Main content
Health and medicine
Course: Health and medicine > Unit 1
Lesson 8: Reproductive system introduction- Welcome to the reproductive system
- Anatomy of the male reproductive system
- Transport of sperm via erection and ejaculation
- Spermatogenesis
- Testosterone
- Basics of egg development
- The ovarian cycle
- Meet the placenta!
- Reproductive cycle graph - Follicular phase
- Reproductive cycle graph - Luteal phase
- Estrogen
- Breast anatomy and lactation
© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice
Reproductive cycle graph - Luteal phase
Created by Vishal Punwani.
Want to join the conversation?
- How does the "sperm cell"come to know into which fallopian tube to travel to get fertilized as both the ovaries has equal chances to produce a secondary oocyte?(6 votes)
- Actually some sperm do enter each fallopian tube. However, more do enter the tube with the ovum and it is thought there are chemical signals that encourage that. Research is in progress now on this question. https://www.mpg.de/5050272/attractants_sperm(11 votes)
- There are some cases of menstruation during pregnancy, most if not all of them leading to a miscarraige, possibly premature birth(Unless it is like ectopic or something).
What causes these cases of menstruation during pregnancy? I mean it would most likely have something to do with progesterone.
And also some women ovulate during menstruation which can last anywhere from 2-10 days and still be of normal length making pregnancy rare but possible during menstruation.
How would the sperm be able to swim against the current of the blood and tissue and how would the embryo be able to implant into the uterus?(8 votes)- I know women can bleed during early pregnancy and that is actually common. The blood could be coming from the pregnancy that is failing, or it could be coming from a Subchorionic hematoma (SH) that forms in the uterus, which is just a collection of blood, like a clot. It can cause miscarriage if it is of significant size compared to the size of the pregnancy, but sometimes it comes out like a period and pregnancy will carry on as normal. The cause for the formation of SH is unknown.(1 vote)
- The magnitude of the amount of tissue replaced by repeated cycles of shedding and regeneration of the endometrium seems very high to me. I wonder, are uterine cancers more common than others, due to all of this cell turnover, presence of hormones, and angiogenesis coming from the spiral arteries?(7 votes)
- So you cant get pregnant when you are pregnant because the reproductive cycle stops because of the exsisting pregnancy ?(6 votes)
- Normally yes. However there are a few cases of becoming pregnant when you are already pregnant. This is because of an extended fertile window and delayed implantation combined so that you ovulate more than once(and that is a few days apart) and then once both eggs have been fertilized they both implant into the uterine lining. This is called superfetation.(3 votes)
- In pregnancy, after the placenta fully develops and decrease secretion of HCG, does the corpus luteum then degrade?(4 votes)
- Yes, the corpus luteum degrades later in pregnancy as the placenta matures and changes from producing HCG to producing progesterone itself. I know progesterone increases to support the pregnancy around 12 weeks,but I am unsure exactly when the CL atrophies in the human being. In some other animals, the CL must continue to produce progesterone as the placenta does not produce enough. View this page:
http://www.vivo.colostate.edu/hbooks/pathphys/reprod/placenta/endocrine.html(3 votes)
- If fertilization of the egg occurs, does the corpus luteum remain in the ovary and continue to function from there?(2 votes)
- Yes. The follicle grows in the ovary and produces mostly estrogen and some progesterone, then it ovulates, which sends the secondary oocyte into the fallopian tube. During this time the uterine lining or endothelium proliferated. The remnant follicular tissue in the ovary becomes the corpus luteum and it produces mostly progesterone and some estrogen for 14 days and maintains the uterine endothelium so that it starts the Secretory phase. If no fertilization occurs, the corpus luteum stops producing hormones, and menses occurs and then another follicle starts to grow. If fertilization occurs then the corpus luteum continues to produce progesterone in response to the embryo producing hCG. After about 3 months, the placenta starts producing progesterone to support the pregnancy and suppress additional ovulation.(4 votes)
- How do birth control pills work? I read in the PR Bio/Biochem Reproductive Systems chapter that birth control pills maintain high estrogen and progesterone levels. This causes the endometrial lining to be maintained. But because of constant levels of estrogen and progesterone, there is no sudden surge in estrogen/progesterone levels, which results in no LH spike. As a result ovulation does not occur.
