Glossary
725
electrolyte
(ee-LEK-troh-lite) substance that
dissociates into ions when in aqueous solution
electromagnetic radiation
radiation composed
of waves with electrical and magnetic
components; includes gamma rays, x-rays, and
ultraviolet, visible light, infrared, and radio
waves
electron
(ee-LEK-tron) subatomic particle that
carries one unit of negative charge
electron transport chain
a series of metal-
containing proteins within mitochondria
that participate in the fl ow of electrons from
proteins to molecular oxygen; they are key
components of the energy-producing processes
in all cells
embryo
(EM-bree-oh) organism during early
stages of development; in human beings, the
fi rst two months of intrauterine life
emission
(ee-MISH-un) movement of male
genital duct contents into urethra prior to
ejaculation
emotional behavior
outward expression and
display of inner emotions
emulsifi
cation
(eh-mul-suh-fah-KAY-shun)
division of large lipid droplets into very small
droplets
end-diastolic volume (EDV)
(dy-ah-STAH-
lik) amount of blood in ventricle just prior to
systole
endocrine gland
(EN-doh-krin) group of
epithelial cells that secrete into the extracellular
space hormones that then diffuse into
bloodstream; also called a
ductless gland
endocrine system
all the body’s hormone-
secreting glands
endocytosis
(en-doh-sy-TOH-sis) process
in which plasma membrane folds into the
cell, forming small pockets that pinch off
to produce intracellular, membrane-bound
vesicles;
see also
phagocytosis
endogenous cryogen
chemical messenger
released by the hypothalamus and other tissues,
which acts to reset the body’s thermostat and
reduce fever
endogenous opioid
(en-DAHJ-en-us OH-
pee-oid) an example of certain neuropeptides—
endorphin, dynorphin, or enkephalin
endogenous pyrogen (EP)
(en-DAHJ-en-us
PY-roh-jen) any of the cytokines (including
interleukin 1 and interleukin 6) that act
physiologically in the brain to cause fever
endolymph
extracellular fl uid found in the
cochlea and vestibular apparatus
endometrium
(en-doh-MEE-tree-um) glandular
epithelium lining uterine cavity
endoperoxide
see
cyclic endoperoxide
endoplasmic reticulum
(en-doh-PLAS-
mik reh-TIK-you-lum) cell organelle that
consists of interconnected network of
membrane-bound branched tubules and
fl attened sacs; two types are distinguished:
rough,
with ribosomes attached, and
smooth,
which is smooth-surfaced (does not contain
ribosomes)
endosome
(EN-doh-some) intracellular
vesicles and tubular elements between Golgi
apparatus and plasma membrane; sorts
and distributes vesicles during endo- and
exocytosis
endothelial cell
see
endothelium
endothelin-1
(en-doh-THEE-lin) one member
of a family of peptides secreted by many tissues
that can act as a paracrine or hormonal signal;
one major action is vasoconstriction
endothelium
(en-doh-THEE-lee-um) thin layer
of cells that lines heart cavities and blood
vessels
endothelium-derived relaxing factor
(EDRF)
nitric oxide and possibly other
substances; secreted by vascular endothelium,
it relaxes vascular smooth muscle and causes
arteriolar dilation
end-plate potential (EPP)
depolarization of
motor end plate of skeletal muscle fi ber in
response to acetylcholine; initiates action
potential in muscle plasma membrane
end-product inhibition
inhibition of a metabolic
pathway by fi nal product’s action upon
allosteric site on an enzyme (usually the rate-
limiting enzyme) in the pathway
end-systolic volume (ESV)
(sis-TAH-lik) amount
of blood remaining in ventricle after ejection
energy
ability to produce change; measured by
amount of work performed during a given
change
enkephalin
(en-KEF-ah-lin) peptide
neurotransmitter at some synapses activated by
opiate drugs; an endogenous opioid
enteric nervous system
(en-TAIR-ik) neural
network residing in and innervating walls of
gastrointestinal tract
enterochromaffi
n-like (ECL) cell
histamine-
secreting cell of the stomach
enteroendocrine cell
cell located in the gastric
gland in the stomach; secretes gastrin
enterogastrones
