embryo
American Heritage Dictionary:
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em·bry·o
(ĕm'brē-ō') 
n., pl., -os.
n., pl., -os.
- An organism in its early stages of development, especially before it has reached a distinctively recognizable form.
- An organism at any time before full development, birth, or hatching.
- The fertilized egg of a vertebrate animal following cleavage.
- In humans, the prefetal product of conception from implantation through the eighth week of development.
- Botany. The minute, rudimentary plant contained within a seed or an archegonium.
- A rudimentary or beginning stage: "To its founding fathers, the European [Economic] Community was the embryo of the United States of Europe" (Economist).
[Medieval Latin embryō, from Greek embruon : en-, in; see en-2 + bruein, to be full to bursting.]
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Early stage of development of an organism in the egg or the uterus, during which its essential form and its organs and tissues develop. In humans, the organism is called an embryo for the first seven or eight weeks after conception, after which it is called a fetus. In mammals, the fertilized egg or zygote undergoes cleavage (cell division without cell growth) to form a hollow ball or blastocyst. During the second week following fertilization, gastrulation (cell differentiation and migration) results in the formation of three tissue types. These three types of tissue develop into different organ systems: the ectoderm develops into the skin and nervous system; the mesoderm develops into connective tissues, the circulatory system, muscles, and bones; and the endoderm develops into the lining of the digestive system, lungs, and urinary system. In humans, by about the fourth week, the head and trunk can be distinguished and the brain, spinal cord, and internal organs begin to develop. By the fifth week, limbs begin to appear and the embryo is about .33 in. (.8 cm) long. By the end of eight weeks, the embryo has grown to about 1 in. (2.5 cm) long and all subsequent change is limited primarily to growth and specialization of existing structures. Any congenital disorders begin in this stage. pregnancy.
For more information on embryo, visit Britannica.com.
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An organism in its early stages of development. The developing human is known as an embryo for about its first two months in the womb. Conventions differ in defining when the name first applies — whether it is immediately after fertilization or after implantation of the fertilized ovum in the uterus a week or so later.
— Stuart Judge
See antental development.
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embryo
Columbia Encyclopedia:
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embryo
embryo (ĕm'brēō), name for the developing young of an animal or plant. In its widest definition, the embryo is the young from the moment of fertilization until it has become structurally complete and able to survive as a separate organism. Embryology, the scientific study of embryonic development, deals with the period from fertilization until the hatching or birth of an animal or the germination of a plant. However, since the young animal may undergo metamorphosis or may remain wholly dependent on the mother for some time after birth, and since the seedling derives nourishment from food stored in its fleshy cotyledons even after it has sprouted, the exact limit of the time during which an organism is an embryo has not generally been well defined.
Modern embryology, using the techniques of molecular biology, genetics, and other disciplines, has focused on the question of what makes the embryo differentiate (see differentiation), what genetically directed molecular signals tell a single cell to divide and follow the specific pattern of growth and specialization that results in a complex multicellular organism with species-specific and individual characteristics.
Karl Ernst von Baer, who developed the biogenetic law, is generally regarded as the founder of embryology. E. H. Haeckel's "ontogeny recapitulates phylogeny" gave weight to the theory of evolution (see recapitulation). Other researchers in the field of embryology have included C. F. Wolff, M. J. Schleiden, and T. Schwann, developers of the cell theory; F. M. Balfour; H. Spemann; O. Hertwig; F. R. Lillie; and R. Levi-Montalcini.
Developmental Stages
Among humans, the developing young is known as an embryo until eight weeks following conception, after which time it is described, until birth, as a fetus. In organisms that reproduce sexually, the union of the sperm with the ovum results in a zygote, or fertilized egg, which begins a rapid series of cell divisions called cleavage, or segmentation (see mitosis). Each kind of organism has its own characteristic sequence of development, and related species usually have similar developmental patterns.
In a typical animal, cleavage proceeds in the following pattern. Early divisions produce a hollow ball one cell thick, called a blastula, which encloses the blastocoel, or cleavage cavity. The cells divide more rapidly in the area where the nucleus of the ovum was located; this results in an invagination (inpushing) of these cells to form a ball two cells thick (the gastrula). The new cavity thus formed is the gastrocoel, also known as the primitive gut or archenteron, and its opening is the blastopore. The outer layer of cells is called the ectoderm, the inner layer the endoderm. Among the coelenterates (e.g., sponges and jellyfish), these two layers become the chief functional tissues of the adult.
