Excitatory postsynaptic potential (EPSP)
An electrical change (depolarization) in the membrane of a postsynaptic neuron caused by
the binding of an excitatory neurotransmitter from a presynaptic cell to a postsynaptic
receptor; makes it more likely for a postsynaptic neuron to generate an action potential.
Excretion
The disposal of nitrogen-containing waste products of metabolism.
Excretory
Of, relating to, or used in excretion: excretory organs.
Excretory organs
An organ that separates waste substances form the blood and discharges them.
Excretory system
The organ system that disposes of nitrogen-containing metabolic wastes.
Exergonic reaction
A spontaneous chemical reaction in which there is a net release of free energy.
Exocrine glands
Glands, such as sweat glands and digestive glands, that secrete their products into ducts
that empty onto surfaces, such as the skin, or into cavities, such as the interior of the
stomach.
Exocytosis
The cellular secretion of macromolecules by the fusion of vesicles with the plasma
membrane.
Exodermis
A layer of cells lying immediately below the epidermis.
Exon
The coding region of a eukaryotic gene that is expressed. Exons are separated from each
other by introns.
Exoskeleton
A hard encasement on the surface of an animal, such as the shells of mollusks or the cuticles
of arthropods, that provides protection and points of attachment for muscles.
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