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Glossary - Human Factors

accommodation The ability of the eye to change its refractive power to focus light from either near or distant objects.
acid Compounds which combine with alkalis to form salts. In the body, acidity is determined by the concentration of hydrogen ion H+.
adenosine triphosphate A molecule produced by all cells, which contains high energy phosphate bonds. When these bonds are broken, the body is able to utilise the energy for its needs.
aerobic In the presence of oxygen.
aerodontalgia Tooth pain caused by expanding gas within a cavity of the tooth on ascent to altitude.
alkali (base) A substance which neutralises an acid to form a salt. Bicarbonate ion HCO3- a base which combines with H+ in the body to form carbonic acid.
alveoli Small air sacs in the lungs involved in gas exchange.
anaemia Inadequate red blood cells of haemoglobin in the blood.
anaerobic In the absence of oxygen.
angina (pectoris) Pain in the centre of the chest related to ischaemic heart disease, which usually occurs on exertion.
aorta The main artery providing outflow from the left ventricle of the heart, carrying oxygenated blood to the whole body.
aqueous humour Fluid of the anterior chamber of the eye, between the lens and the cornea.
arterioles A small artery.
artery A muscular walled blood vessel, which carries blood away from the heart.
atelectasis Collapse of alveoli in the lungs.
atria The uppermost chambers of the heart, which receive the inflow from the veins, then help to fill the ventricles prior to their contraction.
autokinesis The apparent motion of a single point source of light.
autonomic nervous system A branch of the nervous system which regulates many unconscious bodily functions such as the constriction of blood vessels and movement of the gastrointestinal tract.
barany chair A rotating chair used for demonstrating or testing the functions of the vestibular system.
barometric pressure The pressure of atmospheric gases.
barometric time release unit Mechanism, which automatically controls the ejection sequence of an ejection seat.
baroreceptor A sensor of arterial blood pressure. Baroreceptors are located in the carotid sinus at the bifurcation of the internal and external carotid arteries.
base See alkali.
bends Pains in the joints as a result of decompression illness.
bronchioles Small airways within the lungs.
bronchus The trachea divides into the right and left bronchi, which conduct air to either the right or left lung.
capillaries Tiny blood vessels one cell thick forming a network through all tissues, supplying them with oxygenated blood. They join arteries to veins.
carbonic acid H2CO3––Formed in the body when carbon dioxide gas reacts with water aided by the enzyme carbonic anhydrase. Carbon dioxide exists in the body almost exclusively in this form.
carotid artery Branch of the aorta coursing upwards in the neck to supply the head and brain with oxygenated blood.
cell Smallest structural division of living tissue which can self-replicate, consisting of an outer cell membrane, cytoplasm, nucleus containing genetic material, and other organelles.
central nervous system That part of the nervous system which consists of the brain and the spinal cord.
cerebral arterial gas embolism Sudden collapse or severe neurological impairment caused by a gas bubble occluding the cerebral circulation following a rapid decompression. Often associated with pulmonary barotrauma.
chemoreceptor A sensory cell which detects the concentration of chemical substances within body fluids.
chokes Respiratory manifestations of decompression illness, usually consisting of shortness of breath, chest pain and a cough.
cochlea The organ of hearing, located in each inner ear.
convergence Movement of the eyes inwards towards the midline when focussing on an object nearer to the observer.
cornea The clear membrane at the front of the eye where light enters and is first refracted.
creeps Cutaneous manifestations of decompression illness, consisting of itching, crawling sensations, or rashes.
cutaneous Pertaining to the skin.
decibel scale dB A logarithmic method of quantifying sound pressure levels.
density Mass per unit volume.
diaphragm Dome shaped muscular partition between the thoracic and abdominal cavities. Responsible largely for inspiration and expiration.
diastole (-ic) The phase of the cardiac cycle where the heart is relaxed. Diastolic pressure is the pressure in the arteries at this time.