(en-ter-oh-GAS-trones)
collective term for hormones released by
intestinal tract; inhibit stomach activity
enterohepatic circulation
(en-ter-oh-hih-PAT-ik)
reabsorption of bile salts (and other substances)
from intestines, passage to liver (via hepatic
portal vein), and secretion back to intestines
(via bile)
enterokinase
(en-ter-oh-KY-nase) enzyme
in luminal plasma membrane of intestinal
epithelial cells; converts pancreatic trypsinogen
to trypsin
entrainment
(en-TRAIN-ment) adjusting
biological rhythm to environmental cues
enzyme
(EN-zime) protein catalyst that
accelerates specifi c chemical reactions but does
not itself undergo net chemical change during
the reaction
enzyme activity
rate at which enzyme converts
reactant to product; may be measure of the
properties of enzyme’s active site as altered by
allosteric or covalent modulation; affects rate of
enzyme-mediated reaction
eosinophil
(ee-oh-SIN-oh-fi l) polymorphonuclear
granulocytic leukocyte whose granules take up
red dye eosin; involved in parasite destruction
and allergic responses
ependymal cell
(ep-END-ih-mel) type of glial
cell that lines internal cavities of the brain and
produces cerebrospinal fl uid
epicardium
(epp-ee-KAR-dee-um) layer of
connective tissue closely affi xed to outer
surface of the heart
epididymis
(ep-ih-DID-eh-mus) portion of male
reproductive duct system located between
seminiferous tubules and vas deferens
epiglottis
(ep-ih-GLOT-iss) thin cartilage fl ap
that folds down, covering trachea, during
swallowing
epinephrine (E)
(ep-ih-NEF-rin) amine hormone
secreted by adrenal medulla and involved in
regulation of organic metabolism; a biogenic
amine (catecholamine) neurotransmitter; also
called
adrenaline
epiphyseal closure
(ep-ih-FIZ-ee-al) conversion
of epiphyseal growth plate to bone
epiphyseal growth plate
actively proliferating
cartilage near bone ends; region of bone
growth
epiphysis
(eh-PIF-ih-sis) end of long bone
epithelial cell
(ep-ih-THEE-lee-al) cell at
surface of body or hollow organ; specialized
to secrete or absorb ions and organic
molecules; with other epithelial cells, forms
an
epithelium
epithelial tissue
one of the four major tissue
types in the body, comprised of aggregates of
epithelial cells
epithelial transport
molecule movement from
one extracellular compartment across epithelial
cells into a second extracellular compartment
epithelium
(ep-ih-THEE-lee-um) tissue that
covers all body surfaces, lines all body cavities,
and forms most glands
epitope
(EP-ih-tope) antigenic portion of a
molecule complexed to the MHC protein and
presented to the T cell; also called an
antigenic
determinant
equilibrium
(ee-quah-LIB-ree-um) no net
change occurs in a system; requires no energy
equilibrium potential
voltage gradient across a
membrane that is equal in force but opposite
in direction to concentration force affecting a
given ion species
erection
penis or clitoris becoming stiff due to
vascular congestion
ergocalciferol (vitamin D
2
)
plant vitamin D
error signal
steady-state difference between level
of regulated variable in a control system and set
point for that variable
erythrocyte
(eh-RITH-roh-site) red blood cell
erythropoiesis
(eh-rith-roh-poy-EE-sis)
erythrocyte production
erythropoietin
(eh-rith-roh-POY-ih-tin) peptide
hormone secreted mainly by kidney cells;
stimulates red blood cell production; one of
the hematopoietic growth factors
esophagus
(eh-SOF-uh-gus) portion of digestive
tract that connects throat (pharynx) and
stomach
essential amino acid
amino acid that cannot be
formed by the body at all (or at a rate adequate
to meet metabolic requirements) and so must
be obtained from diet
essential nutrient
substance required for normal
or optimal body function but synthesized
by the body either not at all or in amounts
inadequate to prevent disease
estradiol
(es-tra-DY-ol) steroid hormone of
estrogen family; major female sex hormone
estriol
(ES-tree-ol) estrogen present in pregnancy;
produced primarily by the placenta
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