Fluid Compartments and Electrolyte Balance - Lecture Notes

Vocabulary flashcards covering key terms related to body fluid compartments, transport mechanisms, and common electrolyte disorders.

ICF (Intracellular Fluid)

Fluid contained within cells; ~28 L; about two-thirds of total body water.

ECF (Extracellular Fluid)

Fluid outside cells; ~16 L; subdivided into intravascular fluid, interstitial fluid, and transcellular fluid.

Intravascular Fluid (Plasma)

Fluid within blood vessels; part of the ECF.

Interstitial Fluid

Fluid in the interstices between cells; part of the ECF.

Transcellular Fluid

Third functional subdivision of the ECF (includes CSF, synovial, pericardial, pleural, etc.).

Capillary Hydrostatic Pressure

Fluid pressure that pushes fluid out of capillaries; ≈35 mm Hg at the arterial end.

Blood Colloid Osmotic Pressure

Osmotic pressure due to plasma proteins; tends to pull water into capillaries; ≈25 mm Hg.

Net Filtration Pressure

Overall pressure difference determining filtration vs reabsorption along a capillary; arterial end positive, venous end negative.

Arterial End Filtration (Starling Force)

Net outward movement of fluid from capillary due to higher capillary hydrostatic pressure.

Venous End Reabsorption (Starling Force)

Net inward movement of fluid into capillary when capillary hydrostatic pressure falls below oncotic pressure.

Isotonic Solution

Solution with osmolality similar to body fluids; no net water movement across membranes.

Hypotonic Solution

Lower osmolality than body fluids; causes water to enter cells, potentially causing lysis.

Hypertonic Solution

Higher osmolality than body fluids; draws water out of cells, causing shrinkage.

Osmosis

Movement of water across a semipermeable membrane toward higher solute concentration.

Osmotic Equilibrium

Balance of solute concentrations and water across compartments via osmosis.

Chemical Disequilibrium

Unequal distribution of major intracellular vs extracellular ions (e.g., K+ inside, Na+ outside).

Electrical Disequilibrium

Membrane potential difference (inside negative vs outside) that enables nerve and muscle activity.

Depolarization

Change in membrane potential toward zero or positive, enabling action potentials.

Na+ (Sodium)

Major extracellular cation; key in depolarization; water follows sodium.

K+ (Potassium)

Major intracellular cation; critical for resting membrane potential.

Ca2+ (Calcium)

Ion essential for muscle contraction, neurotransmitter release, and blood clotting; largely extracellular.

Cl- (Chloride)

Major extracellular anion; forms HCl; exchanges with HCO3- during CO2 transport; follows Na+.

HCO3- (Bicarbonate)

Major extracellular buffer; part of CO2 transport; maintains acid-base balance.

Aldosterone

Mineralocorticoid increasing Na+ reabsorption in kidney; water follows; regulates K+.

ADH (Antidiuretic Hormone, Vasopressin)

Hormone promoting water reabsorption in kidneys; regulates body water.

ANP (Atrial Natriuretic Peptide)

Hormone promoting Na+ excretion and water loss; lowers blood volume.

Osmotic Diuresis

Increased urine production due to high solute (e.g., glucose) in urine pulling water with it.

Ketoacidosis

Metabolic acidosis in diabetes with ketone bodies; shifts H+ leading to potential hyperkalemia.

Hyperkalemia

Elevated potassium in blood; risk of cardiac arrhythmias.

Hypokalemia

Low blood potassium; can cause weakness and arrhythmias.

Hypernatremia

Elevated serum sodium; often with hyperosmolality; dehydration risk.

Hyponatremia

Low serum sodium; can cause confusion, seizures; often with SIADH or overhydration.

Hypovolemia

Volume depletion; loss of water and Na+; can cause hypotension and shock.

Dehydration

Loss of water with disproportionate Na+ loss; raises plasma osmolality.

Hypervolemia

Excess body water and Na+; volume overload.

Hypotonic Hydration

Water excess with relatively low sodium; dilutional hyponatremia.

Edema

Sequestration of fluid in the interstitial space.

Third Spacing

Fluid shifts from intravascular space to nonfunctional compartments; edema risk.

Ascites

Fluid accumulation in the peritoneal cavity, common in liver cirrhosis.

Effusion

Fluid accumulation in a body cavity (e.g., pleural effusion).

Burns (fluid shifts)

Increased capillary permeability leading to hypovolemia and electrolyte shifts.

Crush Injury/Rhabdomyolysis

Cell lysis releasing potassium and phosphate; hyperkalemia risk.

Diabetes Mellitus (DM)

Metabolic disease with hyperglycemia; osmotic diuresis and electrolyte disturbances; polydipsia/polyuria.

Diabetes Insipidus (DI)

ADH deficiency or kidney insensitivity; extreme thirst and large urine volumes; risk of hypernatremia.

Syndrome of Inappropriate ADH (SIADH)

Excess ADH causing water retention and hyponatremia.

Addison’s Disease

Adrenal insufficiency with low aldosterone; orthostatic hypotension and hyperpigmentation via ACTH.

Hyperparathyroidism

Excess parathyroid hormone; hypercalcemia; bones, stones, groans, and thrones.

Secondary Hyperparathyroidism

Hyperparathyroidism due to chronic renal failure (renal disease-related PTH rise).

Liver Cirrhosis

Chronic liver damage causing ascites and impaired renal perfusion via RAAS disruption.

Acidosis

Excess H+ in body fluids; shifts K+ to ECF, increasing risk of hyperkalemia.

Alkalosis

Decrease in H+; H+ movement from cells to compensate can cause hypokalemia.

Polydipsia

Excessive thirst often seen in DM and DI.

Polyuria

Excessive urination; common in DM and DI.