00:00:06
iein engineers what we're gonna do in
00:00:08
this video is we're gonna begin our
00:00:09
embryology series okay so if you guys
00:00:11
haven't already we're gonna start from
00:00:13
the end of fertilization which is on a
00:00:14
reproductive playlist if you guys
00:00:16
haven't seen that already go watch that
00:00:17
first we're not going to go into a ton
00:00:18
of detail on that we're kind of just
00:00:20
going to skip over pieces and begin the
00:00:22
development within the first week then
00:00:24
after that what we'll do is we'll go
00:00:25
into the next video which is going to be
00:00:27
the development up until the second week
00:00:28
right so we're gonna go for gastrulation
00:00:30
then we'll have another video what we're
00:00:32
going to the development during up to
00:00:34
week three which is gonna involve dinner
00:00:35
elation process and then we'll discuss
00:00:37
the the formation of the nervous system
00:00:38
and we'll just continue to keep going
00:00:40
from there until the development of the
00:00:42
entire embryo alright so let's go ahead
00:00:44
and get started I'm user so let's go
00:00:46
ahead and get started then so first off
00:00:48
we have to talk about before we kind of
00:00:50
get into all the cellular events I want
00:00:52
us to really kind of correlate our
00:00:53
Anatomy with kind of the bigger picture
00:00:55
then we'll get down to the cellular
00:00:57
events so if you guys remember from the
00:00:59
fertilization video just a little bit
00:01:01
about your uterine anatomy right so very
00:01:03
simple here there's gonna be the vagina
00:01:04
they also call it the sheath right then
00:01:06
you're gonna have this portion right
00:01:07
here right which is called the cervix of
00:01:10
the uterus then we'll kind of get into
00:01:11
the body of the uterus right here up
00:01:13
this top like portion here which is kind
00:01:15
of rounded out like that that's gonna be
00:01:17
the fundus of the uterus and then here
00:01:20
you're gonna have your fallopian tubes
00:01:21
right and then at the end of the
00:01:24
fallopian tube you kind of have this
00:01:25
little dilated region right there that's
00:01:27
called the ampulla of the fallopian
00:01:28
tubes that's where fertilization is
00:01:30
supposed to occur right then you got
00:01:32
your little fingers little same brain
00:01:33
right and then after that you got the
00:01:35
ovaries right so what's important is
00:01:38
that an order for us to really kind of
00:01:39
talk about the cellular events we have
00:01:41
to understand the physiology going into
00:01:43
this so what happens usually around day
00:01:47
14 or day 15 of a female's menstrual
00:01:51
cycle right I'm sorry
00:01:54
they start to release a specific type of
00:01:57
hormone right called luteinizing hormone
00:01:59
so if you guys remember here let's draw
00:02:01
like a little diagram here we're gonna
00:02:04
have this guy but you guys remember this
00:02:06
diagram it's pine grain into your brain
00:02:08
right now we're gonna have
00:02:12
the hypothalamus with the poster
00:02:15
pituitary and anti pituitary that's not
00:02:16
nutsacks okay so just remember that now
00:02:19
what happens the hypothalamus starts
00:02:21
releasing specific types of neuro
00:02:24
peptides what are these neuro peptides
00:02:25
called they're called ganado tropen
00:02:28
releasing hormone and then what is gonna
00:02:31
a - open releasing woman do lots of it -
00:02:33
it stimulates the anterior pituitary
00:02:36
what does it tell the anterior pituitary
00:02:38
to do it tells it to start secreting
00:02:41
large amounts of luteinizing hormone
00:02:46
alright and this is also kind of playing
00:02:49
a role not just with the GnRH but if you
00:02:51
guys remember a little bit back from
00:02:53
you're kind of the dimensional
00:02:56
physiology
00:02:57
there's also another very big trigger
00:02:59
here and that's going to be a sturgeon
00:03:01
