Implantation & Pregnancy | Human Reproduction Part 7 | Biology Class 12 | HINDI


the topic of this presentation is implantation and pregnancy Cleavage is a special kind of mitotic division which starts in zygote and continues till formation of blastula the daughter calls formed during cleavage are known as blastomeres G1 phase of cell cycle does not occur during cleavage recall cell cycle, cytoplasm content of daughter cell increases during G1 phase due to which newly formed daughter cells grow when G1 is not occurring, it means that cytoplasmic content of blastomeres does not increase it means that whatever amount of cytoplsm is available in this fertilized egg, will be distributed among subsequent blasomeres consequently, the cytoplasm content in daughter cells keeps on decreasing as the process of cleavage progresses but the size of nucleus in the blastomere remains the same because S phase occurs before cell division in which the DNA doubles itself and such replicated DNA is distributed equally between two daughter cells it means that as the process of cleavage progresses, the size of nucleus remains the same but content of cytoplasm will keep on decreasing due to which Nulceo-cytoplasmic ratio continuously increases during the process of cleavage Cleavage results in formation of blastula normal cell division starts in the growing embryo after formation of blastula and Mammalian blastula is called blastocyst we have discussed structure of blastocyst in detail ahead we will discuss structure of blastocyst with the help of this diagram by now, blastocyst has become a multi-cellular structure some cells hare aggregated in this region to develop a structure called ‘inner cell mass’ a layer of cells around inner cell mass is called trophoblast and the cavity of blastula is called blastocoel coel means cavity so the cavity of blastula is called blastocoel observe one special feature of this structure that- zona pellucida is still intact second layer of egg is called zona pellucida and it is still intact and has not yet disappeared Zona pellucida disappears after blastocyst formation and the developing embryo arrives in the uterus till the blastocyst is formed and is ready for the implantation we will discuss the role of zona pellucida later on first we will discuss the role of trophoblast, Trophoblast is mainly responsible for implantation of embryo we will discuss more about it later Trophoblast is also responsible for the formation of 4 extra embryonic membranes and development of placenta Inner cell mass gets differentiated as embryo proper. embryo proper give rise to body parts of developing individual we have already discussed that, zona pellucida disappears after formation of blastocyst Zona pellucida prevents implantation of blastocyst in fallopian tube. otherwise there was a possibility that trophoblast might contact fallopian tube layer and implantation might have occurred in fallopian tube zona pellucida remains intact to minimize this possibility and when this blastocyst reaches uterus where implatation should occur then this zona pellucida disappears we will discuss the process of implantation in 4 stages this blastocyst has arrived in the uterus now it establishes contact with the uterine lining while establishing contact with endometrium it will orient itself in such a way that inner cell mass faces the uterine lining so in the first stage, blastula establishes contact with endometrium in the next stage, the cells of trophoblast which are in direct contact with the endometrium they will develop finger like outgrowths these finger like outgrowths are called chorionic villi these chorionic villi penetrate into the endometrium will strengthen grip of balstocyst these chorionic villi help the developing embryo draw nutrition from endometrium here I want to make you recall one point that these chorionic villi are endocrine also and start secreting a hormone hCG – human chorionic gonadotrophin we will discuss function of hCG in detail ahead chrionic villi now start secreting lytic enzymes which digest the endometrial tissue locally as a result, this blastocyst will be embedded into the endometrial tissue last stage of implantation is shown in this diagram by this time, blastocyst has been completely embedded into the endometrial tissue and now we will say that implantation has been completed with the help of this diagram, we will discuss all events till implantation fertilization has occurred at this tie of fallopian tube and zygote is formed first cleavage occurs after 24 hours to form 2 celled stage and with subsequent divisions, it forms morula on day 4 as this embryo is growing, it is also moving along fallopian tube- toward uterus and it reaches uterus in about one week by then it develops into blastocyst as it arrives in the uterus and develops in balstula, zona pellucida now disappears releasing the blastocyst and now this blastocyst is ready for the implantation this embryo will contact endometrium and implantation of this developing embryo will take place into the endometrium with the help of this diagram, we will now understand location of embryo inside the endometrial tissue by now we have understood that embryo becomes completely embedded into the endometrial tissue as the embryo grows, endometrial lining also grows around the developing embryo to surround the embryo from all sides so this is the endometrial lining around the embryo the placenta has been developed between embryo and endometrial tissue and placenta is formed of combination of embryonic and maternal tissue we will discuss its detail structure ahead in the presentation and developing embryo is connected to the placenta through a cord like structure called this umblical cord in the diagram, it is the uterine cavity this is the uterine cavity it means that developing embryo is not at all suspended freely