SEHS terms in Communication

The physiological adaptations that develop with repeated or continuous exposure to a stressful environment such as heat, cold or altitude, reducing its strain on the body and improving performance in it.

An illness caused by rapid ascent to high altitude, usually above about 2,500 m, with headache, nausea, fatigue, dizziness and poor sleep, which usually ease within a few days.

A pair of endocrine glands on top of the kidneys; the adrenal medulla releases epinephrine and norepinephrine, and the adrenal cortex releases hormones such as cortisol and aldosterone.

The part of the peripheral nervous system that carries nerve impulses from receptors towards the central nervous system; also called the sensory division.

Training or living at altitude, usually about 1,800–3,000 m, or in simulated low-oxygen conditions, to increase red cell mass and haemoglobin and so improve endurance performance.

Tiny, thin-walled air sacs at the ends of the bronchioles, surrounded by capillaries, where oxygen diffuses into the blood and carbon dioxide diffuses out of it.

The increase in heart rate and other sympathetic responses before exercise begins, caused by sympathetic stimulation and the release of epinephrine in response to the expectation of exercise.

A hormone made by the hypothalamus and released by the posterior pituitary when the blood is too concentrated, which increases water reabsorption by the kidneys; also called vasopressin.

A small branch of an artery leading into a capillary network, whose muscular wall narrows or widens to control how much blood flows into the capillaries it supplies.

The difference between the oxygen content of arterial and mixed venous blood, usually in mL of oxygen per 100 mL of blood, showing how much oxygen the tissues extract.

A blood vessel that carries blood away from the heart under high pressure, with a thick wall of smooth muscle and elastic tissue and a relatively narrow lumen.

The enlargement of the heart, especially the left ventricle, caused by regular intense training, which increases stroke volume and maximal cardiac output as a healthy adaptation.

A group of specialised cells between the atria and ventricles that receives the impulse from the atria and delays it by about 0.1 s before passing it to the bundle of His.

One of the two thin-walled upper chambers of the heart, which receives blood from the veins and pumps it into the ventricle below.

The branch of the efferent division that controls involuntary functions through cardiac muscle, smooth muscle and glands; it has sympathetic and parasympathetic divisions.

A stretch receptor in the walls of the aortic arch and carotid arteries that detects changes in blood pressure and informs the cardiovascular control centre.

The homeostatic control of blood glucose concentration by negative feedback, in which the pancreas releases insulin when glucose rises and glucagon when it falls.

A measure of the hydrogen ion concentration of the blood; the more hydrogen ions, the lower the pH. Normal arterial pH is about 7.35–7.45.

The force exerted by blood on the walls of the blood vessels, usually measured in the large arteries in mmHg and written as systolic over diastolic pressure, such as 120/80 mmHg.

The change in the distribution of cardiac output during exercise, in which vasodilation increases flow to working muscles and vasoconstriction reduces flow to less active organs such as the gut and kidneys.

The rightward shift of the oxygen–haemoglobin dissociation curve caused by more carbon dioxide, higher acidity and higher temperature, so haemoglobin releases more oxygen at a given pO₂.

A resting heart rate below 60 beats min⁻¹; in trained endurance athletes a normal result of a large stroke volume and high parasympathetic activity.

A type of fat tissue, plentiful in newborns and present in smaller amounts in adults, whose mitochondria release energy from fat directly as heat in non-shivering thermogenesis.

A substance in a body fluid that resists changes in pH by combining with or releasing hydrogen ions; the main blood buffer is hydrogen carbonate (bicarbonate).

A bundle of specialised conducting fibres that carries the impulse from the AV node down the septum of the heart, dividing into left and right bundle branches.

The smallest blood vessel, with a wall one cell thick and a lumen about the width of a red blood cell, where substances are exchanged between blood and tissues by diffusion.

The sequence of events in one heartbeat: contraction (systole) and relaxation (diastole) of the atria and ventricles, with the opening and closing of the valves.

The volume of blood pumped by the left ventricle per minute, equal to heart rate multiplied by stroke volume and measured in L min⁻¹; about 5 L min⁻¹ at rest.

