Water, electrolyte and acid base balance Anatomy and Physiology 2

What are electrolytes?

Molecules that release ions in water and affect water concentration

What is intracellular fluid compartment?

All water and electrolytes inside cells; makes up ~63% of body water

What is extracellular fluid compartment?

All fluids outside cells including plasma, interstitial fluid, and lymph; makes up ~37% of body water

Transcellular fluid is

Specialized extracellular fluids like cerebrospinal, synovial, pleural, and pericardial fluid

Most body water is

Located inside the cells (intracellular fluid)

Main extracellular ions are (3)

Sodium (Na⁺), Chloride (Cl⁻), and Bicarbonate (HCO₃⁻)

Main intracellular ions are (3)

Potassium (K⁺), Magnesium (Mg²⁺), and Phosphate (PO₄³⁻)

Fluid movement regulation is

Controlled by hydrostatic pressure and osmotic pressure

Osmosis is

Movement of water across a semi-permeable membrane to equalize solute concentrations

Water balance

Exists when water intake equals water output

Main sources of water intake

60% beverages, 30% moist food, 10% metabolic water

Main water output methods

Urine, feces, sweat, skin evaporation, and lungs

ADH (Antidiuretic Hormone)

Reduces urine output by increasing water reabsorption in the kidneys

ADH release trigger

Increased plasma osmolarity detected by osmoreceptors in the hypothalamus

Sodium reabsorption hormone

Aldosterone, which increases sodium reabsorption in kidneys

Potassium regulation

Excreted when sodium is reabsorbed; regulated by aldosterone

Calcium regulation

Controlled by parathyroid hormone (raises Ca²⁺) and calcitonin (lowers Ca²⁺)

Acidosis

Blood pH below 7.35; usually due to excess hydrogen ions (H⁺)

Alkalosis

Blood pH above 7.45; usually due to loss of hydrogen ions or excess base

Buffer systems

Chemical (bicarbonate, phosphate, protein), respiratory, and renal

Main blood buffer

Bicarbonate buffer system

Respiratory regulation of pH

Controls CO₂ levels to manage carbonic acid (H₂CO₃) balance

Renal regulation of pH

Kidneys excrete H⁺ or retain HCO₃⁻ to maintain pH

Respiratory acidosis

Caused by CO₂ buildup due to hypoventilation, injury, or disease

Metabolic acidosis

Caused by loss of base (vomiting/diarrhea) or acid accumulation (diabetes, kidney failure)

Respiratory alkalosis

Caused by excessive CO₂ loss due to hyperventilation (e.g., panic attack)

Metabolic alkalosis

Caused by loss of H⁺ (vomiting) or excess base (antacid use)