Chapter 24

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

Body Fluids

• Body fluids account for 55-60% of total body weight.

• Intracellular Fluid (ICF): 65% of total body fluids, located inside cells.

• Extracellular Fluid (ECF): 35% of body fluids, divided into:

  • Interstitial fluid: 25%

  • Blood plasma and lymph: 8%

  • Transcellular fluid: 2%

• Fluid balance is achieved when water and solutes are in proper proportions.

Body Water Gain and Loss

• Typical gain and loss of water: 2500 mL/day.

• Sources of Water Gain:

  • Ingested liquids: 1600 mL

  • Ingested foods: 700 mL

  • Metabolic water (from cellular respiration): 200 mL

• Sources of Water Loss:

  • Urine production: 1500 mL

  • Sweat: 100 mL

  • Cutaneous transpiration: 400 mL

  • Expired air: 300 mL

  • GI tract excretion: 200 mL

Regulation of Body Water Gain

• Influenced by fluid intake; controlled by the thirst center in the hypothalamus.

• Dehydration stimulates thirst and can lead to life-threatening consequences if not addressed.

Regulation of Water and Solute Loss

• Primarily occurs through urine excretion.

• ADH (Antidiuretic Hormone) regulates water loss.

• Angiotensin II, aldosterone, and ANP regulate sodium and chloride loss.

Consequences of Excess Water

• Excess water is usually eliminated by producing dilute urine.

• Overconsumption of water can overwhelm renal capacity, affecting osmolarity and leading to potential cell issues, including seizures or coma.

• Rehydration therapy must include sufficient solutes to balance osmolarity.

Electrolytes in Body Fluids

• Blood plasma: High levels of Na+, Cl-; low levels of K+, Mg2+, phosphate, sulfate.

• Interstitial fluid: Similar to blood plasma composition.

• Intracellular fluid: High levels of K+, phosphate; low levels of Na+, Cl-.

• Calcium is stored in bones, with minimal presence in body fluids.

• Bicarbonate maintains acid-base homeostasis, alongside protein anions.

Blood Electrolyte Imbalances

Sodium (Na+)

• Normal range: 136-148 mEq/L

  • Hyponatremia: Low sodium; can cause weakness, confusion.

  • Hypernatremia: High sodium; can cause thirst, agitation.

Chloride (Cl-)

• Normal range: 95-105 mEq/L

  • Hypochloremia: Low chloride; related to vomiting, renal issues.

  • Hyperchloremia: High chloride; linked to dehydration.

Potassium (K+)

• Normal range: 3.5-5.0 mEq/L

  • Hypokalemia: Low potassium; symptoms include weakness and fatigue.

  • Hyperkalemia: High potassium; can cause cardiac issues.

Calcium (Ca2+)

• Total: 9.0-10.5 mg/dL

  • Hypocalcemia: Low calcium can lead to spasms.

  • Hypercalcemia: High levels can cause weakness and confusion.

Phosphate (HPO4²-)

• Normal range: 1.7-2.6 mEq/L

  • Hypophosphatemia: Low phosphate; symptoms include weakness.

  • Hyperphosphatemia: High phosphate, associated with renal issues.

Magnesium (Mg2+)

• Normal range: 1.3-2.1 mEq/L

  • Hypomagnesemia: Low levels may cause confusion.

  • Hypermagnesemia: High magnesium linked to renal failure.

Acid-Base Balance

• pH is vital; three mechanisms regulate it:

  • Buffer Systems: Maintain pH levels by reacting with added acids/bases.

  • Exhalation of CO2: Decreases acidity by converting carbonic acid.

  • Renal Excretion of H+: Reduces hydrogen ion concentration in blood.

Buffer Systems

• Composed of weak acids and their salts.

  • Protein Buffer System: Buffers found in tissues and blood, utilizing amino groups and carboxyl groups.

  • Carbonic Acid-Bicarbonate Buffer System: Key regulatory system for blood pH.

  • Phosphate Buffer System: Important in intracellular fluid and urine.

Acid-Base Imbalances

• Acidosis (< 7.35): Can disrupt synaptic transmission, leading to severe complications.

• Alkalosis (> 7.45): Causes overstimulation of the nervous system, which can be dangerous.

• Treatment approaches vary based on whether the issue is respiratory or metabolic in nature, typically focusing on correcting the root cause and restoring balance.