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(1)Fertilization(1)Fertilization : :

It is the process by which mature male & female gametes fuse to It is the process by which mature male & female gametes fuse to form zygoteform zygote

Normal site - in ampulla of uterine tube. Normal site - in ampulla of uterine tube. 200 – 300 million of spermatozoa deposit in female genital tract200 – 300 million of spermatozoa deposit in female genital tract Out of them 300 – 500 reach the site of fertilizationOut of them 300 – 500 reach the site of fertilization Out of them only one is needed for fertilization, others help in Out of them only one is needed for fertilization, others help in

penetrating the corona radiatapenetrating the corona radiata

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(2)Penetration of corona radiata (2)Penetration of corona radiata Capacitation - removal of glycoprotein from acrosome /high Capacitation - removal of glycoprotein from acrosome /high

motility of sperm without morphologic change motility of sperm without morphologic change Corona radiata cells are dispersed by combined action of sperm Corona radiata cells are dispersed by combined action of sperm

(Hyaluronidase ) & tubal mucosal enzymes. (Hyaluronidase ) & tubal mucosal enzymes.

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(3)Penetration(3)Penetration of Zona pellucida – of Zona pellucida – It is penetrated by sperm with the aid of enzyme released by the It is penetrated by sperm with the aid of enzyme released by the

inner acrosomal membrane, (acrosin)inner acrosomal membrane, (acrosin) Zona reaction - Impermeability to other sperm by lysosomal Zona reaction - Impermeability to other sperm by lysosomal

enzymes of 2nd Oocyte enzymes of 2nd Oocyte

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(4)Fusion of oocyte –sperm cell membrane(4)Fusion of oocyte –sperm cell membrane Leaving behind plasma membrane, head & tail enter the cytoplasm Leaving behind plasma membrane, head & tail enter the cytoplasm

of oocyte of oocyte

The Egg responds in 3 waysThe Egg responds in 3 ways Cortical & Zonal reactionCortical & Zonal reaction Resumption of 2Resumption of 2ndnd meiotic division meiotic division Metabolic activation on the eggMetabolic activation on the egg

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(5)Pronucleus formation(5)Pronucleus formation Female – after fusion of cell membrane oocyte completes its 2Female – after fusion of cell membrane oocyte completes its 2ndnd

meitotic division. One of the 2 daughter cell forms the pronucleusmeitotic division. One of the 2 daughter cell forms the pronucleus Male Nucleus from the head of the sperm becomes swollen to form Male Nucleus from the head of the sperm becomes swollen to form

pronucleuspronucleus DNA replication – This occurs in both Pronuclei DNA replication – This occurs in both Pronuclei Mitosis – Pronuclei meet, their nuclear membrane dissapear & Mitosis – Pronuclei meet, their nuclear membrane dissapear &

chromosomes arranged in distinct manner for mitosischromosomes arranged in distinct manner for mitosis

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(6)Results of fertilization (6)Results of fertilization restoration of the diploid number of chromosomes restoration of the diploid number of chromosomes new combination of chromosomes new combination of chromosomes primary sex determination primary sex determination initiation of cleavage initiation of cleavage

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(7)Cleavage(7)Cleavage zygote --> zygote --> 2-cell stage(blastomeres) -->2-cell stage(blastomeres) --> 16-cells(morula) --> 16-cells(morula) --> BlastocystBlastocyst

BlastomereBlastomere Each of the cells results from Each of the cells results from

cleavage of zygote is calledcleavage of zygote is calledBlastomereBlastomere

Morula:Morula: The name of the embryo atThe name of the embryo at

the 16 to 32 cell stage. the 16 to 32 cell stage.

