Hello! I am Dr Aizaz from medicovisual.com back with another visual lecture on the topic of post
ovulatory changes during the female menstrual cycle. So, previously we had discussed the
process of ovulation and in that what happened that as the ovulation occurred, the secondary
oocyte was released into uterine tube ultimately and the structure that remain behind, structure
that remains behind it was turned into, it was called corpus luteum and it started secreting
Progesterone. Right, so, this post ovulatory phase it is orchestrated mainly by progesterone hormone.
So, level of progesterone will rise up in blood and why it is rising? Because this corpus luteum
is releasing lots of progesterone and it is not just producing progesterone but it is
it is also secreting some oestrogen as well but the amount of oestrogen that is being secreted
it is much less as compared to the quantity of progesterone being produced.
FSH and LH they are not much needed during this phase so they will remain at a baseline level.
Now, in the pre ovulatory part of the cycle we had discussed how the proliferative changes occurred
in the endometrium. That endometrium has had acquired two extra layers the stratum spongiosum
and compactum. So, it was like the empty home for the baby and now when now there could be
two possibilities now either this secondary oocyte that is released into uterine tube
it may either get fertilized or it may not get fertilized. Right, so, let's suppose, let's first
discuss that what happens if it get Fertilized. So, if let's suppose this is secondary oocyte it
comes here and here at the ampullary region of uterine tube or fallopian tube a sperm may come
and fertilize this. Right, from this point onward it will undergo a series of mitotic divisions
or cleavage to ultimately form a blastocyst we will not discuss the details that how it occur
but it will ultimately form blastocyst. So, the point here is that it has to ultimately
come into uterine, uterine cavity and it will have to travel all the way from this point up to here.
So, now as it, as it will enter the uterine tube it needs some food after that tiring
Voyage. Right, so, during this phase, this post ovulatory phase the mother's uterus it starts
creating something for the nutritious needs of the baby. So, that was this empty house,
that endometrium but now tables will be set on, table with a fruit basket will be set on
On, this in, this house along with that, these windows will become well developed and from these
windows she will start throwing out fruits. Right, and this tree will acquire some Fruits. It will
become a beautiful fruity Tree. Now, what I mean by this is that during this stage and as I have
told you this phase is mostly, mainly orchestrated by progesterone. So, during this phase under the
action of progesterone that was being released by corpus luteum from the ovary, right, so, during
this phase under the influence of Progesterone, progesterone will act on the endometrium of,
on the endometrium of uterus to prepare for the nutritious needs of the baby. So, what will happen
that these blood vessels, these are like Trees, these blood vessels will,
will become large and tortuous, engorged blood vessels. Right, and then these cells,
they will become filled with glycogen. And finally these , these windows will become
well developed and they will start secreting nutritious rich fluid. Right, nutritious fluid
will be secreted out of these glands. Right, that is like throwing out that fruit out of the
out of the windows of house. So, this secretion that it will produce it is called uterine milk.
And remember these changes will occur whether or not fertilization occur. Even if fertilization
does not occur it will still, these changes will still occur each month under the influence of
Progesterone. now, what is the significance, what is the benefit of these changes? Now,
let's see. So, here is the embryo at blastocyst stage as soon as it enters the the uterus it
will drink this fluid. Right, it will get the nutrition from this fluid. Right, within that
uterine cavity it has not yet penetrated the wall within the uterine cavity it can get the nutrition
because of this uterine milk and then when it will grow a bit further it will burrow inside
the endometrium and as it will burrow inside the endometrium it will eat those glycogen.
Right, it will implant inside and it will get the nutrition from this glycogen filled cell
and ultimately this, this future baby he or she will learn to fetch the fruit from the trees.
What I mean by this is that it will learn to get nutrition from the uterine blood vessels. Right,
so utero placental circulation will start. What is utero-placental circulation we will discuss
that later in the in the upcoming lectures. So, what's the important point here is that
three things are being done for the nutritious needs of the baby. what are those three things?
That uterine glands start secreting uterine milk under the influence of progesterone
then glycogen filled cells are formed and even the blood vessels are engorged. Right,
out of these changes the hallmark is the secretion that start oozing out from This, from these
uterine glands. So, because of this we call this phase as secretary phase of uterine cycle. What
it is? It is secretory phase of uterine cycle. Because secretion start oozing out of uterine
glands and regarding the ovary what is happening in the ovary? Corpus luteum is being formed,
corpus luteum is there so that is why it is luteal phase of ovarian cycle. Then what happens that
these trophoblastic cells of this embryo they will secrete a special chemical Messenger, a good news
messenger will be secreted from this trophoblastic cells and this message will go to blood,
it will be released in blood and it will also be released in urine as well, right, so this through
blood it will ultimately come to the ovary and in ovary what is, what is this? This corpus luteum,
corpus luteum waiting for that good news Message, as soon as this, it receives this
good news message it will become very happy and it will proliferate and it will enlarge
and it will secrete lots of progesterone to maintain the pregnancy.
