WEBVTT - How Does Human Conception Work?

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<v Speaker 1>Welcome to brain Stuff, a production of iHeart Radio. Hey

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<v Speaker 1>brain Stuff, Lauren Vogel Bomb Here. The human body is complicated,

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<v Speaker 1>and a lot of us who are wandering around in

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<v Speaker 1>one have a perhaps less than complete idea of how

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<v Speaker 1>it works. So let's talk about it today. Let's talk

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<v Speaker 1>specifically about how conception works. Don't worry or apologies, I'm

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<v Speaker 1>not getting graphic. We're mostly talking about cells. Most people

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<v Speaker 1>who are assigned female at birth are born with millions

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<v Speaker 1>of immature eggs, which are contained in fluid filled sacks

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<v Speaker 1>called follicles within the ovaries. Hundreds of these will mature

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<v Speaker 1>over the course of the person's lifetime about one per month,

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<v Speaker 1>from the onset of puberty through menopause. People who get

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<v Speaker 1>a period get them in cycles that repeat about every

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<v Speaker 1>twenty eight days, though it's normal for cycles to last

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<v Speaker 1>anywhere from one to thirty five days, or even as

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<v Speaker 1>much as forty five day is for young people. Between periods,

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<v Speaker 1>ovulation happens in which a mature egg releases from one

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<v Speaker 1>of the two ovaries. Ovulation usually occurs about a week

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<v Speaker 1>before or after a woman's period, though it can be

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<v Speaker 1>very irregular and can occur even during the period. Itself.

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<v Speaker 1>Here's how it happens. Well. Once every cycle, the hypothalamus

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<v Speaker 1>in the brain sends a signal to the pituitary gland

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<v Speaker 1>to release follical stimulating hormone. This hormone prompts several follicles

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<v Speaker 1>to begin developing the immature egg that they each contain.

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<v Speaker 1>One of these will usually grow dominant over the others,

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<v Speaker 1>and within two to three days following its maturity, the

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<v Speaker 1>follical will rupture and release the egg out of the

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<v Speaker 1>wall of the ovary and into the fallopian tube, which

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<v Speaker 1>connects the ovary to the uterus. Some people feel an

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<v Speaker 1>ache in their ovary during ovulation. You can also sometimes

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<v Speaker 1>tell if you're ovulating because your cervical secretions will be

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<v Speaker 1>wetter and more slippery, and ovulation usually causes a small

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<v Speaker 1>dip in body temperature followed by a spike, so people

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<v Speaker 1>often measure their temperature when trying to detect ovulation. But

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<v Speaker 1>back down to the cellular level, the follicle that additionally

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<v Speaker 1>released the egg sends out a call for increased estrogen

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<v Speaker 1>and progesterone production. These hormones are the body's que that

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<v Speaker 1>an egg is now mature and that it should get

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<v Speaker 1>ready to nurture it in case it gets fertilized, and

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<v Speaker 1>normally only one egg passes from either of the two

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<v Speaker 1>ovaries through its fallopian tube and only once per cycle.

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<v Speaker 1>Sometimes two eggs or rarely more, are released within a

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<v Speaker 1>single twenty four hour span. If multiple eggs are fertilized,

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<v Speaker 1>it can result in a multiple fraternal pregnancy, but a

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<v Speaker 1>mature egg only has about twenty four hours to find

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<v Speaker 1>a partner, a key master to its gatekeeper, a sperm

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<v Speaker 1>cell that can penetrate the eggs outer layer. It's normal

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<v Speaker 1>for three out of tens firm cells to be abnormally formed,

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<v Speaker 1>and for four out of ten to be bad swimmers.

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<v Speaker 1>The odds are poor for any single sperm cell. For

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<v Speaker 1>one thing, it has about a quarter billion competitors that

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<v Speaker 1>will be joining it in the vagina within minutes of ejaculation.

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<v Speaker 1>Most of the sperm cells released will die due to

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<v Speaker 1>the acidic nature of the vagina. They're viewed initially, at

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<v Speaker 1>least by the person's immune system, as foreign bodies that

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<v Speaker 1>should be destroyed. From there, they must enter the cervix,

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<v Speaker 1>swim through the cervical mucus, enter the uterus, and find

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<v Speaker 1>the opening to the fallopian tube. The flopian tube is

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<v Speaker 1>where fertilization usually occurs. As opposed to the vagina. It's

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<v Speaker 1>a really friendly, nutrient filled environment for both the sperm

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<v Speaker 1>and the egg. The fallopian tubes also contain tiny hair

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<v Speaker 1>like structures called cilia that helped pass the egg through

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<v Speaker 1>the tube from the ovary toward the uterus. The journey

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<v Speaker 1>is only about four inches or ten centimeters in length,

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<v Speaker 1>but takes several days. Of the millions of sperm that

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<v Speaker 1>initially enter the cervix, there may be anywhere from one

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<v Speaker 1>to a couple hundred that arrive at the fallopian tube.

