G-6 Glossaryexogenous products or influences, which arise from
external sources).
endolymph (en 9 d ̆o-limf) The fluid contained within
the membranous labyrinth of the inner ear.
endometrium (en 0 do-me 9 tre-um) The mucous
membrane of the uterus, the thickness and structure
of which vary with the phases of the menstrual cycle.
endoplasmic reticulum (en-do-plaz 9 mik
r ̆e-tik 9 y ̆u-lum) (ER) An extensive system of
membrane-enclosed cavities within the cytoplasm of
the cell. Those with ribosomes on their surface are
called rough endoplasmic reticulum and participate
in protein synthesis.
endorphin (en-dor 9 fin) Any of a group of
endogenous opioid molecules that may act as a
natural analgesic.
endothelin (en 0 do-the 9 lin) A polypeptide secreted
by the endothelium of a blood vessel that serves as
a paracrine regulator, promoting contraction of the
smooth muscle and constriction of the vessel.
endothelium (en 0 do-the 9 le-um) The simple
squamous epithelium that lines blood vessels and the
heart.
endotoxin (en 0 do-tok 9 sin) A toxin found within
certain types of bacteria that is able to stimulate the
release of endogenous pyrogen and produce a fever.
end-plate potential The graded depolarization
produced by ACh at the neuromuscular junction.
This is equivalent to the excitatory postsynaptic
potential produced at neuron-neuron synapses.
end-product inhibition The inhibition of
enzymatic steps of a metabolic pathway by products
formed at the end of that pathway.
enkephalin (en-kef 9 ̆a-lin) Either of two short
polypeptides, containing five amino acids, that have
analgesic effects and are grouped as endorphins.
enteric (en-ter 9 ik) A term referring to the intestine.
enteric nervous system The neurons found within
the wall of the gastrointestinal (GI) tract. These
include sensory, association, and motor neurons.
They coordinate peristalsis and other GI functions.
enterochromaffin (en 0 ter-o-kro 0 maf 9 in) -like
(ECL) cells Cells of the gastric epithelium that
secrete histamine. The ECL cells are stimulated by
the hormone gastrin and by the vagus nerve; the
histamine from ECL cells, in turn, stimulates gastric
acid secretion from the parietal cells.
enterohepatic (en 0 ter-o-h ̆e-pat 9 ik) circulation The
recirculation of a compound between the liver and
small intestine. The compound is present in the bile
secreted by the liver into the small intestine. It is then
reabsorbed and returned to the liver via the hepatic
portal vein.
entropy (en 9 tr ̆o-pe) The energy of a system that
is not available to perform work. A measure of the
degree of disorder in a system, entropy increases
whenever energy is transformed.
enzyme (en 9 zim) A protein catalyst that increases
the rate of specific chemical reactions.
epididymis (ep 0 ̆ı-did 9 ̆ı-mis); pl., epididymides
A tubelike structure outside the testes. Sperm pass
from the seminiferous tubules into the head of
the epididymis and then pass from the tail of the
epididymis to the ductus (vas) deferens. The sperm
mature, becoming motile, as they pass through the
epididymis.
epinephrine (ep 0 ̆ı-nef 9 rin) A catecholamine
hormone secreted by the adrenal medulla in response
to sympathetic nerve stimulation. It acts together
with norepinephrine released from sympathetic nerve
endings to prepare the organism for “fight or flight;”
also known as adrenaline.
epithelium (ep 0 ̆ı-the 9 le-um) One of the four
primary tissue types; the type of tissue that coverselectrolyte ( ̆e-lek 9 tro-l ̄ıt) An ion or molecule that is
able to ionize and thus carry an electric current. The
most common electrolytes in the plasma are Na^1 ,
HCO 3 −, and K^1.
electrophoresis ( ̆e-lek 0 tro-f ̆o-re 9 sis) A bio chemical
technique in which different mole cules can be
separated and identified by their rate of movement in
an electric field.
element, chemical A substance that cannot be
broken down by chemical means into simpler
substances. An element is composed of atoms that
all have the same atomic number. An element can,
however, include different forms of a given atom
(isotopes) that have different numbers of neutrons,
and thus different atomic weights.
elephantiasis (el 0 ̆e-fan-ti 9 ̆a-sis) A disease in which
the larvae of a nematode worm block lymphatic
drainage and produce edema. The lower areas of the
body can become enormously swollen as a result.
embryonic (em-bre-on 9 ik) germ layers This
term refers to the three tissue layers—endoderm,
mesoderm, and ectoderm—formed by gastrulation of
the embryo.
EMG electromyogram ( ̆e-lek 0 tro-mi 9 ̆eo-gram) An
electrical recording of the activity of skeletal muscles
through the use of surface electrodes.
embryonic stem cells Also called ES cells, these
are the cells of the inner cell mass of a blastocyst.