At this stage now this corpus luteum is called corpus luteum Graviditatis. It's very difficult
name you can just call it corpus luteum of pregnancy and by the way what is this good news
messenger? It is human chorionic gonadotropin, hcg. It is human chorionic gonadotropin.
Now, let's see what happens if fertilization does not occur. So, again secondary Oocyte is released
and this time fortunately or unfortunately it does not get fertilized. So, what happens
it will come ultimately into the uterine Cavity.
So, here it will come but this time because it is not fertilized, it is not an embryo so
it cannot implant, it cannot burrow inside the endometrium of uterus. So, it will remain there
and within a day or two it will be destroyed by Macrophages. It will be eaten up by macrophages
then what will happen? As it is eaten up by macrophages there will be no good news message,
there will be no secretion of Hcg into blood. So, this poor corpus luteum it will keep on waiting
for that good news message from, for the Hcg but of course hcg will not come. So,
after about 10 or 11 days it will become very sad, it will become disappointed and hopeless
and it will degenerate and ultimately it will be converted into a scar tissue, whitish scar tissue
and that that is called corpus albicans. Corpus mean “body”, albican mean “white”. So,
it will be converted into that scary white body that we call corpus albicans. Corpus albicans
may remain there in the ovary for about two to three months. Right,
and then it may be replaced by normal tissue. And by the way what happens to the corpus
luteum graviditatis? It may also remain there for about two to three months
and later on that is also destroyed and the question is then who secretes Progesterone?
Then placenta develops and placenta will start secreting Progesterone. It’s on progesterone,
right, we will discuss the details Later. So, here what will happen that as soon as This,
this corpus luteum start degenerating the level of progesterone as well as oestrogen starts declining
and FSH and LH remains normal except at the end of this, this phase as they will have to start,
there will be slight rise at the end of cycle as they have to start a new cycle.
What will happen that as the progesterone level falls as the progesterone level declines
this house will be destroyed. what I mean by this is that these two additional or functional
layers of endometrium they will be shed off and that will lead to bleeding. Why they will shed
off? Because progesterone is needed to maintain these Layers, right, progesterone is actually
pro-gestational steroid. This, this name progesterone it comes from these three words
pro-gestational, gestation mean pregnancy it is steroid in nature. Chemically it is steroid
hormone and it is pro gestational, it maintains the Pregnancy, it is the hormone of pregnancy.
So, as its level declines what will happen that this uterine, additional two layers of
endometrium they will undergo ischemic necrosis. Let's see how? They will stop
secreting that uterine milk and there will be severe vasoconstriction,
there will be severe vasoconstriction in the basal layer. As there will be severe vasoconstriction
these two layers they will not get enough blood. So, there will be ischemia in these layers
and they will then shed off and bleeding will occur and that is called Menstruation. Right,
this cycle as the menstruation occurs new cycle starts. Right, and then nature will again keep
on trying to get Fertilized, get the secondary oocyte fertilized. And if Secondary oocyte does
not get fertilized again new cycle start and this cycle will continue and continue and continue.
Well, I think that nature here is trying to teach us something. Nature is trying to teach
us that if you fail one time just keep on trying and trying until you Succeed. And of course, you
may succeed one day so that is what happens here that the cycle will continue and continue until
the pregnancy stop*, pregnancy starts and if the pregnancy starts this cycle will temporarily cease
and then it will again start. Right, to start a new pregnancy. Right, so the cycle will
continue and continue till this lady becomes very old with her wrinkled skin and old body
when it becomes very difficult for her body to efficiently maintain and sustain Pregnancy.
At that time the cycle stops permanently and that is called menopause. Menopause occurs at
the age of about 50 Years. Right, so that is menopause, when the cycle permanently stops.
So, here is the review slide again what happens here is that as the corpus luteum forms
this phase, this ovarian, this post ovulatory phase of the cycle is luteal phase of,
luteal phase of ovarian cycle and it is dominated by progesterone mainly. Right, so with the,
on with the influence of progesterone this uterus, it becomes well developed to maintain
the nutritious needs of the Baby. These blood vessels become engaged, Engorged and tortuous.
These glands become deep and specialized. Right, and then these cells become filled with glycogen
and these glands start secreting uterine milk. As they start secreting uterine milk
this phase is that is why this phase is named as secretory phase. The post ovulatory phase
is also luteal phase of ovarian cycle and it is also secretary phase of uterine cycle. Clear?
And what happens to this cervix? The cervical mucosa again under the influence of progesterone
it becomes very thick. It becomes thick because there is no need at this time for sperm to enter.
Right, so that is why it becomes thick to prevent the entry of sperm or even it will prevent the
entry of many of the pathogens inside the uterine cavity. Right, and regarding the basal body
temperature, under the influence of progesterone the basal body temperature slightly rises,
probably to create that motherly warmth for the future baby. Right, so this is
post ovulatory changes that occur during female menstrual cycle. I hope you understood this. If
you have any confusion please ask me in the comment section and of course remember that
at the end of this cycle bleeding will occur and new cycle will start and again same changes will
repeat itself. Right, So, I tried my best to simplify this
as much as possible. Hope you will understand this. Thank you so much for watching this video.