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”