Zygote Development
- Natasha
- Apr 9, 2016
- 3 min read
Was hoping to update this earlier this week, but I've been super busy with work. So, on Wednesday they called me to update the progress of my embryos and 7 were still growing. Today I got an update, they were able to biopsy 4 embryos on Day 5 and then froze them, and 1 embryo on day 6 and froze that one, for a total of 5 embryos off for PGS testing! I drew this picture on Wednesday when I got the update about 7 embryos, and I just happen to draw the first 2 differently and didn't like it so colored them in differently after that, guess I predicted 5!
I decided to return to my own text books from my post-graduate work, and have been reviewing my embryology textbook. Something I used to do to learn anatomy is to re-draw things I was studying, such as the heart, or muscles, or even cells. I think I got into it because in high school I had an anatomy course that the teacher would require us to draw things we saw in our microscope. I loved it! I love drawing anatomy things, and cells, and labeling things! I had so much fun going through and drawing out the zygote development. I'm going to post my pictures along with describing what they represent.
Hope that these things make sense, and helps with better understanding of the fertilization of the egg to form the embryo development on a cellular level!
This illustration is of the secondary oocyte (female egg) surrounded by several sperm, 2 have penetrated the corona radiate. Only 1 will get in, but the other sperm help with making it easier for the 1 to break through the shell (zone pellucida). So, this is where Intracytoplasmic Sperm Injection (ICSI) could be used to help the sperm get through the shell, especially if you're dealing with lower sperm counts and such. As far as I know, we didn't need to do this step for fertilization.
In this illustration the corona radiate has disappeared, a sperm has entered the oocyte, and the second meiotic division has occurred, forming a mature oocyte. The nucleus of the oocyte is now the female pronucleus.
Next step, the sperm head has enlarged to form the male pronucleus. This cell, an ootid, contains the male and female pronuclei.
Now the 2 pronuclei are fusing, 23 + 23 from mom and dad to form 46 for the embryo, at least that is what is suppose to happen. Now the sperm determines the sex of the embryo. The oocyte is X, so if a sperm is an X-bearing sperm you'll get a girl, but if it's a Y-bearing sperm you'll get a boy!
The zygote has formed in this illustration, and it should contain 46 chromosomes. Now it will divide in half, and each cell will keep dividing over the next 5-6 days in the petri dish for the IVF cycle; for natural conception it would be occurring in the fallopian tube, so that it should be a blastocyst by the time it reaches the uterus.
These illustrations are of the continuing cleavage (cell division) of the zygote on it's way to becoming a morula then the blastocyst.
This is an illustration of an early blastocyst; the zona pellucida is starting to disappear.
Now we arrive by day 5 or 6 to the blastocyst phase, no more zona pellucida The blastocyst formation normally occurs in the uterus. Once the zona pellucida disappears the blastocyst starts to enlarge.
So, now I have 5 frozen embryos at, what I believe must be the late blastocyst phase!
Next post will be about the PGS!
Best,
Natasha
Source: Moore, Keith L., and T. V. N. Persaud. The Developing Human: Clinically Oriented Embryology. Philadelphia, PA: Saunders, 2003. Print.
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