Embryo

Warning: mkdir() [function.mkdir]: Permission denied in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: mkdir() [function.mkdir]: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: fopen(/home/templatecore2cache//*cluesnet.com/84/84888eaf1a83ef87add6cedf77a4b11d1eef5bdf.tc2cache) [function.fopen]: failed to open stream: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 130

Warning: fwrite(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 131

Warning: fclose(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 132

) of the wrinkled frog (Rana rugosa)An embryo (Greek language: , plural ) is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg (biology), or germination. In humans, it is called an embryo from the moment of fertilisation until the end of the 8th week of gestational age, whereafter it is instead called a fetus.

Development The development of the embryo is called embryogenesis. In organisms that sexual reproduction, once a spermatid fertilizes an ovum, the result is a cell (biology) called the zygote that has all the DNA of two parents. The resulting embryo derives 50 percent of its genetic makeup from each parent. 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.

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 blastocoele, surrounded by a sphere or sheet of cells, also called blastomeres.

. A rotatable 3D version of this photo is available here, and a drawing is available here. During gastrulation the cells of the blastula undergo coordinated processes of cell division, invasion, and/or migration to form two (diploblasty) or three (triploblasty) tissue layers. In triploblastic organisms, the three germ layers are called endoderm, ectoderm and mesoderm. However, the position and arrangement of the germ layers are highly species-specific, 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 (biology) to respond, prompt the further differentiation of organ-specific cell types. For example, in neurogenesis, a subpopulation of ectoderm cells is set aside to become the brain, spinal cord and peripheral nervous system. Modern developmental biology is extensively probing the molecular basis for every type of organogenesis, including angiogenesis (formation of blood vessels), 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 other in an embryo; this general observation is sometimes summarized by the phrase "recapitulation theory."Gould, Stephen. Ontogeny and Philogeny, page 206 (1977): "recapitulation was not 'disproved'; it could not be, for too many well-established cases fit its expectations." 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 human brain, develops last. This rule is not absolute, but it is recognized as being partly applicable to development of the human embryo.

Embryos of plants and animals

Plants: 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 germination — 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.
Animals: The embryo of a placental mammal is defined as the organism between the first cell division of the zygote (a fertilized ovum) until it becomes a fetus. In humans, the embryo is defined as the product of conception from implantation in the uterus through the eighth week of development. An embryo is called a fetus at a more advanced stage of development and up until childbirth or hatching. In humans, this is from the eighth week of gestation.

The human embryo Growth Week 1-4 5-7 days after fertilization, the blastula 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.

Week 5-6 Chemicals produced by the embryo stop the woman's menstrual cycle. Neurogenesis is underway, showing brain wave activity at about the 6th week. The heart will begin to beat around the same time. Limb buds appear where the 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.

Week 7-8 The embryo's blood type becomes apparent. Myogenesis and neurogenesis have progressed to where the embryo is capable of motion, and the eyes begin to form. Organogenesis and growth continue. At the end of the 8th week, the embryonic stage is over, and the fetus stage begins.

Status The status of the human embryo is debated among Bioethics. Some ethicists believe that an embryo does, in fact, possess Person. Gilbert Meileander, for example, identifies conception as the point at which a new individual human being comes into existence, since "when sperm and ovum join to form the zygote, the individual's genotype is established."Gilbert Meilander, Bioethics: A Primer for Christians (2nd ed.; Grand Rapids: Eerdmans, 2005), p. 29. However, human embryos Cloning#Embryo, in which case no new genotype is established.

Footnotes

See also

Embryogenesis
Embryology
In vitro fertilization
Plant embryogenesis
Embryo space colonization
Pregnancy
Embryo adoption
Sexual

External links

Chart of human fetal development
A Comparative Embryology Gallery
Development of the human embryo
The Visible Embryo from fertilization to birth
The Human Fertilisation and Embryology Authority (HFEA)

Embryo - Wikipedia, the free encyclopedia
An embryo (from Greek: ἔμβρυον, plural ἔμβρυα, lit. "that which grows," from en- "in" + bryein "to swell, be full") is a multicellular diploid eukaryote in its ...

embryo
Dear All, Just to inform you that I am recruiting for both of the courses I coordinate @ Tower Hamlets College (London UK). They are Access (one year) courses.

Science Museum | Dolly the sheep, 1996-2003 | Reprogramming DNA
The resulting embryo was implanted into the womb of a third, surrogate sheep. Dolly was born on 5 July 1996, and her birth was announced in early 1997.

Definition: embryo from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.

BBC NEWS | Health | UK scientists clone human embryo
Report on research involving introduction of DNA from embryonic stem cells, surviving in egg genome from 11 women, for three to five days, the country's first patient specific ...

BBC NEWS | Health | Three-parent embryo formed in lab
Scientists say the creation of a human embryo with three separate parents could be used to tackle serious genetic diseases.

Miscarriage Causes: Embryo Toxic Factor (ETF)
Some of the common causes of miscarriage are due to pregnancy complications such as blighted ovum, ectopic pregnancy or molar pregnancy. However, women who experience multiple ...

London Fertility Clinic | Sperm and Embryo Donation/Surrogacy
Sperm and Embryo Donation/Surrogacy SPERM DONATION Sperm donation is an option if the male partner does not have any sperm, i.e., he is azoospermic or if he has ...

embryo - Hutchinson encyclopedia article about embryo
Hutchinson encyclopedia article about embryo. embryo. Information about embryo in the Hutchinson encyclopedia.

BabyCentre glossary - E
... female reproductive cell produced by the ovaries. After fertisation by a sperm (a male reproductive cell), the two cells fuse together to form a single cell, from which an embryo ...