Body Fluids, Regulation & Acid-Base Balance – Key Vocabulary

These vocabulary flashcards cover the major terms and concepts from the chapter on body fluids, their regulation, acid–base balance, disorders, and therapeutic interventions.

Intracellular Fluid (ICF)

Fluid located inside body cells; also called cytosol.

Extracellular Fluid (ECF)

All body fluid outside cells, including interstitial fluid, blood plasma, lymph, and special compartment fluids.

Interstitial Fluid

ECF found in the microscopic spaces between tissue cells.

Blood Plasma

Liquid portion of blood; an extracellular fluid compartment rich in proteins.

Lymph

ECF that circulates within lymphatic vessels and nodes.

Electrolyte

Compound that dissociates into ions in solution, conducting electricity and helping regulate fluid balance, pH, and nerve/muscle function.

Cation

Positively charged ion (e.g., Na⁺, K⁺, Ca²⁺).

Anion

Negatively charged ion (e.g., Cl⁻, HCO₃⁻, PO₄³⁻).

Sodium Ion (Na⁺)

Most abundant cation in extracellular fluid; major determinant of plasma osmolarity.

Potassium Ion (K⁺)

Major intracellular cation; crucial for resting membrane potential and muscle contraction.

Metabolic Water

Water generated inside the body during aerobic cellular respiration.

Thirst Mechanism

Hypothalamic drive that increases water intake when plasma osmolarity rises or blood volume falls.

Plasma Osmolarity

Concentration of solutes in blood plasma; influences water movement between compartments.

Aldosterone

Adrenal cortex hormone that promotes renal Na⁺ reabsorption and K⁺ secretion, increasing water retention and blood pressure.

Antidiuretic Hormone (ADH)

Posterior pituitary hormone that increases water reabsorption in kidney collecting ducts, concentrating urine.

Renin

Enzyme released by juxtaglomerular cells that initiates formation of angiotensin II.

Angiotensin II

Potent vasoconstrictor that raises blood pressure and stimulates ADH and aldosterone release.

Juxtaglomerular Apparatus (JGA)

Structure where the distal tubule contacts the afferent arteriole; senses tubular Na⁺ and regulates renin release.

Atrial Natriuretic Peptide (ANP)

Hormone from atrial myocardium that promotes Na⁺ and water excretion, lowering blood pressure.

Buffer

Chemical system that minimizes pH changes by binding or releasing hydrogen ions (e.g., bicarbonate).

pH Scale

Logarithmic scale (0–14) expressing H⁺ concentration; 7 is neutral, lower is acidic, higher is alkaline.

Acidosis

Condition in which arterial blood pH falls below 7.35; depresses the nervous system.

Ketoacidosis

Acidosis caused by excess ketone bodies, often in uncontrolled diabetes or starvation.

Alkalosis

Condition in which arterial blood pH exceeds 7.45; may cause tingling, muscle spasms, dizziness.

Edema

Abnormal accumulation of interstitial fluid causing tissue swelling.

Effusion

Escape of fluid into a body cavity; abdominal effusion is called ascites.

Hyponatremia

Low blood sodium concentration, often from overhydration; may lead to cerebral edema.

Dehydration

Fluid deficit due to excessive loss or inadequate intake of water.

Polydipsia

Excessive thirst; often a response to dehydration or high plasma osmolarity.

Diabetes Insipidus

Condition of ADH deficiency leading to excessive dilute urine and intense thirst.

Isotonic Solution

IV fluid with osmolarity equal to plasma (e.g., 0.9% normal saline).

Hypertonic Solution

IV fluid with higher osmolarity than plasma (e.g., 5% dextrose in 0.45% saline).

Hypotonic Solution

IV fluid with lower osmolarity than plasma (e.g., 5% dextrose in water).

Ringer Lactate

Balanced electrolyte IV solution resembling plasma; used to replace fluids and electrolytes.

Serum Albumin 25%

Hypertonic protein solution administered to expand plasma volume via oncotic pressure.

Normal Saline

0.9% sodium chloride solution; common isotonic IV fluid.

Bicarbonate Ion (HCO₃⁻)

Primary extracellular buffer that helps regulate blood pH.

Respiratory Compensation

Adjustment of ventilation rate to alter CO₂ (an acid) exhalation and regulate pH.

Renal Compensation

Kidney processes that excrete H⁺, generate bicarbonate, and provide long-term pH control.

Osmoreceptors

Hypothalamic neurons that detect changes in plasma osmolarity and influence ADH release.

Angiotensin-Converting Enzyme (ACE)

Enzyme that converts angiotensin I to angiotensin II in the lungs and vascular endothelium.

Ascites

Accumulation of serous fluid in the peritoneal (abdominal) cavity, a type of effusion.

Semipermeable Membrane

Barrier that allows some molecules to pass while restricting others; basis of osmosis.

Osmosis

Movement of water across a semipermeable membrane from lower solute concentration to higher.

Fluid Homeostasis

Maintenance of stable body fluid volume, composition, and distribution via integrated feedback loops.