Biology/Biology on the human body
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Question
I would like to know what forms on a human first the head or the anus. We were talking about it in Biology 1 and our teacher told us if we could find someone to tell us about it then we would get extra creidt.
Thanks for using AllExperts, Becca. Humans, like all sexually reproducing animals, begin life as a single cell known as the zygote. This cell divides multiple times to form a solid ball of cells known as the morula; the morula then rearranges further to form a hollow ball known as the gastrula. At this point, the cells have already begun to differentiate--that is, the cells are starting down the path to their ultimate fate as bone, skin, muscle, etc. By 17-19 days after ovulation, the embryo has formed the structure that will become the nervous system. By 25-27 days, the head itself has become clearly identifiable. The anus formally develops when it becomes differentiated from the urinary tract, about 5 weeks after ovulation; up to that point, the rectal and urinary tracts were joined together as a single tract, the cloaca. Thus, the head and nervous system develop first in human embryos. If you're strictly discussing which structure forms first, it's the head in human embryos.
Here's a website that charts in detail the entire process of embryo development:
http://www.visembryo.com/baby/index.html
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Answers by Expert:
John Locke
Expertise
I will answer all biology-related questions through the undergraduate level. I will explain unclear concepts and suggest approaches to solving problems, but would prefer not to completely solve homework problems for you. If you are completely stumped on homework, tell me what you already know and I will help you as much as possible. Please do not ask me for ideas on school research projects; part of research is determining a suitable area of investigation, and that's not a task that should be completed by someone else. Please don't simply send me your homework for solutions. If you are having difficulty after you have started an analysis, I will be happy to direct your thinking; in particular, I would prefer to not simply solve pedigrees for students, but I will be happy to assist in solving pedigrees that you have already started. If you don't understand how to analyze a pedigree, I'd highly recommend watching this video, in which a biology professor explains the basic concepts of pedigree analysis: http://www.youtube.com/watch?v=HbIHjsn5cHo
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I have a BS in Bioengineering with a concentration in Chemical Engineering (which included a heavy focus on biology), and have taught biology, biochemistry, and related subjects for some time now.
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BS Bioengineering, Penn State University
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