Speaker 1: Welcome to brain Stuff, a production of iHeart Radio. Hey
Speaker 1: brain Stuff, Lauren Vogel Bomb Here. The human body is complicated,
Speaker 1: and a lot of us who are wandering around in
Speaker 1: one have a perhaps less than complete idea of how
Speaker 1: it works. So let's talk about it today. Let's talk
Speaker 1: specifically about how conception works. Don't worry or apologies, I'm
Speaker 1: not getting graphic. We're mostly talking about cells. Most people
Speaker 1: who are assigned female at birth are born with millions
Speaker 1: of immature eggs, which are contained in fluid filled sacks
Speaker 1: called follicles within the ovaries. Hundreds of these will mature
Speaker 1: over the course of the person's lifetime about one per month,
Speaker 1: from the onset of puberty through menopause. People who get
Speaker 1: a period get them in cycles that repeat about every
Speaker 1: twenty eight days, though it's normal for cycles to last
Speaker 1: anywhere from one to thirty five days, or even as
Speaker 1: much as forty five day is for young people. Between periods,
Speaker 1: ovulation happens in which a mature egg releases from one
Speaker 1: of the two ovaries. Ovulation usually occurs about a week
Speaker 1: before or after a woman's period, though it can be
Speaker 1: very irregular and can occur even during the period. Itself.
Speaker 1: Here's how it happens. Well. Once every cycle, the hypothalamus
Speaker 1: in the brain sends a signal to the pituitary gland
Speaker 1: to release follical stimulating hormone. This hormone prompts several follicles
Speaker 1: to begin developing the immature egg that they each contain.
Speaker 1: One of these will usually grow dominant over the others,
Speaker 1: and within two to three days following its maturity, the
Speaker 1: follical will rupture and release the egg out of the
Speaker 1: wall of the ovary and into the fallopian tube, which
Speaker 1: connects the ovary to the uterus. Some people feel an
Speaker 1: ache in their ovary during ovulation. You can also sometimes
Speaker 1: tell if you're ovulating because your cervical secretions will be
Speaker 1: wetter and more slippery, and ovulation usually causes a small
Speaker 1: dip in body temperature followed by a spike, so people
Speaker 1: often measure their temperature when trying to detect ovulation. But
Speaker 1: back down to the cellular level, the follicle that additionally
Speaker 1: released the egg sends out a call for increased estrogen
Speaker 1: and progesterone production. These hormones are the body's que that
Speaker 1: an egg is now mature and that it should get
Speaker 1: ready to nurture it in case it gets fertilized, and
Speaker 1: normally only one egg passes from either of the two
Speaker 1: ovaries through its fallopian tube and only once per cycle.
Speaker 1: Sometimes two eggs or rarely more, are released within a
Speaker 1: single twenty four hour span. If multiple eggs are fertilized,
Speaker 1: it can result in a multiple fraternal pregnancy, but a
Speaker 1: mature egg only has about twenty four hours to find
Speaker 1: a partner, a key master to its gatekeeper, a sperm
Speaker 1: cell that can penetrate the eggs outer layer. It's normal
Speaker 1: for three out of tens firm cells to be abnormally formed,
Speaker 1: and for four out of ten to be bad swimmers.
Speaker 1: The odds are poor for any single sperm cell. For
Speaker 1: one thing, it has about a quarter billion competitors that
Speaker 1: will be joining it in the vagina within minutes of ejaculation.
Speaker 1: Most of the sperm cells released will die due to
Speaker 1: the acidic nature of the vagina. They're viewed initially, at
Speaker 1: least by the person's immune system, as foreign bodies that
Speaker 1: should be destroyed. From there, they must enter the cervix,
Speaker 1: swim through the cervical mucus, enter the uterus, and find
Speaker 1: the opening to the fallopian tube. The flopian tube is
Speaker 1: where fertilization usually occurs. As opposed to the vagina. It's
Speaker 1: a really friendly, nutrient filled environment for both the sperm
Speaker 1: and the egg. The fallopian tubes also contain tiny hair
Speaker 1: like structures called cilia that helped pass the egg through
Speaker 1: the tube from the ovary toward the uterus. The journey
Speaker 1: is only about four inches or ten centimeters in length,
Speaker 1: but takes several days. Of the millions of sperm that
Speaker 1: initially enter the cervix, there may be anywhere from one
Speaker 1: to a couple hundred that arrive at the fallopian tube.