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<v Speaker 1>They can survive there for a few days, and like

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<v Speaker 1>I said, an egg survives for about twenty four hours,

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<v Speaker 1>so a sexual encounter either before or after ovulation can

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<v Speaker 1>result in a pregnancy. A sperm have receptors that allow

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<v Speaker 1>them to detect eggs, or rather to detect progesterone. Eggs

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<v Speaker 1>are surrounded by cells that release progesterone, and sperm cells

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<v Speaker 1>get really active when an egg is present. A progesterone

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<v Speaker 1>makes sperm so active that they've sloughugh off layers of

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<v Speaker 1>proteins that surgeon activity. Along with the loss of those

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<v Speaker 1>proteins enables sperm to pierce the egg. This process is

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<v Speaker 1>called capacitation. The head of the sperm, once making contact

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<v Speaker 1>with the exterior of the egg, will more or less

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<v Speaker 1>pop releasing enzymes that allow it to cross through the barrier. On.

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<v Speaker 1>Once a sperm cell penetrates the exterior of the egg,

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<v Speaker 1>fertilization occurs. The sperms DNA payload is delivered as it's

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<v Speaker 1>absorbed by the egg, and as the two combine, a

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<v Speaker 1>complete genetic blueprint is formed. Once a single sperm enters

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<v Speaker 1>the egg, the eggs protective protein covering changes and doesn't

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<v Speaker 1>allow other sperm to enter. Usually, meanwhile, the uterus, prompted

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<v Speaker 1>by those hormonal signals released by the follicle that formed

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<v Speaker 1>the egg, will have created an internal lining a called

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<v Speaker 1>an endometrium, a rich in blood and nutrients that's prepared

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<v Speaker 1>to house and nurture the egg should it become fertilized.

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<v Speaker 1>If no fertilization occurs, the egg disintegrates into the uterine

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<v Speaker 1>lining and the uterus sloughs it off and passes it

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<v Speaker 1>out through the vagina during the person's period. But if

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<v Speaker 1>fertilization does occur, that's conception and the fertilized egg is

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<v Speaker 1>known as a zygote. Information encoded in the collective DNA

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<v Speaker 1>of the egg and sperm cell instructs the zygote to

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<v Speaker 1>continue its development. Within twenty four hours after forming, a

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<v Speaker 1>zygoat will begin the process of cellular division. A solid

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<v Speaker 1>cluster of cells forms up within what's called a blasticyst,

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<v Speaker 1>hollow structure that the massive cells continues to develop within.

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<v Speaker 1>If everything goes right, the cluster of cells inside the

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<v Speaker 1>structure will become an embryo, while the outer wall will

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<v Speaker 1>become the placenta and other nutrient providing tissues that the

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<v Speaker 1>growing embryo will need. But first, the zygoat makes that

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<v Speaker 1>four day journey down the fallopian tube towards the uterus,

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<v Speaker 1>aided by those tiny cilia lining the tube. By the

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<v Speaker 1>fifth day, the zygote should have made its way into

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<v Speaker 1>the uterus, and by the sixth the massive cells will

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<v Speaker 1>hatch from the thin walled sack. And now the blasticyst

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<v Speaker 1>is ready to make direct contact with the endometrium. If

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<v Speaker 1>it does, the endometrium and the blasticyst exchange hormones, allowing

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<v Speaker 1>the blasticyst to connect to the uterine wall. A process

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<v Speaker 1>known as implantation. People may experience about forty eight hours

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<v Speaker 1>of light bleeding or spotting during this process, which can

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<v Speaker 1>sometimes be mistaken for a period. As this process occurs,

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<v Speaker 1>the cervix will be closed with a mucous plug, with

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<v Speaker 1>the zygote now known as an embryo, safely in the

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<v Speaker 1>blood and nutrient rich uterine lining. The pregnancy has taken

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<v Speaker 1>a big step toward viability because it's only in this

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<v Speaker 1>environment that the embryo can grow and that the pregnant

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<v Speaker 1>person's body can withstand the enormous nutritive demands of that

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<v Speaker 1>growing embryo. Again, this is assuming that everything goes right.

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<v Speaker 1>Human bodies are complicated and there are all kinds of

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<v Speaker 1>things that can go wrong that aren't anybody's fault. Only

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<v Speaker 1>one third or fewer zygotes survived to become embryos. About

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<v Speaker 1>one in every fifty will implant somewhere that isn't the

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<v Speaker 1>uterus and won't have to be removed. That's called an

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<v Speaker 1>ectopic pregnancy, and it can't be reimplanted because, as we've covered,

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<v Speaker 1>the implantation is part of the growing embryo, and even

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<v Speaker 1>after a pregnancy is clinically confirmed, About one in ten

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<v Speaker 1>will end in spontaneous miscarriage before twenty weeks, and sometimes

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<v Speaker 1>the dead embryo will have to be removed. Sometimes the

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<v Speaker 1>developmental process goes wrong after that and the fetus will

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<v Speaker 1>never be able to live outside of the womb. Pregnancy

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<v Speaker 1>is a whole other episode or mini series, really, but

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<v Speaker 1>all of these possibilities are why it's so important for

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<v Speaker 1>people who can become pregnant to have access to reproductive

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<v Speaker 1>information and healthcare. We like to say around here that

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<v Speaker 1>the world is understandable and worth understanding, and that includes

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<v Speaker 1>the worlds within ourselves. Today's episode is based on the

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<v Speaker 1>article understanding the conception process on how stuff works dot Com,

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<v Speaker 1>written by Tom Shave. Brain Stuff is production of iHeart

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<v Speaker 1>Radio in partnership with how stuff works dot Com, and

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<v Speaker 1>it's produced by Tyler Clang. Before more podcasts from my

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<v Speaker 1>heart Radio, visit the I heart Radio app, Apple Podcasts,

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<v Speaker 1>or wherever you listen to your favorite shows,