Fluid and Electrolyte Balance Courtney Shelton CST, BA ST 120

Objectives  List, describe, and compare the body fluid compartments and their subdivisions.  Discuss how water enters and leaves the body and the mechanisms that maintain fluid balance.

Objectives, cont’d  Discuss the nature and importance of electrolytes in body fluids and explain the aldosterone mechanism of extracellular fluid volume control.  Explain the interaction between capillary blood pressure and blood proteins.  Give examples of common fluid imbalances.

Body Fluids  The most abundant fluid in the body is WATER

Body Fluids  60% of body weight in males ~40 L  50% of body weight in females  Adipose tissue contains the least amount of water, so the more fat present, the less the total water content per pound of body weight

Body Fluids  Infants have more water in their cells ~80%  In elderly people, the amount of water per pound of body weight also decreases

Body Fluid Compartments  Extracellular Fluid Compartment Mainly the liquid fraction of whole blood called plasma Found in the interstitial fluid that surrounds the cells Lymph CSF Humors of the eyes Joint fluids

Body Fluid Compartments  Intracellular Fluid Compartment Largest volume of water by far Located inside the cells

Maintaining Fluid Balance  Homeostasis of the total volume of water in the body is maintained primarily by devices that adjust output to intake, and secondarily by mechanisms that adjust only fluid intake

Maintaining Fluid Balance  Chief mechanism is to adjust levels so that……… OUTPUT = INPUT

Fluid Output  Occurs in 4 organs: Kidney Lungs Skin Intestines

Fluid Balance  The rate of water and salt resorption by the renal tubules is the most important factor in determining urine volume.  Urine volume is regulated by ADH, aldosterone, and ANH

Fluid Balance  3 factors influence plasma, IF, and ICF volumes: Concentration of electrolytes in ECF Capillary blood pressure Concentration of proteins in blood

Regulation of Fluid Intake  When dehydration develops, salivary secretions decrease prompting the individual to drink water.  This fluid intake compensates for previous losses

Electrolytes  Nonelectrolytes do not dissociate in water  Electrolytes such as NaCl dissociate in water  Dissociated particles of an electrolyte carry a charge, therefore they are ions

Importance of Electrolytes  Many ions are important trace elements  Needed for cellular activities  Influence movement of water

Sodium  Where sodium goes, water follows  Most is completely reabsorbed in the large intestine  Very little is lost in feces

Capillary Blood Pressure  Pushes fluid out of the blood in capillaries into the IF (interstitial fluid)  If capillary blood pressure decreases, less fluid filters out of blood into IF

Capillary Blood Pressure, cont’d  Blood proteins are a water-holding force  If the concentration of blood proteins decreases, less water moves into the blood from the interstitial fluid

Fluid Imbalances  Dehydration occurs in the cases of prolonged diarrhea or vomiting  Overhydration is less common, but just as dangerous

Edema  Retention of electrolytes (Na + )  Increase in capillary blood pressure  Decrease in plasma proteins

End of Fluids and Electrolytes Any Questions???