Harvey Kleiman

And there... The PP13 attracts the entire police force, SWAT team, everybody of the mother's immune system.

And blood fountains into the placenta. It's bathed in all these nutrients and goes, buffet time. Let me see what I need.

And that fetus is demanding more and more horsepower, more and more nutrients to actually grow.

Called human placental lactogen.

Says, okay, you're eating. I get that. But none of that actually is for you. You're not going to get to store it. All those nutrients are going to stay in your blood. So I, the placenta, can suck up those nutrients.

And by the third trimester, Harvey says, 20 to 25 percent of all the blood flow of the mother is going into the placenta.

If the placenta and the fetus together say, hey, I'm not getting enough blood, I'm just going to force her body to start pumping more blood into me, into the fountaining system. And this is a condition we call preeclampsia.

Mom, of course, doesn't want to die. She doesn't want the fetus to take all her nutrients. But if she is successful and wins the battle, if you will, the placenta is too small, the fetus is too small, and the pregnancy may not survive.

Good guess.

All right, are we ready for the moment?

And this is the placenta, which is in the standard Ziploc bag. That's what it's in right now.

It's kind of bloody, isn't it?

And so I'm going to open the Ziploc bag.

Like a normal term placenta is about 550 grams, which is just about a pound. It's about eight to nine inches in diameter.

I think this is another miracle. So the baby goes first and... The uterus is elastic and has muscle, so it contracts down. And it's that contracting down that actually shears the placenta off, the lining of the uterus, and the placenta gets delivered. And then... All those blood vessels that have been supplying blood to the placenta for all those weeks and months have to close down.

And thank it?

Thank you, placenta, for making me survive and be alive.

Monday, actually. Monday late afternoon. So there's a little cute baby someplace who is happy and alive because of this placenta.

We can't know who they are. That's part of the reason we have the placenta.

Yes, we will thank them spiritually.

A whole new organ shows up. Here is our cabinet of placentas.

Whole placentas, pieces of placentas.

It's called the afterbirth for a reason. It's an afterthought that no one thinks about.

The placenta belongs to the embryo, to the fetus, to the baby.

I was kind of like you. I literally had no idea what it did, what its purpose was.

Harvey Kleiman.

MD, PhD, physician scientist at Yale University.

We're sort of running out of room.

Kristen, I think we need another cabinet.

And I'm now a resident at University of Pennsylvania. And I'm in a laboratory.

And in the lab, there was somebody else who was working on the placenta. And they were chopping up the placenta and homogenizing the placenta.

And they wanted me to take a picture of the gradient. Why? Well, on the side, I'm a photographer. I've actually done bar mitzvahs and weddings and things like that. Yeah, I love visual things, I think is what interests me in general. And so I took a picture of the gradient and I asked Jerry, who was running the lab, I said, Jerry, would you mind if I looked at what they are?

He said, sure, go for it. And what Harvey saw was something that no one had ever seen before.

They were like amoeba.

They started moving around and then they came together, they aggregated, then the membranes broke down and they fused to make these multinucleated giant cells.

I said, that is super cool. What's going on here?

So let's start from the beginning. You have an egg, and then if there's sperm around, the sperm will fertilize that egg. And then it divides. Divides into two. And then four. Eight. And 16, et cetera, et cetera.

It's like a tennis ball now.

That will become the embryo. That will become the fetus. That will become the baby, those little inside group of cells. But the cells on the outside... Those cells will become the placenta.

So what happens?

From the mother's point of view, this is immunologically foreign.

Exactly.

If we took a piece of tissue from whoever the father was of a pregnancy and put it into the mother, she would reject it.

It's a foreign invader.

So that's definitely a problem.

The placenta is going to become invisible to the mother. What?

The mother literally doesn't even see that the pregnancy is there.

The next problem that the placenta faces is nutrition.

To make the biggest baby possible, to suck as much nutrients out of the mother as possible. And the pregnant person's mission? Not to die.

But one of its other jobs is that it causes the lining of the uterus to secrete HCG. A protein.

The lining of the uterus makes milk for the embryo.

Into the blood vessels and attack the walls to open them up.

The uterus stops them. Basically putting up a brick wall, very dense tissue.

Now the placenta doesn't give up easily.

We're talking pretty aggressive here.

It has a heart, kidneys, liver.

It's just like, hey, I need to be growing. I need more nutrients for my passenger, the fetus.

But the placenta has a couple of tricks up its sleeve.

Here's an analogy. If we wanted to rob a bank, I don't want the police to be near there. So what I'm going to do is blow up a grocery store, wait for all the police to sort of go around the grocery store. And while they're busy doing that, I'm going to sneak into the bank.