Online Biology Dictionary - E

e (1) electron; (2) electric charge.

E (1) Escherichia; (2) energy; (3) einsteinium; (4) reduction potential; (5) electromotive force.

Diagram of the ear (click to enlarge)

ead Eadem (meaning the same).

EAHF Medical acronym: eczema, asthma, hay fever.

ear, external The external ear is composed all parts of the ear outside the eardrum (tympanic membrane).

ear, internal The internal ear (or inner ear) is composed of the cochlea, the vestibule, and the semicircular canals (see figure at right).

ear, middle The middle ear is a cavity in the temporal bone. Also called the "typanum cavity", it lies just inside the eardrum (tympanic membrane). Anteriorly, the eustachian tube connects it with the pharynx. There are two membrane-covered openings into the inner ear, and three small bones, or ossicles (the malleus, incus, and stapes), which connect the eardrum with one of these openings, the fenestra vestibuli (the "elliptical window").

eburnation /eh-bur-NAY-shun/ Alteration of a bone to make it dense and ivorylike.

ecaudate /ee-CAWD-ate/ Tailless.

ecbolic /ehk-BALL-ik/ Inducing labor or abortion.

ecdysone /EK-duh-sohn/ A hormone that causes molting in arthropods.

echinate /EK-uh-nate/ Spiny.

Consequences of infection with Echinococcus: Hydatid cysts from human lung (click for life- size view)

Echinococcus /eh-KIN-oh-cock-us/ Dog tapeworm; minute tapeworms infesting dogs, humans, and other carnivores. Also infests non-carnivores as intermediate hosts. Within the host, Echinococcus usually attacks the liver first, and then the lungs. In these organs during the larval stage, fluid-filled brood cysts are formed known as hydatids, which may grow for years reaching enormous sizes. PICTURE OF LIFE CYCLE

echinoderm /eh-KINE-oh-derm/ A member of the phylum Echinodermata, marine organisms with internal, calcareous skeletons, five-part radial symmetry, and a water vascular system. Examples are starfishes, sand dollars, crinoids, and sea cucumbers.

echolalia /EK-oh-LAL-ee-yuh/ Parrotlike repetition of the vocalization of others.

echolocation /EK-oh-lo-CAY-shuhn/ A capability of certain organisms, as bats, to locate prey by emitting sounds and listening to the resulting echos.

echopraxia /EK-oh-PRACKS-ee-yuh/ Mechanical, pathological repetition of the actions of others.

eclampsia /ehk-CLAMP-see-yuh/ A pregnancy associated toxemia. Symptoms: high blood pressure, oliguria, albuminuria. Extreme cases may involve convulsions or coma.

ecoid The skeleton of an erythrocyte.

ecological niche /ee-kuh-LODGE-ik-ul, eck-uh-/ The set of conditions, both with respect to the environment and with respect to associations with other organisms, to which a particular type of organism is suited.

ecology /ik-ALL-uh-gee, ee-CALL-/ The study of the interaction of organisms with each other and with their environment.

ECT Electroconvulsive therapy.

ectoderm /ECK-toe-durm/ Outer cell layer of an embryo. During the course of development it gives rise to the nervous system, the sensory organs, and such superficial structures as the epidermis, hair, pigment cells, and mammary glands.

ectoentad /EHK-toh-EHNT-ad/ Inward from the exterior.

ectopia (or ectopy) /ehk-TOPE-ee-yuh/ Abnormal placement of an organ or other bodily structure.

ectopic pregnancy /ehk-TOP-ik or ehk-TOPE-ik/ A life-threatening condition in which the embryo implants outside the uterine cavity.

ectopotomy /ehk-toh-POT-uh-mee/ Surgical removal of an ectopic fetus.

ectosarc /EHK-tuh-sark/ The outer portion of the protoplasm of certain microorganisms (e.g., amoebas).

ectotherm /EHK-toh-therm/ An animal that uses environmental temperatures and behavior to regulate its temperature (commonly termed "cold-blooded").

