how the embryo form in detail
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Answer:
The next stage in development is the embryo, which develops within the amniotic sac, under the lining of the uterus on one side. This stage is characterized by the formation of most internal organs and external body structures. Most organs begin to form about 3 weeks after fertilization, which equals 5 weeks of pregnancy (because doctors date pregnancy from the first day of the woman's last menstrual period, which is typically 2 weeks before fertilization). At this time, the embryo elongates, first suggesting a human shape. Shortly thereafter, the area that will become the brain and spinal cord (neural tube) begins to develop. The heart and major blood vessels begin to develop earlier—by about day 16. The heart begins to pump fluid through blood vessels by day 20, and the first red blood cells appear the next day. Blood vessels continue to develop in the embryo and placenta.
Almost all organs are completely formed by about 10 weeks after fertilization (which equals 12 weeks of pregnancy). The exceptions are the brain and spinal cord, which continue to form and develop throughout pregnancy. Most malformations (birth defects) occur during the period when organs are forming. During this period, the embryo is most vulnerable to the effects of drugs, radiation, and viruses. Therefore, a pregnant woman should not be given any live-virus vaccinations or take any drugs during this period unless they are considered essential to protect her health
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Answer:
Embryo
For other uses, Embryo (disambiguation).
An embryo is an early stage of development of a multicellular organism. In general, in organisms that reproduce sexually, embryonic development refers to the portion of the life cycle that begins just after fertilization and continues through the formation of body structures, such as tissues and organs. Each embryo starts development as a zygote, a single cell resulting from the fusion of gametes (i.e. fertilization of a female egg cell by a male sperm cell). In the first stages of embryonic development, a single-celled zygote undergoes many rapid cell divisions, called cleavage, to form a blastula, which looks similar to a ball of cells. Next, the cells in a blastula-stage embryo start rearranging themselves into layers in a process called gastrulation. These layers will each give rise to different parts of the developing multicellular organism, such as the nervous system, connective tissue, and organs.
Embryo
A newly developing human is typically referred to as an embryo until the ninth week after conception (see human embryogenesis), when it is then referred to as a fetus. In other multicellular organisms, the word “embryo” can be used more broadly to any early developmental or life cycle stage prior to birth or hatching.
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Etymology
First attested in English in the mid-14c., the word embryon derives from Medieval Latin embryo, itself from Greek ἔμβρυον (embruon), lit. "young one",which is the neuter of ἔμβρυος (embruos), lit. "growing in",from ἐν (en), "in" and βρύω (bruō), "swell, be full"; the proper Latinized form of the Greek term would be embryum.
Embryos (and one tadpole) of the wrinkled frog (Rana rugosa)
In animals, fertilization begins the process of embryonic development with the creation of a zygote, a single cell resulting from the fusion of gametes (e.g. egg and sperm).The development of a zygote into a multicellular embryo proceeds through a series of recognizable stages, often divided into cleavage, blastula, gastrulation, and organogenesis.
Cleavage is the period of rapid mitotic cell divisions that occur after fertilization. During cleavage, the overall size of the embryo does not change, but the size of individual cells decrease rapidly as they divide to increase the total number of cells.Cleavage results in a blastula.
Depending on the species, a blastula stage embryo can appear as a ball of cells on top of yolk, or as a hollow sphere of cells surrounding a middle cavity. The embryo's cells continue to divide and increase in number, while molecules within the cells such as RNAs and proteins actively promote key developmental processes such as gene expression, cell fate specification, and polarity.
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