte Functions
Electrolytes are required for many cellular activities such as nerve conduction (K+), bone formation and blood clotting (Ca++), and hydrochloric acid production in the stomach (Cl-).
Electrolyte Functions
Fluid Volume Variation – “Where sodium goes, water soon follows”
If the concentration of sodium in the blood increases, the volume of blood soon increases.
The kidney’s act as the chief regulator of sodium levels in body fluids
Capillary Blood Pressure and Blood Proteins
Capillary blood pressure is a “water pushing” force. It pushes fluid out of the blood in capillaries into the IF.
It decreases blood volume by increasing IF volume
Water continually moves in both directions through the membranous walls of capillaries.
The concentration of proteins in blood plasma is a water pulling or water holding force – pulls water into the blood plasma
Fluid Imbalances
Dehydration
the fluid imbalance seen most often.
IF volume decreases first, but eventually, if not treated, ICF and plasma volumes also decrease below normal levels.
Caused by too small a fluid intake or too large a fluid output
Overhydration
much less common
puts a heavy burden on the heart
usually from giving intravenous fluids too rapidly
Diuretics meaning “causing urine”