Reference

Glossary

Every key term across the curriculum, in one place — 436 definitions, each linked to the lesson where it's taught. Search or jump by letter.

A

Abbreviation
A shortened form of a word or phrase used to save time in documentation, such as BP for blood pressure. Medical Terminology
ABC
Airway, Breathing, Circulation; the ordered priorities of the primary survey. Emergency Care
Abdominal thrusts
Quick inward and upward thrusts below the ribs used to expel an object blocking the airway of a responsive choking adult. Emergency Care
Absorption
The passage of digested nutrients from the intestine into the blood or lymph. Anatomy
Acid
A substance that donates a hydrogen ion (proton) or increases the hydrogen-ion concentration of a solution. Chemistry
Acidosis
A condition in which blood pH falls below the normal range (about 7.35). Chemistry
Actin and myosin
The thin (actin) and thick (myosin) protein filaments whose interaction produces contraction. Anatomy
Action potential
A rapid, self-propagating reversal of membrane voltage that carries a signal along an axon. Anatomy
Activation energy
The energy barrier that must be overcome for a chemical reaction to proceed; enzymes lower it. Biochemistry
Active immunity
Protection from antibodies and memory cells the body makes itself after infection or vaccination. Immunology
Active site
The pocket on an enzyme where the substrate binds and the reaction is catalyzed. Biochemistry
Active transport
Movement of a substance across a membrane against its concentration gradient, requiring energy such as ATP. Biology
Adrenal gland
A gland atop each kidney that releases stress hormones such as cortisol and adrenaline. Anatomy
AED
Automated external defibrillator; a device that analyzes the heart rhythm and can deliver a shock to restore an effective rhythm. Emergency Care
Aerobe
A bacterium that requires oxygen to grow; an anaerobe grows without oxygen and may be harmed by it. Microbiology
Aerobic respiration
Energy release that requires oxygen and yields a large amount of ATP from glucose. Biochemistry
Agonist
A drug that binds a receptor and activates it, mimicking the body's own signaling molecule. Pharmacology
Airway
The passage through which air travels to and from the lungs, from the mouth and nose down to the bronchi. Emergency Care
Airway obstruction
A blockage of the airway by the tongue, a foreign object, fluid, or swelling. Emergency Care
Alkalosis
A condition in which blood pH rises above the normal range (about 7.45). Chemistry
Allele
One of the alternative versions of a gene that can occupy the same position on a chromosome. Biology
Alveolus
A tiny air sac in the lungs where oxygen and carbon dioxide are exchanged with the blood. Anatomy
Amino acid
The monomer of proteins, containing an amino group, a carboxyl group, and a variable R side chain. Biochemistry
Anabolism
Metabolic reactions that build larger molecules from smaller ones and require energy input. Biochemistry
Analgesic
A medication that relieves pain, either by reducing inflammation or by altering how the nervous system perceives pain. Pharmacology
Anaphylactic shock
Shock caused by a severe allergic reaction that widens blood vessels and narrows the airway. Emergency Care
Anaphylaxis
A severe, rapid, life-threatening allergic reaction affecting breathing and circulation. Emergency Care
Anatomical position
The standard reference posture: standing erect, facing forward, arms at the sides, with palms and toes pointing forward. Medical Terminology
Angina
Chest pain or pressure caused by the heart muscle temporarily not getting enough blood, without permanent damage. Pathophysiology
Antagonist
A drug that binds a receptor but blocks it, preventing the natural signal from producing its effect. Pharmacology
Antibiotic
A drug that kills or inhibits the growth of bacteria, for example by disrupting the cell wall or protein synthesis. Pharmacology
Antibiotic resistance
The ability of bacteria to survive drugs that once killed them, through mutation or acquired genes. Microbiology
Antibody
A Y-shaped protein produced by B cells that binds a specific antigen. Immunology
Anticoagulant
A medication that reduces the blood's ability to clot, lowering the risk of harmful thrombosis. Pharmacology
Antigen
Any molecule the immune system recognizes as foreign and can respond to specifically. Immunology
Antihypertensive
A medication that lowers blood pressure through mechanisms such as relaxing vessels, reducing blood volume, or slowing the heart. Pharmacology
Antimicrobial stewardship
The coordinated effort to use antibiotics only when needed and correctly, to preserve their effectiveness. Microbiology
Antiviral
A drug that interferes with a specific step of viral replication; it does not kill viruses the way antibiotics act on bacteria. Microbiology
Apoptosis
Programmed, orderly cell death in which a cell dismantles itself neatly without spilling contents or triggering inflammation. Pathophysiology
Appendicular skeleton
The 126 bones of the limbs and the pectoral and pelvic girdles that enable movement and manipulation. Anatomy
Assessment
The first step: the deliberate, systematic collection of subjective and objective data about a patient. Nursing Fundamentals
Asthma
A chronic disease in which airways become inflamed and tighten in reversible episodes, causing wheezing and shortness of breath. Pathophysiology
Atherosclerosis
The buildup of fatty plaque within artery walls that narrows the vessel and can trigger clots. Anatomy
Atomic number (Z)
The number of protons in an atom's nucleus, which defines the element's identity. Chemistry
ATP
Adenosine triphosphate, the molecule cells use to store and transfer energy for immediate use. Biochemistry
Auscultation
Listening with a stethoscope to sounds produced by the heart, lungs, and bowels. Nursing Fundamentals
Autonomic nervous system
The involuntary division of the PNS controlling organs, with opposing sympathetic and parasympathetic branches. Anatomy
AV node
The atrioventricular node, which briefly delays the impulse so the atria finish emptying before the ventricles contract. Physiology
AVPU
A quick scale for level of consciousness: Alert, responds to Voice, responds to Pain, Unresponsive. Emergency Care
Axial skeleton
The 80 bones of the skull, vertebral column, and rib cage that form the body's central axis and protect vital organs. Anatomy