Is this correct?
Also, the book also mentions that women take the 21 hormone pills and 7 placebo pills and the placebo pills allow menstruation to occur once estrogen/progesterone levels decrease. If there were no placebo pills, would the endometrial lining just remain in place until the female decides not to take them again?(3 votes) - Why does fertilization occur in the fallopian tubes and not in the uterus?
Also, is there a possibility of the egg being fertilized during menses?(2 votes)- A mature egg cell is only viable for 24 hours following ovulation, so by the time it reaches the actual uterus it's already too old to become fertilized. This is the same reason fertilization can't happen during menses; the egg, as well as the uterine lining, has become too old and needs to be replaced. However, it's possible that if a woman were to have sex during her period, and then ovulates anytime 3 to 7 days later, the sperm could survive and fertilize that new egg.(3 votes)
- whats a embryo ?(1 vote)
- In humans, an embryo is generally considered to be between the first and the eighth week of development after fertilization and from then it is instead called a fetus.(3 votes)
- so why do gastroschisis happens ? and why it happens mostly do young parents ?(2 votes)
Video transcript
- [Voiceover] We kind of looked at the first half of this graph, the follicular phase, and we kind of understood that the follicular phase is all about stimulating growth of the follicles in the ovaries to eventually cause the
ovulation of an egg. This stimulation of the follicles comes from the release
of various hormones, FSH, LH, estrogen, and so on. The second half, after ovulation, is called the luteal phase. It's called the luteal phase because it's about the development of this yellow structure here, called the corpus luteum. So let's talk about it. Here, after ovulation, we have an egg that's been
expelled from the follicle. We therefore have the
remainder of the follicle. At this point, luteinzing
hormone, LH, is really high. Together, LH and FSH are going to induce the old follicle here to turn into a structure
called the corpus luteum. That just means "yellow body" in Latin. It's actually a bit yellowy because of some yellow
pigments it has in it. Remember the follicle was
what released estrogen from its granulosa cells. Since this is not a follicle anymore, it greatly reduces the
amount of estrogen it makes, and it actually begins to
mass-produce progesterone. Just to clarify, though: it
still does make some estrogen. It's just not really its primary product. Progesterone is. So that's why you see
this dip in estrogen here, and this almost uptick in
progesterone that gets produced. Let's think about this for a second. We've ovulated, so there's a chance our egg could get fertilized by a sperm. Once it gets fertilized, it's going to need a place
to hang out and grow. It's going to have to implant into the lining of the uterus
called the endometrium. What would be really
helpful right about now is if we had a nice, vascular,
hospitable uterine lining that our fertilized egg could implant into to support gestation of our new embryo. By the way, at this stage of implantation, our embryo is actually
called a blastocyst. I'll just write that down over here. So in comes progesterone. Let's just look at the word for a second. "Pro," meaning "for," and "gest," referring to gestation. This last part just kind of clues you in that it's a hormone. So progesterone is a
pro-gestation hormone. It's what mainly stimulates
the uterine lining to prepare for implantation and gestation during this phase called
the secretory phase. In this secretory phase, progesterone does a few things. It increases blood flow to the endometrium by stimulating the development
of special arteries in the endometrium called spiral arteries. You can see them here in red. These spiral arteries allow the embryo to eventually have good
access to nutrients from the mother's blood stream. Progesterone also increases
uterine secretions from special glands in the endometrium. These secretions are important for nourishment of the embryo. Finally, progesterone actually
reduces the contractility of the muscles of the uterus. Remember, the uterus has a lot of smooth muscle in its walls. The progesterone actually reduces the contractility of those muscles so that the growing embryo
doesn't really get too disturbed and doesn't get expelled
out of the mother's body too early by those muscles contracting. Since we really want that nice, hospitable
environment for gestation, the corpus luteum produces lots and lots and lots of progesterone. By the way, there's
still a reasonable amount of estrogen kicking around, and it's really both the