In higher forms of life, a third layer of cells, the mesoderm, develops from one or both of the first two layers and fills the blastocoel, and invagination forms a digestive tract with only a single opening at this early stage. The flatworms (e.g., the tapeworm and the fluke) stop developing at this time. In most organisms, however, a later invagination of the ectoderm results in a gut that is open at both ends. The mesoderm then divides into two layers, the space between them being called the coelom, or body cavity. The embryo now roughly resembles a tube within a tube.
From the three primary germ layers, the organs and tissues develop. In general the ectoderm gives rise to the skin, or integument, the skin appendages (e.g., scales, feathers, hair, and nails), and the nervous system. The endoderm forms the digestive glands, as well as the lining of the alimentary tract and lungs. From the mesoderm develop the major internal organs: the skeletal, muscular, and connective tissue and the circulatory, excretory, and reproductive systems. Sense organs and endocrine glands arise from combinations of all three layers.
Nourishment of the Embryo
In lower animals, which lay their eggs in water, the developing embryo is nourished by yolk, absorbing oxygen from and discharging wastes directly into the water. In terrestrial oviparous forms, the egg contains the yolk and also a surrounding fluid (e.g., the albumen of bird eggs). In mammals, accessory membranes, comprising both embryonic and uterine tissue, develop around the embryo-the amnion, filled with liquid, and the chorion and allantois, which help to form the placenta, through which nourishment and oxygen in the blood of the mother diffuse into the fetus and wastes diffuse back. In the higher plants, the divisions of the fertilized ovum and the differentiation of the tissues to form the embryonic root (hypocotyl), stem (epicotyl), and leaves (cotyledons) occur inside the ovule within the ovary at the base of the pistil. The matured ovule is the seed; the fruit, when it is produced, is the developed ovary.
Word Tutor:
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embryo
IN BRIEF: An animal in the early stages of its development. Also: The part of a seed from which a plant develops.
A plant seed contains an embryo as well as all the food it needs to get a good start.
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The Dream Encyclopedia:
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Embryo
An embryo can represent the most vulnerable part of ourselves, the "inner child." (Also see Baby, Miscarriage, Pregnant.)
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(em-bree-oh)
The term is occasionally used to denote a new or developing idea or project: “The idea for the complete theory was already present in his work, in embryo form, in 1950.”
A developing plant or animal. A plant embryo is an undeveloped plant inside a seed. An animal embryo is the animal as it develops from the single cell of the zygote until birth. Among humans and most other mammals, the embryo is carried in the mother's womb.
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the structure that develops from a zygote, up to the time of birth or hatching in eutherian animals, or of germination in plants. In mammals the term is restricted to the structure present in the early part of gestation that develops into a fetus.
—embryonic, embryonal adj.
| embolus, em+, elymoclavine | |
| embryogenesis, embryology, embryonated |
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A new organism in the earliest stage of development, i.e. from the time that the fertilized embryo begins to develop a long axis up to the time that the major structures have begun to develop, when it becomes a fetus.
- e. collection — collection of an embryo from the genital tract for the purposes of embryo transfer; surgical and nonsurgical techniques available.
- e. cryopreservation — preservation of embryos by freezing.
- hexacanth e. — the larva with six hooks present in the cestode egg when it escapes from the uterus of the adult tapeworm. Called also oncosphere.
- e. micromanipulation — handling of an embryo under a microscope, for examination, dissection.
- e. transfer — collection of fertilized ova from one female before they become implanted and transfer to another female to complete the gestation. The donor is usually superovulated and then inseminated. Collection may be surgical via a laparotomy or nonsurgical by flushing through the cervix. Collected embryos must be stored carefully. They are evaluated in terms of fertilization, possibly cleaved artificially to create clones, and washed to eliminate the possibility of transferring infection with the embryo. Long-term storage by freezing is a practicable procedure. The recipient needs to be in appropriate stage of uterine receptivity, effected by synchronizing the estrus cycle with that of the donor.
- e. transplant — see embryo transfer (above).
Mosby's Dental Dictionary:
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embryo
n
An organism in the earliest stages of development; in humans, the stage between the time of implantation of the fertilized ovum until the end of the seventh or eighth week of gestation.
Random House Word Menu:
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categories related to 'embryo'
- Reproductive System - embryo: developing human in womb during first eight weeks after conception
- Reproduction and Development - embryo: organism in early stages of development before birth
- Pregnancy and Birth - embryo: unborn child developing in mother’s womb
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Embryo
For other uses, see Embryo (disambiguation).
