BIOS 256 Week 5: Fluid, Electrolyte, and Acid/Base Balance

Comprehensive vocabulary flashcards covering fluid compartments, electrolyte regulations, clinical imbalances, chemical buffer systems, and arterial blood gas (ABG) interpretations.

Total Body Water (TBW) Compartment Distribution

The physiological division of bodily water into intracellular fluid ($2/3$ of TBW) and extracellular fluid ($1/3$ of TBW), with extracellular fluid being subdivided into interstitial fluid ($2/3$ of ECF) and intravascular volume ($1/3$ of ECF).

Extracellular Fluid (ECF)

Fluid residing outside the cells that accounts for approximately $1/3$ of total body water, comprising intravascular fluid (blood plasma), interstitial fluid between cells, transcellular fluids (e.g., CSF, ocular humors), sweat, saliva, and urine.

Intracellular Fluid (ICF)

Fluid contained within the plasma membrane of cells (the cytoplasm), which accounts for approximately $2/3$ of total body water.

Filtration

The pressure-driven movement of fluid across a semipermeable membrane from the intravascular compartment into the interstitial space, governed by hydrostatic pressure.

Reabsorption (Fluid Dynamics)

The movement of fluid from the interstitial space back into the intravascular compartment, driven predominantly by osmotic pressure.

Metabolic Water

Water synthesized internally as a byproduct of cellular respiration, contributing about $200\,mL/\text{day}$ toward the body's daily fluid intake.

Fluid Intoxication

A condition occurring when water intake exceeds water output, causing blood plasma to become hypotonic and leading to cellular swelling; signs include mental confusion, seizures, coma, and death.

Antidiuretic Hormone (ADH)

A hormone that promotes fluid retention by increasing water reabsorption in the distal convoluted tubules (DCT) and collecting ducts of the kidneys; its release is inhibited by alcohol.

Aldosterone

A mineralocorticoid hormone secreted by the adrenal cortex that stimulates sodium reabsorption in the DCT and collecting ducts, increasing osmotic pressure to draw water back into the bloodstream.

Atrial Natriuretic Peptide (ANP)

A cardiac hormone released by the atria that promotes natriuresis (urinary sodium excretion) and vasodilation of glomerular capillaries, decreasing osmotic pressure, blood volume, and blood pressure.

Natriuresis

The excretion of an abnormally large amount of sodium in the urine, stimulated by atrial natriuretic peptide (ANP).

Hypernatremia

A serum sodium concentration greater than $148\,mEq/L$, commonly caused by dehydration or elevated sodium intake; signs include lethargy, confusion, tachycardia, and seizures.

Hyponatremia

A serum sodium concentration below $136\,mEq/L$, caused by vomiting, diarrhea, diuretic use, or excessive water intake; signs include weakness, dizziness, hypotension, confusion, and coma.

Hyperkalemia

A serum potassium concentration exceeding $5\,mEq/L$, caused by high intake, renal failure, crushing injuries, or low aldosterone; symptoms include ventricular fibrillation, vomiting, weakness, and irritability.

Hypokalemia

A serum potassium level below $3.5\,mEq/L$, caused by vomiting, diarrhea, diuretics, or elevated aldosterone; symptoms include fatigue, confusion, bradypnea, polyuria, and paralysis.

Hypercalcemia

A serum calcium level above $5.5\,mEq/L$, caused by hyperparathyroidism, cancer, or excessive vitamin D intake; manifestations include anorexia, vomiting, polyuria, bone pain, lethargy, and coma.

Hypocalcemia

A serum calcium level below $4.5\,mEq/L$, caused by osteoporosis, hypoparathyroidism, or low vitamin D intake; manifested by muscle cramps, hyperactive reflexes, fractures, and convulsions.

Hypermagnesemia

A serum magnesium concentration greater than $2.1\,mEq/L$, caused by renal failure, antacid overuse, hypothyroidism, or hypoaldosteronism; manifests with weakness, hypotension, vomiting, and paralysis.

