FCPS Part-I key terms

The body's active regulation of internal conditions such as temperature, pH, glucose and fluid balance around a set point, achieved through negative feedback loops that sense change and trigger corrective responses.

A control mechanism in which the output of a system reduces the stimulus that produced it, restoring a variable toward its set point; the dominant regulatory principle in endocrine and physiological control.

A hormone that opposes the action of another to protect against extremes, such as glucagon, cortisol, adrenaline and growth hormone rising to raise blood glucose when insulin action predominates.

The concentration of osmotically active particles per kilogram of solvent. Plasma osmolality is normally about 275-295 mOsm/kg and is estimated as 2×sodium plus glucose/18 plus urea/2.8.

Increased urine output caused by non-reabsorbable solutes such as glucose or mannitol retaining water in the tubule, producing polyuria, dehydration and risk of hypernatraemia if water intake is inadequate.

The balance of hydrostatic and oncotic pressures across a capillary wall that governs net fluid movement between plasma and interstitium; imbalance produces oedema or intravascular depletion.

The component of osmotic pressure exerted by plasma proteins, chiefly albumin, that draws water into the capillary and opposes filtration; low albumin reduces it and predisposes to oedema.

A rapid, all-or-none reversal of membrane potential generated by voltage-gated sodium influx followed by potassium efflux, propagating electrical signals along neurons and muscle fibres.

The interval after an action potential during which a neuron cannot fire again (absolute) or needs a stronger stimulus (relative), limiting firing frequency and ensuring one-way propagation.

Jumping propagation of action potentials between nodes of Ranvier in myelinated axons, greatly increasing conduction velocity; demyelination slows or blocks transmission.

Damage to the corticospinal or corticobulbar pathway above the anterior horn cell, producing spasticity, hyperreflexia, extensor plantar responses and weakness without marked early wasting.

Damage to the anterior horn cell, motor root or peripheral nerve, producing flaccid weakness, wasting, fasciculation, hypotonia and reduced or absent reflexes in the affected distribution.

The principle that increasing ventricular preload (end-diastolic fibre stretch) increases stroke volume within physiological limits, so cardiac output rises with venous return until overstretch reduces efficiency.

The ventricular wall stress at end-diastole, determined mainly by venous return and blood volume; it is the load that stretches myocardium before contraction and drives stroke volume.

The resistance the ventricle must overcome to eject blood, determined by systemic vascular resistance, aortic pressure and outflow obstruction; raised afterload lowers stroke volume.

Reduced tissue responsiveness to insulin, especially in muscle, fat and liver, causing compensatory hyperinsulinaemia and later hyperglycaemia; central to type 2 diabetes and metabolic syndrome.

Glycated haemoglobin reflecting mean blood glucose over roughly the preceding 8-12 weeks; used for diagnosis and monitoring of diabetes, but unreliable in haemoglobinopathies, anaemia and recent transfusion.

Serum potassium above the reference range, typically over 5.5 mmol/L; dangerous because it depolarises myocardium, causing peaked T waves, widened QRS and risk of ventricular arrhythmia.

The difference between measured cations and anions (sodium minus chloride and bicarbonate), used to classify metabolic acidosis into high-gap causes such as ketoacidosis or lactate versus normal-gap causes such as diarrhoea.

The interval containing the central 95% of results from a defined healthy population, used to interpret laboratory values; results outside it are not automatically pathological and must be read in context.

The proportion of people with disease who test positive; a highly sensitive test is useful for ruling out disease when negative, and low sensitivity means many false negatives.

The proportion of people without disease who test negative; a highly specific test is useful for ruling in disease when positive, since false positives are uncommon.

The probability that a person with a positive test truly has the disease; unlike sensitivity and specificity it depends on disease prevalence, so it falls when prevalence is low.

The number of patients who must receive an intervention for one additional patient to benefit, calculated as the reciprocal of the absolute risk reduction; a small value indicates greater clinical benefit.

The arithmetic difference in event rates between control and treatment groups, expressed as a proportion; it reflects true clinical impact better than relative risk reduction, which can exaggerate small effects.

A range of values within which the true population estimate is likely to fall with a stated probability, usually 95%; its width reflects precision and its position relative to no effect guides interpretation.

The probability of observing a result at least as extreme as the study finding if the null hypothesis were true; it indicates statistical significance but not the size or importance of an effect.

The ratio of a drug's toxic dose to its effective dose; a narrow index, as with digoxin, lithium or warfarin, means small dose changes or interactions can cause toxicity, warranting monitoring.

Measurement of plasma drug concentration to individualise dosing for drugs with narrow therapeutic indices or unpredictable kinetics, interpreting levels against timing of the last dose.

A harmful, unintended response to a medicine at normal doses; classified as type A (dose-dependent, predictable) or type B (idiosyncratic, unpredictable) and a key target of pharmacovigilance reporting.

Presystemic elimination of an orally administered drug by gut wall and liver before it reaches systemic circulation, reducing oral bioavailability and explaining large differences between oral and intravenous doses.

The fraction of an administered dose reaching systemic circulation unchanged; intravenous dosing is defined as 100%, while oral bioavailability is reduced by incomplete absorption and first-pass metabolism.

The apparent volume relating the amount of drug in the body to its plasma concentration; a large value indicates extensive tissue uptake, and it determines the loading dose needed.

The volume of plasma cleared of drug per unit time, reflecting hepatic metabolism and renal excretion; it determines the maintenance dose rate needed to sustain a target steady-state concentration.

A patient's voluntary agreement to an investigation or treatment after receiving adequate information about purpose, risks, benefits and alternatives, given by a patient with decision-making capacity.

A patient's ability to understand, retain, weigh and communicate a decision about their care; assessed for the specific decision at that time and presumed present unless demonstrated otherwise.

The professional obligation to be open and honest with patients when something goes wrong in their care, including apologising, explaining what happened and describing what will be done to prevent recurrence.