ectotoxemia /EHK-toh-tox-EEM-ee-yuh/ Toxemia resulting from a toxin that has been introduced into the body.

eczema /EHK-zim-uh/ An inflammatory skin condition characterized by erythema, itching and oozing, scaling lesions. PICTURE1 PICTURE2

edema /i-DEEM-uh/ Excessive fluid in the bodily tissues.

edentate /ee-DEHNT-ayt/ (1) toothless; (2) a member of an order, Edentata, of New World mammals, including sloths, armadillos, and tamanduas (among these, only tamanduas are toothless); (3) being or pertaining to an edentate.

edentia /ee-DEHN-shee-yuh/ Lack of teeth.

edentulous /ee-DEHN-chuh-luhs/ Toothless.

EEG Electroencephalogram.

EF Elongation factor; elongation factors are proteins facilitating translational elongation.

efferent /EF-er-ruhnt/ Leading or carrying away.

EGF Epidermal growth factor, a molecule important in the regulation of cell growth, proliferation, and differentiation. It acts by binding to the epidermal growth factor receptor (EGFR).

egg (1) female sex cell or gamete (ovum); (2) externally laid, fertilized ova.

eiloid /EYE-loid/ Coil-like.

ejaculation /uh-JACK-yuh-lay-shun, ee-JACK-/ Discharge of fluid from a duct, in particular from the male urethra, or vaginal glands.

elastin /uh-LAST-in or ee-LAST-in/ A protein that is the main component of yellow elastic tissue.

elastinase /uh-LAST-in-aze/ An enzyme that breaks down elastin.

electrolysis /uh-leck-TROL-uh-sis/ Production of a chemical change by means of the application of an electrical current.

electrolyte /uh-LECK-truh-lite/ (1) a solution that conducts electricity; (2) any substance that conducts electricity when in solution.

electronegativity /uh-LECK-truh-NEG-uh-TIV-uh-tee/ Ability of an atom to attract electrons to itself.

electrophoresis /uh-leck-truh-for-EE-suhs/ A method of separating large molecules of different sizes and/or electrical charges. Typically the molecules are allowed to migrate under the influence of an electric current through an acrylamide or agarose gel. The molecules in question are usually proteins or nucleic acid fragments. The rate of migration depends on the different molecules' sizes and electrical charges so that distinct classes of molecules become separated as they migrate.

electroporation /uh-leck-truh-pore-AY-shun/ A process that uses high-voltage current to introduce DNA into cells through cell membranes that would otherwise be impermeable. See also: transfection.

element /EL-uh-muhnt/ A substance that cannot be separated into substances other than itself by chemical means. PERIODIC TABLE

elongation /uh-long-GAY-shun, ee-long-/ (1) the construction of a protein by the successive addition of individual amino acids; (2) the lengthening of any chainlike molecule by means of the successive addition of individual units.

elytritis /el-uh-TRITE-uhs/ Vaginal inflammation.

elytroptosis /EL-uh-trawp-TOE-suhs/ Vaginal prolapse.

elytrostenosis /EL-uh-troh-stuh-NO-suhs/ Narrowing of the vagina.

embolism Obstruction of a blood vessel.

embryo The earliest of stage of development of a plant or animal. In humans, embryo is used up to the third month of pregnancy. Thereafter, once the basic body shape has formed, the term fetus is employed.

embryoblast The inner cell mass within a blastocyst. PICTURE

embryology The study of embryos.

embryonic tissue Undifferentiated tissue with the potential to develop into any of the various specialized tissues.

embryonic stem (ES) cells An embryonic cell that can continue to replicate indefinitely and serve as a source of cells that can change into other, specialized kinds of cells.

embryo sac A structure composed of eight haploid cells found in angiosperms. It forms by division of a megaspore and represents the female gametophyte stage of the plant's life cycle.

encephalitis Inflammation of the brain.

encyst To form a cyst.

endergonic A nonspontaneous chemical reaction that absorbs free energy.

endocrine glands /END-uh-kruhn, -krin/ Glands secreting into the bloodstream or lymphatic system (and not onto an epithelial surface).

