G-8 glossary
embryonic disk In early development, the oval, flattened cell
mass that gives rise to the embryo shortly after implantation.
emerging disease Disease caused by a new strain of an
existing pathogen or one that is now exploiting an increased
availability of human hosts.
emulsification In digestion, the breaking of large fat globules
into a suspension of fat droplets coated with bile salts.
encapsulated receptor Receptor surrounded by a capsule of
epithelial or connective tissue; common near the body surface.
endangered species Endemic (native) species highly
vulnerable to extinction.
endemic disease A disease that occurs more or less
continuously in a region.
endergonic reaction A reaction in which there is a net
increase in energy in the product compound.
endocrine gland A ductless gland that secretes hor-
mones, which usually enter interstitial fluid and then the
bloodstream.
endocrine system System of cells, tissues, and organs that is
functionally linked to the nervous system and that exerts con-
trol by way of hormones and other chemical secretions.
endocytosis (en-doe-sigh-toe-sis) Movement of a substance
into cells in which the substance becomes enclosed by a patch
of plasma membrane that sinks into the cytoplasm, then
forms a vesicle around it. Phagocytic cells also engulf patho-
gens this way.
endoderm [Gk. endon, within, and derma, skin] The inner pri-
mary tissue layer, or germ layer, of an embryo, which gives
rise to the inner lining of the gut and organs derived from it.
endomembrane system System in cells that includes the
endoplasmic reticulum, Golgi bodies, and various kinds of
vesicles, and in which new proteins are modified into final
form and lipids are assembled.
endometrium (en-doh-meet-ree-um) [Gk. metrios, of the
womb] Inner lining of the uterus consisting of connective tis-
sue, glands, and blood vessels.
endoplasmic reticulum (ER) (en-doe-plaz-mik reh-tik-
yoo-lum) An organelle that begins at the nucleus and curves
through the cytoplasm. In rough ER (which has many ribo-
somes on its cytoplasmic side), new polypeptide chains acquire
specialized side chains. In many cells, smooth ER (with no
attached ribosomes) is the main site of lipid synthesis.
endotherm Organism such as a human that maintains body
temperature from within, generally by metabolic activity and
controls over heat conservation and dissipation.
enzyme (en-zime) One of a class of proteins that greatly
speed up (catalyze) reactions between specific substances.
The substances that each type of enzyme acts upon are called
its substrates.
eosinophil Fast-acting, phagocytic white blood cell that
targets worms, fungi, and other large pathogens.
epidemic A disease outbreak in an area or population that
occurs above predicted or normal levels.DNA sequencing A process that provides information about
genes, including their size, their location on chromosomes,
and the order of their nucleotides.
dominant allele In a diploid cell, an allele that masks the
expression of its partner on the homologous chromosome.
duodenum (doo-oh-dee-num) The first section of the small
intestine.
duplication A change in a chromosome’s structure resulting
in the repeated appearance of a gene sequence.
dysplasia An abnormal change in the sizes, shapes, and
organization of cells in a tissue.
ecological footprint The sum total of resources used by a
population or an individual, together with the resulting waste
products.
ecological pyramid A way to represent the energy relation-
ships of an ecosystem.
ecology [Gk. oikos, home, and logos, reason] Study of the
interactions of organisms with one another and with their
physical and chemical environment.
ecosystem [Gk. oikos, home] An array of organisms and
their physical environment, all of which interact through a
flow of energy and a cycling of materials.
ectoderm [Gk. ecto, outside, and derma, skin] The outermost
primary tissue layer (germ layer) of an embryo, which gives
rise to the outer layer of the integument and to tissues of the
nervous system.
effector A muscle (or gland) that responds to signals from
an integrator (such as the brain) by producing movement (or
chemical change) that helps adjust the body to changing
conditions.
effector cell Of the differentiated subpopulations of lym-
phocytes that form during an immune response, the type of
cell that engages and destroys the antigen-bearing agent that
triggered the response.
efferent arteriole In the urinary system, the arteriole that
carries filtered blood from the nephron.
egg See ovum.
elastic connective tissue A form of dense connective tissue
found in organs that must stretch; made up mostly of the pro-
tein elastin, it is quite flexible.
electrolyte Any chemical substance, such as a salt, that
ionizes and dissociates in water and is capable of conducting
an electrical current.
electron transport system An organized array of enzymes
and cofactors, bound in a cell membrane, that accept and
donate electrons in sequence. When such systems operate,
hydrogen ions (H+) flow across the membrane, and the flow
drives ATP formation and other reactions.
element Any substance that cannot be decomposed into sub-
stances with different properties.
embryo (em-bree-oh) [Gk. en, in, and probably bryein, to
swell] Of animals, a new individual that forms by cleavage,
gastrulation, and other early developmental events.
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