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(8)Formation of Blastocyst(8)Formation of Blastocyst

Morula when it is filled with uterine fluid is called BlastocystMorula when it is filled with uterine fluid is called Blastocyst Morula eners the uterine cavity 60 – 72 hours after fertilizationMorula eners the uterine cavity 60 – 72 hours after fertilization At the same time fluid enters into the intercellular spaces of At the same time fluid enters into the intercellular spaces of

inner cell mass through zona pellucidainner cell mass through zona pellucida Intercellular spaces become confluent & finally a single cavity is Intercellular spaces become confluent & finally a single cavity is

formed called Blastocoeleformed called Blastocoele At this time zona pellucida dissappears & the zygote is then At this time zona pellucida dissappears & the zygote is then

known as Blastocyst known as Blastocyst

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(9)Blastocyst(9)Blastocyst: :

PartsParts EmbryoblastEmbryoblast:(Forms Embryo) :(Forms Embryo) The cells on the inside. The cells on the inside. Trophoblast:(Forms Placenta)(Nutrient providing cells) Trophoblast:(Forms Placenta)(Nutrient providing cells)

The cells surrounding the outside. The cells surrounding the outside. Blastocyst cavityBlastocyst cavity

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(11)Implantation (11)Implantation

Process of placement of blastocyst into the wall of the uterus is Process of placement of blastocyst into the wall of the uterus is called implantation (Erode)called implantation (Erode)

Normal Site – Posterior wall of the uterus close to the fundusNormal Site – Posterior wall of the uterus close to the fundus initiated 6-7 days after fertilization initiated 6-7 days after fertilization

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(12)Mechanism (12)Mechanism Uterine mucosa already undergoes several changes (menstrual Uterine mucosa already undergoes several changes (menstrual

cycle) to receive blastocyst.cycle) to receive blastocyst. Duing implantation the mucosa is in secretory phase & poseses 3 Duing implantation the mucosa is in secretory phase & poseses 3

layerslayers Polar trophoblast now adhers to the uterine mucosa & starts Polar trophoblast now adhers to the uterine mucosa & starts

penetraion into it by eroding the surface(by release of proteolytic penetraion into it by eroding the surface(by release of proteolytic enzymes )enzymes )

By erosion ,trophoblast forms a cavity in the mucosa into which By erosion ,trophoblast forms a cavity in the mucosa into which the blastocyst becomes embededthe blastocyst becomes embeded

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(13)Uterus after the implantation (13)Uterus after the implantation

DeciduaDecidua After implantation of blastocyst the endometrium is called deciduaAfter implantation of blastocyst the endometrium is called decidua

Decidual ReactionDecidual Reaction After implantation the stromal cells of endometrium enlarge become vacuolated & After implantation the stromal cells of endometrium enlarge become vacuolated &

store glycogen & lipidstore glycogen & lipid These changes in stromal cells are called decidual reactionThese changes in stromal cells are called decidual reaction

Divisions of deciduaDivisions of decidua Decidua Basalis – portion where placenta is to be formedDecidua Basalis – portion where placenta is to be formed Decidua Capsularis – portion which separates embryo form uterine cavity Decidua Capsularis – portion which separates embryo form uterine cavity Decidua Parietalis – rest part of decidua Decidua Parietalis – rest part of decidua

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(14)Formation of germ layers ( Gastrulation)(14)Formation of germ layers ( Gastrulation) By day 8, The trophoblast differentiates into:By day 8, The trophoblast differentiates into:

An inner An inner cytotrophoblastcytotrophoblast surrounding the blasocyst surrounding the blasocyst An outer layer of proliferating cells An outer layer of proliferating cells syncitiotrophoblastsyncitiotrophoblast..

The blastocyst is more deeply embeded in the endometrium by day The blastocyst is more deeply embeded in the endometrium by day 9, & the penetration defect is closed by fibrin coagulum9, & the penetration defect is closed by fibrin coagulum

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(15)Embryoblast splits into 2 layers: (15)Embryoblast splits into 2 layers: The The epiblastepiblast (primitive ectoderm) (primitive ectoderm) TheThe hypoblast hypoblast (primitive endoderm), thus forming the (primitive endoderm), thus forming the bilaminar bilaminar

germ discgerm disc.. Within the epiblast, the Within the epiblast, the amniotic cavityamniotic cavity develops develops Epiblast cells adjacent to cytotrophoblast is called Epiblast cells adjacent to cytotrophoblast is called amnioblastsamnioblasts Cells at the periphery of the hypoblast migrate over the inner surface Cells at the periphery of the hypoblast migrate over the inner surface

of the cytotrophoblast, forming a thin layer called of the cytotrophoblast, forming a thin layer called exocoelomicexocoelomic ((Heuser’s membrane)Heuser’s membrane), with the blasocyst cavity hence forth called , with the blasocyst cavity hence forth called the the primary yolk sac (Exocoelomic Cavity)primary yolk sac (Exocoelomic Cavity). .