A region of the medulla oblongata that receives information from receptors and higher brain centres and regulates heart rate, force of contraction and blood vessel diameter through the autonomic nervous system.

The organ system made up of the heart, blood vessels and blood, which transports oxygen, carbon dioxide, nutrients, hormones, heat and waste products around the body.

The brain and spinal cord, which receive sensory information from the whole body, integrate it and send out instructions to muscles and glands.

A receptor that detects changes in the chemical composition of the blood, mainly carbon dioxide, hydrogen ions (pH) and oxygen; found in the medulla and in the carotid and aortic bodies.

The transfer of heat by direct contact between the skin and a cooler or hotter solid, liquid or gas, such as cold water or a cold surface.

The part of a homeostatic system, usually in the brain or an endocrine gland, that compares information from receptors with the set point and signals effectors to correct any difference.

The transfer of heat to or from the skin by a moving fluid such as air or water; heat loss increases with wind speed or movement through water.

The temperature of the deep tissues of the body, such as the brain, heart and abdominal organs, normally kept at about 37 ± 1 °C.

A dome-shaped sheet of skeletal muscle separating the thoracic and abdominal cavities, which contracts and flattens to enlarge the thoracic cavity; the main muscle of inspiration.

The phase of the cardiac cycle in which heart muscle relaxes and the chambers fill with blood, with the semilunar valves closed and the atrioventricular valves open.

The lowest pressure in the arteries, reached while the ventricles relax and fill; about 80 mmHg at rest in a healthy young adult.

The passive net movement of molecules from a region of higher concentration or partial pressure to a region of lower concentration, needing no energy.

A muscle or gland that receives a signal from a control centre and produces a response that changes a regulated variable.

The part of the peripheral nervous system that carries nerve impulses from the central nervous system to effectors (muscles and glands); also called the motor division.

A ductless gland that secretes hormones directly into the bloodstream, such as the pituitary, thyroid, adrenal glands, pancreas, ovaries and testes.

The body's endocrine glands and the hormones they release into the blood, which together regulate processes such as metabolism, growth, water balance and reproduction.

A hormone released by the adrenal medulla in response to sympathetic stimulation, which raises heart rate, stroke volume, blood pressure and blood glucose; also called adrenaline.

A hormone produced mainly by the kidneys, in response to low blood oxygen and stimulated by testosterone, which increases red blood cell production in the bone marrow.

Heat loss as water, mainly sweat, changes from liquid to vapour on the skin or in the airways; the main route of heat loss during exercise and the only one when air is hotter than skin.

The maximum volume of air that can be breathed out after a normal expiration; about 1.2 L in a young adult man.

Control of the heart from outside it, by sympathetic and parasympathetic nerves and by hormones such as epinephrine, which change the rate of SA node firing and the force of contraction.

The first phase of the menstrual cycle, from the start of menstruation to ovulation, in which oestrogen rises as ovarian follicles develop while progesterone stays low.

The principle that the more the ventricle is filled and stretched during diastole, the more forcefully it contracts, so greater venous return produces a greater stroke volume.

The freezing of body tissue, usually of the fingers, toes, ears or nose, when skin temperature falls below freezing; severe frostbite can cause permanent tissue loss.

The movement of oxygen and carbon dioxide by diffusion between the alveoli and the blood, and between the blood and the tissues, down partial pressure gradients.

A hormone released by the alpha cells of the pancreas when blood glucose is low, which raises it by stimulating glycogenolysis and gluconeogenesis in the liver.

The production of new glucose in the liver from non-carbohydrate sources such as lactate, glycerol and amino acids, stimulated by glucagon.

The breakdown of glycogen stored in the liver or muscle into glucose, stimulated by glucagon and epinephrine.

A proprioceptor at the junction of a muscle and its tendon that detects tension in the muscle; very high tension causes the muscle to relax, protecting it.

The percentage of the blood volume made up of red blood cells, typically higher in men than in women; raising it increases the oxygen-carrying capacity of the blood.

