A&P Kai

Lecture 5: Disorders of Fluid and Electrolyte Balance

ECF/ICF Osmolarity

Approximately $300 \text{ mOsm}$, primarily maintained by sodium ($\text{Na}^+$).

Aldosterone

Increases $\text{Na}^+$ and water reabsorption to control blood volume and pressure; released in response to low BP/volume.

Antidiuretic Hormone (ADH)

Increases water reabsorption to control blood osmolarity; released when osmolarity is high.

Atrial Natriuretic Peptide (ANP)

Decreases $\text{Na}^+$ and water reabsorption, leading to reduced blood volume.

Starling Forces (Capillary Exchange)

Filtration (fluid out of capillaries due to hydrostatic pressure) and Reabsorption (fluid into capillaries due to colloidal osmotic pressure).

Edema

Accumulation of interstitial fluid due to increased capillary hydrostatic pressure, decreased capillary colloidal osmotic pressure, increased capillary permeability, or lymphatic obstruction.

Isotonic Hypovolemia

Proportionate loss of $\text{Na}^+$ and water, leading to decreased ECF volume with unchanged osmolarity.

Isotonic Hypervolemia

Proportionate increase in ECF $\text{Na}^+$ and water, resulting in increased ECF volume with unchanged osmolarity.

Hyponatremia

Plasma $\text{Na}^+ < 135 \text{ mEq/L}$, leading to cell swelling (brain) and CNS symptoms.

Hypernatremia

Plasma $\text{Na}^+ > 145 \text{ mEq/L}$, causing ECF hypertonicity, cellular dehydration, and CNS symptoms.

Hypokalemia

Plasma $\text{K}^+ < 3.5 \text{ mEq/L}$, causing dysrhythmias and neuromuscular weakness.

Hyperkalemia

Plasma $\text{K}^+ > 5 \text{ mEq/L}$, causing decreased neuromuscular excitability and serious cardiac conduction issues (e.g., peaked T waves, cardiac arrest).

Hypocalcemia Ssx

increased neuromuscular excitability (tetany, positive Chvostek/Trousseau signs).

Hypercalcemia SSx

Calcium Limits Voltage gated Na+ Channel: leading to decreased neural excitability, GI issues, and CV changes.