B

B cell
A lymphocyte that matures in bone marrow and produces antibodies against a specific antigen. Immunology
Bacillus
A rod-shaped bacterium; plural bacilli. Microbiology
Bactericidal
Describes an antibiotic that kills bacteria outright. Microbiology
Bacteriophage
A virus that infects bacteria. Microbiology
Bacteriostatic
Describes an antibiotic that stops bacteria from multiplying so the immune system can clear them. Microbiology
Baroreceptor reflex
A rapid negative feedback loop that adjusts heart rate and vessel diameter to keep blood pressure near its set point. Physiology
Base
A substance that accepts a hydrogen ion or increases the hydroxide-ion concentration of a solution. Chemistry
Bicarbonate buffer system
The main blood buffer, in which carbon dioxide, carbonic acid, and bicarbonate interconvert to resist changes in pH. Physiology
BID
From the Latin 'bis in die', meaning twice a day; a dosing frequency. Medical Terminology
Bile
A fluid made by the liver and stored in the gallbladder that emulsifies fats for digestion. Anatomy
Blood pressure
The force of blood against artery walls, reported as systolic over diastolic pressure in mmHg. Emergency Care
Bond order
The number of bonding electron pairs shared between two atoms; higher order means shorter, stronger bonds. Chemistry
Booster
An additional vaccine dose that renews or strengthens waning immune memory. Immunology
Bronchi
The two large airways branching from the trachea into the right and left lungs. Anatomy
Bronchodilator
A drug that relaxes airway smooth muscle to widen the bronchi and ease breathing. Pharmacology
Bronsted-Lowry acid
A proton (H+) donor; its Bronsted-Lowry base counterpart is a proton acceptor. Chemistry
BSI
Body substance isolation; precautions taken to avoid contact with a patient's blood and body fluids. Emergency Care
Buffer
A solution of a weak acid and its conjugate base that resists changes in pH when acid or base is added. Chemistry

C

Capillary
A microscopic vessel with walls one cell thick where gases, nutrients, and wastes are exchanged with tissues. Anatomy
Capillary refill
The time it takes color to return to a nail bed after it is pressed, a rough measure of circulation. Emergency Care
Capsid
The protein shell that surrounds and protects a virus's genetic material. Microbiology
Cardiac arrest
The sudden loss of effective heart function, when the heart stops pumping blood and the person becomes unresponsive and stops breathing normally. Emergency Care
Cardiac cycle
One complete heartbeat, consisting of contraction (systole) and relaxation (diastole) of the atria and ventricles. Physiology
Cardiac muscle
Striated, involuntary muscle found only in the heart, joined by intercalated discs. Anatomy
Cardiac output
The volume of blood pumped by one ventricle per minute, equal to heart rate multiplied by stroke volume. Physiology
Catabolism
Metabolic reactions that break larger molecules into smaller ones and release energy. Biochemistry
Cell cycle
The ordered sequence of growth, DNA replication, and division that a cell passes through, divided into interphase and the mitotic (M) phase. Biology
Cellular respiration
The set of metabolic reactions that break down glucose to capture energy in the form of ATP. Biology
Central nervous system (CNS)
The brain and spinal cord, where sensory information is integrated and commands are issued. Anatomy
Chain of infection
The sequence of six links—agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host—required for an infection to spread. Microbiology
Chain of Survival
The sequence of actions that improves survival from cardiac arrest, from early recognition and CPR to defibrillation and advanced care. Emergency Care
Chest compressions
Rhythmic pushes on the center of the chest that pump blood when the heart cannot. Emergency Care
Chief complaint
The main problem the patient reports, usually in their own words. Emergency Care
Chronic inflammation
Prolonged, low-grade inflammation lasting weeks to years, in which ongoing injury and repair occur at the same time. Pathophysiology
Chyme
The semi-liquid mix of partially digested food and gastric juice that leaves the stomach. Anatomy
Clonal selection
The process in which an antigen activates only the few lymphocytes that recognize it, which then multiply. Immunology
Coccus
A spherical bacterium; plural cocci (for example, staphylococci in clusters). Microbiology
Codon
A sequence of three nucleotides in mRNA that specifies a particular amino acid or a stop signal. Biology
Coenzyme
An organic cofactor, frequently derived from a vitamin, that assists an enzyme, such as NAD+ from niacin. Biochemistry
Cofactor
A non-protein helper, often a metal ion such as zinc or iron, required for an enzyme to function. Biochemistry
Combining form
A word root plus its combining vowel, written root/vowel (for example, gastr/o). Medical Terminology
Combining vowel
A vowel, almost always 'o', that links a root to another word part to ease pronunciation (as in cardi/o/logy). Medical Terminology
Commensal
A microorganism that lives on or in a host without causing harm, and often provides benefit. Microbiology
Competitive inhibitor
A molecule that resembles the substrate and blocks the active site, competing with the substrate for binding. Biochemistry
Complement system
A group of blood proteins that tag, puncture, and clear microbes and amplify inflammation. Immunology
Compound word
A medical term built from two or more word roots, such as osteoarthritis (oste + arthr + itis). Medical Terminology
Concentration
A measure of how much solute is present in a given amount of solution. Chemistry
Control center
The structure, often in the brain or an endocrine gland, that compares input to the set point and directs a response. Physiology
COPD
Chronic obstructive pulmonary disease, a group of progressive lung diseases, usually from smoking, that block airflow long-term. Pathophysiology
Covalent bond
A bond in which two atoms share one or more pairs of electrons. Chemistry
CPR
Cardiopulmonary resuscitation; chest compressions and, when trained, rescue breaths that circulate oxygenated blood during cardiac arrest. Emergency Care
Critical thinking
The disciplined, reflective reasoning nurses use to interpret data and make sound clinical decisions. Nursing Fundamentals
Crossing over
The exchange of segments between homologous chromosomes during meiosis I, creating new combinations of alleles. Biology