The iron-containing protein in red blood cells that binds reversibly with oxygen, loading it in the lungs and releasing it in the tissues; each molecule carries up to four oxygen molecules.

The number of times the heart beats per minute, measured in beats min⁻¹; typically 60–80 beats min⁻¹ at rest in an adult.

Flaps of tissue between the chambers of the heart and at the exits of the ventricles that open and close in response to pressure differences, so blood flows in one direction only.

The adaptations to repeated exercise in hot conditions over about 1–2 weeks, including earlier and greater sweating, more dilute sweat, larger plasma volume and lower heart rate and core temperature at a given workload.

A heat illness in which the cardiovascular system cannot meet the demands of muscles and skin, usually with dehydration, causing fatigue, dizziness, nausea and sometimes collapse, with core temperature usually below 40 °C.

A life-threatening failure of thermoregulation in which core temperature rises above about 40 °C with central nervous system dysfunction such as confusion or collapse; it needs immediate whole-body cooling.

The self-regulating processes that keep the body's internal environment relatively stable, within narrow limits, so that cells and organs function optimally despite internal and external changes.

A chemical messenger released by an endocrine gland into the blood, which carries it to target cells elsewhere in the body, where it changes their activity.

A region at the base of the brain that links the nervous and endocrine systems; it controls body temperature, thirst and water balance, makes ADH and controls the pituitary gland.

A fall in core temperature below 35 °C, when heat loss exceeds heat production, causing shivering, then confusion, loss of coordination and, if it continues, unconsciousness and death.

A shortage of oxygen reaching the body's tissues; at altitude it results from the lower partial pressure of oxygen, which reduces the saturation of haemoglobin with oxygen.

The maximum volume of air that can be breathed in after a normal inspiration; about 3 L in a young adult man.

A hormone released by the beta cells of the pancreas when blood glucose is high, which lowers it by increasing glucose uptake into muscle, liver and fat cells and its storage as glycogen.

Two layers of muscle between the ribs: the external intercostals lift the ribs up and out in inspiration, and the internal intercostals pull them down and in during forced expiration.

A neuron within the central nervous system that links sensory neurons to motor neurons and allows information to be integrated.

Control of the heartbeat from within the heart by its conduction system (SA node, AV node, bundle of His and Purkinje fibres), without input from nerves or hormones.

A proprioceptor in the capsule and ligaments of a joint that detects the joint's angle, its movement and the pressure on it.

An altitude training strategy in which athletes live or sleep at moderate or simulated altitude to stimulate red blood cell production but train at low altitude to maintain training intensity.

The phase of the menstrual cycle after ovulation, lasting about 14 days, in which the corpus luteum secretes progesterone and oestrogen, so both hormones are relatively high.

The highest heart rate an individual can reach during maximal exercise; it falls with age and is often estimated as 220 minus age in beats min⁻¹.

The process by which respiratory muscles change the volume of the thoracic cavity, creating pressure differences between the lungs and the atmosphere that move air in and out.

The lowest part of the brainstem, which contains the cardiovascular and respiratory control centres that regulate heart rate and breathing without conscious thought.

The recurring cycle of hormone-controlled changes in the ovaries and uterus that prepares the body for a possible pregnancy, counted from the first day of menstruation and lasting about 21–35 days.

The volume of air breathed in or out per minute, equal to tidal volume multiplied by respiration rate and measured in L min⁻¹; about 6–8 L min⁻¹ at rest.

A neuron that carries impulses from the central nervous system to an effector, such as a skeletal muscle or gland.

A proprioceptor lying between skeletal muscle fibres that detects the length of the muscle and how quickly it is stretched, and can trigger the stretch reflex.

The thick middle layer of the heart wall, made of cardiac muscle, which contracts rhythmically and involuntarily to pump blood.

A control mechanism in which a change in a regulated variable triggers a response that reverses the change, returning the variable towards its set point; the basis of homeostasis.

A nerve cell, specialised to carry electrical impulses, with a cell body, dendrites that receive signals and an axon that carries impulses away.

