Definitions in Physiology, Pharmacology, Physics & Statistics

This is a collection of definitions that I considered to be essential knowledge for the CICM basic sciences primary exam. It is not intended to be an exhaustive list but if you think there are definitions that should be included, please send them this way.

Define and conquer!


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afterloadMyocardial wall tension during systole. Alternatively, resistance to the ejection of stroke volume.
vitaminOrganic substance required in the diet in small amounts for normal health and is not an energy substrate.
mineralInorganic substance required in the diet in small amounts for normal health.
preloadAverage myocardial sarcomere length at onset of systole. Approximates with end diastolic volume.
myocardial contractilityIntrinsic ability of the heart to contract and generate systolic pressure independent of preload and afterload.
pathogenicityTendency of an organism to cause disease.
pathogenOrganism that causes disease.
virulenceSeverity of disease caused by a pathogen.
commensalOrganism that colonises a host without causing disease.
essential fatty acidFat/ oil required in the diet in small amounts for normal health. Differs from vitamins in that EFAs may be used as energy substrate.
closing capacityLargest lung volume at which there is some degree of airway collapse in the dependent regions.
functional residual capacity (FRC)Volume of gas in the lungs at the end of expiration in normal tidal breathing. 30ml/kg.
Huffner constantHaemoglobin capacity for oxygen. Maximal volume of oxygen that can be held by a mass of haemoglobin. Value = 1.39 mls/g theoretical maximum and 1.34 mls/g allowing for physiological amounts of methaemoglobin and carboxyhaemoglobin.
hypoxiaLow oxygen delivery.
hypoxaemiaLow oxygen content in arterial blood.
re-feeding syndromePotentially fatal shifts in electrolytes and fluids associated with the reinstatement of nutrition in a malnourished person.
painUnpleasant sensory and emotional experience associated with actual or potential tissue damage.
bufferSolution containing either weak acids, weak bases or both that tend to limit changes in hydrogen ion concentration when further acid or base is added to the solution.
saturated vapour pressurePressure exerted by a vapor in equilibrium with its liquid state for a given temperature.
Fick principleBlood flow is equal to uptake / production of an indicator by an organ divided by the arteriovenous concentration difference.


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opioidSubstance exogenous or endogenous that exerts morphine like properties via the opioid receptors and antagonised by naloxone.
opiateEndogenous non-peptide opioid.
acid (Bronsted-Lowry)Proton donating molecule.
acid (Lewis)Electron pair accepting molecule.
acid (Arrhenius)Molecule that tends to decrease pH when in solution with water.
pKaNegative logarithm of the acid dissociation constant for an acid or base.
drugSubstance which, when administered, alters body function.
ion trappingThe phenomenon where weak acids tend to ionise and accumulate in alkali fluid compartments and vice versa.
volume of distributionTheoretical volume into which a drug would need to be dissolved to give the plasma concentration.
clearanceVolume of plasma cleared of a substance per unit time.
bioassayA test to compare the relative potency of two drug preparations.
potencyInverse drug dose required to achieve an effect.


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blood pressureForce per unit area exerted on the vascular tree by its contents.
boiling pointTemperature at which a liquid's saturated vapour pressure equals the surrounding atmospheric pressure.
absolute humidityMass of water per unit volume of a gas. Usually expressed as mg/l or g/m3.
relative humidity Ratio of absolute humidity to humidity at saturation for a given temperature and pressure.
viscosityThe resistance of a fluid to flow. On a mathematical level it is the ratio of shear force to shear rate.
vapourSubstance in a gas-like state below its critical temperature. Example: nitrous oxide at room temperature.
triple pointTemperature at which a substance can exist as solid, liquid and vapour.
saturated vapour pressurePressure exerted by a saturated vapour, ie where it is in equilibrium with its liquid state.
Lambert LawIntensity of light transmitted through a solution decreases exponentially with the length of path.
Beer LawIntensity of light transmitted through a solution decreases exponentially with the concentration of solution.
Fourier analysisMathematical separation of a complex waveform into simple constituent sine waves.
natural frequencyOscillations per unit time of unforced vibration in a system. Abbreviated to Fn.
resonant frequencyOscillations per time of forcing vibration that generates the greatest amplitude of vibration in a system. Equates to natural frequency in most systems.
dampingTendency for the amplitude of vibration in a system to decay over time.
fundamental frequencyThe lowest resonant frequency of a system. Also known as the first harmonic. Abbreviated to F0.
critical temperatureTemperature at which a substance cannot be converted from a vapor into a liquid by increases in pressure.
gasSubstance above its critical temperature.
absolute pressureTrue force per unit area exerted by a substance on its container.
gauge pressurePressure difference to atmospheric pressure.
adhesionAttraction between molecules of different substance.
cohesionAttraction between molecules of the same substance.
Doppler effectApparent change in frequency of wave when there is relative movement of the source towards or away from the observer.


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variableValue based on empirical measurement.
parameterValue based on assumptions about the distribution of data.
parametric methodsStatistical analysis based on assumptions about the distribution of data.
non-parametric methodsDirect statistical analysis on empirical data without assumptions about the distribution of data. Otherwise known as rank tests.
type 1 errorIncorrectly rejecting the null hypothesis. (Finding a difference between two populations where none actually exists.)
type 2 errorIncorrectly accepting the null hypothesis. (Failing to find a difference between two populations where one does exist.)
null hypothesisThe assumption that there is no difference between populations.
statistical powerThe probability that a study will correctly reject the null hypothesis. Equal to 1 − β. Usually 80%.