D

Defibrillation
The delivery of an electrical shock to reset a chaotic heart rhythm such as ventricular fibrillation. Emergency Care
Dehydration
A fluid volume deficit in which output exceeds intake, reducing circulating volume. Nursing Fundamentals
Dehydration synthesis
A reaction that joins two monomers by removing a molecule of water, forming a covalent bond. Biochemistry
Denaturation
The loss of a protein's three-dimensional shape, and therefore its function, usually caused by heat or extreme pH. Biochemistry
Depolarization
A shift of the membrane potential toward zero or positive values, usually caused by sodium entering the cell. Physiology
Desired dose
The amount of drug ordered by the prescriber, the numerator in the dose formula. Pharmacology
Diabetic ketoacidosis
A dangerous emergency, mainly in type 1 diabetes, in which a lack of insulin forces the body to burn fat and produce acidic ketones. Pathophysiology
Diaphoresis
Profuse sweating, often cool and clammy, that can accompany shock. Emergency Care
Diaphragm
The dome-shaped muscle beneath the lungs whose contraction draws air in during inhalation. Anatomy
Diaphysis
The shaft of a long bone, made of compact bone surrounding the marrow cavity. Anatomy
Diastole
The phase when a heart chamber relaxes and fills with blood. Anatomy
Diastolic pressure
The lower blood pressure number, measured while the heart relaxes between beats. Emergency Care
Dilution
The process of lowering a solution's concentration by adding more solvent. Chemistry
Diploid
Having two complete sets of chromosomes (in humans, 46), as in most body cells. Biology
Dipole moment
A measure of the separation of positive and negative charge across a bond or molecule. Chemistry
Direct pressure
Firm pressure applied directly onto a bleeding wound, the first and most important step to control external bleeding. Emergency Care
Disinfection
A process that kills most pathogens on surfaces or objects but may not destroy all spores. Microbiology
DNA ligase
The enzyme that seals the nicks between Okazaki fragments to create a continuous strand. Biology
DNA polymerase
The enzyme that adds nucleotides to a growing DNA strand, always in the 5' to 3' direction. Biology
Do Not Use list
A set of error-prone abbreviations that The Joint Commission and ISMP advise writing out in full to prevent mistakes. Medical Terminology
Documentation
The accurate, timely, and legal recording of patient care and observations in the health record. Nursing Fundamentals
Dominant
An allele that is expressed in the phenotype even when only one copy is present. Biology
Dorsal cavity
The posterior body cavity containing the cranial cavity (brain) and vertebral cavity (spinal cord). Medical Terminology
Dose on hand
The strength of the drug that is available in stock, such as milligrams per tablet or milligrams per milliliter. Pharmacology
Drop factor
The number of drops that equal one milliliter for a given IV tubing set, printed on the package. Pharmacology
Drug class
A group of medications that share a similar chemical structure, mechanism of action, or therapeutic use. Pharmacology
Dynamic equilibrium
A steady overall state maintained by continuous small adjustments rather than by a fixed, unchanging value. Physiology

E

Edema
Swelling caused by excess fluid trapped in the body's interstitial tissues. Nursing Fundamentals
Effector
A muscle or gland that carries out the response commanded by the control center. Physiology
Ejection fraction
The percentage of blood in a filled ventricle that is pumped out with each beat; normally 55% or more. Anatomy
Electrolyte
A mineral that carries an electric charge when dissolved, such as sodium, potassium, calcium, or chloride. Physiology
Electron configuration
The arrangement of an atom's electrons among its orbitals and subshells. Chemistry
Electron transport chain
A series of proteins in the inner mitochondrial membrane that uses electrons to drive the bulk of ATP production, with oxygen as the final acceptor. Biochemistry
Electronegativity
A measure of an atom's tendency to attract shared electrons in a chemical bond. Chemistry
EMS
Emergency Medical Services; the coordinated network of people, vehicles, and facilities that provides emergency care outside the hospital. Emergency Care
Endocrine gland
A ductless gland that releases hormones directly into the bloodstream. Anatomy
Endoplasmic reticulum
A membrane network for protein synthesis (rough ER) and lipid synthesis and detoxification (smooth ER). Biology
Enteral route
Administration through the gastrointestinal tract, such as oral, sublingual, or rectal routes. Pharmacology
Envelope
An outer lipid membrane, taken from the host cell, surrounding some viruses such as influenza and HIV. Microbiology
Enzyme
A protein that speeds a chemical reaction, such as breaking a food molecule into smaller units. Anatomy
Epinephrine auto-injector
A device that delivers a premeasured dose of epinephrine to treat anaphylaxis. Emergency Care
Epiphyseal plate
The growth plate of hyaline cartilage where long bones lengthen until it closes in early adulthood. Anatomy
Eukaryote
A cell with a true membrane-bound nucleus and organelles, including fungi, protozoa, plants, and animals. Microbiology
Evaluation
The final step: judging whether goals were met and deciding whether to continue, revise, or end the plan of care. Nursing Fundamentals
Extracellular fluid
Fluid outside cells, including interstitial fluid between cells and plasma within blood vessels. Physiology

F

Fall prevention
Measures such as risk screening, bed alarms, and keeping call lights in reach that reduce patient falls. Nursing Fundamentals
FAST
A stroke-recognition tool: Face drooping, Arm weakness, Speech difficulty, Time to call for help. Emergency Care
Fermentation
Anaerobic breakdown of glucose that regenerates carriers for glycolysis without oxygen, producing little ATP. Biochemistry
Fever
A regulated rise in body temperature that slows pathogen growth and speeds immune activity. Immunology
Fibrosis
Replacement of damaged tissue with collagen scar rather than functional cells, common when regeneration is not possible. Pathophysiology
Filtration
The first step of urine formation, in which water and small solutes pass from blood into the nephron. Anatomy
First-pass effect
The loss of active drug as an orally absorbed dose passes through the liver before reaching the general circulation. Pharmacology
First-pass metabolism
The reduction in the amount of active drug reaching the bloodstream after an oral dose is processed by the liver before entering general circulation. Pharmacology
Fluid compartments
The spaces holding body water: intracellular fluid inside cells and extracellular fluid outside cells, which includes plasma and interstitial fluid. Nursing Fundamentals
Fluid overload
A fluid volume excess in which intake exceeds output, expanding circulating volume and causing edema. Nursing Fundamentals
Frontal (coronal) plane
A vertical plane dividing the body into anterior (front) and posterior (back) portions. Medical Terminology

G

Gas exchange
The diffusion of oxygen into the blood and carbon dioxide out of it across the alveolar wall. Anatomy
Gastrointestinal (GI) tract
The continuous muscular tube from mouth to anus through which food passes and is digested. Anatomy
Gene
A segment of DNA that codes for a functional product, usually a protein, and serves as a unit of heredity. Biology
General impression
The immediate sense of how sick or injured a patient looks, formed within the first moments of contact. Emergency Care
Genetic code
The set of rules relating three-nucleotide codons to amino acids; it is triplet, degenerate, and nearly universal. Biology
Genotype
The specific combination of alleles an individual carries for a given gene. Biology
Glomerulus
A tuft of capillaries in the nephron where blood plasma is filtered under pressure. Anatomy
Glucagon
A pancreatic hormone that raises blood glucose by prompting the liver to release stored glucose. Pathophysiology
Glycolysis
The breakdown of glucose into two pyruvate molecules in the cytoplasm, producing a small net amount of ATP. Biochemistry
Golgi apparatus
The organelle that modifies, sorts, and packages proteins and lipids for delivery or secretion. Biology
Gram stain
A staining method that classifies bacteria as gram-positive (purple) or gram-negative (pink) based on cell-wall structure. Microbiology