if you guys remember that positive
00:03:04
feedback cycle when estrogen levels
00:03:06
increase again right during the second
00:03:08
time that's also a big stimulator of
00:03:11
luteinizing hormone as well all right
00:03:13
anyway luteinizing hormone it's released
00:03:16
it gets into the blood goes down to the
00:03:17
over what does it do
00:03:18
well if you guys remember it tells the
00:03:20
ovary to kind of start producing a lot
00:03:21
of fluid alright so it tells the ovary
00:03:24
start making a lot of fluid but
00:03:25
pressurize that follicle because
00:03:27
remember we have that graafian follicle
00:03:28
which is the guy who's gonna have that
00:03:30
secondary oocytes what does he do he
00:03:33
triggers the release of certain types of
00:03:34
prostaglandins to dilate the vessels to
00:03:36
increase a lot of the leakiness out of
00:03:38
the capillaries around that graafian
00:03:40
follicle and activate certain types of
00:03:42
enzymes metalloproteinase is to break
00:03:45
down the connective tissue around it and
00:03:46
guess what that helps helps to pop that
00:03:48
little OA site out and then what happens
00:03:51
is the fimbriae they get all kinds of
00:03:53
cool and they start kind of moving that
00:03:55
actual oh a site towards what the
00:03:58
ampulla then this little oh a site here
00:04:02
we're going to draw it right here and
00:04:04
here is going to be the corona radiata
00:04:06
around it it gets popped out here right
00:04:09
so now that's our secondary oocytes I
00:04:13
think eyes remember I talked about it
00:04:15
and the kind of the whole ovulation
00:04:17
cycle that this is the secondary oocyte
00:04:19
what that means is if it's are
00:04:21
undergoing meiosis one and it's getting
00:04:23
ready to go into meiosis
00:04:25
- right it's getting ready to finish
00:04:26
meiosis - but it hasn't yet what stage
00:04:29
is it particularly in well if you guys
00:04:31
remember we said that once it's ovulates
00:04:34
it's stuck in a specific phase it's a
00:04:37
secondary Oh a site in metaphase -
00:04:43
that's an important thing to remember
00:04:45
secondary oocytes stuck in metaphase -
00:04:48
the reason why is it's waiting for a
00:04:51
sperm cell to touch it and then once it
00:04:53
does it says oh what I need is here I'm
00:04:56
gonna go ahead and finish meiosis to get
00:04:58
myself prepared for this nucleus from
00:05:00
the sperm cell and then I'm gonna fuse
00:05:02
with it so it's waiting and waiting and
00:05:05
who is awaiting on it's waiting on the
00:05:08
lucky son of a gun
00:05:09
right who gets the sperm cells where
00:05:12
they need to go and what happens is the
00:05:15
sperm once it's ejaculated it goes into
00:05:17
the vagina up through the cervix of the
00:05:20
uterus up through the body it makes its
00:05:23
way through the fallopian tubes and it
00:05:25
meets that nice little secondary oocytes
00:05:27
phase - at the ampulla all right and it
00:05:31
says hey I want to go ahead and touch
00:05:32
you now not in a creepy way though
00:05:35
alright so it goes ahead and it touches
00:05:36
it and then guess what starts happening
00:05:38
well let's go ahead and dig into that so
00:05:39
what we're gonna do is we're gonna
00:05:40
imagine that these guys are touching one
00:05:42
another right here in this kind of like
00:05:43
zone we're going to blow it up and we're
00:05:45
gonna take a look see so now we're
00:05:47
blowing it up here and here we're gonna
00:05:48
have that egg right so we have that
00:05:50
secondary oocytes stuck in metaphase -
00:05:52
this is the one then we got that sperm
00:05:55
cell and that sperm cell is coming over
00:05:57
here to meet this egg alright but in
00:06:02
order for it to be able to touch it you
00:06:04
guys remember it has to go through a
00:06:05
process called capacitation where has to
00:06:07
clean off a bunch of cholesterol
00:06:09
molecules and things off of the head of
00:06:11
it and then it has to attach to a