Endoplasmic Reticulum and Golgi Apparatus: 1. Nuclear    envelope,2. Nuclear pore, 3. Rough endoplasmic    reticulum (rER), 4. Smooth endoplasmic reticulum (sER),    5. Ribosome attached to rER, 6. Macromolecules,    7. Transport vesicles, 8. Golgi apparatus, 9. Cis face of    Golgi apparatus (the face toward the nucleus), 10. Trans    face of Golgi apparatus (the face away from the    nucleus), 11. Cisternae of Golgi apparatus

endoderm (also entoderm) /EN-doe-derm, EN-toe-derm/ The inner layer of cells of an embryo. During the course of development it gives rise to the digestive system and its associated glands, including the liver, the respiratory organs, the urethra, urinary bladder, and the vagina.

endogenous virus /ehn-DAWJ-uh-nuhs/ A virus inherited from a parent (because copies of it were present in the parent's genome).

endonuclease /EHN-do-N(Y)OOK-lee-ayz/ See: restriction endonucleases.

endoplasmic reticulum /EHN-doh-PLAZ-mik ruh-TIK-yuh-luhm/ A complex and extensive structure present in eukaryotic cells; it is joined to the nuclear envelope and composed of rough (ribosome studded) and smooth (ribosome-free) regions.

endosarc /EHN-duh-sark/ The inner portion of the protoplasm of certain microorganisms (e.g., amoebas).

endosymbiont theory /END-oh-SYM-bigh-ont/ A theory, now largely accepted, that the chloroplasts and mitochondria of eukaryotic cells are the descendants of free-living prokaryotes.

endosymbiosis /END-oh-SYM-bigh-oh-suhs/ A special form of symbiotic association between cells, in which one type of the cell lives inside the another. See: endosymbiont theory.

endosymbiotic /END-oh-SYM-bigh-OT-ik/ Characterized by endosymbiosis.

endotherm An animal that uses metabolic heat to regulate its temperature (commonly termed "warm-blooded").

enteritis /ehn-ter-I-tis/ Inflammation of the intestines, especially of the mucous membranes of the small intestine.

entoderm See: endoderm.

entomology The study of insects.

enzyme A protein catalyst.

Eocene /EE-oh-seen/ An epoch of the Tertiary Period of the Cenozoic Era. It lasted from 55.8 ± 0.2 to 33.9 ± 0.1 mya. GEOLOGIC TIME SCALE

eosin /EE-uh-sin/ An acid stain that acts as a fluorescent red dye, much used in microscopy; stains collagen, cytoplasm, and muscle fibers; most often used as a counterstain to haematoxylin in haematoxylin and eosin (H&E) staining, a primary technique in histology.

eosinophil (also eosinophile) /ee-oh-SIN-uh-fil, ee-oh-SIN-uh-file/ A leukocyte that stains red with eosin. Eosinophils target parasites and play a role in allergic reactions.

ependyma /ep-END-uh-muh/ the membrane that lines the ventricals of the cerebrum and the spinal canal.

ependymitis /EP-end-uh-MY-tis/ Inflammation of the ependyma.

epiblast /EP-uh-blast/ The outer layer of cells on a blastoderm.

epidermis /EHP-uh-DERM-uhs/ (1) in plants: the dermal tissue system; (2) in animals: the outer layer of the skin.

epididymis /EHP-uh-DID-uh-muhs/ A small structure attached to the testis, composed of a long, convoluted tube connecting the efferent ducts of the testis with the ductus deferens.

epididymoorchitis /EHP-uh-DID-uh-moh-or-KY-tis/. Inflammation of the epididymis and testis

epilepsy /EP-uh-LEP-see/ A chronic neurological disorder characterized by periodic losses of consciousness, which may be accompanied by seizures.