little bit of estrogen plus the lots and lots
and lots of progesterone that helps to ready the
endometrium for pregnancy. The corpus luteum's hormones are doing other things, too, though. The progesterone and the
little bit of estrogen produced by the corpus luteum, they're going to suppress
the FSH and LH production by the anterior pituitary, by that process of negative feedback. So you can see their levels
dipping pretty low here. On top of the estrogen and progesterone negatively feeding back
on FSH and LH release, the corpus luteum is
also producing inhibin. You can see the amount
of inhibin peak here when the corpus luteum reaches
around its maximum size. That inhibin actively inhibits FSH release from the anterior pituitary. Unfortunately for the corpus luteum, it kind of needs FSH and LH to survive. Since they're being suppressed by the corpus luteum's
own hormone release, the corpus luteum starts to atrophy. It starts to wither away and die off. When it dies off, progesterone
and estrogen levels drop. And when progesterone and
estrogen begin to drop, two things happen. The first thing is that the end of the
luteal phase is triggered. You can see, we've reached
the end of the graph here. Basically, we've triggered
the end of the luteal phase, but the start of the
next follicular phase. At this point, menstruation
begins to occur and the endometrial lining
that has built itself up and prepared itself for
implantation starts to shed, and it'll be lost
through the vaginal canal in what we commonly call
the menstrual period, or menses. Notice that that sort of takes place at the beginning of
each reproductive cycle. Generally speaking, menstruation is a sign that pregnancy has not occurred. This period can last anywhere
from two to seven days. FYI, women lose usually
around 40 milliliters of blood per menstrual phase. The second thing that happens when estrogen and progesterone levels drop is that they stop exerting
their negative feedback effects on FSH and LH release from
the anterior pituitary. So the FSH and LH levels
begin to go back up again. This increasing FSH then goes on to stimulate more follicular
development in the ovaries to start the whole cycle all over again over the course of another 28 days. Now, what I told you
about the corpus luteum withering away and dying is only actually true when
no pregnancy is occurring. That's the case in most
reproductive cycles, and that's why I covered that first. But it's important to know that things are a little different if pregnancy does occur and a fertilized egg is indeed implanted into the endometrium. We said that the corpus luteum's estrogen and progesterone release suppresses FSH and LH, and suppression of FSH and LH, in turn, cause the corpus luteum to atrophy, right? That's because the corpus luteum needs luteinizing hormone to survive. Well, when a blastocyst
implants into the endometrium and gets established there, the resulting embryo that
develops from the blastocyst starts to produce a special hormone called human chorionic gonadotropin, or HCG. This HCG is structurally
really, really similar to luteinizing hormone, so much so that levels of
HCG produced by the embryo are enough to keep the
corpus luteum alive. Because remember, we said
that the corpus luteum relies on LH to stay alive. So now with the corpus
luteum remaining alive, it can continue to produce
that estrogen and progesterone that's necessary to maintain
the endometrial lining and keep it nice and
supportive of the pregnancy. There's a couple implications of this. First, because the HCG production is unique to the embryo, most pregnancy tests work by checking for the
presence of HCG in the blood or in the urine. Second, the corpus luteum
doesn't produce progesterone for the entirety of the pregnancy. It does most of the
progesterone production for about the first two to three months, and after that, a joint organ of exchange shared between the mother and the fetus, called the placenta, that starts to take over as the major producer of progesterone. Third, the corpus luteum being rescued, or kept alive, means that
its continued hormone release maintains that endometrial lining. So the lining isn't lost in menstruation. It's kept in order to
support the pregnancy. Just to recap: if no pregnancy occurs, then the corpus luteum withers away and the reproductive cycle
just continues to repeat itself for about 28 daily. And if pregnancy does occur, the implanted embryo
starts to produce HCG, which rescues the corpus
luteum from atrophying and the endometrium is thus maintained. No menstruation happens because you're not losing the endometrium and the reproductive cycle is put on hold for the duration of the pregnancy.