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This documentation needs attention from an expert on the subject. Please add a reason or a talk parameter to this template to explain the issue with the documentation. WikiProject Biology or the Biology Portal may be able to help recruit an expert. (November 2008) |
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| Embryos (and one tadpole) of the wrinkled frog (Rana rugosa) | |
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An embryo (irregularly from Greek: ἔμβρυον, plural ἔμβρυα, lit. "that which grows," from en- "in" + bryein, "to swell, be full"; the proper Latinate form would be embryum) is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination. In humans, it is called an embryo until about eight weeks after fertilization (i.e. ten weeks Last Menstrual Period or LMP), and from then it is instead called a fetus.
The development of the embryo is called embryogenesis. In organisms that reproduce sexually, once a sperm fertilizes an egg cell, the result is a cell called the zygote, which possesses half the DNA of each of its two parents. In plants, animals, and some protists, the zygote will begin to divide by mitosis to produce a multicellular organism. The result of this process is an embryo.
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Animal embryos
In animals, the development of the zygote into an embryo proceeds through specific recognizable stages of blastula, gastrula, and organogenesis. The blastula stage typically features a fluid-filled cavity, the blastocoel, surrounded by a sphere or sheet of cells, also called blastomeres. The embryo of a placental mammal is defined as the organism between the first division of the zygote (a fertilized ovum) until it becomes a fetus. An ovum is fertilized in a fallopian tube through which it travels into the uterus. In humans, the embryo is defined as the product of conception after it is implanted in the uterus wall through the eighth week of development. An embryo is called a fetus at a more advanced stage of development and up until birth or hatching. In humans, this is from the eighth week of gestation. However, animals which develop in eggs outside the mother's body are usually referred to as embryos throughout development, e.g. one would refer to a chick embryo, not a "chick fetus" even at late stages.
During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, and/or migration to form two (diploblastic) or three (triploblastic) tissue layers. In triploblastic organisms, the three germ layers are called endoderm, ectoderm, and mesoderm. The position and arrangement of the germ layers are highly species-specific, however, depending on the type of embryo produced. In vertebrates, a special population of embryonic cells called the neural crest has been proposed as a "fourth germ layer", and is thought to have been an important novelty in the evolution of head structures.
During organogenesis, molecular and cellular interactions between germ layers, combined with the cells' developmental potential, or competence to respond, prompt the further differentiation of organ-specific cell types.[citation needed] For example, in neurogenesis, a subpopulation of ectoderm cells is set aside to become the brain, spinal cord, and peripheral nerves. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis (formation of new blood vessels from pre-existing ones), chondrogenesis (cartilage), myogenesis (muscle), osteogenesis (bone), and many others.
Generally, if a structure pre-dates another structure in evolutionary terms, then it often appears earlier than the second in an embryo; this general observation is sometimes summarized by the phrase "ontogeny recapitulates phylogeny".[1] For example, the backbone is a common structure among all vertebrates such as fish, reptiles, and mammals, and the backbone also appears as one of the earliest structures laid out in all vertebrate embryos. The cerebrum in humans, which is the most sophisticated part of the brain, develops last. This sequencing rule is not absolute, but it is recognized as being partly applicable to development of the human embryo.
Fossilised animal embryos
Main article: Fossil embryos
Fossilised animal embryos are known from the Precambrian, and are found in great numbers during the Cambrian period. Even fossilised dinosaur embryos have been discovered.
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The human embryo
See also: Human embryogenesis and Prenatal development
- Week 1–3
- 5–7 days after fertilization, the blastocyst attaches to the wall of the uterus (endometrium). When it comes into contact with the endometrium it performs implantation. Implantation connections between the mother and the embryo will begin to form, including the umbilical cord. The embryo's growth centers around an axis, which will become the spine and spinal cord. The brain, spinal cord, heart, and gastrointestinal tract begin to form.[2]
- Week 4–5
- Chemicals produced by the embryo stop the woman's menstrual cycle. Neurogenesis is underway, showing brain activity at about the 6th week.[3] The heart will begin to beat around the same time. Limb buds appear where arms and legs will grow later. Organogenesis begins. The head represents about one half of the embryo's axial length, and more than half of the embryo's mass. The brain develops into five areas. Tissue formation occurs that develops into the vertebra and some other bones. The heart starts to beat and blood starts to flow.[2]
- Week 6–8
- Myogenesis and neurogenesis have progressed to where the embryo is capable of motion, and the eyes begin to form. Organogenesis and growth continue. Hair has started to form along with all essential organs. Facial features are beginning to develop. At the end of the 8th week, the embryonic stage is over, and the fetal stage begins.[2]
Abortion
See also: Miscarriage
Some embryos do not survive through to the fetal stage, which begins about two months after fertilization (10 weeks LMP). Embryos may be aborted spontaneously or purposely.