H

Half-life
The time it takes for the plasma concentration of a drug to fall by half. Pharmacology
Hand hygiene
Cleaning the hands with soap and water or alcohol-based rub to remove or kill microorganisms; the most effective way to prevent healthcare-associated infection. Microbiology
Handoff
The transfer of patient information and responsibility from one caregiver to another, such as at shift change. Nursing Fundamentals
Hands-only CPR
CPR using continuous chest compressions without rescue breaths, recommended for untrained bystanders of an adult in cardiac arrest. Emergency Care
Haploid
Having a single set of chromosomes (in humans, 23), as in eggs and sperm. Biology
Head-tilt/chin-lift
A maneuver that opens the airway by tilting the head back and lifting the chin, used when no spinal injury is suspected. Emergency Care
Head-to-toe assessment
A systematic, ordered examination of every body system from head downward to ensure nothing is missed. Nursing Fundamentals
Heart attack
Damage to heart muscle caused by a blocked coronary artery, also called a myocardial infarction. Emergency Care
Heart failure
A condition in which the heart cannot pump enough blood to meet the body's needs, causing fatigue and fluid buildup. Pathophysiology
Helicase
The enzyme that unwinds and separates the two strands of the double helix at the replication fork. Biology
Helminth
A parasitic worm, such as a tapeworm or roundworm, that can infect humans. Microbiology
Hematopoiesis
The production of blood cells, which occurs in the red marrow of spongy bone. Anatomy
Hemorrhage
Significant bleeding, either external (from a wound) or internal (inside the body). Emergency Care
Hemorrhagic stroke
A stroke caused by a blood vessel bursting and bleeding into or around the brain. Pathophysiology
Herd immunity
Indirect protection that occurs when enough of a population is immune to slow a pathogen's spread. Immunology
Heterozygous
Having two different alleles for a gene (for example, Aa); a carrier for a recessive trait. Biology
High-alert medication
A drug that carries a heightened risk of serious harm if used in error, such as insulin, anticoagulants, or concentrated electrolytes. Nursing Fundamentals
Homeostasis
The maintenance of a stable internal environment despite changing external conditions. Physiology
Homologous chromosomes
A matched pair of chromosomes, one inherited from each parent, carrying the same genes in the same order. Biology
Homozygous
Having two identical alleles for a gene (for example, AA or aa). Biology
Hormone
A chemical messenger secreted into the blood by an endocrine gland to act on distant target cells. Anatomy
Hydrogen bond
A weak attraction between a hydrogen bonded to N, O, or F and a lone pair on another electronegative atom. Chemistry
Hydrolysis
A reaction that breaks a bond between monomers by adding a molecule of water, the reverse of dehydration synthesis. Biochemistry
Hyperglycemia
Abnormally high blood glucose, the hallmark of poorly controlled diabetes. Pathophysiology
Hypertension
Chronically high blood pressure that forces the heart to work harder and damages arteries over time. Pathophysiology
Hyperthyroidism
An overactive thyroid producing too much thyroid hormone, which speeds up the body's metabolism. Pathophysiology
Hypertonic solution
An IV fluid more concentrated than plasma that pulls water out of cells, causing them to shrink. Nursing Fundamentals
Hypoglycemia
Abnormally low blood sugar, which can cause confusion, sweating, and unresponsiveness. Emergency Care
Hypothyroidism
An underactive thyroid producing too little thyroid hormone, which slows the body's metabolism. Pathophysiology
Hypotonic solution
An IV fluid more dilute than plasma that moves water into cells, causing them to swell. Nursing Fundamentals
Hypovolemic shock
Shock caused by low blood or fluid volume, often from severe bleeding. Emergency Care
Hypoxia
A deficiency of oxygen reaching the tissues, which starves cells of the fuel they need to make energy. Pathophysiology

I

Immunization
The process of becoming protected against a disease, most often through vaccination. Immunology
Inactivated vaccine
A vaccine made from a pathogen killed so it cannot replicate but can still be recognized. Immunology
Incident report
An internal record of an error or near-miss used to analyze and improve safety, kept separate from the patient's chart. Nursing Fundamentals
Induced fit
The model in which the active site changes shape slightly to grip the substrate more snugly after binding. Biochemistry
Infiltration
Leakage of IV fluid into surrounding tissue when the catheter dislodges from the vein, causing swelling and coolness. Nursing Fundamentals
Inflammation
A protective response to injury or infection marked by redness, heat, swelling, and pain. Immunology
Innate immunity
The set of defenses present from birth that respond rapidly and non-specifically to any pathogen. Immunology
Inspection
Systematic visual examination of the patient, using sight and smell to note color, shape, symmetry, and movement. Nursing Fundamentals
Insulin
A pancreatic hormone that lowers blood glucose by moving it into cells. Anatomy
Intake and output (I&O)
A record comparing all fluids taken in against all fluids lost, used to track fluid balance. Nursing Fundamentals
Interphase
The portion of the cell cycle (G1, S, and G2) during which the cell grows and copies its DNA in preparation for division. Biology
Intracellular fluid
The fluid inside cells, the largest fluid compartment, holding roughly two-thirds of body water. Physiology
Intramuscular (IM)
Injection into a muscle, which absorbs the drug steadily through its rich blood supply. Pharmacology
Intravenous (IV)
Injection directly into a vein, giving the fastest onset and 100% bioavailability. Pharmacology
Ion
An atom or group of atoms carrying a net electric charge from gaining or losing electrons. Chemistry
Ionic bond
An electrostatic attraction between oppositely charged ions formed by electron transfer, typically between a metal and a nonmetal. Chemistry
Ionization energy
The energy required to remove an electron from a gaseous atom or ion. Chemistry
Ischemia
Reduced blood supply to a tissue, cutting off both oxygen and nutrients and removing waste less effectively than hypoxia alone. Pathophysiology
Ischemic stroke
A stroke caused by a blocked artery cutting off blood flow to part of the brain. Pathophysiology
Isotonic solution
A solution with the same effective solute concentration as the cell interior, causing no net water movement; 0.9 percent saline is an example. Chemistry
Isotope
Atoms of the same element that share a proton number but differ in neutron number. Chemistry
IV drip rate
The speed at which an intravenous fluid is infused, measured in drops per minute or milliliters per hour. Pharmacology

