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admin
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Joined: 08 Dec 2003
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 Posted: Thu Jul 16, 2009 9:22 am Post subject: Q. 2 |
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dmolaie8980
Joined: 23 Feb 2009
Posts: 1 Posted: 02 Jul 2009 06:15 pm Post subject Q. 2
| Quote: |
"BIO 14.5
You must be familiar with the stages of embryogenesis to answer this question."
Question: What are the stages of embryogenesis we need to know detailed? |
jellywing_2058
Joined: 04 May 2009
Posts: 68 Posted: 14 Jul 2009 02:36 pm Post subject: Q. 2
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Embryogenesis is the formation of the embryo.
The first step is fertilization occurring in the Fallopian tubes with a sperm and an ovum. The fusion of their nuclei is called a zygote (2n).
The second event is cleavage, which consists in many mitotic divisions. However the cells formed, called blastomeres, get smaller and smaller because the volume of cytoplasm remains constant.
The third step is blastulation, where a morula (group of ~ 16 blastomeres) creates fluid in a cavity, making it a blastula or blastocyst. The zona pellucidum deteriorates so the blastula can implant in the uterine lining (endometrium).
The fourth step is gastrulation, which involves the blastula to form 3 primary germ layers (ectoderm, mesoderm and endoderm) and forming a gastrula.
The fifth step is neurulation which is the formation of the neural tube (read for further information) and the product is called a neurula.
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klaw19867026
Joined: 19 Jul 2010
Posts: 2
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| Posted: Sun Jul 25, 2010 8:20 pm Post subject: |
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| So I think this question is wrong. I put that the implantation of the blastulla happened prior to gastrulation. Even the post above puts that right before gastruation, specifically the last part of step 4. |
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calena7178147
Joined: 26 Jan 2010
Posts: 44
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| Posted: Fri Aug 06, 2010 10:54 am Post subject: |
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| The question is not wrong. Implantation of the blastula in the endometrium occurs prior to gastrulation, as stated in answer C. From your statement, you must have picked the correct answer. |
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bribercar2809
Joined: 23 May 2011
Posts: 11
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| Posted: Mon May 30, 2011 12:31 pm Post subject: Two Answers |
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The way this question is worded, makes it appear to have more then one answer. First of all cleavage proceeds gastrulation. In cleavage, the zygote rapidly divides by mitosis, into smaller cells without an overall increase in size. According to Langman's Medical Embryology text, page 52, Implantation occurs in the end of first week. Page 64 Gastrulation occurs in the third week. In your wording you say, "Immediately prior to gastrulation",
Their is a complete week, between implantation and gastrulation, and one week, in this stage of development, is a long time.
I don't see how you cannot say, from the time of implantation, which occurs at the end of week one, you have a full week of time, in which the blastocyst, undergoes, many mitotic divisions, it is enlarging, and gaining more cells, which are smaller then the parent cells. specifically you have embryoblast and trophoblast cells, which are not fully developed cells. And after a full week of this you finally get gastrulation in the 3rd week? |
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mcat_premed3832
Joined: 19 Oct 2006
Posts: 413
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