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Glossary of Physiology Terms – E
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Edema
Definition:
Accumulation of fluid in the interstitial compartment, which usually leads to a visible swelling of the affected tissue.



Efferent
Definition:
Leading away from a region or structure of interest.

In the nervous system, efferent fibers (i.e., neurons) transmit information from the central nervous system to peripheral effector organs (i.e., muscles or glands). Therefore, the cells bodies of efferent neurons reside within the central nervous system, whereas their axonal projections exit the central nervous system to make synaptic contact with effector organs in the periphery. Efferent neurons are also referred to as motor neurons.

In the kidneys, the efferent arteriole carries blood away from the glomerular capillaries.

Related glossary terms/phrases:
Afferent



Efflux
Definition:
Movement of a substance out of the cell.

Efflux is reported as a rate. It is the amount of substance that moves through a given area of the plasma membrane per unit time.

Related glossary terms/phrases:
Flux
Influx
Unidirectional flux
Net flux



Electrical gradient
Definition:
In biological solutions, electrical gradient refers to the electrical potential that acts on an ion to drive the movement of the ion in one or another direction (see Resting Membrane Potential - Establishment of the Membrane Potential).

Related glossary terms/phrases:
Chemical gradient
Electrochemical gradient



Electrocardiogram
Abbreviation:
ECG or EKG

Definition:
A recording of the electrical activity of the heart measured by placing multiple (3 to 10) electrodes on the surface of the skin.



Electrochemical driving force
Abbreviation:
VDF

Definition:
When an ion is not at its electrochemical equilibrium, an electrochemical driving force (VDF) acts on the ion, causing the net movement of the ion across the membrane down its own electrochemical gradient.

The electrochemical driving force is generally expressed in millivolts and is calculated according the following equation:

VDF = VmVeq

where VDF is the electrochemical driving force, Vm is the membrane potential, and Veq is the equilibrium potential.

Related glossary terms/phrases:
Membrane potential
Equilibrium potential
Electrochemical gradient

See also:
Resting Membrane Potential - Electrochemical Driving Force Acting on Ions
Electrochemical Driving Force Calculator



Electrochemical gradient
Definition:
Refers to the balance of chemical and electrical gradients that act on an ion, particularly as it relates to the movement of an ion across a biological membrane (see Resting Membrane Potential - Establishment of the Membrane Potential and Resting Membrane Potential - Nernst Equilibrium Potential).

Related glossary terms/phrases:
Chemical gradient
Electrical gradient



Electrochemical potential difference
Definition:
Electrochemical gradient

See:
Electrochemical gradient



Electrochemical potential gradient
Definition:
Electrochemical gradient

See:
Electrochemical gradient



Electrogenic pump
Definition:
Electrogenic pumps are primary active transporters that hydrolyze ATP and use the energy released from ATP hydrolysis to transport ions across biological membranes leading to the translocation of net charge across the membrane.

For example, the Na+/K+ ATPase (sodium pump) is an electrogenic pump because during every transport cycle, it transports 3 Na+ ions out of the cell and 2 K+ ions into the cell. This leads to the movement of one net positive charge out of the cell making this process electrogenic.

Related glossary terms/phrases:
Electrogenic



Electrogenic
Definition:
An electrogenic transport process is one that leads to the translocation of net charge across the membrane. For example, ion channels such as Na+, K+, Ca2+, and Cl channels are electrogenic.

The Na+/K+ ATPase is electrogenic because for every ATP molecule hydrolyzed, 3 Na+ ions are transported out of the cell and 2 K+ ions are transported into the cell (leading to the translocation of one net positive charge out of the cell).

Many secondary active transporters are also electrogenic. For example, the Na+/glucose cotransporter (found in the small intestine and kidney proximal tubules), transports 2 Na+ ions and 1 glucose molecule into the cell across the plasma membrane (leading to the translocation of two net positive charges into the cell per transport cycle).