00:06:14
specific type of protein on the surface
00:06:17
and what is this protein if you remember
00:06:20
we have what's called zp3 receptors and
00:06:24
these zp3 receptors are really important
00:06:27
because once the actual sperm touches so
00:06:30
zp3 receptors once the sperm cell
00:06:33
touches it it activates the sperm cell
00:06:36
and then the head of the sperm cell whew
00:06:39
with the zone with the oocytes membrane
00:06:41
starts releasing a bunch of different
00:06:42
enzymes lysosomes hydrolytic enzymes
00:06:45
from its acrosome and it starts
00:06:47
burrowing its way through this then what
00:06:50
it does is it releases its nucleus you
00:06:53
see this little green guy it releases
00:06:55
its nucleus into the cytoplasm so here's
00:06:58
going to be this nucleus now in the
00:07:02
nucleus you know that there's
00:07:03
chromosomes right 23 chromosomes are
00:07:06
going to be in the sperm cell nucleus
00:07:07
and 23 chromosomes are going to be in
00:07:09
d.o.a sites nucleus well what happens is
00:07:13
let's see here 23 are gonna be paternal
00:07:16
and 23 of the other chromosomes are
00:07:19
going to be maternal these are going to
00:07:22
fuse when they fuse how many you gonna
00:07:25
get was 23 plus 23 it's 46 right so
00:07:27
you're gonna get 46 chromosomes now and
00:07:30
this is going to be a diploid cell but
00:07:33
we're also going to call it as I go so
00:07:35
again how many chromosomes 23 plus the
00:07:37
23 23 maternal 23 paternal 46 total
00:07:41
chromosomes and this is going to give us
00:07:43
our zygote now it's pretty amazing when
00:07:49
you think about it that from this one
00:07:51
cell this one cell we're actually gonna
00:07:54
be able to make an entire human body
00:07:56
that's pretty amazing so how does this
00:07:58
happen this zygote guess what
00:08:00
it starts undergoing lots and lots of
00:08:03
lots of proliferation so it starts going
00:08:05
through achieve one sg2 mitosis and just
00:08:08
starts replicating and replicating and
00:08:09
replicating what is that call whenever
00:08:12
it starts replicating and making two
00:08:14
cells then four cells then eight cells
00:08:16
then sixteen cells
00:08:17
that's called cleavage so it's very
00:08:19
simple we've already talked about
00:08:20
fertilization now what do we have to go
00:08:22
through we have to go through a bunch of
00:08:24
stages called cleavage so it's very
00:08:26
simple now now it's just a matter of
00:08:28
counting it up now what I'm gonna do is
00:08:31
I'm going to divide this cell it was
00:08:33
once one cell guess what I'm gonna do
00:08:35
now I'm gonna now have two cells now
00:08:38
here's the important thing to remember
00:08:39
remember I told you that this pink
00:08:41
membrane had a protein called the zona
00:08:43
pellucida three receptor that pink
00:08:45
protein is called the zona pellucida so
00:08:48
you're gonna have it in fertilization
00:08:49
you're gonna have it in the zygote and
00:08:51
you're
00:08:51
so gonna have it in this cell where it
00:08:53
divides what's this cell called this is
00:08:55
now called the two cell stage it's very
00:08:58
simple right so zygote you're gonna go
00:09:00
into the two cell stage guess what it's
00:09:04
then gonna do then it's then gonna
00:09:06
divide again it's gonna go from two
00:09:08
cells and you're gonna double that so
00:09:09
now it's going to be four cells so let
00:09:11
me do this now so there is going to be
00:09:14
four cells so this is the four cell
00:09:17
stage then what I bet you already
00:09:22
guessed it it's going to divide again
00:09:24
and it's going to turn into the eight
00:09:26
cell stage and then what do you think
00:09:29
it's going to go to after that it's
00:09:32
gonna go to the sixteen cell stage so
00:09:37
throughout that process now if you
00:09:40
imagine we're gonna have eight cells
00:09:42
here and then before you know we're not
00:09:49
gonna draw in all sixteen cells here