J

Jaw-thrust
A maneuver that opens the airway by pushing the jaw forward without moving the neck, used when spinal injury is suspected. Emergency Care
Just culture
A workplace approach that responds to honest mistakes with learning and system fixes rather than blame, while holding people accountable for reckless behavior. Nursing Fundamentals

K

Kidney
A bean-shaped organ that filters blood, removes waste, and regulates fluid and electrolyte balance. Anatomy
Km (Michaelis constant)
The substrate concentration at half-maximal reaction velocity, reflecting enzyme-substrate affinity. Chemistry
Krebs cycle
The citric acid cycle in the mitochondrial matrix that oxidizes fuel and loads electron carriers with high-energy electrons. Biochemistry

L

Leading strand
The strand synthesized continuously in the same direction the replication fork moves. Biology
Live-attenuated vaccine
A vaccine using a weakened but living pathogen that cannot cause serious disease in healthy people. Immunology
Lysosome
A vesicle filled with hydrolytic enzymes that digests macromolecules and worn-out cell components. Biology

M

Macromolecule
A large molecule built from many smaller repeating units; the four biological classes are carbohydrates, lipids, proteins, and nucleic acids. Biochemistry
Mass number (A)
The total count of protons and neutrons in a nucleus (A = Z + N). Chemistry
Mechanism of injury
The forces and events that caused a patient's trauma, which help predict likely injuries. Emergency Care
Medical asepsis
Clean technique that reduces the number and spread of microorganisms, such as hand hygiene and cleaning surfaces. Nursing Fundamentals
Medical direction
The physician oversight, through protocols or direct orders, under which EMS providers operate. Emergency Care
Medication error
Any preventable event that may cause inappropriate medication use or patient harm. Nursing Fundamentals
Medication order
A provider's authorization specifying the drug, dose, route, frequency, and any special instructions. Nursing Fundamentals
Medication reconciliation
Comparing a patient's current medications across care transitions to prevent omissions, duplications, or interactions. Nursing Fundamentals
Medulla oblongata
The brainstem region that sets the basic automatic rhythm of breathing. Anatomy
Meiosis
Two rounds of division that produce four genetically unique haploid gametes from one diploid cell. Biology
Memory cell
A long-lived B or T cell that enables a faster, stronger response on re-exposure to an antigen. Immunology
Metabolism
The sum of all chemical reactions in a cell, including those that build molecules and those that break them down. Biochemistry
MHC molecule
A cell-surface protein that displays antigen fragments so T cells can inspect them. Immunology
Microorganism
A living thing too small to see with the naked eye, such as a bacterium, protozoan, or fungus; viruses are usually studied alongside them. Microbiology
Milligram (mg)
A unit of mass equal to one-thousandth of a gram, the most common unit for drug doses. Pharmacology
Mitochondrion
The double-membraned organelle that produces most of the cell's ATP through aerobic respiration. Biology
Mitosis
Division of the nucleus that produces two genetically identical diploid daughter cells. Biology
Mode of transmission
How a pathogen travels from one host to another, for example by contact, droplets, airborne particles, or a vehicle or vector. Microbiology
Molarity (M)
Concentration expressed as moles of solute per liter of solution. Chemistry
Monomer
A single small subunit that links with others to form a larger polymer, such as a monosaccharide or amino acid. Biochemistry
Motor unit
A single motor neuron together with all the muscle fibers it stimulates. Anatomy
mRNA
Messenger RNA; the transcript that carries the coding sequence from DNA to the ribosome. Biology
mRNA vaccine
A vaccine that delivers genetic instructions for cells to make a pathogen protein that triggers immunity. Immunology
MRSA
Methicillin-resistant Staphylococcus aureus, a strain resistant to many common antibiotics. Microbiology
Myelin sheath
An insulating glial wrapping around axons that speeds signal conduction. Anatomy
Myocardial infarction
A heart attack, in which blood flow to part of the heart muscle is blocked long enough to kill that tissue. Pathophysiology
Myocardium
The thick muscular middle layer of the heart wall that contracts to pump blood. Anatomy

N

NADH
An electron carrier that delivers high-energy electrons from earlier stages to the electron transport chain. Biology
Natural killer (NK) cell
An innate lymphocyte that destroys virus-infected and tumor cells without prior exposure. Immunology
Necrosis
Uncontrolled cell death from severe injury, in which cells swell and rupture and spill their contents, provoking inflammation. Pathophysiology
Negative feedback
A control mechanism in which a hormone's effect signals its own secretion to slow, keeping levels stable. Anatomy
Nephron
The microscopic functional unit of the kidney that filters blood and forms urine. Anatomy
Neuromuscular junction
The synapse where a motor neuron releases acetylcholine to trigger a muscle fiber's contraction. Anatomy
Neuron
The excitable cell that transmits information as electrical and chemical signals; the functional unit of the nervous system. Anatomy
Neurotransmitter
A chemical messenger (such as acetylcholine, glutamate, or dopamine) released at a synapse to influence the next cell. Anatomy
Neutralization
The reaction of an acid with a base to produce water and a salt. Chemistry
Never event
A serious, largely preventable safety error, such as surgery on the wrong site, that should never occur. Nursing Fundamentals
Nondisjunction
The failure of chromosomes or chromatids to separate properly during division, producing cells with an abnormal chromosome number. Biology
Normal flora
The community of microorganisms that normally lives on the skin and mucous membranes of a healthy person; also called the microbiome. Microbiology
NPO
From the Latin 'nil per os', meaning nothing by mouth; the patient should not eat or drink. Medical Terminology
NSAID
Nonsteroidal anti-inflammatory drug; reduces pain, fever, and inflammation by blocking cyclooxygenase (COX) enzymes. Pharmacology
Nucleotide
The monomer of nucleic acids, made of a five-carbon sugar, a phosphate group, and a nitrogenous base. Biochemistry
Nucleus
The membrane-bound organelle that houses the cell's DNA and directs gene expression. Biology
Nursing diagnosis
A clinical judgment about a patient's response to a health problem that nurses are licensed to treat, distinct from a medical diagnosis of disease. Nursing Fundamentals
Nursing process
A systematic, five-step method (ADPIE) nurses use to identify patient needs, plan care, act, and judge results. Nursing Fundamentals