A chemical released from the end of a neuron that crosses a synapse and passes the signal to the next neuron or to an effector cell, such as acetylcholine or norepinephrine.

Heat production without muscle contraction, by raising the metabolic rate of tissues, especially brown adipose tissue, under the control of sympathetic nerves and hormones such as thyroxine and epinephrine.

A hormone of the adrenal medulla and the neurotransmitter of most sympathetic nerve endings, which raises heart rate and constricts blood vessels in non-active tissues; also called noradrenaline.

A group of reproductive hormones released mainly by the ovaries, which control the follicular phase of the menstrual cycle, promote fat use and glycogen sparing and help maintain bone density.

The release of an egg from an ovary, triggered by a surge of luteinising hormone (LH) around the middle of the menstrual cycle.

An S-shaped graph of the percentage saturation of haemoglobin with oxygen against the partial pressure of oxygen, showing loading in the lungs and release at the lower pO₂ of the tissues.

The division of the autonomic nervous system that dominates at rest and conserves energy (rest and digest), for example by slowing heart rate through the vagus nerve.

The pressure exerted by one gas in a mixture of gases, proportional to its share of the mixture, written pO₂ for oxygen and pCO₂ for carbon dioxide.

The part of the total pressure of a gas mixture caused by oxygen, equal to the total pressure multiplied by the oxygen fraction; it falls with altitude and drives oxygen diffusion into the blood.

All the nerves and receptors outside the brain and spinal cord, which carry information between the central nervous system and the rest of the body.

A small endocrine gland below the hypothalamus that releases hormones such as ADH, FSH, LH and growth hormone, many of which control other endocrine glands.

The liquid part of the blood, about 90% water, in which nutrients, hormones, carbon dioxide, electrolytes, proteins and waste products are dissolved and transported.

A control mechanism in which a change triggers a response that increases the change further until an outside event stops it, as in blood clotting and childbirth.

Lowering core and skin temperature before exercise in the heat, for example with ice slurry, ice vests or cold-water immersion, so that more heat can be stored before it limits performance.

A ring of smooth muscle where a capillary branches off an arteriole, which contracts to close the capillary and relaxes to open it, controlling blood flow into a capillary bed.

A reproductive hormone released mainly by the corpus luteum after ovulation, which prepares the uterus for pregnancy and raises core body temperature by about 0.3–0.5 °C in the luteal phase.

A receptor in a muscle, tendon or joint that detects body position, movement, muscle length or tension and sends this information to the central nervous system.

The circuit that carries deoxygenated blood from the right ventricle through the pulmonary arteries to the lungs and returns oxygenated blood through the pulmonary veins to the left atrium.

Specialised conducting fibres in the ventricle walls that spread the impulse rapidly through the ventricular muscle, so that the ventricles contract together from the apex upward.

The transfer of heat as infrared waves between the skin and surrounding objects without contact; the body loses heat to cooler surroundings and gains it from the sun and hot surfaces.

A specialised cell or group of cells that detects a change in a regulated variable and sends information about it to a control centre, usually as nerve impulses.

A biconcave, disc-shaped blood cell with no nucleus, packed with haemoglobin, whose function is to carry oxygen from the lungs to the tissues.

The amount of water vapour in the air as a percentage of the most the air could hold at that temperature; high relative humidity slows the evaporation of sweat.

The volume of air that remains in the lungs after a maximal expiration, about 1.2 L in a young adult man; it cannot be measured with a simple spirometer.

The number of breaths taken per minute, also called breathing frequency; about 12–16 breaths min⁻¹ at rest in an adult.

A region of the medulla oblongata, working with the pons, that sets the rate and depth of breathing by sending impulses to the diaphragm and intercostal muscles.

The mechanism by which pressure changes in the chest and abdomen during breathing squeeze blood from abdominal veins into the veins of the chest and towards the heart.

The organ system of airways, lungs and breathing muscles that moves air into and out of the lungs and exchanges oxygen and carbon dioxide between the air and the blood.

