Overview
Clinical Meaning
Total body water (TBW) comprises approximately 60% of body weight in adult males and 50% in females, distributed between intracellular fluid (ICF, 2/3 of TBW) and extracellular...
FNP
FNP
Total body water (TBW) comprises approximately 60% of body weight in adult males and 50% in females, distributed between intracellular fluid (ICF, 2/3 of TBW) and extracellular fluid (ECF, 1/3 of TBW). The ECF is further divided into intravascular (plasma, 25% of ECF) and interstitial (75% of ECF) compartments. Fluid movement between compartments is governed by Starling forces: capillary hydrostatic pressure pushes fluid out of vessels, while plasma oncotic pressure (primarily from albumin) pulls fluid in. Serum osmolality (normal 275-295 mOsm/kg) is tightly regulated by ADH from the posterior pituitary (released in response to increased osmolality or decreased blood volume) and the RAAS (activated by decreased renal perfusion). Sodium is the primary determinant of ECF osmolality and volume — hyponatremia represents relative water excess while hypernatremia represents relative water deficit. The clinician must differentiate between volume depletion (loss of isotonic fluid), dehydration (pure water loss), and fluid overload, as each requires different management strategies. Disorders of fluid balance frequently coexist with electrolyte and acid-base disturbances requiring systematic evaluation.
Unlock full lesson + practice questions
4 more sections with scenarios, priorities, and review drills.
Next study step
Finish the lesson first, then choose a focused activity to apply what you just reviewed.
Continue studying
Sign in to save progress on this lesson.
Unlock the interactive lesson quiz with a plan that includes this FNP pathway. You can still explore topic-filtered questions from the bank hubs below.