JMC Human Medicine Exam key terms

The body's tendency to keep internal conditions such as temperature, pH, and blood glucose within narrow ranges despite external change, achieved through negative feedback loops involving sensors, control centres, and effectors.

A control mechanism in which the output of a process suppresses its own trigger, restoring the variable toward a set point; the dominant regulatory principle in physiology, seen in thermoregulation and blood pressure control.

A rapid, all-or-none reversal of membrane potential in excitable cells caused by sequential opening of voltage-gated sodium then potassium channels, propagating electrical signals along axons and triggering muscle contraction or transmitter release.

The volume of plasma filtered by both kidneys per unit time, normally about 125 mL/min; determined by filtration pressure, surface area, and permeability, and used clinically as the best overall index of kidney function.

The volume of blood ejected by one ventricle per minute, equal to stroke volume multiplied by heart rate; a key determinant of tissue oxygen delivery, adjusted by preload, afterload, and contractility.

The principle that cardiac muscle generates greater contractile force when stretched by increased end-diastolic volume, so stroke volume rises with venous return within physiological limits; the basis of the Frank-Starling relationship.

Fast, jumping propagation of action potentials between nodes of Ranvier in myelinated axons, which reduces membrane capacitance and concentrates ion channels at gaps, greatly increasing conduction velocity without increasing axon diameter.

A network of spinal nerve roots C5 to T1 located in the lower neck and axilla that gives rise to all major nerves of the upper limb, including the radial, median, ulnar, musculocutaneous, and axillary nerves.

An oblique passage through the lower anterior abdominal wall transmitting the spermatic cord in males and the round ligament of the uterus in females; its walls are formed by aponeuroses and muscles, and it is the commonest site of hernia.

An arterial ring at the base of the brain formed by the anterior cerebral, anterior communicating, internal carotid, posterior communicating, and posterior cerebral arteries, providing collateral circulation between the anterior and posterior systems.

Weakness of the shoulder and arm caused by injury to the upper trunk of the brachial plexus, usually C5 and C6, producing a waiter's-tip posture with the limb internally rotated and the forearm pronated.

The cytoplasmic pathway that converts one glucose molecule into two pyruvate molecules with net gain of two ATP and two NADH, functioning both with and without oxygen and providing the sole energy source for mature red cells.

The mitochondrial sequence of reactions that oxidises acetyl-CoA derived from carbohydrate, fat, and protein to carbon dioxide, generating reduced cofactors NADH and FADH2 that feed the electron transport chain.

ATP synthesis driven by a proton gradient across the inner mitochondrial membrane, built by electron transfer through respiratory complexes and used by ATP synthase; the main source of cellular energy in aerobic tissues.

The substrate concentration at which an enzyme works at half its maximum velocity, expressed as Km; it reflects enzyme affinity for substrate, with a low value indicating tight binding, and helps distinguish competitive from non-competitive inhibition.

Reversible enzyme inhibition in which a structurally similar molecule binds the active site and competes with substrate, raising apparent Km while leaving maximum velocity unchanged; overcome by increasing substrate concentration.

Acetoacetate, beta-hydroxybutyrate, and acetone produced in the liver from fatty acid oxidation during prolonged fasting or uncontrolled diabetes; water-soluble fuels exported to brain and muscle, with acetone causing fruity breath.

Programmed cell death in which caspases dismantle the cell into membrane-bound bodies cleared without inflammation; essential for development and tissue turnover and dysregulated in cancer and autoimmune disease.

Uncontrolled cell death from severe injury such as ischaemia or toxin exposure, causing cell swelling, membrane rupture, and leakage of contents that provokes surrounding inflammation; classified by pattern as coagulative, liquefactive, caseous, or fat.

A compact collection of activated macrophages, often with multinucleated giant cells and a rim of lymphocytes, formed when an irritant resists elimination; characteristic of tuberculosis, sarcoidosis, and foreign-body reactions.

Reversible replacement of one mature differentiated cell type by another better suited to chronic stress, such as squamous change in smoker's bronchial epithelium; an adaptive response that may predispose to malignancy.

The ratio of a drug dose producing toxicity to the dose producing the desired effect; a narrow index, as with digoxin, warfarin, or lithium, means small dose changes risk serious harm and demands monitoring.