00:09:51
what you know here is that you're gonna
00:09:53
have tons and tons and tons of cells and
00:09:56
what this is gonna do is it's going to
00:10:00
form a kind of structure which is very
00:10:04
interesting what do I mean okay you're
00:10:06
gonna have these cells and they're going
00:10:07
to be surrounding the entire thing
00:10:10
surrounding this entire structure right
00:10:12
so it's entire circle you have these
00:10:14
cells surrounding it but inside the
00:10:16
center of it is hollow there's nothing
00:10:19
in there okay so if you were to imagine
00:10:21
let's imagine I took like a
00:10:22
cross-section here here's going to be
00:10:26
all the cells right forming the outer
00:10:29
coat
00:10:30
there's our cells forming the outer coat
00:10:33
but inside of this there's nothing it's
00:10:35
completely Hollow what do we call this
00:10:37
anything from 16 cells and up until we
00:10:40
get our blastocyst we call this the
00:10:42
marula so we call this one the marula
00:10:47
and this is basically going to be a
00:10:51
hollow ball of cells which is going to
00:10:54
be 16 or + cells
00:10:57
and what they call these they'd like to
00:10:58
give these cells a special name these
00:11:00
little circular blue cells here once
00:11:03
it's at the level of the marula they
00:11:04
call these blastomeres blasto mears okay
00:11:13
so that's important to remember now from
00:11:17
here what's gonna happen then okay so
00:11:19
now we have this marula right the marula
00:11:22
guess what it starts to do it starts to
00:11:24
take the cells right you have the cells
00:11:27
right here forming the edge what's going
00:11:29
to happen is a bunch of the cells in the
00:11:31
center there's gonna be a bunch of cells
00:11:33
that start compacting towards one edge
00:11:35
alright so you're gonna have the cells
00:11:37
lining the edge of this cell so let's do
00:11:39
it like this here you're gonna have
00:11:41
these cells they're gonna be kind of
00:11:43
lining the edge and they're gonna form
00:11:46
one type of cell structure that's very
00:11:48
important because this helps to go on
00:11:49
and form a part of the placenta okay
00:11:53
then another group of the cells around
00:11:56
that are gonna group towards one side
00:11:58
and kind of clump together let's do that
00:12:01
in a different color so that we don't
00:12:02
confuse this let's do this in the screen
00:12:04
here now we're gonna have these other
00:12:08
cells and they're going to be kind of
00:12:10
grouping together here and now we had a
00:12:15
hollow ball now what we do is we have a
00:12:17
cell lining around the edge and we had
00:12:19
to have just a bunch of group of cells
00:12:20
just clumped together in this one edge
00:12:22
over here what do we call this this is
00:12:25
going to be our blastocyst so the
00:12:27
process of what we're going from the
00:12:28
marula into the blastocyst is your blast
00:12:30
chelation process so now what do we have
00:12:33
here we're gonna have our blast
00:12:37
chelation
00:12:40
and we're gonna form here our blastocyst
00:12:45
which is so darn cool now within the
00:12:48
blastocyst you're gonna have this fluid
00:12:52
filled cavity so it's going to be all
00:12:53
fluid in here right
00:12:55
but then this group right here this
00:12:57
bunch of cells that are going to be kind
00:12:58
of clumped here together
00:13:00
this becomes a specific thing right we
00:13:03
call this part here the inner cell mass
00:13:10
okay and then the cells around the edge
00:13:13
or the periphery of it this is going to
00:13:16
be called D and very simple outer cell
00:13:21
mass now what happens is these cells
00:13:28
they start to differentiate and become
00:13:30
more functional right and what happens
00:13:32
is they become a little bit more
00:13:34
differentiate a little bit more
00:13:35
functional and then they become a
00:13:36
different type of name we just like to
00:13:37
change names for things all the time so