Studies using very sensitive early pregnancy tests have found that 25% of embryos are aborted by the sixth week LMP (since the woman's last menstrual period), even if a woman does not realize it.[4][5] Abortions after the sixth week LMP happen in 8% of pregnancies.[5] The risk of them is "virtually complete by the end of the embryonic period," with a rate of only two percent after 8.5 weeks LMP.[6]
The most common natural cause of abortion of an embryo is chromosomal abnormality,[7] which accounts for at least 50% of sampled early pregnancy losses.[8] Advancing maternal age and a patient history of previous spontaneous abortions are the two leading risk factors.[8]
Induced abortion
See also: Abortion
The majority of induced abortions occur during the embryonic period. For example, in England and Wales during 2006, 68% of them occurred by the end of the embryonic period.[9]
Induced (i.e. purposeful) abortion of an embryo may be accomplished by a variety of methods, including both pharmaceutical and surgical techniques. Suction-aspiration is the most common surgical method of aborting an embryo within the United States.[10]
Common reasons for purposely aborting an embryo include a desire to delay or end childbearing, concern over the interruption of work or education, issues of financial or relationship stability, perceived immaturity and health concerns.[11][12]
Use in ART and diagnosis
Embryos are used in various techniques of assisted reproductive technology, such as in vitro fertilization and embryo donation. They may be subject to embryo cryopreservation for later use if IVF procedures have resulted in more embryos than is currently needed. Some aspects, e.g. selective reduction, are issues in the beginning of pregnancy controversy.
Prenatal diagnosis or preimplantation diagnosis involves testing embryos for diseases or conditions.
Viability
A human embryo is not considered viable, because it cannot survive outside the uterus. Current medical technology does not allow an embryo to be transplanted from the uterus of one woman to that of another.[13]
Research
Human embryos are being researched to determine their use in treating diseases. Their use in stem cell research, reproductive cloning, and germline engineering are currently being explored. The morality of this type of research is debated because an embryo is often used.[14][15][16]
Plant embryos
Further information: Sporophyte
In botany, a seed plant embryo is part of a seed, consisting of precursor tissues for the leaves, stem (see hypocotyl), and root (see radicle), as well as one or more cotyledons. Once the embryo begins to germinate — grow out from the seed — it is called a seedling. Plants that do not produce seeds, but do produce an embryo, include the bryophytes and ferns. In these plants, the embryo is a young plant that grows attached to a parental gametophyte.
Footnotes
- ^ Gould, Stephen. Ontogeny and Philogeny, p. 206 (1977): "recapitulation was not 'disproved'; it could not be, for too many well-established cases fit its expectations."
- ^ a b c NIH Medical Encyclopedia http://www.nlm.nih.gov/medlineplus/ency/article/002398.htm
- ^ Gazzaniga, Mike S.The Ethical Brain "not until the end of week 5 and into week 6 (usually around forty to forty-three days) does the first electrical brain activity begin to occur. This activity, however, is not coherent activity of the kind that underlies human consciousness, or even the coherent activity seen in a shrimp's nervous system."
- ^ Wilcox AJ, Baird DD, Weinberg CR (1999). "Time of implantation of the conceptus and loss of pregnancy.". New England Journal of Medicine 340 (23): 1796–1799. doi:10.1056/NEJM199906103402304. PMID 10362823.
- ^ a b Wang X, Chen C, Wang L, Chen D, Guang W, French J (2003). "Conception, early pregnancy loss, and time to clinical pregnancy: a population-based prospective study.". Fertil Steril 79 (3): 577–84. doi:10.1016/S0015-0282(02)04694-0. PMID 12620443.
- ^ Rodeck, Charles; Whittle, Martin. Fetal Medicine: Basic Science and Clinical Practice (Elsevier Health Sciences 1999), p. 835.
- ^ Stöppler, Melissa Conrad; William C. Shiel, Jr., ed.. "Miscarriage (Spontaneous Abortion)". MedicineNet.com. http://www.medicinenet.com/miscarriage/page1.htm. Retrieved 2009-04-07.