epiphysis /eh-PIF-uh-suhs/ A small bone separated from an larger bone by cartilage in early life, and that later fuses with the larger bone.

epistasis The masking of one gene by another. For example, a gene causing baldness would mask the effect of a hair-color gene.

epithelial tissue (also ephithelium) Broadly: A sheet of enclosing tissue; Specifically: cells that line (1) the outer surface of the body, (2) the inner surfaces of the internal organs, (3) the passages leading to those organs.

epithelialization The formation of epithelial tissue in a region where it was absent.

epoch A portion of a geological period.

eponychia (sing eponychium) In the embryo, the horny structures from which the nails develop.

equilibrium A state in which opposing forces are equal.

ER endoplasmic reticulum.

erbium (Er) metallic element; atomic weight 167.26; atomic number 68. PERIODIC TABLE

erectile Capable of becoming erect or stiff.

erg (1) the amount of work done by a force of one dyne acting through a displacement of one centimeter; (2) a desert region of shifting sands.

erythema /er-rith-EE-muh/ Abnormal redness of the skin.

erythrocytes /er-RITH-ruh-sights/ Red blood corpuscles, cells that function in transporting oxygen to the body's tissues.

ES cells See: embryonic stem cells.

Escherichia coli. /esh-uh-RICK-ee-yuh KOE-lie/ A rod-shaped bacterium found in the lower digestive tract. The most common bacterium used in genetic engineering due to its normal lack of pathogenicity, small genome size, and easy propagation.

Escherichia coli bacteria: Some cells have formed colonial   groupings, others have remained isolated as single cells.

esophageal /uh-SAWF-uh-GEE-uhl/ Of or pertaining to the esophagus.

esophagectasis (also esophagectasia) /uh-SAWF-uh-jehk-TAY-suhs, uh-SAWF-uh-jekt-TAY-zhuh/ Dilation of the esophagus.

esophagostenosis /uh-SAWF-uh-go-stuh-NO-suhs/ Narrowing of the esophagus.

esophagus /uh-SAWF-uh-guhs, ee-SAWF-/ The tube through which food and drink pass from the pharynx to the stomach; commonly known as the gullet. It has three coats: (1) an internal or mucous coat; (2) a middle or areolar coat; (3) an external or muscular coat. The muscular coat is made up of two thick layers of muscle fibers, an internal circular, and and external longitudinal layer. The areolar coat provides a loose connection between the internal and external coats. The mucous coat is thick and has longitudinal folds that disappear when the passage is distended with food.

essential amino acid An amino acid required in the diet of mammals.

EST An Expressed sequence tag required in the diet of mammals.

ester /ES-ter/ A compound formed by the combination of an alcohol with an organic acid.

esthesiology /es-theez-ee-AWL-uh-jee/ The scientific study of sensation.

esthesiology /es-theez-ee-AWM-uh-tree/ The measurement of sensory discrimination.

estrus /ES-truhs/ In female non-primate mammals, the periodically recurrent state of sexual receptivity ("heat").

estrogen /ES-truh-jen/ A hormone, produced by the ovaries, that prepares the uterus for embryo implantation.

ethmoid bone /ETH-moid/ A sievelike bone, filled with air cells, forming the roof of the nasal cavity and floor of the anterior portion of the braincase.

ethmomaxillary Pertaining to the ethmoid bone and maxilla.

ethology /ee-THAWL-uh-gee/ The study of animal behavior.

euchromatin /YOO-krome-uh-tuhn, -tin/ Chromatin that is uncoiled (not condensed) during interphase. Euchromatin reaches maximal condensation during mitotic metaphase.

eugenics /yoo-JEN-icks/ A political movement, without scientific foundation, promoting the idea that humanity can, and should be improved, by artificial selection; selective breeding of humans. The Nazis applied this pernicious policy with disastrous effect.