A neuron that carries impulses from a receptor to the central nervous system; sensory neurons make up the afferent division.

The target value of a regulated variable, such as a core temperature of about 37 °C, around which control systems keep it fluctuating within a normal range.

Heat production by rapid, involuntary contractions of skeletal muscle, triggered by the hypothalamus when core temperature falls; nearly all the energy released becomes heat.

The heart's pacemaker: a group of specialised cells in the wall of the right atrium that generates the electrical impulse starting each heartbeat.

The mechanism by which contracting skeletal muscles squeeze nearby veins and, with the valves in the veins, push blood back towards the heart.

The branch of the efferent division that controls skeletal muscle, mostly under voluntary (conscious) control.

An instrument that measures the volume of air inspired and expired over time, producing a trace from which lung volumes and capacities can be read.

The volume of blood ejected by the left ventricle in one contraction, measured in mL; about 70 mL at rest in an untrained adult.

The secretion of sweat by eccrine sweat glands, stimulated by the sympathetic nervous system when core or skin temperature rises, so that heat is lost as the sweat evaporates.

The division of the autonomic nervous system that prepares the body for activity and stress (fight or flight), for example by increasing heart rate, force of contraction and blood glucose.

The junction between a neuron and another neuron or an effector cell, across which a signal is passed by a chemical neurotransmitter.

The circuit that carries oxygenated blood from the left ventricle through the aorta to all body tissues and returns deoxygenated blood through the veins and venae cavae to the right atrium.

The phase of the cardiac cycle in which heart muscle contracts and pushes blood out of a chamber; ventricular systole ejects blood into the aorta and pulmonary artery.

The highest pressure in the arteries, reached when the left ventricle contracts and ejects blood; about 120 mmHg at rest in a healthy young adult.

A cell that has specific receptors for a particular hormone, so that the hormone changes its activity; cells without the receptor do not respond.

A reproductive (androgen) hormone released mainly by the testes, which stimulates muscle protein synthesis, bone formation and erythropoietin production.

A sensory receptor that detects temperature; central thermoreceptors in the hypothalamus detect blood temperature and peripheral thermoreceptors in the skin detect skin temperature.

The homeostatic regulation of core body temperature, in which the hypothalamus balances heat production and gain against heat loss to keep core temperature at about 37 ± 1 °C.

The volume of air breathed in or out in one normal breath; about 0.5 L at rest in an adult, rising to 2–3 L in heavy exercise.

The volume of air in the lungs after a maximal inspiration, equal to vital capacity plus residual volume; about 6 L in a young adult man.

The cranial nerve that carries parasympathetic impulses from the medulla to the heart and other organs; its stimulation slows the SA node and lowers heart rate.

Forcefully breathing out against a closed airway, as when straining to lift a heavy load, which raises pressure in the chest and causes large rises in blood pressure.

The narrowing of arterioles when the smooth muscle in their walls contracts, reducing blood flow to the tissue they supply, such as the skin when the body is cold.

The widening of arterioles when the smooth muscle in their walls relaxes, increasing blood flow to the tissue they supply, such as the skin when the body is hot.

A blood vessel that carries blood towards the heart under low pressure, with a thin wall, a wide lumen and, in the limbs, valves that prevent backflow.

The narrowing of veins by contraction of the smooth muscle in their walls, stimulated by sympathetic nerves, which reduces the blood stored in the veins and increases venous return.

The volume of blood returning to the right atrium through the veins per minute, aided by the skeletal muscle pump, respiratory pump, venous valves and venoconstriction.

One of the two thick-walled lower chambers of the heart, which pumps blood into the arteries: the right ventricle to the lungs and the left ventricle to the rest of the body.

The maximum volume of air that can be breathed out after a maximal inspiration, equal to tidal volume plus the inspiratory and expiratory reserve volumes; about 4–5 L in adults.

An index of environmental heat stress combining the natural wet-bulb temperature (humidity and air movement), black globe temperature (radiation) and dry-bulb air temperature, weighted 0.7, 0.2 and 0.1 outdoors.