M, Embry, Lecture I

8/10/2019 M, Embry, Lecture I

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Lecture ILecture I

Fertilization:Fertilization:Site.Site.

Time.Time.Sperm conditioning.Sperm conditioning.ProcessProcess of of fertilization.fertilization.ResultsResults ofof fertilization.fertilization.

Applied.Applied.


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FertilizationFertilization

@ Fertilaziation@ Fertilaziation is fusion between a singleis fusion between a single spermsperm and anand an ovumovum to form ato form a zygotezygote ..

@ Site:@ Site: It occurs inIt occurs in ampullaampulla (( lateral !"lateral !" ) of uterine) of uterinetube.tube.

@ Time:@ Time: WithinWithin #$ %ours#$ %ours from ovulation. Secondaryfrom ovulation. Secondaryoocyte is viable for only 24 hours by that time, itoocyte is viable for only 24 hours by that time, ithas just reached lateral !" of #allo$ian tube.has just reached lateral !" of #allo$ian tube.

@ &uration:@ &uration: It lasts for 24 hours.It lasts for 24 hours.


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@ Fertilaziation@ Fertilaziation is $recededis $receded byb

y sperm conditioningsperm conditioning (Where(Wheres$erms de$osited in female genital tract must undergos$erms de$osited in female genital tract must undergo t'ot'oc%angesc%anges before they can fertili%e an ovum).before they can fertili%e an ovum).

( )apacitation( )apacitation ofof sperms:sperms: ** It occurs inIt occurs in uterusuterus andand uterine tu+euterine tu+e and ta&es ' hours.and ta&es ' hours. ** lyco$rotein coat and seminal $lasma $roteins are removed fromlyco$rotein coat and seminal $lasma $roteins are removed from cell membrane covering acrosomal ca$ of s$erms, whichcell membrane covering acrosomal ca$ of s$erms, which

increasesincreases activityactivity of s$erms.of s$erms.

#( Acrosome reaction#( Acrosome reaction of of sperms:sperms: ** It occurs only inIt occurs only in ampullaampulla ofof uterine tu+euterine tu+e , only when ca$acitated, only when ca$acitated

s$erms come in contact with secondary oocyte, under in uence of as$erms come in contact with secondary oocyte, under in uence of asubstance $roduced by corona radiata.substance $roduced by corona radiata.

** #usion occurs between outer acrosomal membrane and cell#usion occurs between outer acrosomal membrane and cell

membrane of corona radiate with relase of acrosomalmembrane of corona radiate with relase of acrosomal enzymesenzymes .. ** *ulti$le $erforations develo$ in acrosome of s$erms leading to*ulti$le $erforations develo$ in acrosome of s$erms leading torelease of en%ymes (acrosin, %onalysin, hyaluronidase) thatrelease of en%ymes (acrosin, %onalysin, hyaluronidase) thatfacilitatefacilitate $rocess of$rocess of fertilizationfertilization ..

,, +yaluronidase -igestion of corona radiate.+yaluronidase -igestion of corona radiate.

,, crosin and %onalysin $enetration of %ona $ellucida.crosin and %onalysin $enetration of %ona $ellucida.


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ProcessProcess of of fertilization:fertilization:

@ Penetration@ Penetration ofof corona radiatacorona radiata byby manymany s$erms with aid ofs$erms with aid ofhyaluronidase.hyaluronidase.

@ Penetration@ Penetration ofof zona pellucidazona pellucida by aby a singlesingle s$erm, followeds$erm, followedimmediately byimmediately by zonal reaction -zona +loc (zonal reaction -zona +loc ( , which ma&es, which ma&es%ona $ellucida im$ermeable to other s$erms.%ona $ellucida im$ermeable to other s$erms.

@ Penetration@ Penetration of of vitelline mem+rane:vitelline mem+rane: #usion of cell#usion of cellmembranes of s$erm and secondary oocyte. /nly head andmembranes of s$erm and secondary oocyte. /nly head and

nec& of s$erm $enetrate forming male $ronucleus. 0itellinenec& of s$erm $enetrate forming male $ronucleus. 0itellinemembrane (now calledmembrane (now called fertilizationfertilization mem+ranemem+rane ) becomes) becomesim$ermeable to other s$erms. 1his is called cortical reaction orim$ermeable to other s$erms. 1his is called cortical reaction orvitelline +loc vitelline +loc .. 1his is immediately followed by com$letion of 1his is immediately followed by com$letion ofsecond meiotic divisionsecond meiotic division of secondary oocyte forming aof secondary oocyte forming amature ovummature ovum and aand a second polar +odysecond polar +ody ..

@ Formation@ Formation ofof malemale andand female pronuclei:female pronuclei: ,, ucleus of head of s$erm se$arate and enlarge to formucleus of head of s$erm se$arate and enlarge to form malemale pronucleuspronucleus .. ,, ucleus of mature ovum formsucleus of mature ovum forms female pronucleusfemale pronucleus ..