diffusion Random collisions between molecules of a gas or solute result in the intermingling and movement of that solute or gas from a region of higher concentration to a region of lower concentration.
ebullism Vaporisation of gas within body tissues which occurs when the ambient pressure around the body equals the water vapour pressure of water in the body at 37°C (47 mmHg).
embolism A bolus of foreign material carried in the blood stream, which may lodge in and block smaller blood vessels.
epiglottis A flap of tissue which seals the top of the trachea at the larynx to prevent the aspiration of foreign material into the lungs.
erythrocytes Red blood cells, containing haemoglobin.
eustachian tube A passage between the middle ear cavity and the pharynx, which allows equalisation of pressures between the two regions.
exosphere The outermost layer of the atmosphere.
flatus A collection of gas in the bowel. Often expelled noisily from the anus during hypobaric chamber runs.
flight level Height above the 1013.2 hPa pressure datum, which is mean sea level barometric pressure in the ICAO standard atmosphere. All aircraft use this value as barometric pressure at sea level when setting their altimeters for flight above 13 000 feet.
freznel manoeuvre A manoeuvre for raising the pressure in the nasopharynx by occluding the glottis, lips and nostrils, and contracting the muscles in the floor of the mouth and pharynx.
glycogen A sugar created by the body for the storage of glucose.
greenhouse effect The warming of the earth’s surface caused by trapping of incoming solar radiation by the atmosphere.
haemoglobin A large molecule contained within red blood cells used for the transport of oxygen. It consists of a protein molecule (globin) and an iron-containing pigment (haem).
homeostasis Maintenance of a constant internal environment.
hyperthermia A rise in core body temperature caused by heat stress.
hyperventilation Breathing in excess of the body’s need to eliminate carbon dioxide, resulting in a decline in the level of carbon dioxide within body fluids.
hypoglycaemia Low blood glucose levels.
hypothalamus A region deep within the brain concerned with the regulation of hormonal function, the autonomic nervous system, and many vital processes such as sleep, hunger, thirst, reproductive activity, and temperature regulation.
hypothermia Low core body temperature resulting in clinical symptoms.
hypoventilation Inadequate ventilation of the lungs to meet the body’s requirements of oxygenation and elimination of carbon dioxide.
hypoxia Lack of oxygen to the tissues sufficient to cause impairment of function.
IMSAFE Illness, Medication, Stress, Alcohol/Drugs, Fatigue, Eating
intercostal muscles Muscles between the ribs, which aid in respiration.
International Civil Aviation Organisation standard atmosphere A fictitious atmosphere with defined physical parameters, which resembles the atmosphere at 45 degrees north latitude.
larynx Cartilaginous structure surrounding the vocal cords at the upper end of the trachea.
leucocytes White blood cells, concerned mainly with immunity.
mediastinum The space in the chest which lies between the two lungs.
mesosphere The middle layer of the atmosphere, from 158 000 feet to 290 000 feet.
metabolism All the physical and chemical processes by which a living organism is maintained.
mitochondria Rod-like organelles with the cellular cytoplasm which contain enzymes necessary for the oxidative production of energy. They are known as the cell’s ‘power plants’.
mmHg Millimetres of mercury, a unit of pressure measurement.
myopia Short-sightedness.
noise induced hearing loss A permanent high frequency sensorineural hearing loss related to prolonged or repeated exposure to loud noise.
oculogyral illusion Apparent motion of the visual scene as a result of stimulation of the semicircular canals.
ossicles Three tiny bones in each middle ear (hammer, anvil, and stirrup) which transduce sound vibrations from the tympanic membrane to the inner ear.
ozone Tri-atomic oxygen, O3. Formed by the action of ultraviolet radiation on molecular oxygen in the stratosphere.
PACO2 The partial pressure of carbon dioxide in the alveolus.
PAO2, PaO2 PAO2: The partial pressure of oxygen in the alveolus.