Hypomagnesemia

A serum magnesium level below $1.3\,mEq/L$, commonly caused by alcoholism, diabetes, or malnutrition; manifests with arrhythmias, vomiting, weakness, convulsions, and delirium.

Hyperchloremia

A serum chloride concentration exceeding $105\,mEq/L$, caused by dehydration, renal failure, or elevated aldosterone; symptoms include weakness, lethargy, tachypnea, and metabolic acidosis.

Hypochloremia

A serum chloride concentration below $95\,mEq/L$, caused by vomiting, overhydration, congestive heart failure, or diuretics; symptoms include cramps, bradypnea, hypotension, and metabolic alkalosis.

Hyperphosphatemia

A serum phosphate level greater than $2.6\,mEq/L$, associated with renal failure, high intake, or cancer; signs include vomiting, weakness, hyperactive reflexes, and tachycardia.

Hypophosphatemia

A serum phosphate level below $1.7\,mEq/L$, caused by excess urinary loss or reduced intestinal absorption; signs include memory loss, seizures, lethargy, and chest or muscle pain.

Phosphate Buffer System

An intracellular and urinary buffer system where monohydrogen phosphate ($\text{HPO}_4^{2-}$) absorbs $\text{H}^+$ during acidosis, and dihydrogen phosphate ($\text{H}_2\text{PO}_4^-$) releases $\text{H}^+$ in alkaline conditions.

Protein Buffer System

An amphoteric buffering mechanism in which the free amino group ($-\text{NH}_2$) of an amino acid binds excess $\text{H}^+$ during acidosis, while the carboxylic acid group ($-\text{COOH}$) releases $\text{H}^+$ during alkalosis.

Hemoglobin Buffer System

The primary buffer system in erythrocytes and ECF where reduced hemoglobin binds excess free hydrogen ions ($\text{H}^+$) generated by the dissociation of carbonic acid, facilitating oxygen release to tissue cells.

Respiratory Compensation

A physiological mechanism acting within minutes to adjust the respiratory rate and eliminate or retain $\text{CO}_2$, thereby counteracting systemic pH deviations via Le Chatelier’s principle.

Renal Compensation

The body's most effective and durable method of regulating systemic pH, where renal tubule cells actively secrete $\text{H}^+$ and reabsorb bicarbonate ($\text{HCO}_3^-$), reaching maximum effect over several days.

Respiratory Acidosis

An acid-base disturbance characterized by a blood $\text{pH} < 7.35$ and an elevated $\text{PaCO}_2 > 45\,mmHg$, typically resulting from hypoventilation.

Respiratory Alkalosis

An acid-base imbalance characterized by a blood $\text{pH} > 7.45$ and a decreased $\text{PaCO}_2 < 35\,mmHg$, typically induced by hyperventilation.

Metabolic Acidosis

A systemic acid-base disorder marked by a blood $\text{pH} < 7.35$ and an abnormally low bicarbonate level ($\text{HCO}_3^- < 22\,mEq/L$), caused by conditions such as diarrhea, ketosis, or renal dysfunction.

Metabolic Alkalosis

An acid-base disorder defined by a blood $\text{pH} > 7.45$ and an abnormally high bicarbonate concentration ($\text{HCO}_3^- > 26\,mEq/L$), caused by prolonged vomiting, gastric suctioning, or excessive antacid intake.

Complete Compensation

An arterial blood gas state wherein homeostatic mechanisms have successfully brought systemic blood pH back within normal limits ($7.35 - 7.45$), while both $\text{PaCO}_2$ and $\text{HCO}_3^-$ remain abnormal.

Partial Compensation

An arterial blood gas interpretation where both $\text{PaCO}_2$ and $\text{HCO}_3^-$ are abnormal and altering their values to compensate, but blood pH remains outside the normal range ($7.35 - 7.45$).

Uncompensated State

An acid-base condition in which systemic blood pH is abnormal alongside an abnormality in either $\text{PaCO}_2$ or $\text{HCO}_3^-$, while the opposing regulatory parameter remains within normal limits.