Water, Electrolyte and Acid-Base Balance

Comprehensive vocabulary flashcards covering water distribution, electrolyte functions and imbalances, and acid-base regulation based on the lecture notes.

Total body water (TBW)

The total amount of water in the body, accounting for approximately $60\%$ of total body weight, or about $40\,L$ in a $150\,lb.$ male.

Intracellular fluid (ICF)

The fluid compartment located inside cells, containing approximately $65\%$ of the total body water.

Extracellular fluid (ECF)

The fluid compartment outside of cells, containing approximately $35\%$ of total body water, subdivided into tissue fluid ($25\%$), blood plasma and lymph ($8\%$), and transcellular fluid ($2\%$).

Metabolic water

Water gained internally through aerobic metabolism and dehydration synthesis, totaling about $200\,mL/day$.

Performed water

Water ingested through external sources, specifically food ($700\,mL/day$) and drink ($1,600\,mL/day$).

Insensible water loss

Water loss that an individual is not conscious of, occurring via expired breath and cutaneous transpiration.

Obligatory water loss

Unavoidable water loss including expired breath, cutaneous transpiration, sweat, feces, and a minimum urine output of $400\,ml/day$.

Hypothalamic osmoreceptors

Sensors in the brain that trigger the thirst mechanism and ADH production in response to increased ECF osmolarity.

Aquaporins

Membrane proteins synthesized by the kidney collecting ducts in response to ADH to channel water back into the renal medulla.

Hypovolemia (Volume depletion)

A fluid deficiency where total body water declines while osmolarity remains normal, often caused by hemorrhage, severe burns, or chronic vomiting.

Dehydration

A fluid deficiency where total body water declines and osmolarity rises, often due to lack of drinking water, diabetes, or profuse sweating.

Hypotonic hydration

A fluid excess where more water than $Na^+$ is retained or ingested, causing the ECF to become hypotonic and potentially leading to cellular swelling.

Edema

The most common form of fluid sequestration, characterized by an accumulation of fluid in the interstitial spaces.

Pleural effusions

A type of fluid sequestration where several liters of fluid accumulate in the lungs, often due to infection.

Sodium ($Na^+$)

The principal cation of the ECF that accounts for $90-95\%$ of its osmolarity and is essential for membrane potentials and the $Na^+-K^+$ pump.

Aldosterone

The 'salt retaining hormone' that stimulates the renal tubules to increase $Na^+$ reabsorption and increase $K^+$ secretion.

Atrial natriuretic factor (ANF)

A hormone released in response to high blood pressure that causes the kidneys to excrete more $Na^+$ and water.

Hypernatremia

A plasma sodium concentration exceeding $145\,mEq/L$, resulting in water retention, hypertension, and edema.

Potassium ($K^+$)

The most abundant cation of the ICF and a key determinant of intracellular osmolarity; imbalances of this electrolyte are the most dangerous.

Hyperkalemia

An electrolyte imbalance where extracellular $K^+$ levels are elevated, which can make nerve and muscle cells abnormally excitable or less excitable depending on the rate of onset.

Hypokalemia

Low extracellular $K^+$ levels, often from sweating or chronic vomiting, making nerve and muscle cells less excitable, leading to muscle weakness and arrhythmias.

Chloride shift

A function of chloride ($Cl^-$) involving the loading and unloading of $CO_2$ in red blood cells.

Hypercalcemia

A condition where calcium levels exceed $12\,mEq/L$, inhibiting depolarization and causing muscular weakness, depressed reflexes, and cardiac arrhythmias.

Hypocalcemia

Low calcium levels that increase membrane $Na^+$ permeability, making systems abnormally excitable and potentially resulting in tetanus or laryngospasm.

Physiological buffer

A system that controls the output of acids, bases, or $CO_2$, such as the urinary system (slow, large quantity) and respiratory system (fast, within minutes).

Bicarbonate buffer system

A chemical buffer system in the ECF involving the reversible reaction $CO_2 + H_2O \rightleftharpoons H_2CO_3 \rightleftharpoons HCO_3^- + H^+$.

Phosphate buffer system

A buffer system important in the ICF and renal tubules, where phosphates are more concentrated and function near an optimum pH of $6.8$.

Protein buffer system

The most concentrated chemical buffer system, especially in the ICF, where amino and acidic side groups bind or release $H^+$.

Respiratory acidosis

An acid-base imbalance occurring when alveolar ventilation fails to keep pace with $CO_2$ production, leading to a drop in pH.

Metabolic acidosis

An acid-base imbalance caused by increased production of organic acids (lactic acid, ketones), acidic drugs, or loss of base (chronic diarrhea).

Hypercapnia

An increase in $CO_2$ levels that stimulates pulmonary ventilation as a compensatory mechanism for acid-base imbalances.