Cap 18 Water, Electrolyte, and Acid-Base Balance

Comprehensive vocabulary flashcards covering fluid compartments, water and electrolyte regulation, chemical and physiological buffer systems, and acid-base disorders.

Electrolytes

Molecules or compounds that break down and release ions in water, which are intimately related to water balance in body fluids.

Intracellular Fluid Compartment (ICF)

The fluid compartment consisting of all water and electrolytes enclosed within cells, accounting for approximately $63\%$ of total body water.

Extracellular Fluid Compartment (ECF)

The fluid compartment consisting of all fluids outside of cells, accounting for $37\%$ of total body water, and composed of interstitial fluid, blood plasma, lymph, and transcellular fluid.

Transcellular Fluid

A specialized fraction of the extracellular fluid compartment that includes cerebrospinal fluid, fluids within the eyeball, synovial joint fluid, serous fluid, and secretions of exocrine glands.

Colloid Osmotic Pressure

The inward osmotic force exerted by plasma proteins that pulls fluid back into capillaries from interstitial space at their venular ends.

Metabolic Water

Water generated as a by-product of nutrient metabolism, contributing roughly $10\%$ ($250\,\text{mL}$) to the average daily water intake.

Osmoreceptors

Sensory receptors located in the thirst center of the hypothalamus that detect an increase in the osmotic pressure of extracellular fluid, triggering thirst after as little as a $1\%$ decrease in total body water.

Antidiuretic Hormone (ADH)

A hormone released by the posterior pituitary that enhances the permeability of the distal convoluted tubules (DCTs) and collecting ducts (CDs) to water, promoting water reabsorption and reducing urine volume.

Dehydration

A fluid imbalance in which water output exceeds water intake, concentrating extracellular fluid, pulling water out of cells by osmosis, and potentially precipitating hyperthermia.

Hypotonic Hydration (Water Intoxication)

A condition occurring when water intake exceeds water output, rendering extracellular fluid hypotonic, causing water to swell cells by osmosis, and causing hyponatremia.

Edema

An abnormal accumulation of extracellular fluid within interstitial spaces, triggered by hypoproteinemia, lymphatic obstruction, elevated venous pressure, inflammation, or increased capillary permeability.

Aldosterone

An adrenal cortical hormone stimulated by elevated plasma potassium levels that directs renal tubules to conserve sodium ions while secreting potassium ions into urine.

Parathyroid Hormone (PTH)

A hormone secreted in response to declining calcium concentrations in body fluids that acts to elevate calcium ion levels in the extracellular fluid.

Acids

Electrolytes that ionize in water to liberate hydrogen ions ($H^+$).

Bases

Substances that ionize in water to release ions (such as hydroxide or bicarbonate) capable of binding free hydrogen ions ($H^+$).

Chemical Buffer Systems

Rapid-acting combinations of weak acids and weak bases present in all body fluids that represent the first line of defense against shifts in $\text{pH}$.

Bicarbonate Buffer System

A chemical buffer system utilizing carbonic acid ($H_2CO_3$) as a weak acid to donate $H^+$ during basic shifts and bicarbonate ion ($HCO_3^-$) to sequester $H^+$ during acidic shifts.

Phosphate Buffer System

A chemical buffer system operating in intracellular fluids and renal tubules, utilizing monohydrogen phosphate ($HPO_4^{2-}$) to bind excess $H^+$ and dihydrogen phosphate ($H_2PO_4^-$) to release $H^+$ in alkaline settings.

Protein Buffer System

A chemical buffer consisting of cellular proteins, albumins, and hemoglobin, wherein amino groups ($-\text{NH}_2$) accept $H^+$ in acidic states and carboxyl groups ($-\text{COOH}$) release $H^+$ in basic states.

Physiological Buffer Systems

The second line of defense against $\text{pH}$ changes consisting of the respiratory mechanism (controlling $CO_2$ excretion within minutes) and the renal mechanism (controlling $H^+$ excretion over $1$ to $3$ days).

Acidosis

A pathological state in which blood $\text{pH}$ falls below $7.35$, stemming from the accumulation of acids or loss of bases, leading to central nervous system depression.

Alkalosis

A pathological state in which blood $\text{pH}$ climbs above $7.45$, resulting from the loss of acids or accumulation of bases, often manifesting with tingling sensations and tetanic muscle contractions.

Respiratory Acidosis

An acid-base disturbance caused by hypoventilation, airway obstruction, or reduced gas exchange that causes carbon dioxide ($CO_2$) and carbonic acid ($H_2CO_3$) to accumulate.

Metabolic Acidosis

An acid-base disturbance caused by an excessive accumulation of nonrespiratory acids (e.g., ketone bodies in diabetes mellitus or renal failure) or excessive loss of bases (e.g., prolonged diarrhea or loss of alkaline intestinal secretions).

Respiratory Alkalosis

An acid-base disturbance resulting from hyperventilation (such as from fever, anxiety, or high altitude) that drives excessive pulmonary loss of $CO_2$, reducing $H_2CO_3$ and $H^+$ concentrations.

Metabolic Alkalosis

An elevated blood $\text{pH}$ driven by an excessive loss of hydrogen ions (via gastric drainage or vomiting stomach secretions) or an abnormal gain of bases (such as through ingestion of antacids).

Compensation

The physiological and chemical processes by which buffers, respiratory adaptations, and renal modifications work to restore body fluid $\text{pH}$ back toward its normal range ($7.35\text{--}7.45$).