A calculated apparent space relating the amount of drug in the body to its plasma concentration; a large value indicates extensive tissue uptake, while a small value suggests confinement to plasma and poor dialysability.

Presystemic elimination of an orally absorbed drug by gut wall and liver before it reaches systemic circulation, reducing oral bioavailability; drugs with heavy first-pass loss may need higher oral doses or parenteral routes.

Increased synthesis of cytochrome P450 enzymes after repeated exposure to certain drugs, speeding metabolism of co-administered substrates and reducing their effect; rifampicin and carbamazepine are classic inducers.

The lowest concentration of an antimicrobial that visibly prevents growth of a standardised bacterial inoculum in vitro; used to guide susceptibility reporting and dosing, and interpreted against clinical breakpoints.

The ability of microorganisms to survive drug concentrations that would normally inhibit or kill them, arising through enzymatic inactivation, target alteration, reduced permeability, or efflux; accelerated by inappropriate prescribing and spread by plasmids.

An enzyme produced by many bacteria that hydrolyses the beta-lactam ring of penicillins and cephalosporins, abolishing activity; countered by combining the drug with a beta-lactamase inhibitor such as clavulanate.

Indirect protection of susceptible individuals when a sufficient proportion of a population is immune, interrupting chains of transmission; the threshold rises with pathogen transmissibility and depends on vaccine efficacy.

Sensitivity is the proportion of truly diseased people correctly identified by a test; specificity is the proportion of truly healthy people correctly identified as negative. Together they describe test accuracy independent of prevalence.

The probability that a person with a positive test result actually has the disease; it rises with prevalence, unlike sensitivity and specificity, and is the figure most relevant when counselling a patient about a result.

Death of tissue caused by interruption of its arterial supply or venous drainage, producing a wedge-shaped coagulative lesion in solid organs such as kidney and spleen, or a pale or haemorrhagic area elsewhere.

A metabolic emergency of absolute insulin deficiency causing hyperglycaemia, ketonaemia, and high-anion-gap metabolic acidosis; managed with fluids, insulin infusion, and potassium replacement, with careful monitoring for cerebral oedema and hypokalaemia.

The difference between measured serum cations and anions, calculated as sodium minus chloride plus bicarbonate; a raised value indicates accumulation of unmeasured acids such as ketones, lactate, or toxins.

A gene whose normal product restrains cell division or repairs DNA; loss of both alleles removes that brake and permits uncontrolled growth, as with TP53 in many cancers and RB1 in retinoblastoma.

Systematic testing of apparently healthy people to detect disease at an early, treatable stage; justified only when the condition is important, a suitable test exists, and effective treatment improves outcome.

A pregnancy-specific disorder after 20 weeks marked by new hypertension with proteinuria or maternal organ dysfunction; a leading cause of maternal and fetal morbidity, treated definitively by delivery.

The occurrence of generalised tonic-clonic seizures in a woman with pre-eclampsia, without another identifiable cause; a life-threatening obstetric emergency requiring magnesium sulphate and urgent delivery.

Bleeding from the genital tract after 24 weeks of pregnancy and before delivery; causes include placenta praevia, placental abruption, and uterine rupture, and assessment must avoid digital vaginal examination until praevia is excluded.

Implantation of the placenta in the lower uterine segment, partly or completely covering the cervical os; presents with painless vaginal bleeding and usually requires caesarean delivery.

Yellow discoloration of skin and sclera in the first weeks of life from raised unconjugated bilirubin; common and usually physiological, but severe or early cases require exclusion of haemolysis, sepsis, or biliary obstruction.

Destruction of fetal red cells by maternal IgG antibodies crossing the placenta, most often anti-RhD in a sensitised Rh-negative mother; prevented by antenatal anti-D prophylaxis and treated by phototherapy or exchange transfusion.

Permanent neurological damage from bilirubin deposition in the basal ganglia and brainstem of a jaundiced newborn, causing hypotonia, deafness, choreoathetosis, and developmental delay; prevented by timely treatment of severe hyperbilirubinaemia.

A nerve of the brachial plexus supplying most forearm flexors and the thenar muscles; compression at the wrist causes carpal tunnel syndrome with numbness of the lateral three and a half digits.

The end product of anaerobic glucose metabolism, produced when pyruvate cannot enter mitochondria; accumulation lowers blood pH, and a raised level signals tissue hypoperfusion or impaired clearance and predicts outcome in shock.