Electrolyte Imbalance and Hormonal Regulation

Molecular Movement

• Molecules naturally move down the concentration gradient.
• Equilibrium is achieved when solute concentrations are equal on both sides.
• Diffusion requires no energy and occurs through a permeable membrane.

Types of Transport

• Facilitated Diffusion: Requires a carrier molecule for transport; e.g., glucose needs insulin for entry into cells.
• Active Transport: Movement against the concentration gradient, necessitating energy (ATP) produced in mitochondria; e.g., sodium-potassium pump.

Osmosis

• Primary method for water movement across cell membranes.
• Water moves from areas of higher concentration to lower concentration across a selectively permeable membrane.
• Movement ceases when concentrations equalize or when hydrostatic pressure exceeds osmotic pressure.

Pressure Concepts

• Osmotic Pressure: The pressure required to halt water movement due to osmosis.
• Hydrostatic Pressure: Pressure exerted by a fluid in a compartment; e.g., blood pressure.
• Proteins exert osmotic pressure by attracting water into their compartment (colloid osmotic pressure).

Osmolality vs. Osmolarity

• Osmolality: Measurement of solute concentration per weight of the solvent (kg of body water).
• Osmolarity: Measurement of solute concentration per volume of solution (liters).

Fluid Movement

• Isotonic: Equal solute concentration; minimal fluid movement.
• Hypotonic: Surrounding fluid is less concentrated; fluid moves into the cell, potentially causing rupture.
• Hypertonic: Surrounding fluid is more concentrated; fluid moves out, leading to cell shrinkage.

Fluid and Electrolyte Regulation

• Osmosis regulates fluid movement between intracellular and extracellular compartments.
• Key determinants include potassium (K+) and sodium (Na+) levels.
• Imbalances lead to shifts in fluid and can cause cellular dehydration or damage.

Hydration Status and Weight Changes

• Weight changes indicate fluid gain or loss; e.g., 1 liter of water equals 2.2 lbs or 1 kg.
• Sudden weight loss (e.g., from diuretics) can signify fluid loss.

Types of Dehydration

• Isosmotic: proportional loss of electrolytes and water; e.g., from bleeding or burns.
• Hyperosmotic: elevated extracellular osmolality; caused by conditions like diabetes insipidus or excessive sodium intake.
• Hypo-osmotic: sodium loss leads to water retention; commonly observed in adrenal insufficiency.

Hyponatremia

• Defined as serum sodium < 135 mEq/L; can arise from sodium loss, inadequate intake, or dilution.
• Classifications: hypovolemic (greater sodium loss than water), euvolemic (sodium loss without major water loss), hypervolemic (fluid overload scenario).

pH and Electrolyte Influence

• Acidosis leads to H+ ions moving into cells, causing hyperkalemia (increased potassium levels).
• Alkalosis causes H+ ions to move out, leading to hypokalemia (decreased potassium levels).

Calcium Functions and Regulation

• Critical for bone structure, blood clotting, hormone secretion, muscle contraction, and nerve impulse transmission.
• Regulated by:
  • Parathyroid Hormone: Raises extracellular calcium by promoting absorption.
  • Calcitonin: Lowers extracellular calcium by promoting deposition in bones.

Hypocalcemia

• Defined as serum calcium < 8.5 mg/dL; causes include hypoparathyroidism, vitamin D deficiency, and multiple blood transfusions.
• Symptoms: anxiety, irritability, tetany, and numbness. Signs include Trousseau's and Chvostek's responses.