Week 4: Gastrulation

Week 4:

What is the most important event in your life?  When you were born?  Met your mate?  Reached the top of a mountain, began your own company?  Right now, there is a cacophony of divisions and major life events occurring to our little zygote.  They happen to be at the cellular level, so I am not privy to anything momentous, but for the zygote, and the life that follows, many embryologists argue that this is the most important time in anyone's life.

CNP, 2014.  Gastrulation

The period after fertilization is marked by rapid cell divisions.  The zygote divides into two cells, then 8, 16, 32, and so on, until there are 128 cells that form a sphere called the blastula.  This all occurs in five days!  At about the sixth day, the little ball of cells burrows into the lining of the uterus, and continues to develop...

...and here is where some women might get an iota of an idea that they are carrying, as the blastula releases human chorionic gonadotropin once it burrows in to the uterine lining, or hcg.  Why is hcg important?  This hormone is what is detected in pregnancy tests.  It is a small protein, only 237 amino acids long, but it stimulates the development of the placenta.  HCG also decreases the localized immune response of the woman, so she doesn't treat the blastula like an enemy.  AND it may cause ridiculous morning sickness.  Suddenly tired?  A little nauseous, but haven't missed your period yet?  Don't worry if you miss the early signs.  Soon your pregnancy will be abundantly clear.

But what about this gastrulation, and why do embryologists consider it so important?  When the hollow ball of cells folds inwards, cells start receiving their "orders" for their destiny--what types of tissues and roles they will have for the rest of their lives in the organism.  Some become destined for the skin or the nervous system.  Others will become the lining of the gut and organs.  A third type start growing and dividing to form the muscles, bones, and heart.  One third to one half of all zygotes never make it beyond the first three weeks of development.  So gastrulation and implantation shape the earliest part of your destiny as a being.

Gastrulation.  http://2.bp.blogspot.com

Luckily, our bodies for the most part take care of themselves, and the zygote is pretty well adapted to make a home for itself in the uterus.  I'll find out in a few days that I am pregnant.  Right now?

Still oblivious:

CNP, 2014.  Week 4.

Until next week,
Cat