@ Fusion@ Fusion of of malemale andand female pronucleifemale pronuclei with loss of theirwith loss of their

nuclear membranes to form a new cell callednuclear membranes to form a new cell called zygotezygote ..


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ResultsResults of of fertilization:fertilization:

A(A( InIn zygote:zygote:** Secondary oocyte com$letes itsSecondary oocyte com$letes its second meiotic divisionsecond meiotic division , giving rise to a, giving rise to a

mature ovummature ovum andand second polar +odysecond polar +ody ..** 3estoration of3estoration of diploid num+erdiploid num+er ofof c%romosomesc%romosomes (4 ).(4 ).** InitiationInitiation of of cleavagecleavage of %ygote, which is a series of ra$id successiveof %ygote, which is a series of ra$id successive

mitotic divisions.mitotic divisions.** Se/ determination:Se/ determination: ,, #ertili%ation by#ertili%ation by 00 5 bearing s$erm will form 66 %ygote giving rise to a5 bearing s$erm will form 66 %ygote giving rise to a

femalefemale .. ,, #ertili%ation by#ertili%ation by 1 1 5 bearing s$erm will form 67 %ygote giving rise to a5 bearing s$erm will form 67 %ygote giving rise to a

malemale ..

2(2( InIn ovary:ovary:** 3vulation stops3vulation stops due to feed bac& inhibition of $ituitary gland by highdue to feed bac& inhibition of $ituitary gland by high

levels of oestrogen and $rogesterone $roduced by ovary.levels of oestrogen and $rogesterone $roduced by ovary.** )orpus luteum)orpus luteum enlargesenlarges and formsand forms corpus luteumcorpus luteum of of pregnancypregnancy ,,

which remains active for 8rst half of gestation.which remains active for 8rst half of gestation.

)()( InIn uterus:uterus:** 4enstrual cycle stops4enstrual cycle stops ..** Secretory $hase of endometrium (under e9ect of hormones of cor$usSecretory $hase of endometrium (under e9ect of hormones of cor$us

luteum) continues to grow formingluteum) continues to grow forming deciduadecidua of of pregnancypregnancy ..


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2( Applied:2( Applied:

#( In7 8itro Fertilization -I8F(:#( In7 8itro Fertilization -I8F(:@@ method of treatment in method of treatment in sterilitysterility , es$ecially if there is, es$ecially if there is occlusionocclusion ofof

#allo$ian tubes. Wife is given a drug to stimulate multi$le ovulations.#allo$ian tubes. Wife is given a drug to stimulate multi$le ovulations.Secondary oocytes are collected by an endosco$e and are $ut in aSecondary oocytes are collected by an endosco$e and are $ut in aglass $late containing a s$ecial uid medium. S$erms collected fromglass $late containing a s$ecial uid medium. S$erms collected fromhusband are added immediately. fter fertili%ation is observed underhusband are added immediately. fter fertili%ation is observed undermicroso$e, dividing %ygotes are transferred to uterus of wife. Successmicroso$e, dividing %ygotes are transferred to uterus of wife. Successrate is low and $rocedure is very e:$ensive.rate is low and $rocedure is very e:$ensive.

"( Part%enogenesis:"( Part%enogenesis:@@ nn unfertilized oocyteunfertilized oocyte ty$icallyty$ically diesdies within 24 hours. In e:tremelywithin 24 hours. In e:tremelyrare occasions, it may undergorare occasions, it may undergo spontaneous cleavagespontaneous cleavage and grows toand grows toform anform an em+ryoem+ryo . 3esulting embryo is de8nitely a. 3esulting embryo is de8nitely a femalefemale ((0000 ). 1his). 1hismay occurmay occur inin animalsanimals butbut notnot in humans.in humans.

$( )%romosomal anomalies:$( )%romosomal anomalies:A(A( Se/Se/ c%romosome anomalies:c%romosome anomalies: ,, Turner syndromeTurner syndrome (44= 6/)(44= 6/) :: FemaleFemale with rudimentary ovaries.with rudimentary ovaries.

,, 9linefelter syndrome9linefelter syndrome (44= 667)>(44= 667)> 4ale4ale with rudimentary testis.with rudimentary testis.

2(2( AutosomalAutosomal anomalies:anomalies: re$resented byre$resented by &o'n syndrome&o'n syndrome orortrisomytrisomy ofof c%romosome #c%romosome # ((mongolismmongolism ) in which %ygote contains) in which %ygote contains

4' chrosomes either 4?= 67 (male) or 4?= 66 (female).4' chrosomes either 4?= 67 (male) or 4?= 66 (female).


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M, Embry, Lecture I