Fluid & Electrolyte Imbalances

Vocabulary-style flashcards covering fluid compartments, transport mechanisms, pressure laws, and electrolyte imbalances including lab values and clinical signs.

Solvent

Water, which makes up approximately $60\%$ of the body.

Solutes

Substances such as proteins and electrolytes that are dissolved in water.

Albumin

The major protein found in the blood that contributes to oncotic pressure.

Anions

Negatively charged electrolytes, such as Phosphate ($PO_4^-$) and Bicarbonate ($HCO_3^-$).

Cations

Positively charged electrolytes, such as Sodium ($Na^+$), Potassium ($K^+$), Magnesium ($Mg^{++}$), and Calcium ($Ca^{++}$).

Intracellular fluid (ICF)

The fluid compartment located inside the cells, comprising $40\%$ of total body fluid.

Extracellular fluid (ECF)

Also known as intravascular fluid, it comprises $20\%$ of total body fluid and contains electrolytes, oxygen, and nutrients.

Interstitial fluid (ISF)

A fluid compartment containing mainly $Na^+$ and water; it does not contain proteins unless inflammation is present.

Diffusion

A passive process where a solute moves from an area of higher concentration to lower concentration until equilibrium is reached.

Osmosis

A passive process where water moves through a semi-permeable membrane from a lower to higher solute concentration.

Facilitated Transport

The movement of molecules across a membrane with assistance from carrier proteins, such as insulin helping glucose enter a cell.

Active Transport

A process that requires $ATP$ (energy) to move molecules like sodium and potassium against a concentration gradient.

Na+/K+ ATPase Pump

An active transport mechanism that pumps $3\,Na^+$ molecules out of the cell and $2\,K^+$ molecules into the cell.

Starling’s Law of Capillary Forces

The theory explaining fluid movement in capillary beds based on the two major opposing forces: hydrostatic and osmotic pressure.

Hydrostatic Pressure

The pushing force exerted by water in the bloodstream, created by the cardiac pump.

Osmotic Pressure

A pulling force exerted by solutes in a solution that favors fluid movement from the $ICF$ into the $ECF$ (capillary).

Oncotic Pressure

Also known as colloidal pressure, this is osmotic pressure exerted specifically by albumin in the bloodstream to attract water.

Osmolarity

The number of osmoles of solute per liter of solvent.

Osmolality

The number of osmoles of solute per kilogram of solvent, used to evaluate hydration status (Normal range: $285-295\,mOsm/L$).

Isotonic Solution

A solution with the same tonicity as blood (e.g., $0.9\%\,NaCl$ or Lactated ringers) that does not cause fluid shifts.

Hypotonic Solution

A solution with fewer particles than blood (e.g., $0.45\%\,NaCl$) that causes fluid to shift from the $ECF$ into the $ICF$, causing cells to swell.

Hypertonic Solution

A solution with more particles than blood (e.g., $3\%\,NaCl$ or Mannitol) that pulls water from the $ICF$ into the $ECF$, causing cells to shrink.

RAAS (Renin-Angiotensin-Aldosterone System)

A system triggered by hypotension or low cardiac output that results in the release of renin, angiotensin II, and aldosterone.

Aldosterone

A hormone that increases sodium and water reabsorption and potassium secretion by the kidneys.

Natriuretic Peptides

Hormones ($ANP$ and $BNP$) triggered by excess fluid volume that cause the kidneys to excrete large amounts of sodium and water.

Edema

An excess of fluid in the $ISF$ and $ICF$ compartments occurring when hydrostatic pressure is high or oncotic pressure is low.

Third-spacing

The sequestration of fluids in body cavities such as the pericardial sac, pleural space, or peritoneum.

Dehydration

A state of diminished water volume in the body (hypovolemia) that results in cellular dehydration and cell shrinkage.

Magnesium ($Mg^+$)

An intracellular cation ($1.5-2.5\,mEq/L$) primarily responsible for muscle and nerve relaxation.

Hypermagnesemia

A magnesium level greater than $2.5\,mEq/L$, characterized by muscle weakness, decreased $DTRs$, and hypotension.

Hypomagnesemia

A magnesium level less than $1.5\,mEq/L$, resulting in muscular excitement, tetany, and increased $DTRs$.

Potassium ($K^+$)

The main intracellular electrolyte ($3.5-5\,mEq/L$) vital for muscle and nerve conduction, especially cardiac and skeletal muscle.

Hyperkalemia

A serum $K^+$ level greater than $5.0\,mEq/L$, which can cause tall peaked T waves and muscle cramping; often caused by acidosis.

Hypokalemia

A potassium level below $3.5\,mEq/L$, which can cause muscle weakness, flattened T waves, and cardiac arrhythmias.

Calcium ($Ca^{++}$)

An electrolyte ($8.6-10.2\,mg/dL$) that stabilizes neuronal excitability; most is stored in bones and teeth.

Hypercalcemia

A calcium level greater than $10.2\,mg/dL$, leading to decreased muscle contractions, constipation, and lethargy.

Hypocalcemia

A calcium level lower than $8.6\,mg/dL$, causing increased muscle contractions, tetany, and Chvostek’s or Trousseau’s signs.

Chvostek’s Sign

A positive sign of hypocalcemia indicated by a facial spasm after tapping the facial nerve.

Trousseau’s Sign

A positive sign of hypocalcemia indicated by a carpal spasm when a blood pressure cuff is inflated above systolic level for $2$ minutes.

Sodium ($Na^+$)

The major $ECF$ cation ($135-145\,mg/dL$) responsible for fluid balance and extracellular excitation.

Hyponatremia

A sodium level less than $135\,mEq/L$, primarily causing neurological symptoms like headache, confusion, and seizures due to cerebral edema.

Hypernatremia

A sodium level greater than $145\,mg/L$, which causes cellular dehydration, thirst, and dry mucus membranes.