Ch24 - Water, Electrolytes, & pH

Chapter 24: Water, Electrolyte, and Acid-Base Balance

Homeostatic Balance: Water, electrolyte, and acid-base balance managed by multiple body systems (urinary, respiratory, digestive, etc.).

Water Balance: Body water composition varies:

• Newborns: ~75%

• Young men: 55-60%

• Women: ~50%

• Obese/elderly: ≤45%

• Total Body Water (TBW) for 70 kg male: ~40 L.

Fluid Compartments: 65% Intracellular Fluid (ICF), 35% Extracellular Fluid (ECF). Water moves by osmosis, regulated by electrolytes; daily gains (~2,500 mL) equal losses. Thirst is driven by dehydration, blood volume reduction, or increased osmolarity, with osmoreceptors in the hypothalamus.

Electrolyte Balance: Major roles in metabolism and cell membrane electrical potential. Key electrolytes:

• Cations: Na+, K+, Ca2+, H+

• Anions: Cl−, HCO3−, PO43−.

Sodium is the principal cation in ECF, critical for fluid balance regulation.

Acid-Base Balance: Normal pH: 7.35 to 7.45, maintained by buffers (bicarbonate, phosphate, protein systems). Compensation for imbalances involves respiratory adjustments (ventilation changes) and renal adjustments (H+ secretion and bicarbonate reabsorption).

Fluid Replacement Therapy: Essential for managing ill patients, using oral intake and parenteral routes (I.V.), and isotonic solutions to restore blood volume, with specific strategies for acidosis and alkalosis adjustments.