Embryonic stem cells are pluripotent, and so are
potentially capable of differentiating into all tissue
types except the trophoblast cells of a placenta.
emmetropia (em 0 ̆ı-tro 9 pe- ̆a) A condition of normal
vision in which the image of objects is focused on
the retina, as opposed to near sightedness (myopia) or
farsightedness (hyperopia).
emphysema (em 0 f ̆ı-se 9 m ̄a em 0 f ̆ı-ze 9 m ̆a) A lung
disease in which alveoli are destroyed and the
remaining alveoli become larger. It results in decreased
vital capacity and increased airway resistance.
emulsification ( ̆e-mul 0 s ̆ı-f ̆ı-ka 9 shun) The process
of producing an emulsion or fine suspension. In the
small intestine, fat globules are emulsified by the
detergent action of bile.
end plate potential An end plate is the specialized
postsynaptic membrane of a skeletal muscle fiber.
Upon stimulation by ACh released by a somatic
motor axon, the end plate produces a graded
depolarization, the end plate potential (EPP), which
is the stimulus for the production of muscle fiber
action potentials.
end-diastolic (di 0 ̆a-stol 9 ik) volume The volume
of blood in each ventricle at the end of diastole,
immediately before the ventricles contract at systole.
endergonic (en 0 der-gon 9 ik) Denoting a chemical
reaction that requires the input of energy from an
external source in order to proceed.
endocannabinoids (endo-can-ab 9 in-oids)
Endogenous molecules that act like
tetrahydrocannabinol in marijuana, and are believed
to serve as retrograde neurotransmitters.
endocrine (en 9 d ̆o-krin) glands Glands that secrete
hormones into the circulation rather than into a duct;
also called ductless glands.
endocytosis (en 0 do-si-to 9 sis) The cellular uptake of
particles that are too large to cross the
cell membrane. This occurs by invagination
of the cell membrane until a membrane-enclosed
vesicle is pinched off within the cytoplasm.
endoderm (en 9 d ̆o-derm) The innermost of the
three primary germ layers of an embryo. It gives rise
to the digestive tract and associated structures, the
respiratory tract, the bladder, and the urethra.
endogenous (en-doj 9 ̆e-nus) Denoting a product or
process arising from within the body (as opposed tobrain. L-dopa is used in the treatment of Parkinson’s
disease to stimulate dopamine production.
dopamine (do 9 p ̆a-m ̄en) A type of neurotrans mitter
in the central nervous system; it is also the precursor
of norepinephrine, another neurotransmitter
molecule.
dopaminergic (do 0 p ̆a-m ̄en-er 9 jik) pathways
Neural pathways in the brain that release dopamine.
The nigrostriatal pathway is involved in motor
control, whereas the mesolimbic dopamine pathway
is involved in mood and emotion.
2,3-DPG 2,3-diphosphoglyceric (di-fos 9 fo-glis-
er 0 ik) acid. A product of red blood cells,
2,3-DPG bonds with the protein component
of hemoglobin and increases the ability of
oxy hemoglobin to dissociate and release its oxygen.
ductus arteriosus (duk 9 tus ar-tir 0 e-o 9 sus) A fetal
blood vessel connecting the pulmonary artery
directly to the aorta.
dwarfism A condition in which a person is
undersized because of inadequate secretion of growth
hormone.
dyspnea (disp-ne 9 ̆a) Subjective difficulty in
breathing.
dystrophin (dis-trof 9 in) A protein associated
with the sarcolemma of skeletal muscle cells that
is produced by the defective gene of people with
Duchenne muscular dystrophy.E
eccentric (ek-sen 9 trik) contraction A muscle
contraction in which the muscle lengthens despite its
contraction, due to a greater external stretching force
applied to it. The contraction in this case can serve
a shock absorbing function, as when the quadriceps
muscles of the leg contract eccentrically upon
landing when a person jumps from a height.
ECG electrocardiogram ( ̆e-lek 0 tro-kar 9 de-
̆o-gram) (also abbreviated EKG) A recording of
electrical currents produced by the heart.
E. coli (e ko 9 li) A species of bacteria normally
found in the human intestine; full name is
Escherichia (esh 0 ̆ı-rik 9 e- ̆a) coli.
ectopic focus An area of the heart other than the
SA node that assumes pacemaker activity.
ectopic pregnancy Embryonic development that
occurs anywhere other than in the uterus (as in the
uterine tubes or body cavity).
edema ( ̆e-de 9 m ̆a) Swelling resulting from an
increase in tissue fluid.
EEG electroencephalogram ( ̆e-lek 0 tro-en-sef 9 ̆a-
l ̆o-gram) A recording of the electrical activity of the
brain from electrodes placed on the scalp.
effector ( ̆e-fek 9 tor) organs A collective term for
muscles and glands that are activated by motor
neurons.
efferent (ef 9 er-ent) Conveying or transporting
something away from a central location. Efferent
nerve fibers conduct impulses away from the central
nervous system, for example, and efferent arterioles
transport blood away from the glomerulus.
eicosanoids (i-ko 9 s ̆a-noidz) The biologically
active derivatives of arachidonic acid, a fatty acid
found in cell membranes. The eicosanoids include
prostaglandins and leukotrienes.
ejection fraction The ratio of the stroke volume
to the end-diastolic volume of a ventricle. This is
normally about 60% at rest.
elasticity ( ̆e 0 las-tis 9 ̆ı-te) The tendency of a
structure to recoil to its initial dimensions after being
distended (stretched).fox36375_glo_G1-G19.indd 6fox36375_glo_G1-G19.indd 6 2/4/15 12:29 PM2/4/15 12:29 PM