O

Objective data
Measurable, observable information gathered by the nurse, such as vital signs, lab values, or a visible wound; also called signs. Nursing Fundamentals
Obligate intracellular parasite
An organism or particle that can only reproduce inside a living host cell, as all viruses must. Microbiology
Obstructive disorder
A breathing problem in which narrowed or blocked airways make it hard to move air out of the lungs. Pathophysiology
Okazaki fragments
The short stretches of DNA synthesized discontinuously along the lagging strand, later joined together. Biology
Onset of action
The time between administering a drug and the beginning of its noticeable effect. Pharmacology
Opioid
An analgesic that binds opioid receptors in the nervous system to blunt pain signaling; carries risks of sedation, dependence, and respiratory depression. Pharmacology
Opportunistic infection
An infection caused by an organism that is usually harmless but becomes pathogenic when host defenses are weakened. Microbiology
OPQRST
A pain-assessment mnemonic: Onset, Provocation, Quality, Region/Radiation, Severity, Time. Emergency Care
Optimum
The temperature or pH at which a given enzyme works fastest. Biochemistry
Organelle
A specialized subcellular structure that carries out a specific function, often bounded by its own membrane. Biology
Osmosis
The movement of water across a semipermeable membrane from lower to higher solute concentration. Chemistry
Osteoblast
A bone-forming cell that lays down new bone matrix and becomes an osteocyte once trapped within it. Anatomy
Osteoclast
A large multinucleated cell that breaks down (resorbs) bone by secreting acid and enzymes. Anatomy
Osteoporosis
A condition of reduced bone mass and density that makes bones fragile and prone to fracture. Anatomy
Oxidative phosphorylation
The production of ATP driven by the proton gradient the electron transport chain builds across the inner mitochondrial membrane. Biology
Oxygen saturation (SpO2)
The percentage of hemoglobin carrying oxygen, measured non-invasively with a pulse oximeter. Nursing Fundamentals

P

Pain scale
A standardized tool, such as a 0-to-10 numeric rating, used to quantify a patient's self-reported pain. Nursing Fundamentals
Palpation
Using the hands and fingers to feel for texture, temperature, moisture, tenderness, and masses. Nursing Fundamentals
Pancreas
An accessory organ that secretes digestive enzymes and bicarbonate into the small intestine. Anatomy
Parenteral route
Administration that bypasses the gastrointestinal tract, most often by injection (IV, IM, or subcutaneous). Pharmacology
Passive immunity
Temporary protection from antibodies received from another source, such as across the placenta. Immunology
Patent airway
An airway that is open and unobstructed, allowing air to move freely. Emergency Care
Pathogen
A disease-causing organism such as a bacterium, virus, fungus, or parasite. Immunology
Peptide bond
The covalent bond linking amino acids in a protein, formed by a condensation (dehydration) reaction. Chemistry
Peptidoglycan
The mesh-like polymer that forms the bacterial cell wall and gives it strength; a common antibiotic target. Microbiology
Percussion
Tapping the body surface to produce sounds that reveal whether underlying tissue is air-filled, fluid-filled, or solid. Nursing Fundamentals
Perfusion
The delivery of oxygen-rich blood to the body's tissues and organs. Emergency Care
Peripheral nervous system (PNS)
All the nerves outside the brain and spinal cord that carry signals to and from the body. Anatomy
Peristalsis
Waves of smooth-muscle contraction that push food along the digestive tract. Anatomy
Personal protective equipment (PPE)
Barriers such as gloves, gowns, masks, and eye protection worn to prevent contact with infectious material. Microbiology
pH
A logarithmic measure of hydrogen-ion concentration, equal to the negative base-10 logarithm of [H+]. Chemistry
Phagocyte
A white blood cell, such as a neutrophil or macrophage, that engulfs and digests microbes and debris. Immunology
Phagocytosis
The process by which a cell engulfs a particle or microbe into a vesicle for digestion. Immunology
Pharmacodynamics
The study of a drug's biochemical and physiological effects and its mechanism of action — 'what the drug does to the body.' Pharmacology
Pharmacokinetics
The study of how the body absorbs, distributes, metabolizes, and excretes a drug over time — 'what the body does to the drug.' Pharmacology
Phenotype
The observable trait produced by a genotype interacting with the environment. Biology
Phospholipid
A lipid with a phosphate-containing hydrophilic head and two hydrophobic fatty acid tails; the main building block of cell membranes. Biochemistry
Phospholipid bilayer
A double layer of phospholipids that forms the basic structure of all cell membranes. Chemistry
Pituitary gland
The 'master gland' at the base of the brain that controls many other endocrine glands under hypothalamic direction. Anatomy
Planning
Setting patient-centered goals and selecting nursing interventions to reach them. Nursing Fundamentals
Plaque
A deposit of cholesterol, cells, and other material within an artery wall that can grow, harden, and rupture. Pathophysiology
Plasma membrane
The selectively permeable phospholipid bilayer that forms the outer boundary of the cell. Biology
Pneumonia
An infection that inflames the air sacs of the lungs, which may fill with fluid or pus and impair gas exchange. Pathophysiology
Polar covalent bond
A covalent bond with unequal electron sharing, producing a partial charge separation (dipole). Chemistry
Polymer
A large molecule made of many monomers joined by covalent bonds, such as a polysaccharide or protein. Biochemistry
Portal of exit
The route by which a pathogen leaves its reservoir, such as respiratory secretions, blood, or stool. Microbiology
Positive feedback
A loop that amplifies a change, driving the variable further from its starting value until an external event ends it. Physiology
Postictal state
The period of confusion and drowsiness that follows a seizure as the brain recovers. Emergency Care
PPE
Personal protective equipment such as gloves, eye protection, and masks that create a barrier against infectious material. Emergency Care
Prefix
A word part at the beginning of a term that modifies its meaning, often indicating number, position, time, or degree. Medical Terminology
Primary survey
The rapid initial assessment that finds and treats immediate threats to life, focused on airway, breathing, and circulation. Emergency Care
Primase
The enzyme that synthesizes a short RNA primer to provide a starting point for DNA polymerase. Biology
PRN
From the Latin 'pro re nata', meaning 'as needed'; describes medication given only when required. Medical Terminology
Prokaryote
A cell that lacks a membrane-bound nucleus and organelles, including all bacteria and archaea. Microbiology
Proofreading
The 3' to 5' exonuclease activity of DNA polymerase that removes incorrectly paired nucleotides, lowering the error rate. Biology
Proximal
Nearer to the point of attachment of a limb to the trunk; the opposite of distal. Medical Terminology
Pulse
The rhythmic expansion of an artery felt with each heartbeat, reported as beats per minute. Emergency Care
Punnett square
A grid used to predict the probability of offspring genotypes and phenotypes from a cross. Biology
Pyruvate oxidation
The conversion of pyruvate to acetyl-CoA, releasing carbon dioxide and producing NADH, as it enters the mitochondrion. Biology