eukaryote /yoo-KARE-ee-yuht, -ee-ote/ Organisms, both unicellular and multicellular, in which there is a membrane-bounded cell nucleus and other well-developed organelles. All organisms other than viruses and prokaryotes are eukaryotes. See also: prokaryote, chromosome. MORE INFORMATION

Euramerica in the Devonian (click to enlarge)

Euramerica (sometimes called "the Old Red Continent") /yer-am-MARE-ick-uh/ A supercontinent formed by the collision of Avalonia, Baltica, and Laurentia. It existed in the Late Silurian and in the Devonian. It later became part of Pangea, and still later, part of Laurasia. Today, the corresponding deposits, which are usually red in color, underlie Greenland and much of Europe and North America.

eustachian tube /yoo-STAY-shun/ The narrow passage connecting the middle ear with the upper pharynx. SEE PICTURE

eutherian /yoo-THIR-ee-uhn/ A member of the major division Eutheria of Class Mammalia, the other two major divisions being marsupials and monotremes. Eutherian mammals nourish their young within the uterus to mored advanced stage of development than do most marsupials.

eutrophication Superabundant growth of plants in lakes and rivers resulting from the release of nitrogen- and phosphorous-containing fertilizers. In the end this leads to accelerated decomposition of the dead plants by bacteria, which uses up oxygen, causing fish and other aquatic organisms to die of suffocation.

evaporite A deposit of minerals, such as anhydrite, gypsum, and halite, that remains after evaporation of seawater.

evolution The production of new types of organisms over time, as documented in the fossil record.

evolutionary biology The branch of biology concerned with the modes of origin of new forms of life.

evolutionarily conserved See: conserved sequence.

excision /ex-SISH-uhn/ Cutting out or away, removal by cutting.

excrement Feces.

excreta (1) in a medical context: feces; (2) more broadly, any waste product of the body or of a cell.

excretion The process of expelling waste materials from the body, or from an individual cell.

exine The outer covering of a pollen grain.

exocrine gland A gland that secretes its contents onto an epithelial surface (and not into the bloodstream or lymphatic system).

Used with permission. Courtesy Chris Patton, Stanford Sea Urchin Embryology Lab

Exocytosis

exocytosis The expulsion of macromolecules from a cell. The molecules are first sequestered within a vesicle. The vesicle then moves to, and fuses with, the plasma membrane (see animation at right). In the animation, the surface proteins of the plasma membrane are shown in red, those of the vesicle membrane, in green. Note that when the vesicle fuses with the plasma membrane the membrane's proteins are displaced by the surface proteins of the vesicle and the macromolecules in the vesicle are expelled.

exogenesis /EKS-o-GEHN-uh-suhs/ One of the two major hypotheses concerning the origin of life on Earth. It proposes that life on this planet arrived from elsewhere in the universe, presumably in the form of frozen particles containing prokaryotes and, perhaps, other simple organisms. This hypothesis is sometimes called panspermia, but this latter term, strictly speaking, refers to the claim that the "seeds of life" are spread throughout the universe and begin to develop wherever suitable environments exist. The other major hypothesis, opposed to exogenesis, is primordial-abiogenesis.

exogenous virus /ehks-OJ-ehn-us/ A virus of contagious origin, not inherited from a parent.

exon A protein-coding portion of a gene. See also: intron.

exoskeleton A hard case on the external surface of many invertebrates, such as the shell of a mollusk or the cuticle of an insect.

exonuclease /EKS-o-N(Y)OOK-lee-aze/ An enzyme that digests DNA, beginning at the end (as opposed to an endonuclease).

expressed gene See: gene expression.

expressed sequence tag (EST) A short portion of a cDNA molecule serving to identify a gene. Used in locating genes on chromosomes. See also: sequence tagged site.

extremophile An organism that thrives under extreme conditions, such as extreme heat or salinity.

exude To pass or ooze through a tissue (said of fluids).