Confused as to what some words mean? Look no further! Here are some helpful definitions…

Adipose tissue – a body tissue that contains stored fat as a source of energy.

Adenosine triphosphate (ATP) – ATP contains a large amount of chemical energy stored in its high-energy phosphate bonds. It releases energy when it is broken down. ATP is considered as the universal energy currency for metabolism.

Aerobic dive limit (ADL) – The original definition was the dive duration after which there is an increase in post-dive concentration of lactate in the blood of Weddell seals freely diving in the field. The only other species this phenomenon has been measured in is emperor penguins. For all other species, aerobic dive limit has been calculated (cADL) by dividing usable oxygen stores with an estimation of the rate of oxygen consumption during diving. NB. ADL and cADL are not measures of the same thing.

Aerobic respiration – A form of cellular respiration that requires oxygen in order to generate energy.

Affinity – the likelihood of one thing binding to another (e.g. oxygen is more likely to bind to myoglobin than haemoglobin, therefore it can be said to have a greater affinity to myoglobin.)

Anaerobic respiration – a form of cellular respiration which generates energy in the absence of oxygen.

Arrhythmic – when the heart beat becomes irregular

Blood deoxygenation levels – the extent to which the amount of oxygen in the diver’s blood has decreased.

Bouts – a repeated series of short dives without extended periods of time spent at the surface.

Bradycardia – the slowing of the rate of the heart’s beat (most often measured in beats per minute).

Caisson working – working in a water-tight structure for engineering purposes, for example building the foundations of a bridge.

Cardiac output – the volume of blood pumped out by the heart in a given period of


Cardiac responses – responses to diving which relate to the heart of the diver.

Cardiovascular – encompasses both the heart and the blood vessels, refers to all of the circulatory system.

Classic dive response – the set of physiological changes which take place when a diver is forced underwater. Namely: bradycardia, peripheral vasoconstriction, reduced aerobic metabolism and an increase in anaerobic metabolism over time)

Decompression sickness – this is a condition often related to diving (most commonly scuba diving) which results from bubbles forming in the blood upon re-surfacing.

Depressurisation – changing from a high pressure environment to a lower one (e.g. upon re-surfacing from a dive)

Endothermic – endothermic animals are able to generate their own heat, and therefore do not necessarily match the heat of the environment around them (unlike exothermic animals)

Forced-submersion experiments – tests done on diving mammals which are forced to dive underwater. The results of these experiments cannot be compared directly to those obtained from natural dives: In many studies, the characteristics of the dive response are much more extreme during forcible, as opposed to voluntary, submersion. As a result, the dive response is considered to be a defensive or emergency measure used during extended or unplanned submersion in the wild. One example of when this might occur is during an extended exploratory dive under the ice. All diving physiology experiments used to use forced-submersion methods.

Free-diving – when humans dive underwater a supply of pressurised breathing-gas. A form of breath-hold diving.

Haematocrit – The ratio of red blood cells to the total volume of blood.

Haemoglobin – the oxygen binding protein which is found in the blood.

Henry’s Law – the solubility of a gas in a liquid at a particular temperature is proportional to the pressure of that gas above the liquid.

Hepatic sinus

Hypoxia – environmental condition where there is severely reduced oxygen.

Inert gas – Any of the elements in Group 0 of the periodic table, including helium, neon and argon, amongst others. They are chemically stable and therefore unreactive. They are also known as noble gases.

Lactic acid (lactate) – a waste product from anaerobic respiration. Lactic acid is the cause of the feeling of ‘burning’ in human muscles after strenuous exercise and also causes stiffness/soreness of muscles.

Lean tissue – muscle tissue without fat.

Myoglobin – a muscle protein which bins oxygen and acts as an oxygen store in diving species.

Nitrogen narcosis – A drowsy state induced by breathing air under higher than atmospheric pressure (e.g. scuba diving)

Otariid seals – a family of seals which includes the sea lion and the fur seal. This family are more adapted the shallower dives and are able to swim in faster bursts, as a result they utilise anaerobic respiration more frequently.

Peripheral vasoconstriction – Vasoconstriction causes the radius of blood vessels to decrease, reducing blood flow. Peripheral blood vessels are usually considered those not in the core of the body and not those that supply skeletal muscles.

Phocid seals – a family of seals which includes the most accomplished deep-diving seals (e.g. the elephant seal and the Weddell seal)

Physiology – the term ‘physiology’ simply means the study of the way in which a living organism or specific body part functions.

Pulmonary shunt – a condition where the alveoli of the lung are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region

Radiotransmitters – these tools facilitate analysis of freely diving birds and mammals in the field. They measure parameters such as heart beat and transmit the readings via radio waves to a recorder at the surface.

Skeletal muscles – One of three types of muscle tissue in the body (skeletal, smooth, cardiac) which represents the majority of the muscular tissue in the body. Skeletal muscle is the type of muscle which powers movement of the skeleton.

Smooth muscle – Muscle tissue that contracts without conscious control, having the form of thin layers or sheets. It is found in the walls of the internal organs, such as the stomach, intestine, bladder and blood vessels.

Spleen – an organ involved in the production and removal of blood cells in most vertebrates and forming part of the immune system.

Static apnea – holding one’s breath whilst remaining stationary (in this case, underwater)

Streamlined – a shape which reduces drag as an animal moves through the water.

Sympathetic nervous system – A division of the (vertebrate) autonomic nervous system that is chiefly involved in producing an immediate and effective response (e.g. fight-or-flight response) during stress or emergency situations. It also controls increases in heart rate and constriction of blood vessels.

Tachycardia – an increase in heart rate (often measured in beats per minute)

Time-depth recorder (TDR) – these are tools which attach to a diver and record the depth and duration of dives in the wild.

Ventilation – adaptations which refer to the breathing and respiratory system of a diver

Viscous – thick.

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