NPMCN Primary key terms

The body's active regulation of internal conditions such as temperature, pH, glucose and fluid balance within narrow limits, achieved through negative and positive feedback loops acting on sensors, integrators and effectors.

A control mechanism in which the output of a system reduces the original stimulus, restoring the variable toward its set point; the dominant regulatory principle in physiology, illustrated by baroreflex control of blood pressure.

A rapid, all-or-none reversal of membrane potential produced by sequential opening of voltage-gated sodium then potassium channels, propagating along axons and forming the basis of neural and muscle signalling.

The steady electrical difference across a cell membrane at rest, typically about minus 70 millivolts in neurons, set mainly by potassium permeability and the sodium-potassium ATPase pump.

Fast, jumping propagation of action potentials between nodes of Ranvier along myelinated axons, which increases conduction velocity without increasing axon diameter; lost in demyelinating disease.

The volume of plasma filtered by both kidneys per unit time, normally about 125 millilitres per minute; determined by net filtration pressure, renal blood flow and the filtration coefficient.

The arrangement of descending and ascending loops of Henle plus vasa recta that generates and preserves the medullary osmotic gradient, allowing production of concentrated or dilute urine under hormonal control.

The four pressures governing fluid movement across capillary walls: capillary hydrostatic pressure, interstitial hydrostatic pressure, plasma oncotic pressure and interstitial oncotic pressure; imbalance produces oedema.

The cytoplasmic pathway converting one glucose molecule into two pyruvate molecules with net gain of two ATP and two NADH, functioning with or without oxygen and regulated at phosphofructokinase-1.

The mitochondrial sequence that oxidises acetyl-CoA to carbon dioxide, generating reduced cofactors NADH and FADH2 plus GTP; also called the citric acid or tricarboxylic acid cycle.

ATP synthesis driven by the proton gradient across the inner mitochondrial membrane, generated by electron transfer through respiratory chain complexes and used by ATP synthase.

Synthesis of glucose from non-carbohydrate precursors such as lactate, glycerol and amino acids, occurring mainly in liver and kidney and using four bypass reactions to reverse irreversible glycolytic steps.

Hepatic production of acetoacetate, beta-hydroxybutyrate and acetone from excess acetyl-CoA during prolonged fasting or uncontrolled diabetes, providing alternative fuel for brain and muscle.

The substrate concentration at which an enzyme works at half its maximum velocity; an inverse indicator of enzyme affinity for substrate and a key parameter in inhibition studies.

Reversible enzyme inhibition in which an inhibitor resembling the substrate binds the active site, raising apparent Michaelis constant while leaving maximum velocity unchanged; overcome by more substrate.

Programmed, energy-dependent cell death with cell shrinkage, chromatin condensation and apoptotic body formation without inflammation, mediated by caspases and regulated by Bcl-2 family proteins.

Pathological cell death from severe injury, characterised by swelling, membrane rupture, enzyme leakage and surrounding inflammation; classified as coagulative, caseous, liquefactive, fat or fibrinoid.

Reversible replacement of one mature differentiated cell type by another better adapted to stress, such as squamous change in bronchial epithelium of smokers; a risk factor for dysplasia.

Disordered growth with loss of uniformity and architectural orientation of cells, showing nuclear atypia and pleomorphism; graded as low or high and a precursor of invasive malignancy.

A focal collection of activated macrophages, often with multinucleated giant cells and a rim of lymphocytes, formed in chronic inflammation such as tuberculosis, leprosy and sarcoidosis.

Autonomous, heritable new growth of cells that persists after removal of the initiating stimulus; benign tumours remain localised while malignant tumours invade and metastasise.

A gene whose loss of function permits uncontrolled proliferation, typically requiring inactivation of both alleles; examples include TP53, RB1 and APC.

A mutated or overexpressed cellular gene that drives neoplastic transformation through gain of function; derived from proto-oncogenes such as RAS, MYC and HER2.

The apparent volume relating total amount of drug in the body to its plasma concentration; a large value indicates extensive tissue uptake and influences loading dose calculation.

The volume of plasma cleared of drug per unit time by all eliminating organs; determines maintenance dose rate together with target concentration, independent of volume of distribution.

The time required for plasma drug concentration to fall by half during first-order elimination; determines time to steady state and dosing interval, and equals 0.693 times volume divided by clearance.

Presystemic elimination of an orally administered drug in gut wall and liver before reaching systemic circulation, reducing oral bioavailability and explaining large oral-to-intravenous dose ratios.

A ratio comparing the dose causing toxicity with the dose producing the desired effect; a narrow index, as with digoxin, warfarin or aminoglycosides, demands close monitoring.

The lowest concentration of an antimicrobial agent that visibly prevents growth of a standardised bacterial inoculum, used to define susceptibility and guide antibiotic selection.

The ability of microorganisms to survive drug concentrations that would normally inhibit or kill them, acquired through enzymatic inactivation, target alteration, efflux or reduced permeability.

An exaggerated or inappropriate immune response to antigen causing tissue injury; classified into four types based on mechanism, from immediate IgE-mediated to delayed cell-mediated.

A cluster of genes encoding cell-surface molecules that present peptide antigens to T lymphocytes; class I presents to CD8 cells and class II to CD4 cells, and allelic variation affects transplant matching.

The number of new cases of a disease arising in a defined population over a specified period, divided by the population at risk; a measure of risk used in aetiological studies.

The total number of existing cases of a disease in a population at a point or over a period, divided by the population; increases with longer duration and better survival.

The ratio of disease incidence in exposed compared with unexposed groups; the preferred measure of association in cohort studies, with a value of one indicating no association.

The ratio of odds of exposure among cases to odds among controls; the standard measure of association in case-control studies and an approximation of relative risk for rare diseases.

Sensitivity is the proportion of truly diseased people correctly identified by a test; specificity is the proportion of truly healthy people correctly classified as negative.

The probability that a person with a positive test result actually has the disease; depends on sensitivity, specificity and the prevalence of the condition in the tested population.

A range of values, calculated from sample data, that is likely to contain the true population parameter with a stated probability, commonly 95 percent; its width reflects precision.

The probability of observing a result at least as extreme as that obtained, assuming the null hypothesis is true; conventionally compared with 0.05 but not a measure of effect size.

A patient's voluntary agreement to investigation or treatment after receiving adequate information about purpose, benefits, risks and alternatives, given by someone with capacity and properly documented.

The professional duty to keep patient information private and disclose it only with consent or where legally or ethically justified, such as notifiable disease reporting or serious public risk.

Failure to provide the standard of care expected of a reasonably competent practitioner, causing harm; proving it requires a duty of care, breach, causation and actual damage.

A network of spinal nerve roots C5 to T1 supplying the upper limb; its cords and branches are injured in Erb and Klumpke palsies and in birth trauma.

The area of skin supplied by sensory fibres of a single spinal nerve root, mapped clinically to localise the level of a spinal cord or root lesion.

An anatomical region of the anterior thigh bounded by the inguinal ligament, sartorius and adductor longus, containing the femoral nerve, artery and vein in lateral-to-medial order.

Systematic bedside testing of the twelve cranial nerves, assessing olfaction, vision and pupils, eye movements, facial sensation and movement, hearing, swallowing and tongue movement to localise lesions.