in the uterine cavity instead, it is completely surrounded by the endometrial layer embryo is completely embedded within the endomettrial tissue let’s discuss structure of placenta and umblical cord placenta is formed of maternal and embryonic tissues placenta is developed at the site of implantation and developing fetus is connected to placenta through a cord like structure called umbilical cord now in this diagram, we will discuss detailed structure of placenta this is the maternal portion and this is the fetal portion these are the maternal veins and arteries oxygen and nutrients reach placenta through arteries CO2 and other waste products from embryo reach mothers body through veins umblical vein and artery are present in the umblical cord and these are the fetal capillaries which are completely embedded into the maternal tissue umblical vein collects oxygen and nutrients from placenta and umblical arteries bring waste products from embryo to the placenta now we will understand relation between menstrual cycle and implantation recall menstrual cycle, ovulation occurs on 14th day of menstrual cycle if the cycle is of 28 days Fertilization occurs within 2 days of ovulation (14th -16th day of menstrual cycle) as the lifespan of secondary oocyte is of 2 days only Fertilization can occur 14th -16th day of menstrual cycle if fertilization occurs, then results in formation of zygote which converts to blastocyst within a week and this blastocyst reaches uterus within a week it means that blastocyst reaches uterus till 21st day of the menstrual cycle Blastocyst gets implanted into endometrium within 48 hours it means implantation of blastocyst occurs till 23rd day of menstrual cycle after learning all these facts , understanding the hormonal regulation of pregnancy will become very easy we will discuss the hormonal regulation of pregnancy with the help of this diagram but before that let’s recall menstrual cycle in brief ovulation occurs on 14th day of menstrual cycle after ovulation ruptured graafian follicle converts into corpus luteum and starts secreting estrogen and progesterone hormones concentration of these two hormones reach their peak up to mid post ovulatory phase but after mi post ovulatory phase, degeneration of corpus luteum starts as a result, the level of these two hormones starts falling when the concentration of these two hormones falls below a critical level then starts the degeneration of endometrium and the next menstrual cycle starts in that female’s body, but if the fertlization of egg occurs, then this fertilized egg, within 7 to 10 days, converts into blastocyst and reaches uterus here in the uterus, blastocyst will undergo implantation now the chorionic villi of blastocyst will start secreting hCG hormone this hCG hormone mimics the action of LH hormone and maintains corpus luteum and thus secretion of estrogen and progesterone hormones continue both of these hormones are absolutely required for maintaining the pregnancy in the first trimester – first 3 months or 12 weeks of the pregnancy, placenta is fully developed and start releasing sufficient quantities of estrogen and progesterone hormones it means that secretion of hCG is not at all required as a result, the concentration of hCG abruptly falls in the blood and corpus luteum also degenerates now placenta releases sufficient quantities of estrogen and progesterone Pregnancy test kit actually tests for hCG using ELISA mechanism The kit contains antibodies to hCG if hCG present in urine then it interacts with antibodies to produce color and that color confirms the pregnancy he test kit can detect pregnancy as early as first day of missed menstrual period Link of animated video of ‘How does Pregnancy Test Kit work?’ is available in the description box. now we will discuss Functions of Placenta it facilitates supply of oxygen and nutrients to embryo. carbon dioxide and waste materials produced by embryo are sent to mother’s body this CO2 is excreted through mother’s lungs and waste materials are excreted through mother’s kidneys it also Acts as an endocrine tissue and produces hormones like human chorionic gonadotropin (hCG), human placental lactogen (hPL), estrogens, progesterons etc. IgG passes through placenta and provides immunity to developing fetus. let’s discuss Functions of Pregnancy Hormones estrogen and progesterone hormones maintain endometrium and pregnancy we have already discuss about hCG in detail Human Placental Lactogen (hPL) prepares mammary glands for lactation. Relaxin increases flexibility of pubic symphysis and dilates uterine cervix during labor. in normal cases the embryo must be implanted in these regions of uterus but instead of these regions, embryo gets implanted in fallopian tube or in the cervix then it is called ectopic pregnancy if implantation occurs in fallopian tube then it is called tubal pregnancy and implantation in cervix is called cervical pregnancy there could be many Reasons for Ectopic Pregnancy but cigarette smoking is associated with ectopic pregnancy as the cigarette smoke contain a chemical called nicotine which paralyzes cilia in lining of fallopian tube due to which developing fails to reach uterus within one week and the zona pellucida will disappear in the fallopian tube itself and this embryo will implant itself in the fallopian tube there could be other reasons also, like inflammation of uterine lining previous surgery of fallopian tube or uterus if ectopic pregnancy is not detected in early stage then it could pose a life threatening situation to that female

22 Replies to “Implantation & Pregnancy | Human Reproduction Part 7 | Biology Class 12 | HINDI”

  1. hi..kya ap embryology k baqi lecture bhe bnaen gy.. i need them.. i m med student mbbs.. weeks of developmnt py bnaen plz your lec r very help ful

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