00:00
Well let's go through the menstrual cycle. First, the follicle ripens. Then 1 ripe follicle ruptures
and the egg is released. When the ruptured follicle then turns into the corpus luteum. See this
to me is so cool because like nothing is wasted. Right? You've got a follicle, it ripens. It lets go
of the egg and then that just doesn't disappear, turns into something useful. That ruptured follicle
turns into a corpus luteum. I think it's awesome. You talk about recycling. That corpus luteum
will atrophy if pregnancy doesn't occur. So then it will go away but if pregnancy occurs, this
is going to cause some extra changes in the uterus. If it doesn't happen, hormone levels will
drop when the corpus luteum atrophies in the uterine lining sheds. So, that's just a monthly
cycle. The follicle ripens, it releases an egg, then that ruptured follicle turns into the corpus
luteum and if a pregnancy doesn't happen that corpus luteum will atrophy, that' when it stops,
it kind of dies away, and so the hormone levels will drop when it atrophies and that's what causes
the uterine lining to shed. Ta-da, you're welcome. That's your monthly menstrual cycle, kind of
in a nutshell right there. Now, I love the drawing we have for you here of this ovary. It's kind of
intense looking but it does a really good job helping you understand what we just talked about.
01:26
Now look, it's not important that you memorize all those different names but it let you sees are
these primordial follicle, then a primary follicle, then you got the oocyte. Remember what that
is. Write in your notes what you remember an oocyte to be. Right. It's an immature egg then it
goes into the secondary follicle, in the Graafian follicle. This is the 1st half of the menstrual
cycle. Now what hormone is rising during this 1st half of the cycle? Right, estradiol. Okay. So
the estrogens are produced by the maturing follicles. So don't rush over this. Look at that maturing
follicle from the primordial follicle, follow it all the way around to the Graafian follicle. I want
you to write in your own words so you remember that this is where estrogen or estradiol is
being produced. Those are the guys that are doing it. Now the 2nd half of the menstrual cycle,
now we mark that 2nd half and 1st half by ovulation. So see the egg, shooting out there. So,
now there comes the corpus luteum. So the egg has already shut out, we've already ovulated. Now it's
going to start developing into the corpus luteum. So, look at that drawing there. You see the
egg leaving, the blue arrow, the ovum. Now you got the corpus luteum developing and then
you see the corpus luteum there. It develops in that ruptured follicle after the egg has been
released and now that's what can start secreting hormones like progesterone and estrogen but more
progesterone and that's what maintains the uterine lining. If pregnancy doesn't occur, look at
what they have, actually the corpus luteum. It kinds of all shrunk out there to tell you that it
atrophies. So this is the 2nd half of the cycle, the luteal phase. Now, after the corpus luteum
dies and degenerates, we call it the corpus albicans if a pregnancy doesn't develop. Now in the
luteal phase, the 2nd half of that cycle, when it degenerates, estrogen and progesterone levels will
drop and that's what causes the uterus lining to shed. Now they gave you a pretty good picture
there. You can see the uterus there and you can see the lining starting to drip down and become
menstrual fluid. So, this has started when the corpus luteum atrophies or becomes the corpus
albicans when pregnancy doesn't occur and then that's what causes the lining because of that
hormone change. That's what causes the lining to start to shed.