PaO2: The partial pressure of oxygen in arterial blood.
partial pressure The pressure that one of the gases in a mixture of gases would exert if it was present alone and occupied the same volume as the whole mixture.
PB Barometric pressure.
pH A logarithmic scale of hydrogen ion concentration in a solution, giving a measure of acidity or alkalinity. The scale runs from 1 (most acid) to 14 (most alkaline). A pH of 7 is neutral. The pH of body fluid is 7.4.
pharynx The throat.
photochromatic lens An optical lens which can vary the transmissivity of light according to the ambient light levels.
plasma The fluid component of blood.
platelets Cellular components of blood involved in clotting.
pleura The membranes which cover the surface of the lung and the inside of the thoracic cavity. The potential space between the surface of the lung and the chest wall is called the pleural cavity.
pneumomediastinum Air within the mediastinum.
pneumothorax Air within the pleural cavity. Also called a ‘collapsed lung’.
pounds per square inch A unit of pressure.
presbyopia Progressive onset of long-sightedness, which occurs with age as the lens, becomes less compliant, and less able to accommodate for near vision.
pressure Force per unit area.
protein Large molecules within animal and plant tissue comprising chains of amino-acids, including structural components of tissue, enzymes and receptors of various types.
pulmonary Pertaining to the lung.
retina The innermost layer of the eye, which contains photoreceptors involved in the perception of light.
rhodopsin A photopigment contained within photoreceptors in the eye.
shock A clinical syndrome caused by acute blood loss, consisting of pallor, rapid weak pulse, low blood pressure, poor tissue perfusion and clouding of consciousness.
snellen chart A chart with rows of letters of varying size used to estimate visual acuity.
somatogravic illusion A false sense of body attitude due to the effects of acceleration on the Otolith organs.
somatogyral illusion A false sense of rotation caused by stimulation of the semicircular canals.
sphincter A circular band of muscle around an orifice or organ.
staggers Neurological manifestations of decompression illness.
stereopsis The brain’s ability to discriminate distance and depth by using the difference in retinal image between the two eyes.
stratosphere The layer of the atmosphere extending from the top of the tropopause to the mesosphere at 158 000 feet.
surfactant (Surface active agent) a substance which reduces the surface tension of a liquid. Surfactant in the alveoli prevent surface tension from causing them to collapse.
syncope Sudden loss of consciousness; fainting.
systole The phase of the cardiac cycle when the ventricles of the heart are contracting. Systolic pressure is the pressure in the arteries during systole.
thermosphere The layer of the atmosphere extending from 290 000 feet to 290 km.
thorax The chest.
time of useful consciousness The time between initial exposure to an hypoxic environment, and the point at which ability is lost to make purposeful efforts to save one’s own life.
tinnitus Ringing in the ears.
trachea The large airway extending from the larynx to the bronchi.
tropopause The top of the troposphere where temperature remains constant in an isothermal layer. Its altitude varies depending on the surface temperature.
troposphere The lowest layer of the atmosphere extending from sea level to the tropopause.
tympanic membrane The ear drum. A thin membrane of tissue which lies between the external auditory canal and the middle ear, and which vibrates in response to sound.
valsalva manoeuvre A manoeuvre which increases the pressure in the nasopharynx, used to open the eustachian tube and equalise pressure between the throat and the middle ear cavity. It is performed by occluding the nose and lips, while attempting a forced expiration.
vasoconstriction The constriction of blood vessels by smooth muscle in the walls of the vessels.
vasodilatation The dilating of blood vessels, allowing increased blood flow.
vein A thin walled vessel, which carries blood to the heart.
vena cava The largest vein in the body, returning blood to the right atrium of the heart.
ventricle The lower chambers of the heart which are thick walled and muscular. The ventricles pump blood from the heart to the body and the lungs.
venules Small veins.
vitreous humour Gelatinous fluid within the eyeball, located between the lens and the retina. Its pressure maintains the shape of the globe.