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Female reproductive sys, menstruation & fertilisation

Let's explore the female reproductive system in humans. Created by Mahesh Shenoy.

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Video transcript

please note that this video has sexual health content let's look at the female reproductive system in humans so on the right you can see where the repro system is located and on the Left we have a zoomed in version of that so let's look at the different parts of it let's start by these all looking things these are called the ovaries what do ovaries do well the or is one of their main jobs is to create excels create egg cells which are basically the female gametes and and it turns out that once girls obtain puberty basically when their sexual organs start maturing the ovaries will release roughly or an average about one egg per month one egg per month and just to be more clear you see whenever girls are born they already have lots and lots of immature eggs in their ovaries there are lots of them but it's only when they hit puberty that's when those eggs start maturing and then we find that about one egg is released per month and if you're wondering well we have two ovaries so will not be 2x release per month no in general it will be still one egg per month you can kind of imagine one month this over will release the egg the next month this ovary will release the eggs so they will alternate but of course there will be there could be times at which you know both the ovaries might release the eggs so you might have two eggs that's totally possible but in general it's usually one egg per month all right what else do they do well they also secrete some very important sex hormones like progesterone and estrogen this is something we've talked about it in great detail in our videos on endocrine system but it's basically these hormones that help in the development of the secondary sexual characteristics in in in girls during puberty and it's also these hormones that actually regulate the number of eggs that get released from the ovaries okay so let's say this is that mature egg which has been released where is it go now well it enters into this tube it's a very very thin tube and it's also given a name this tube is called the oviduct movie duct and if you look at the name carefully the duct means a passage kind of like a passage and oae means or one meanings egg egg is called om right so it's a passage for egg that's what it literally means it also has another famous name it's called fallopian tube fallopian tube both names are very commonly used so we should be familiar with both of them so what does the oviduct do well it basically pushes the egg all the way into this bag like structure an elastic bag like structure which is called the uterus in common language is also called the womb this is where the baby will be during pregnancy and if you look below over here you can see the opening to the uterus this opening is also given a name it's called the cervix during the childbirth when the baby has to come out it's the cervix that needs to open up and finally we see the vagina this is where the penis is supposed to enter during sexual intercourse so roughly these are the parts of the reproductive system but let's come back to that egg and see what happens once the egg enters into the fallopian tube what happens over there well as I said the fallopian tube starts pushing the egg starts pushing the egg and starts moving it all the way towards the uterus now once the ovaries released the egg they will signal the uterus and tell the uterus hey I have released the egg that egg might get fertilized any time we need to prepare for it the uterus says alright I'm going to prepare for it and as a result you will see that lining of the walls of the uterus start getting to become thicker it starts to become rich with blood well why does that happen because as we will see that if the egg gets fertilized then it requires nutrition and the egg will get the nutrition from this blood and that's why the uterus is basically preparing itself for fertilization all right what happens next well what happens next really depends upon whether there are sperms present here or not so let's say there are no sperms present over here all right then what will happen is that this egg which has been now unfertilized for quite a while that egg cannot survive for too long after a couple of days of release we will see that that egg will disintegrate so it has a pretty short lifetime after it has been released it needs to get fertilized or you just get disintegrated now once it gets disintegrated the ovaries will tell okay their egg is not fertilized it tells the uterus you know what uterus you can get rid of that lining we don't need that anymore so then the uterus will now start getting rid of it and the way it does that is that it starts shedding it out of this system and so as a result you will now see blood coming out from the vagina and this is what we call menstruation and so during this time of menstruation that bleeding might last from two to four to five days depends on the individual until all of that is gotten rid of and then the whole cycle can continue again and therefore menstruation happens almost every month all right but now let's consider what if there were sperms present so let us go back a little bit let's keep that egg again all right so let's say this time there was sexual intercourse and there are sperms present what happens then then you can see lots and lots of sperms will enter into the vagina they will come through the cervix they will enter into the uterus in the process a lot of them will I and eventually they may divide into two halves one will try to go this way in search of the egg another one another will try to go in this way in search of the egg again a lot of spoons will die over here this is not easy journey but eventually the fittest of the fittest sperms will be able to finally go and meet with that egg and fertilize that egg so let's say one of that sperm undergoes and fertilizes the egg meaning what's gonna happen is that the sperm is going to release its genetic material into the egg and once that happens we will say the egg is fertilized after that no more penetration can happen into the egg almost all of the other sperms will die out and as a result will now end up with a fertilized egg which is called the zygote the zygote is basically the fused egg and the sperm and then as the oviduct pushes the zygote towards the uterus we will did see the size I goat starts dividing from one cell to 2 from 2 to 4 from 4 to 8 and so on and so forth until they reach the uterus we will find that the zygote now has converted into a ball of many many cells at this point we will no longer call this as the zygote now we will call this an embryo so let me write that now this ball of cells is the embryo and of course over here the eggs are shown to be much bigger than the width of the fallopian tube just just so that we can see it obviously the eggs are smaller than the width of the fallopian tube anyways after this we will now find that the embryo will firmly attach itself by deeply embedding itself into that thick wall of the uterus this is what we call as the implantation because it's implanting itself and then it starts getting nourished from this particular blood and now the embryo can keep on growing and growing and growing and for the next nine months it'll stay there until it grows into a big baby big enough to finally come out from the cervix come out from the vagina and then we'll have a baby and you know for me when I started this what do my mind is that this means that all babies and all of us including you and me we at one point of time we're a single-celled zygote that is something truly hard for me to comprehend truly mind-boggling anyways before we wind up the video a couple of interesting tidbits one is that when a zygote converts into an embryo sometimes it converts into two embryos splits into two embryos instead of one and he guesses what happens because of that that's when we get identical twins and nobody knows you until date when or how that happens there are some theories there are some hypotheses but so far we have no clue why certain sometimes I go to do that so that uses identical twins when we come from a single zygote on the other hand sometimes what can happen as I already told sometimes you can have two eggs present in the ovary that's totally possible and if both the eggs get fertilized by two different sperms then again we will have twins but they will be not identical twins because they came from two different sperms and different eggs they will have a little different genetic makeup they will be just like any other siblings just that they will be born at the same time so non identical twins and the last curious question you could have is as this embryo starts growing into a bigger and bigger baby its energy demands it's nutrition demands its oxygen demands they all start increasing how does the mother take care of that well this is where we will see slowly the uterus start developing a very specialized tissue to take care of all the babies demands which is what we call the placenta but of course we're going to talk about the placenta in more detail in a future video altogether so let's quickly go ahead and summarize what we learned in this video we always create egg cells about one mature egg per month after puberty once the eggs are released they are collected by the fallopian tube which pushes the egg towards the uterus after the release of the egg the ovary signal the uterus to prepare for if fertilization happens and so it prepares by thickening the lining of its walls stretch T supplied by blood and if the egg doesn't get fertilized and after a couple of days the egg disintegrates and this lining is shed off over a span of few days where she will start bleeding and that's what we call the menstruation and since the cycle repeats every month we call it the menstrual cycle and on the other hand if it does get fertilized and we call that a zygote and as the zygote moves towards the uterus it starts dividing into many many cells and by the time it comes to the uterus it becomes a ball of cells which we call now an embryo which formerly implants itself into the wall of the uterus and starts feeding off from the blood and that nourishes the embryo and the embryo starts growing