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Formation of germ layersFormation of germ layersExocoelomic membrane prolifates & splits to form 2 extraembryonic Exocoelomic membrane prolifates & splits to form 2 extraembryonic mesodermal layresmesodermal layres Extraembryonic somatopleuric mesoderm, Extraembryonic Extraembryonic somatopleuric mesoderm, Extraembryonic splanchnopleuric M.splanchnopleuric M.

Cavity inbetween – Extraembryonic coelom (chorionic cavity)Cavity inbetween – Extraembryonic coelom (chorionic cavity) Maternal sinusoids have grow into the expanding lacunae to supply Maternal sinusoids have grow into the expanding lacunae to supply

the developing membrane the developing membrane

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Hypoblast produce additional cells that migrate along the inside of Hypoblast produce additional cells that migrate along the inside of exocoelomic membrane .exocoelomic membrane .

Cells proliferate & form new cavity is known as secondary or Cells proliferate & form new cavity is known as secondary or definite yolk sacdefinite yolk sac

Large portions of Primitive yolk sack are pinches off as exocoelomic Large portions of Primitive yolk sack are pinches off as exocoelomic cystscysts

The E. mesoderm and 2 two layers of the Trophoblast together form The E. mesoderm and 2 two layers of the Trophoblast together form the the chorion. chorion. It surrounds the embryo and, later, the fetus. It surrounds the embryo and, later, the fetus.

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By end of 2By end of 2ndnd week of development, bilaminar embryonic disc week of development, bilaminar embryonic disc becomes connected to trophoblast by a band of E. mesoderm becomes connected to trophoblast by a band of E. mesoderm called the called the connecting (body) stalk connecting (body) stalk the the future umbilical cord. future umbilical cord.

Slight thickening in the hypoblast region – Prechordal plateSlight thickening in the hypoblast region – Prechordal plate

The embryo is now a bilaminar disc consisting of the:The embryo is now a bilaminar disc consisting of the: Epiblast that forms the floor of the amniotic cavityEpiblast that forms the floor of the amniotic cavity Hypoblast that forms the roof of the yolk sacHypoblast that forms the roof of the yolk sac

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Implantation begins on approximately day 5 and is completed by Implantation begins on approximately day 5 and is completed by the end of the second weekthe end of the second week

Outgrowths from the syncitiotrophoblast invade the deciduasOutgrowths from the syncitiotrophoblast invade the deciduas They erode the maternal blood vessels.They erode the maternal blood vessels. They become surrounded by trophoblastic lacunae containing They become surrounded by trophoblastic lacunae containing

maternal bloodmaternal blood A utero-placental circulation is established by A utero-placental circulation is established by day 13day 13

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Placenta Placenta Is a structure by which fetus is attached to mother & gives Is a structure by which fetus is attached to mother & gives

O2,nutrition to the embryo(fetus) & excretes waste products ,CO2 O2,nutrition to the embryo(fetus) & excretes waste products ,CO2 from fetus to motherfrom fetus to mother

FormationFormation

Maternal sourcesMaternal sources Desua BasalisDesua Basalis

Fetal sourcesFetal sources Chorion frondosumChorion frondosum

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Chorion frondosum formed by following stagesChorion frondosum formed by following stages

Primary villi Primary villi consist of syncitiotrophoblast and cytotrophoblastconsist of syncitiotrophoblast and cytotrophoblast day 13day 13

Secondary villiSecondary villi have a core of extra-embryonic mesodermhave a core of extra-embryonic mesoderm day 16day 16

Tertiary villiTertiary villi have blood vessels in the mesodermhave blood vessels in the mesoderm day 21day 21

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Abnormal implantationAbnormal implantation Normal implantation: posterior / anterior wall in the body of the Normal implantation: posterior / anterior wall in the body of the

uterus.uterus. Ectopic pregnancy/ extra uterine pregnancyEctopic pregnancy/ extra uterine pregnancy Placenta previa - Atypical placental positioning and attachment Placenta previa - Atypical placental positioning and attachment

within the lower third of uterus, which may cover the cervix in within the lower third of uterus, which may cover the cervix in part or fully.part or fully.

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