- ^ a b Jauniaux, E.; P. Kaminopetros and H. El-Rafaey (1999). "Early pregnancy loss". In Martin J. Whittle and C. H. Rodeck. Fetal medicine: basic science and clinical practice. Edinburgh: Churchill Livingstone. p. 837. ISBN 0-443-05357-X. OCLC 42792567.
- ^ Department of Health (2007). "Abortion statistics, England and Wales: 2006". http://www.dh.gov.uk/en/Publicationsandstatistics/Publications/PublicationsStatistics/DH_075697. Retrieved 2007-10-12. "68% were at under 10 weeks"
- ^ Healthwise (2004). "Manual and vacuum aspiration for abortion". WebMD. http://www.webmd.com/hw/womens_conditions/tw1078.asp#tw1112. Retrieved 2008-12-05.
- ^ Bankole, Akinrinola, Singh, Susheela, & Haas, Taylor. (1998). Reasons Why Women Have Induced Abortions: Evidence from 27 Countries. International Family Planning Perspectives, 24 (3), 117–127 & 152. Retrieved 2006-01-18.
- ^ Finer, Lawrence B., Frohwirth, Lori F., Dauphinee, Lindsay A., Singh, Shusheela, & Moore, Ann M. (2005). Reasons U.S. women have abortions: quantitative and qualitative perspectives. Perspectives on Sexual and Reproductive Health, 37 (3), 110–8. Retrieved 2006-01-18.
- ^ Rumbold, Graham. Ethics in nursing practice, p. 120 (Elsevier Health Sciences 1999).
- ^ Freedman, Jeri. "America Debates Stem Cell Research." New York, NY: The Rosen Publishing Group, 2008.
- ^ Sandel, Michael J. "The Case Against Perfection." Michael J. Sandel, 2007.
- ^ Zavos, Panayiotis. “Reproductive Cloning is Moral.” Ed. James Woodward. The Ethics of Human Cloning: At Issue. Farmington Hills, MI: Greenhaven, 2005. 14–24.
See also
- Embryo donation
- Embryo space colonization
- Embryogenesis
- Embryology
- Embryomics
- The Human Embryo: Aristotle and the Arabic and European Traditions (book)
- In vitro fertilization
- Plant embryogenesis
- Pregnancy
- Proembryo
| Preceded by Zygote |
Stages of human development Embryo |
Succeeded by Fetus |
External links
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Wikimedia Commons has media related to: Embryology |
- Chart of human fetal development
- UNSW Embryology - Educational website
- A Comparative Embryology Gallery
- Development of the human embryo
- The Visible Embryo from fertilization to birth
- The Human Fertilisation and Embryology Authority (HFEA)
- 4-H Embryology, University of Nebraska-Lincoln Extension in Lancaster County
- Dignitas Personae, a summary of the embryonic ethical controversies, from a Roman Catholic perspective (reference: [1])
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This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
Translations:
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Embryo
Dansk (Danish)
n. - embryo, foster, kim, spire
idioms:
- in embryo i svøb, in spe
Nederlands (Dutch)
embryo, nog niet volledig ontwikkeld
Français (French)
n. - (lit, fig) embryon
idioms:
- in embryo à l'état embryonnaire
idioms:
- in embryo im Keim
Ελληνική (Greek)
n. - (βιολ., μτφ.) έμβρυο
idioms:
- in embryo σε εμβρυακή κατάσταση
idioms:
- in embryo in embrione
Português (Portuguese)
n. - embrião (m)
idioms:
- in embryo em estado embrionário
Русский (Russian)
зародыш, эмбрион
idioms:
- in embryo в начальной стадии
Español (Spanish)
n. - embrión, germen
idioms:
- in embryo en embrión
中文（简体）(Chinese (Simplified))
胚胎, 胚芽, 胎儿
idioms:
- in embryo 在胚胎阶段, 在未成熟时期
中文（繁體）(Chinese (Traditional))
n. - 胚胎, 胚芽, 胎兒
idioms:
- in embryo 在胚胎階段, 在未成熟時期
idioms:
- in embryo 발달이 덜 된, 무르익지 않은
idioms:
- in embryo 未発達の, 初期の
العربيه (Arabic)
(الاسم) جنين
עברית (Hebrew)
n. - עובר, עובר בשמונה השבועות הראשונים להיריון, דבר לא מפותח או לא בשל
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