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The Embryonic Stage Begins

The fetal period begins at???????/?

The fetal period begins at ______ and ends at ______.
A) the eighth week; birth
B) conception; the second week
C) the end of the second week; the eighth week
D) the sixteenth week; birth

Because most of the major body systems are developing during this prenatal time, the ________ period is considered very vulnerable to the effects of drugs, diseases, and environmental toxins.
A) fetal
B) germinal
C) zygotic
D) embryonic

The inner surface of the _________ becomes the placenta, the amnion, and the chorion.
A) trophoblast
B) endometrium
C) allele
D) teratogen

The ________ is the source of future cells forming the nervous system, the sensory organs, and the skin.
A) ectoderm
B) endoderm
C) mesoderm
D) pachyderm

The ________ is a partially permeable membrane that functions as an exchange terminal that permits entry of food materials, oxygen, and hormones into the embryo from the mother's bloodstream and the exit of carbon dioxide and metabolic wastes from the embryo into the mother's bloodstream.
A) amnion
B) placenta
C) chorion
D) umbilical cord

The cells in the central portion of the embryo thicken and form a slight ridge that divides the developing embryo into right and left halves and which will eventually become the spinal cord. This ridge is referred to as
A) the primitive streak.
B) the chorion.
C) the amnion.
D) cleavage.

Development that commences with the head areas and works its way down the body is called
A) proximodistal development.
B) cephalocaudal development.
C) linear mitotic development.
D) meiotic development.

What's the difference between a fetus and an embryo?

I'm actually amazed at the uninformative answers you got. Telling you that an embryo comes before a fetus, or that an embryo is less developed than a fetus, tells you nothing ... you already knew that. Your question was about when or why we stop calling it an 'embryo' and start calling it a 'fetus' ... in other words "what is the difference?" I especially *love* 'angelyne_heart's response. Calling you an idiot for asking a great question, and then giving you an idiotic response. (E.g., I'd love to know at what point a hamster fetus is "already a human being.") angelyne_heart should be careful calling other people an idiot. The answer (if I understand right ... and I may be wrong) is that the type of cell division going on in an 'embryo' is very undifferentiated. The cells have not yet divided into "heart cells" and "skin cells" and "nerve cells", but are just cells. They do undergo the different layers and foldings that are typical of all embryos in the animal kingdom, but we don't yet have organs or systems. At some point, the cells start to become differentiated, and begin forming into types of tissue, and the tissue into organs. It's at the stage where we say that all the major organs exist, at least in primitive form, that we call it a "fetus."

There's the germinal stage, the embryonic stage, and the fetal stage.Germination stage: The 2 week period after conception is called the germinal stage. About 36 hours after conception, the zygote begins to divide rapidly. The resulting ball of cells moves along the fallopian tube to the uterus. Around 7 days after conception, the ball of cells starts to implant itself in the wall of the uterus. This takes about a week to complete. If implantation fails, as is quite common, the pregnancy terminates. One key feature of the germinal stage is the formation of a tissue called the placenta.The embryonic stage: The embryonic stage lasts from the end of the germinal stage to 2 months after conception. The developing ball of cells is now called an embry. In this stage, all the major organs form, and the embryo becomes very fragile. The biggest dangers are teratogens, which are agents such as viruses, drugs, or radiation that can cause deformities in an embryo or fetus. At the end of the embryonic period, the embryo is only about an inch long.The fetal stage: The last stage of prenatal development is the fetal stage, which lasts from 2 months after conception until birth. About 1 month into this stage, the sex organs of the fetus begin to form. The fetus quickly grows as bones and muscles form, and it begins to move inside the uterus. Organ systems develop further and start to function. During the last 3 months, the brain increases rapidly in size, an insulating layer of fat forms under the skin, and the respiratory and digestive systems start to work on its own.

When sperm and egg meet, the new human being created is at the earliest possible stage of development, and is called a zygote. It is a single cell with 46 chromosomes (23 from each parent). As it travels through the Fallopian tube it undergoes further early development, dividing into a bundle of cells, and is called a blastocyst at this stage. After the blastocyst implants in the uterus, the embryonic period begin and it is known as an embryo. It continues cell division, cell differentiation begins, major systems begin to develop. Eight weeks after the zygote was created, the fetal period begins and the embryo is now called a fetus, until birth where the medical term for the newborn infant is neonate.

Why is stem cell research considered so bad to some people?

Because some people think that the harvesting of stem cells involves killing babies when it's nothing more than the collection of about 100 cells or blastocysts. In any case, with genetics, we can grow stem cells or turn skin cells into stem cells.

@ HeMan: If someone used my embryonic stem cells, I probably wouldn't exist in the first place. And if my mom "cancelled" the birth, I wouldn't have a conciousness to know.

@ fancier_rmv04: What about chimeras? Is that two souls in one body? And your statement begs the question, "Just how do you know what you say is true?"

@ AJ, All You Need is Love: Need more Teflon for your slope?

@ Robert S: Citation needed.

@ DARE: It's not even a fetus yet. It's a collection of about 100 cells. It's a blastocyst. Learn your terms.

@ byHisgrace: And if you didn't have sex back then, your son wouldn't be here. We're not saying your son isn't a life. What we're saying is that a blastocyst is not a life or even comparable to a born human.

@ Cslewisville: So when a friend donates part or a whole organ to his friend, is that also "high-tech cannibalism?"

It would be impossible. Once an oocyte has been fecundated and transported to the uterine cavity, implantation and nidation need to happen. During this process, the fecundated egg has begun a fast process of mitosis and has created several layers of cells (Blastocyst). Each layer has a different function.The outer layer of the blastocyst is called trophoblast, and the trophoblast will form 2 different layers of cells once it attaches to the endometrium; the cytotrophoblast (A layer of individual cells) and the syncytiotrophoblast (One mass with multiple nucleus) Both will conduct the invasion in the endometrium by releasing proteolytic enzymes to create a passage through the tissue and break through blood vessels to receive nutrients. It will also produce hormones, like HCG, that will keep a structure called Corpus Luteum alive in the ovary. The corpus luteum releases progesterone that prevents the uterine lining from shedding. Is during this process that the placenta is created (Combining cells with maternal DNA and embryonic DNA). As the pregnancy progresses, the placenta will grow to allow the exchange of oxygen, nutrients, hormones and waste to and from the embryo (Through the umbilical cord), and sustain an increasing demand as the embryo grows. After 12 weeks, the embryonic stage finishes, and the fetal stage begins. Up to this point, the placenta is firmly attached to the endometrial layer. The placenta has been created to be removable (Under normal circumstances), but once this happens, it cannot be re-attached. The fetus is completely dependent of the placenta to survive, and you cannot simply create one without a fertilized egg. It seems unlikely that we will eventually find a way to transplant a fetus from one uterus to the other, and even if we found a way to create placentas, we would have another problem. A pregnancy produces a number of changes in the way our body works. Our cells become resistant to insulin in order to allow glucose circulation for longer, the amount of blood we have increases, and the uterus takes most of that blood flow in order to provide for the fetus. These are just a few examples, but virtually every single system of organs modifies its functionality during pregnancy. Any abnormalities in the insertion or functionality of the placenta can lead to miscarriage and premature birth, as well as a number of obstetric complications that can even be fatal.