00:13:40
now what happens they continue to
00:13:42
differentiate continue to develop and
00:13:45
now that outer cell mass becomes a
00:13:49
specific type of thing which we call the
00:13:51
trophoblast so now this outer cell mass
00:13:54
is now what we call a trophoblast
00:13:56
becomes a little bit more differentiated
00:13:58
a little bit more specialized and we
00:14:00
call this the trophoblast
00:14:04
then we had that inner cell mass it
00:14:07
starts to become more specialized and
00:14:09
more differentiated and it turns into a
00:14:12
specific thing which is going to be
00:14:14
important and this is going to be called
00:14:16
the embryo blast this is called the
00:14:21
embryo blast so all I want you to really
00:14:23
know is the outer cell mass becomes the
00:14:26
trophoblast and the inner cell mass
00:14:28
becomes the embryo blast why is that
00:14:30
important because guess what eventually
00:14:32
the trophoblast becomes which we're
00:14:33
going to talk about next
00:14:35
it didn't differentiate into two other
00:14:37
specialized layers one is going to be
00:14:41
called the Saito trophoblast which we'll
00:14:45
talk about and the other one is to be
00:14:47
going to be called the syncytium
00:14:50
trophoblast the embryo blast guess what
00:14:55
its gonna start developing into it's
00:14:57
gonna start developing into your by
00:14:58
lemon or disk so and we'll talk about
00:15:01
how that happens but this is going to
00:15:02
start converting into your bi laminar
00:15:08
disk so within this first week right
00:15:14
that we've talked about what happened we
00:15:16
had ovulation was the first step right
00:15:19
so let's go ahead and mark out down our
00:15:21
steps first step was ovulating right
00:15:28
second step was fertilization okay and
00:15:36
that was here this was here and then
00:15:38
continuing on down here this is still
00:15:40
fertilization right so this is still the
00:15:42
fertilization step then what happened
00:15:47
from all the way from the zygote all the
00:15:51
way until the sixteen cell stage this
00:15:53
was all called cleavage so we'll write
00:15:56
that down that was the third step okay
00:16:02
then what happened after that then the
00:16:05
next thing is the marula converted into
00:16:08
the blastocyst okay that's going to be
00:16:10
the fourth stage so the fourth step is
00:16:13
going to be blast elation then after
00:16:16
that the blastula became more
00:16:18
specialized and converted into a
00:16:20
trophoblast which used to be the outer
00:16:21
cell mass and the embryo blast which we
00:16:24
used to become d which used to be the
00:16:26
inner cell mass then they will become
00:16:28
even more specialized in the embryo
00:16:31
blast become the bilaminar disk which is
00:16:33
going to be the EPI blast and the hypo
00:16:35
blast which we'll talk about and the
00:16:37
trophoblast is going to become the Saito
00:16:39
trophoblast and this is serial blast
00:16:41
this is important because these help to
00:16:43
be able to make to your structures like
00:16:45
the placenta okay whereas the embryo
00:16:48
blast is gonna make the embryo right so
00:16:51
this will then go from the by laminar to
00:16:53
the Tri laminar and that will help us to
00:16:54
make our entire embryo so that's why
00:16:56
this is so important this is generally
00:16:57
occurring within the first week
00:17:00
what we'll do next is we'll take this
00:17:03
truffle blast excel with the embryo
00:17:05
blast and we'll talk about how it
00:17:07
sprouts these little things we'll talk a
00:17:08
little bit more about this in seetio
00:17:09
trophoblast with the villi and how it
00:17:12
breaks through the zona pellucida and
00:17:13
then we'll talk a little bit more about
00:17:15
the embryo blast and how that converts
00:17:16
into the bilaminar disk alright so we'll
00:17:19
talk about that in the next video
00:17:26
[Music]
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