R

Reabsorption
The return of useful substances such as water, glucose, and ions from the nephron back into the blood. Anatomy
Receptor
A protein, usually on or in a cell, that a drug binds to in order to produce a biological effect. Pharmacology
Recessive
An allele that is expressed only when two copies are present (no dominant allele masks it). Biology
Recoil
Allowing the chest to return fully to its normal position between compressions so the heart can refill. Emergency Care
Recovery position
A stable position on the side that helps keep the airway of an unresponsive, breathing patient clear. Emergency Care
Regeneration
Healing in which lost cells are replaced by new cells of the same type, restoring normal structure and function. Pathophysiology
Repolarization
The return of the membrane potential toward its negative resting value, driven mainly by potassium leaving the cell. Physiology
Rescue breathing
Providing breaths to a patient who is not breathing adequately but has a pulse. Emergency Care
Reservoir
The place where a pathogen normally lives and multiplies, such as a person, animal, or the environment. Microbiology
Respiratory distress
A state of struggling to breathe, marked by rapid breathing, use of extra muscles, and signs of low oxygen. Pathophysiology
Respiratory rate
The number of breaths a person takes in one minute. Emergency Care
Resting membrane potential
The steady voltage across a resting neuron's membrane, typically about negative 70 millivolts inside relative to outside. Physiology
Restrictive disorder
A breathing problem in which the lungs cannot fully expand, so they hold less air. Pathophysiology
Retrovirus
An RNA virus, such as HIV, that uses reverse transcriptase to copy its RNA into DNA inside the host cell. Microbiology
Reversible injury
Early cell damage, such as swelling, that the cell can recover from if the harmful stress is removed in time. Pathophysiology
Right upper quadrant (RUQ)
One of the four abdominal quadrants; contains the liver, gallbladder, and part of the pancreas and intestines. Medical Terminology
Rights of medication administration
A checklist—right patient, drug, dose, route, time, documentation, reason, response, and refusal—used to give medications safely. Nursing Fundamentals
RNA polymerase
The enzyme that reads a DNA template and builds a complementary RNA strand in the 5' to 3' direction. Biology
Route
How a medication is given, such as by mouth (oral), injection, or topically. Nursing Fundamentals

S

SA node
The sinoatrial node, the heart's natural pacemaker, which sets the resting heart rate. Anatomy
Sagittal plane
A vertical plane dividing the body into right and left portions; the midsagittal plane divides it into equal halves. Medical Terminology
Saltatory conduction
Rapid impulse propagation in which the action potential jumps between nodes of Ranvier on a myelinated axon. Physiology
SAMPLE
A history mnemonic: Signs/symptoms, Allergies, Medications, Past history, Last oral intake, Events leading up. Emergency Care
Sarcomere
The repeating contractile unit of skeletal muscle, bounded by Z-discs and containing actin and myosin. Anatomy
SBAR
A structured communication tool—Situation, Background, Assessment, Recommendation—used to convey information clearly. Nursing Fundamentals
Scene size-up
The rapid assessment of a scene for safety, hazards, number of patients, and mechanism of injury before providing care. Emergency Care
Scope of practice
The set of skills and treatments a provider is legally trained and authorized to perform. Emergency Care
Secondary survey
The more detailed head-to-toe examination and history performed after life threats are addressed. Emergency Care
Secretion
The active transfer of additional wastes and excess ions from the blood into the nephron tubule. Anatomy
Seizure
A burst of abnormal electrical activity in the brain that can cause convulsions or altered awareness. Emergency Care
Semi-conservative replication
The copying mechanism in which each new DNA molecule contains one original (parental) strand and one newly made strand. Biology
Set point
The target value that a regulated variable is kept near, such as roughly 37 degrees Celsius for core body temperature. Physiology
Shock
A life-threatening condition in which the body's tissues do not receive enough blood flow and oxygen. Emergency Care
Sister chromatids
The two identical copies of a chromosome joined at the centromere after DNA replication. Biology
Skeletal muscle
Striated, voluntary muscle attached to bones that moves the skeleton. Anatomy
Sliding-filament model
The mechanism in which myosin heads pull actin filaments inward, shortening the sarcomere without the filaments themselves shortening. Anatomy
SMART goal
An outcome that is Specific, Measurable, Attainable, Relevant, and Time-bound. Nursing Fundamentals
Smooth muscle
Non-striated, involuntary muscle in the walls of hollow organs and blood vessels. Anatomy
SOAP note
A structured chart format with four parts: Subjective, Objective, Assessment, and Plan. Medical Terminology
Sodium-potassium pump
An active transporter that moves three sodium ions out and two potassium ions into the cell per cycle, using ATP to maintain ion gradients. Physiology
Solubility
The maximum amount of a solute that dissolves in a given amount of solvent at a set temperature. Chemistry
Solute
The substance that is dissolved in a solution, present in the smaller amount. Chemistry
Solvent
The substance that does the dissolving, present in the larger amount; in the body this is water. Chemistry
Splicing
The removal of introns and joining of exons to produce mature mRNA. Biology
SpO2
The percentage of hemoglobin saturated with oxygen, measured by a pulse oximeter. Emergency Care
Standard precautions
Infection-control practices applied to all patients regardless of diagnosis, treating all blood and body fluids as potentially infectious. Microbiology
Stat
From the Latin 'statim', meaning immediately; an order to be carried out at once. Medical Terminology
Sterile field
A microorganism-free area created and maintained for procedures requiring surgical asepsis. Nursing Fundamentals
Sterilization
A process that destroys all microorganisms, including bacterial spores, on an object. Microbiology
Stroke
A sudden interruption of blood flow to part of the brain, either from a clot or a bleed. Emergency Care
Stroke volume
The volume of blood ejected by a ventricle in one beat. Anatomy
Strong acid
An acid that dissociates essentially completely in water, such as HCl. Chemistry
Subcutaneous (SubQ)
Injection into the fatty tissue beneath the skin, giving slower, more sustained absorption. Pharmacology
Subjective data
Information reported by the patient that cannot be directly observed, such as pain, nausea, or worry; also called symptoms. Nursing Fundamentals
Sublingual
Placement of a drug under the tongue so it absorbs directly into blood vessels and bypasses the liver's first pass. Pharmacology
Substrate
The specific reactant molecule that an enzyme binds and acts upon. Biochemistry
Subunit vaccine
A vaccine containing only specific pieces of a pathogen, such as a surface protein. Immunology
Suffix
A word part at the end of a term that usually indicates a condition, procedure, or specialty. Medical Terminology
Superior
Toward the head or upper part of a structure; the opposite of inferior. Medical Terminology
Surfactant
A lipid-protein substance that lowers surface tension in alveoli and keeps them from collapsing. Anatomy
Surgical asepsis
Sterile technique that removes all microorganisms, used for invasive procedures and to maintain a sterile field. Nursing Fundamentals
Susceptible host
A person whose defenses are inadequate to resist a pathogen, such as an infant, an elderly person, or an immunocompromised patient. Microbiology
Synapse
The junction where a neuron passes a signal to another cell, usually by releasing a neurotransmitter. Anatomy
Systole
The phase of the cardiac cycle when a heart chamber contracts and ejects blood. Anatomy
Systolic pressure
The higher blood pressure number, measured while the heart contracts. Emergency Care