Speaker 1: They can survive there for a few days, and like
Speaker 1: I said, an egg survives for about twenty four hours,
Speaker 1: so a sexual encounter either before or after ovulation can
Speaker 1: result in a pregnancy. A sperm have receptors that allow
Speaker 1: them to detect eggs, or rather to detect progesterone. Eggs
Speaker 1: are surrounded by cells that release progesterone, and sperm cells
Speaker 1: get really active when an egg is present. A progesterone
Speaker 1: makes sperm so active that they've sloughugh off layers of
Speaker 1: proteins that surgeon activity. Along with the loss of those
Speaker 1: proteins enables sperm to pierce the egg. This process is
Speaker 1: called capacitation. The head of the sperm, once making contact
Speaker 1: with the exterior of the egg, will more or less
Speaker 1: pop releasing enzymes that allow it to cross through the barrier. On.
Speaker 1: Once a sperm cell penetrates the exterior of the egg,
Speaker 1: fertilization occurs. The sperms DNA payload is delivered as it's
Speaker 1: absorbed by the egg, and as the two combine, a
Speaker 1: complete genetic blueprint is formed. Once a single sperm enters
Speaker 1: the egg, the eggs protective protein covering changes and doesn't
Speaker 1: allow other sperm to enter. Usually, meanwhile, the uterus, prompted
Speaker 1: by those hormonal signals released by the follicle that formed
Speaker 1: the egg, will have created an internal lining a called
Speaker 1: an endometrium, a rich in blood and nutrients that's prepared
Speaker 1: to house and nurture the egg should it become fertilized.
Speaker 1: If no fertilization occurs, the egg disintegrates into the uterine
Speaker 1: lining and the uterus sloughs it off and passes it
Speaker 1: out through the vagina during the person's period. But if
Speaker 1: fertilization does occur, that's conception and the fertilized egg is
Speaker 1: known as a zygote. Information encoded in the collective DNA
Speaker 1: of the egg and sperm cell instructs the zygote to
Speaker 1: continue its development. Within twenty four hours after forming, a
Speaker 1: zygoat will begin the process of cellular division. A solid
Speaker 1: cluster of cells forms up within what's called a blasticyst,
Speaker 1: hollow structure that the massive cells continues to develop within.
Speaker 1: If everything goes right, the cluster of cells inside the
Speaker 1: structure will become an embryo, while the outer wall will
Speaker 1: become the placenta and other nutrient providing tissues that the
Speaker 1: growing embryo will need. But first, the zygoat makes that
Speaker 1: four day journey down the fallopian tube towards the uterus,
Speaker 1: aided by those tiny cilia lining the tube. By the
Speaker 1: fifth day, the zygote should have made its way into
Speaker 1: the uterus, and by the sixth the massive cells will
Speaker 1: hatch from the thin walled sack. And now the blasticyst
Speaker 1: is ready to make direct contact with the endometrium. If
Speaker 1: it does, the endometrium and the blasticyst exchange hormones, allowing
Speaker 1: the blasticyst to connect to the uterine wall. A process
Speaker 1: known as implantation. People may experience about forty eight hours
Speaker 1: of light bleeding or spotting during this process, which can
Speaker 1: sometimes be mistaken for a period. As this process occurs,
Speaker 1: the cervix will be closed with a mucous plug, with
Speaker 1: the zygote now known as an embryo, safely in the
Speaker 1: blood and nutrient rich uterine lining. The pregnancy has taken
Speaker 1: a big step toward viability because it's only in this
Speaker 1: environment that the embryo can grow and that the pregnant
Speaker 1: person's body can withstand the enormous nutritive demands of that
Speaker 1: growing embryo. Again, this is assuming that everything goes right.
Speaker 1: Human bodies are complicated and there are all kinds of
Speaker 1: things that can go wrong that aren't anybody's fault. Only
Speaker 1: one third or fewer zygotes survived to become embryos. About
Speaker 1: one in every fifty will implant somewhere that isn't the
Speaker 1: uterus and won't have to be removed. That's called an
Speaker 1: ectopic pregnancy, and it can't be reimplanted because, as we've covered,
Speaker 1: the implantation is part of the growing embryo, and even
Speaker 1: after a pregnancy is clinically confirmed, About one in ten
Speaker 1: will end in spontaneous miscarriage before twenty weeks, and sometimes
Speaker 1: the dead embryo will have to be removed. Sometimes the
Speaker 1: developmental process goes wrong after that and the fetus will
Speaker 1: never be able to live outside of the womb. Pregnancy
Speaker 1: is a whole other episode or mini series, really, but
Speaker 1: all of these possibilities are why it's so important for
Speaker 1: people who can become pregnant to have access to reproductive
Speaker 1: information and healthcare. We like to say around here that
Speaker 1: the world is understandable and worth understanding, and that includes
Speaker 1: the worlds within ourselves. Today's episode is based on the
Speaker 1: article understanding the conception process on how stuff works dot Com,
Speaker 1: written by Tom Shave. Brain Stuff is production of iHeart
Speaker 1: Radio in partnership with how stuff works dot Com, and
Speaker 1: it's produced by Tyler Clang. Before more podcasts from my
Speaker 1: heart Radio, visit the I heart Radio app, Apple Podcasts,
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