Hi. It's Mr. Andersen. And in this podcast I'm going to talk about the reproductive
system. Mostly the human reproductive system. Now you should know that not all organisms
reproduce sexually. And so these right here are sea anemones. Sea anemones have the ability
to reproduce asexually. Basically what they'll do is they'll simply split in half. And they'll
form two new anemones. And all of these right here are clones of one anemone. And these
ones right here are clones from different anemones that are fighting. So this is like
a clone war. But they're all identical. Just like this lizard right here. This is the New
Mexico Whiptail Lizard. The one in the middle. And all of the species of that lizard are
female. And they reproduce through a process called parthenogenesis where actually you
have one egg that just becomes another lizard. And so it's a diploid cell that becomes a
diploid organism. But most life doesn't do that. Most life uses, most animal life uses
sexual reproduction. And the reason why is that it gives us variation. So basically this
is the cycle of life. Through meiosis we produce sperm and egg. Those sperm and egg will fertilized
one another to produce a zygote. And those will make an organism which will eventually
produce gametes through meiosis again. So it just goes over and over and over again
with meiosis and fertilization. On either side, right here would be gametes. Right here
would be organisms. And so what that gives us, meiosis gives us variation. And so the
formation in meiosis, there is crossing over that occurs, where you will actually have
the two chromosomes switching positions. And so you're getting a new chromosome that's
never created. We're making so many different gametes, there is so much variability, that
you get offspring that are totally different than the parents. And that offers them protection
in an environment, especially in an environment that continues to change. But right here we've
got a human sperm fertilizing an egg. And so most of this podcast is about how does
that occur. So we begin with male anatomy. And I'm not going to go into too much detail,
but basically the things that you should be familiar with is the penis and the function
of that is simply to deliver semen into the vagina. We also have the testes. Testes are
going to be right here. They do two things. They're going to secrete sex hormones, mostly
testosterone. But they're also going to be the site of formation of sperm. And so the
sperm are going to form here. They're going to start to develop within the epididymus
which is going to be right on the back of the testes. And then eventually during ejaculation
those sperm are all going to move through this tube. It's called the vas deferens. And
they're going to move on their way, all the way up through here. Through a series of glands.
So this would be the seminal vesicle, the prostate gland, the cowper's gland. But basically
what those glands are doing is they're providing food, nutrients. They're neutralizing the
pH inside the vagina. But they're basically making it safe for the sperm to be headed
on their way. Now we constantly are making sperm over and over and over again throughout
our life. Females however start with just a few eggs, a few hundred thousand eggs when
they're born. So basically if we look at female anatomy, female anatomy, these are going to
be the ovaries right here. Eventually when we release an egg it will go into the oviduct.
And that oviduct is sometimes referred to as the fallopian tube. We have the uterus
which is going to be this big area. That's where the fertilized egg will implant or not.
Then we have the vagina right here. That's just for reception of the semen and then cervix
is going to be the blocking of that or the end of that. Basically the cervix will dilate
when a baby is eventually born. And so that's the anatomy. But let's get to how it actually
works. So right now we're looking inside an ovary. So this would be a diagram of what
occurs in the ovary. So inside here, a female in her ovary is going to have all the eggs
that she'll ever have. And so she's going to have you know, a hundred thousand when
you're born. But you're going to lose them quickly. And so basically once a month, this
is going to happen. One of those eggs will be chosen. And it's going to develop. It develops
into something called a follicle. A follicle is going to look just like that. A follicle
is going to be one egg in the middle and then it's going to have a bunch of support cells
around the outside. So basically during the month, that's going to get bigger and bigger
and bigger and bigger. And eventually it's going to release that egg and the remainder
of the follicle is going to form something called the corpus luteum. And so this is just
a diagram. So basically the part of the follicle that didn't leave becomes the corpus luteum.
It's going to give chemical support to that egg on its way. And so this is a picture of
an ovary. This was actually, it's a cross-section from a human that was given up during a hysterectomy.
But this is the corpus luteum on the top of it. And so basically it's released the egg
and the corpus luteum is going to give off progesterone and estrogen. And that's going
to allow it to keep track of that when it's one its way. And so let's look at this. So
basically this is the menstrual cycle. And so the menstrual cycle, what you're familiar
with is probably just menstruation. So let's kind of start there. So basically what is
menstruation? If this is the uterine lining. So this is the uterine lining. Basically it
will get bigger and bigger and bigger throughout the month. In other words it's going to grow
more and more tissue. It's going to become more and more vascular. Because the idea is
that the egg will eventually be fertilized and it will implant inside that. That lining
of the uterus is called The endometrium. Now let's say an egg doesn't implant. What happens?
Well all of that lining is going to be shed off. And that's what menstruation is. And
so this is a month that goes over and over again. So we've got our 28 days right here.
What is going to be timed with that? Well basically ovulation is. So the release of
that ovum or the release of that egg is timed. So again here's our developing follicle. It's
designed so that ovum will be released. It will float down the oviduct and it will hopefully
be fertilized and implant in that endometrium. We also have chemical control. So this is
FSH and LH. Those are going to be chemicals that are secreted by the pituitary. But then
we have estrogen and progesterone. Estrogen and progesterone are going to be secreted
by the corpus luteum. And so basically around that time of ovulation, we get a peak of PH
and FSH or excuse me FSH and LH, which is just luteinizing hormone. And then we're going
to have a flow of estrogen and progesterone. And basically what that's doing is it's taking
care of the endometrium. It's making sure that we build up an area where that ovum can
eventually implant. Now that ovum or that egg remember is moving its way down the oviduct
and it may or may not be fertilized by a sperm. So how does that occur? Again this would be
that ovum as it's floating down through the oviduct. Basically a sperm just has genetic
material. It then has these enzymes in the front of it. And so once one fertilizes the
egg, no other ones can fertilize it. But basically it's going to release its genetic material
into the egg. Now we've gone from gametes, two gametes, a sperm and an egg to a fertilized
cell. So that one fertilized cell or that zygote is going to divide and divide and divide
and divide. And it keeps dividing until we eventually have what's called a blastula.
Blastula is simply a ball of cells that have divided. So it's dividing through mitosis.
All of them are identical, but that's called a blastula. That blastula will fold in on
the side and it forms something called a gastrula. So gastrula is just formation of this hole
on the side. That, we're not sure exactly what it looks like. Because in humans this
gastrula is going to be implanted into the endometrium. So into that uterine lining.
But basically what we think happens is there's going to be, let me try to get some colors,
there's going to be an outer layer to that. And that eventually forms something called
the ectoderm. The ectoderm is going to form nervous tissue. It's going to form your skin.
We're then going to have the middle layer. The middle layer is this red layer. That's
going to be the mesoderm. That's going to form like your muscles and your bone. And
then finally on the inside we're going to have an endoderm. So the endoderm we could
do that as maybe black, is going to be somewhere in the middle. So the endoderm is going to
form basically the linings of your organs. So the cells of the lungs, thyroid, pancreatic
cells. And so these cells will eventually form organs and then eventually form an organism.
And so this right here is eventually what happens to this gastrula. It eventually becomes
an embryo and eventually becomes a baby. And then in humans after nine months it's eventually
born. And so that's a quick introduction to the reproductive system. We'll talk a little
bit more of development and all these stages later. But I hope that's helpful.