The biological big bang

28 Oct

Baking soda and vinegar: Lots of fun.  Peanut butter and chocolate: Extremely delicious.  Egg and sperm: The most amazing pair in the universe!

They put on an awesome show.

How does 1 cell divide and grow to become a human being that is trillions of cells big?

Mitosis is the spark of life that starts from conception, or the merging of egg and sperm.  It is the most fundamental way in which we grow in our bodies, and the materials of mitosis come from, initially, the mother.

The egg is enormous compared to the sperm because the care package of cellular supplies you find in the world of the egg have got to last from the moment of fertilization to the stage when the ball of cells that’s developing into an embryo is about 128 cells big.

After sperm meets egg, the fertilized egg (zygote) makes a 3 to 5 day journey through the fallopian tube into the uterus, during which time its cells are, through mitosis, dividing.  Once in the uterus, the cells continue to divide, becoming a hollow ball of cells with an unsexy name: A blastocyst.

1 cell becomes 2.  2 become 4.  4 become 8.  8 become 16.  16 become 32. 32 become 64.  64 become 128.  And so on.

It is about at this 128-cell stage that the blastocyst attaches to the uterine wall of the mother and screams, in a chemical voice, “I’m here! I need supplies!  Feed me!”

The uterine cells are devised to be able to tell when one of these very small groups of mitotically active cells hit the wall screaming.

This is the transition, 5 to 10 days after fertilization, when the egg stops being the source of nutrition for the blastocyst and the mother’s body takes over.  The inner cells at the thickest part of this ball of cells will become the embryo.  The outer cells will nestle into the wall of the uterus and become the placenta.

Cell differentiation

So it is mitosis that is allowing these cells of the emerging embryo to double over and over again, and in doing so all of that initial material that was in the egg is being divided and divided.

It’s about at that 128-cell stage where the cells are considered to be what’s called “totipotent.”  The blank slates called stem cells can become anything.  They are generic cells that haven’t “differentiated” into the 200 to 250 cell types that make up our bodies: Muscle cells and blood cells, liver cells and lung cells, etc.  They are progenitors.

These are the cells that are extraordinarily important in medical science right now, because they have this miraculous ability to become anything.  If you can get these cells into a diseased brain or a diseased heart, there is a hope that they could create new, healthy cells, and heal the human body in the same way that many lizards and salamanders can re-grow their lost tails.

When a baby gets to the last stage of development inside of its mother’s womb it becomes almost “totally differentiated.”  It is born with all its cell types, from eye cells to toenail cells.  Each cell type is sort of like a citizen contributing to the functioning of the society of cells that make up you or me.

Over time, mitosis allows just 1 cell to become the 100 trillion cells that are in our bodies, and that are regenerating constantly throughout our lives.


One Response to “The biological big bang”


  1. The Science of Pregnancy Timeline: Week One — Having sex to become pregnant: Why it is necessary? « - August 15, 2012

    […] Look back: Week 0, Menstruation Look ahead: Week 2, Fertilization […]

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