sheet no.34

At ovulation (day 14) the secondary oocyte usually come from the ovary due to the effect of surge (large amount) of luteinizing hormone, at that time it is ready for fertilization.
Each ovulated secondary oocyte at that time is covered by 2 layers :-
-outer layer (corona radiata) which is part of the follicular cells.
-inner layer (zona pellucida) a transparent layer which is produced by the outer follicular cells and composed of glycoprotein.
(the secondary oocyte is in 2nd meiotic stage)


Fertilization:


A process by which haploid male gamete fuse with female gamete to give single diploid nucleus.
Normally occurs 12-24 hours after ovulation while the ovum in the upper part of uterine tube.
N.B
(-only 300-500 sperms out of 300 million can reach ampulla where only one of these fertilize the oocyte
-the trip from cervix to oviduct needs 2-7 hours)
Arrived sperms are unable to fertilize oocyte except after 7 hours of conditioning in female genital tract for
1. capacitation: epithelial interaction between sperms and mucosa.
Only capacitated sperms can enter corona radiata and undergo acrosomal reaction
2. acrosome reaction:
Acrosome which is located at the head of sperm enter the ovum in 3 steps:
*penetration of corona radiata :( not all of sperms enter the corona radiata but only many of them enter) by entering the corona radiata, corona radiata will change interaction with other sperm
*penetration of the zona pellucida: the acrosome will secrete digestive enzyme locate in the acrosome which called acrosomal enzyme specially acrosin which is received by receptors on zona pellucida called ZP3 glycoprotein which act as sperm receptors that trigger acrosin to digest a path through zona pellucida.
*fusion of membranes: after gametes are contacted membranes of gametes fused, head and tail of the sperm penetrated into the cytoplasm
Oocyte response
1- cortical and zona reaction:-depolarization of oocyte membrane prevent poly spermy(entering of more than one sperm) -inactive ZP3
2-resumption of 2nd meiotic division: female pronucleus + 2nd polar body
3-meta bolic activation of oocyte
Result of fertilization:
1-restore diploid number of chromosomes
2-stimulate resuming 2nd meiotic division
3- determines the genetic sex of the new individual
4-initiates cleavage about 24 hours post-fertilization


After fertilization of secondary oocyte it will form female pronucleus and there will be a male pronucleus

Male pronucleus will approximate female and sharing same membrane and chromosome will intermediate (the DNA will duplicate) , then the 2 pronucleii fused forming onr membrane (one nucleus) with male and female chromosome which will aline at equator , then division will occur to give two-cell stage.

Morula: a ball of cells appearing from outside and (the number of cells is 16 at the early morula but it will become 32 at late marula) it will start entering the uterine tube.
At day 6 it will wander inside uterus
(N.B the uterus at that time is in secretary stage under control of progesterone)
When arrive this area the secretion will enter inside the marula
The fluid of uterine will enter between the marular cells separating it into:
-inner cell mass (Embryoblast) which give the embryo
-outer cell mass (trophoblast)
-cavity

At this stage the morula is ready for implantation.

To all my friends specially:

A7md 2bo-7lawe, yazeed al-naif, 5aled 7ajjir, mo2ayyad kettane ,yazeed qayseye, osama 5aleel, qusai al 3azzam, a7md 2bo 5deje, a7md al-shalabi,
Amjd 3yyash (el 8a2ed el ramz), 7amze jassar,m7md al faqeeh, 3omar el 7aj,
Yazan 3toom, nidal matani, m7md qteshat(mesh naseek ylle nasene), m7md sboo3, a7md 7ra7she, 9ohaib el 3badi, ibrahim 2bo deyye ,ibrahim el 93idi, hmmam ryalat, 7azem, m7md tyseer, sami 3abdeen, a7md el 3esa, 3bd el ra7man 3attili, mo3ath el zo3bi, martin qaqeesh, 3'aleb 5erfan, m7md bdr,
m7md 2bo haneye, zaid qandeel, 3amer 7jaj, 3omar el-lozi, mo2men k7aleh, m7md qawasmeh
w slam 5a9 la el shbab msh el 6eb:
Muhannad bdair(Hannood)
Wa2el 3lawne
Nusaiba el jalodi
3omar smrain
Special thanks to yazan 3toom

****With best wishes from
Ma2moun sha3ban

"don't limit your challenges ,but challenge your limits"