T

T cell
A lymphocyte that matures in the thymus; helper (CD4) types coordinate responses and cytotoxic (CD8) types kill infected cells. Immunology
Target cell
A cell bearing the specific receptor for a given hormone, allowing it to respond to that hormone. Anatomy
Therapeutic index
The ratio comparing the dose that causes toxicity to the dose that produces the desired effect; a higher ratio means a wider margin of safety. Pharmacology
Three checks
Verifying the medication label against the order three times: when retrieving it, when preparing it, and before administering it. Nursing Fundamentals
Threshold
The critical level of depolarization, near negative 55 millivolts, that must be reached to trigger an action potential. Physiology
Thyroid gland
A neck gland that secretes thyroid hormone to set the body's overall metabolic rate. Anatomy
Tonicity
The relative solute concentration of a solution compared with the inside of a cell, which determines water movement. Chemistry
Tourniquet
A device tightened around a limb above severe bleeding to stop blood flow when direct pressure fails. Emergency Care
Trachea
The windpipe, the main airway that carries air from the larynx toward the lungs. Anatomy
Transcription
The synthesis of an RNA copy from a DNA template, carried out by RNA polymerase. Biology
Translation
The process by which the ribosome reads mRNA codons and assembles the corresponding chain of amino acids. Biology
Transmission-based precautions
Extra measures—contact, droplet, or airborne—added when a specific route of spread is known or suspected. Nursing Fundamentals
Transverse plane
A horizontal plane dividing the body into superior (upper) and inferior (lower) portions. Medical Terminology
tRNA
Transfer RNA; an adaptor molecule whose anticodon matches a codon while it carries the matching amino acid. Biology
Two identifiers
Confirming patient identity with two independent pieces of information, such as full name and date of birth, before administration. Nursing Fundamentals
Two patient identifiers
Two independent pieces of identifying information, such as name and date of birth, used to confirm the correct patient. Nursing Fundamentals
Type 1 diabetes
A disease in which the immune system destroys the insulin-producing cells, so the body makes little or no insulin. Pathophysiology
Type 2 diabetes
A disease in which cells respond poorly to insulin (insulin resistance) and the pancreas cannot keep up, raising blood glucose. Pathophysiology

U

Urea
The main nitrogen-containing waste product of protein metabolism, excreted in urine. Anatomy
Ureter
The tube that carries urine from a kidney to the bladder. Anatomy

V

Vaccine
A preparation that safely exposes the immune system to part of a pathogen to build protective memory. Immunology
Valence electrons
The electrons in an atom's outermost shell, which govern its chemical reactivity and bonding. Chemistry
Ventilation
The mechanical movement of air into and out of the lungs, i.e., breathing. Anatomy
Ventral cavity
The anterior body cavity containing the thoracic cavity and the abdominopelvic cavity. Medical Terminology
Villi
Tiny finger-like projections of the small intestine lining that greatly increase surface area for absorption. Anatomy
Virus
An acellular infectious particle made of genetic material inside a protein coat that can only replicate inside a living host cell. Microbiology
Vital signs
Measurements of the body's basic functions, including pulse, respirations, blood pressure, temperature, and oxygen saturation. Emergency Care
VSEPR theory
A model that predicts molecular shape by arranging electron pairs to minimize repulsion. Chemistry

W

Weak acid
An acid that only partially dissociates in water, existing in equilibrium with its conjugate base. Chemistry
Weight-based dosing
Calculating a dose from the patient's body weight, expressed in milligrams of drug per kilogram (mg/kg). Pharmacology
Word root
The core of a term that carries its central meaning, usually a body part or system (for example, cardi = heart). Medical Terminology

X

X-linked
Referring to a gene located on the X chromosome, producing sex-dependent inheritance patterns. Biology

#

-ectomy
A suffix meaning surgical removal, as in appendectomy (removal of the appendix). Medical Terminology
-itis
A suffix meaning inflammation, as in appendicitis (inflammation of the appendix). Medical Terminology
9-1-1
The universal emergency access number in the United States that connects a caller to a dispatch center. Emergency Care