in many other animals. It can be pathogenic and is
implicated in a number of food-borne illnesses, with an
estimated 10,000 to 20,000 cases of infection occurring
in the United States each year. There are hundreds of
strains of this one species.
ESE SeeELECTRON SPIN-ECHO SPECTROSCOPY.
ESEEM(Electron spin-echo envelope modulation)
SeeELECTRON SPIN-ECHO SPECTROSCOPY.
esophagus The muscular tube of the digestive tract
between the throat (pharynx) and stomach.
ESR (electron spin resonance) SeeELECTRON PARA-
MAGNETIC RESONANCE SPECTROSCOPY.
essential amino acids Amino acids that cannot be
synthesized in the human body and must be provided
from another source (food). These amino acids are his-
tidine, isoleucine, leucine, lysine, methionine, pheny-
lalanine, threonine, tryptophan, and valine.
See alsoAMINO ACID.
estivation(aestivation) A state of stagnation or dor-
mancy with slow metabolism (no eating, moving, or
growing) during periods of hot temperature and little
water supply; a physiological condition for survival.
estrogens Primary female sex hormones. Estrogens
cause growth and development of female sex organs
and support the maintenance of sexual characteristics,
including growth of underarm and pubic hair and
shaping of body contours and skeleton; increase secre-
tions from the cervix and growth of the endometrium
(inner lining) of the uterus; and reduce concentrations
of bad cholesterol (LDL cholesterol) while increasing
good cholesterol (HDL). Estrogen is produced in the
ovary by the developing follicle and by the corpus
luteum.
See alsoHORMONE.
estrous cycle(heat cycle) The period from one ovula-
tion to the next in female mammals; a period of sexual
receptiveness preceding ovulation; in humans it occurs
every 21 to 23 days. It is characterized by rising and
falling levels of estrogens and progesterone in the
bloodstream.estrus The “heat” cycle in reproduction, the time
when the female is sexually receptive.ethology The study of natural animal behavior.ethylene(C 2 H 4 ) A reactive chemical made from nat-
ural gas or crude-oil components (occurs naturally in
both petroleum and natural gas) that acts as a plant
hormone, the only gaseous hormone. It is used for
accelerating fruit ripening (bananas); maturing citrus
fruit color; increasing the growth rate of seedlings, veg-
etables, and fruit trees; leaf abscission; and aging.etiology(aetiology) The scientific study or theory of
the causes of a certain disease.euchromatin Within a nucleus of eukaryotes there
are two types of a mixture of nucleic acid and protein
called chromatin that make up a chromosome: euchro-
matin and heterochromatin. During interphase, the
genetically active euchromatin is uncoiled and is avail-
able for transcription, while heterochromatin is denser
and usually not transcribed.eudismic ratio The POTENCYof the EUTOMERrela-
tive to that of the DISTOMER.eukaryotes Organisms whose cells have their GENET-
ICmaterial packed in a membrane-surrounded, struc-
turally discrete nucleus and who have well-developed
cell organelles.eumetazoa A subkingdom of the animalia king-
dom that includes all animals with the exception ofeumetazoa 119