Electrophysiology
Definition:
Electrophysiology is the study of the electrical properties of biological macromolecules, cells, tissues, and organs. Electrical signals such as voltage and/or current are generally measured. Examples include measuring changes in the membrane voltage of excitable cells (e.g., neurons, muscle cells, and some endocrine cells) during an action potential. The current carrried by ions as they permeate the pore of ion channels can also be measured - both at the single-channel level (single-channel current), as well as the macroscopic current resulting from the activity of a population of channels. As another example, electrical measurements may involve recording voltage changes at the surface of the skin that result from the activity of skeletal muscles (electromyogram, EMG), cardiac myocytes (electrocardiogram, ECG), or neurons in the brain (electroencephalogram, EEG).



Endocrine cell
Definition:
Endocrine cells are responsible for producing and releasing hormone molecules into the bloodstream. Endocrine cells are typically grouped together in organs referred to as endocrine glands.

Related glossary terms/phrases:
Endocrine gland
Hormone



Endocrine gland
Definition:
Endocrine glands contain clusters of endocrine cells, whose function is to is to release hormones into the bloodstream.

Endocrine glands are ductless glands in that their secretions do not enter a duct (as for example with salivary glands). Rather, endocrine glands release their secretions (i.e., messenger molecules) into the interstitial fluid in highly vascularized regions, where the molecules then enter the bloodstream. The chemical messenger molecule that is released into the bloodstream is referred to as a hormone.

Related glossary terms/phrases:
Endocrine cell
Hormone



Equilibrium potential
Abbreviation:
Veq. or Eeq.

Definition:
Refers to the membrane potential at which there is no net movement of an ion across the plasma membrane into or out of the cell.

See also:
Resting Membrane Potential - Establishment of the Membrane Potential
Resting Membrane Potential - Nernst Equilibrium Potential
Nernst Potential Calculator



Euthyroidism
Definition:
Normal thyroid gland function.

Related glossary terms/phrases:
Hypothyroidism
Hyperthyroidism



Exchange
Definition:
A type of secondary active transport across a biological membrane in which a transport protein couples the movement of an ion (usually Na+ or H+) down its electrochemical gradient to the movement of another ion or molecule against a concentration or electrochemical gradient. The ion moving down its electrochemical gradient is referred to as the driving ion. The ion/molecule being transported against a chemical or electrochemical gradient is referred to as the driven ion/molecule.

In exchange, the driving ion and the driven ion/molecule are transported across the biological membrane in opposite directions.

An example is the Na+/Ca2+ exchanger (NCX), which couples the movement of 3 Na+ ions into the cell down its electrochemical gradient to the movement of 1 Ca2+ ion out of the cell against its electrochemical gradient.

Exchange is also commonly referred to as antiport.

Transport proteins that are involved in this type of transport are referred to as exchangers or antiporters.

See:
Antiport

Related glossary terms/phrases:
Secondary active transport
Cotransport

See also:
Lecture notes on Secondary Active Transport



Excitable cell
Definition:
Refers to the ability of some cells to be electrically excited resulting in the generation of action potentials. Neurons, muscle cells (skeletal, cardiac, and smooth), and some endocrine cells (e.g., insulin-releasing pancreatic β cells) are excitable cells.

See also:
Resting Membrane Potential - Introduction



Excretion
Definition:
Excretion refers to the elimination of waste substances from the body. The kidneys and lungs are mainly responsible for excreting metabolites and waste products.

See also:
Secretion



Exophthalmia
Definition:
Exophthalmos

See:
Exophthalmos



Exophthalmos
Definition:
Protrusion or bulging of one or both eyeballs out of the orbit. It may be caused by swelling of orbital tissue in response to trauma, or by hyperthyroidism (especially primary hyperthyroidism).

It is also referred to as exophthalmus, exophthalmia, proptosis, or exorbitism.

Other resources:
Exophthalmos (Wikipedia)



Exophthalmus
Definition:
Exophthalmos

See:
Exophthalmos



Exorbitism
Definition:
Exophthalmos

See:
Exophthalmos









Posted: Sunday, October 17, 2010
Last updated: Saturday, November 21, 2015