Where Do Babies Come From?

I just found out that one of my favorite people in the world is pregnant! That means we need some embryology…

Human embryology is actually a VERY complicated and complex process! I took the class my junior year as an undergrad and realized right off the bat that it was not easy to understand. One fun part to know (that is not too overly complex and easy to explain without a crap-ton of jargon) is fertilization.

Right after a boy and a girl (for all my boy-boy and girl-girl friends – we get babies different ways) boom boom pow (and the boy forgets to cover up) his sperm is released into his lady. Millions of sperm are released and all start swimming towards the egg (we will assume the girl just released an egg that day). The sperm will only survive for up to 48 hours inside the girl before they run out of stored energy and die, so the race is on!

First the sperm have to cross through a lining of the cervix (cervical mucus). Once through they need to swim up the uterus and then pick a Fallopian tube. There are 2 tubes, but only 1 has an egg in it. By this point only about 1000 sperm have made it to the tubes and picked the right one to be able to continue on to the egg. But then an egg is in sight…

Hundreds of sperm will attack the egg, each binding to the egg at the outer membrane and using its head (acrosome) to create a reaction that will allow it to get through the membrane. The egg knows when one gets through and rapidly depolarizes (creates an electrical zap, if you will) that helps get rid of the other sperm that were good swimmers but not good diggers. The depolarization also releases a substance (cortical granules) that basically makes a wall to keep more sperm out. The egg only wants one sperm; otherwise there is too much DNA to work with.

Once the cortical reaction is over, the egg knows that no more sperm can get in, so it does some quick genetic stuff (a second round of meiosis which produces a haploid number) and … well then a lot of very technical genetic things happen. Basically just know that specific things have to happen so the sperm and egg can fuse the genetic material without problems and have the cell ready to divide. The sperm and egg chromosomes come together and the cell then begins dividing and heading down the Fallopian tube so that it can implant and begin the trillions of other steps it needs to take to become a baby.

This is super basic and I left a lot out (like all of the genetic things that need to happen, i.e. meiosis and mitosis), but it should give you an idea of what goes on during fertilization. It is not easy to get pregnant. A lot of things need to happen at the right time in the right place. There are also a lot of things that can go wrong. Luckily evolution has really fine tuned this process for us!

And luckily this already all happened for my love!! :)