Fertilization and Embryo Development 

The stage of the embryo that is finally eligible for implantation on the uterine surface 

THE  OOCYTE AT OVULATION 

ovulation in the human embryo when the oocyte has reached the meta phase of the second meiotic division. it carries a haploid set of 23 chromosome which lies in the previtline space.the human oocyte is approximately 100 microns in diameter and surrounded by two layers of distinctly recognize layer of cells. the immidiate surrounded layer is the corona radiates . which has cell process interdigitating with the micro-villi of oocyte,transfering nutrients, and proteins.

THE SPERMATOZOON AFTER SPERMATOGENESIS 

The human spermatozoon once relesed in the ejaculate consist of a head, mid piece and a tail. The entire spermatozoon like other cell is enclosed within a plasma membrane. The head has a flattened pyriform shape, measuring 4-5 micrometer in length and 2.5 - 3.5 micrometer width. The head has a large nucleus made up 23 compacted chromosome and an apical ridge 

CHANGES IN GAMETES  PRIOR TO FERTILIZATION 

The oocyte unlike the sperm undergoes less changes prior to fertilization while getting in the ampula of the fallopian tube. perheps the main changes undergone by the oocyte are maturation   accomplish by expansion and loosening of the cumulus  and corona cell and migration of the cortical granules before fertilization. since oocyes are aspirated at various stage of maturation in the in vitro fertilizzation procedure, a brief incubation 4-6 hours at 37`c, in a 6% CO2 incubator is necessary to complete maturation in many oocyte. The sperm before it can engage itself in fertilization undergoes change as follows 

capacitation 

Acrosome rea ion 

Hypermotility 

FERTILIZATION 

Fertilization involves the union of two germ cells, sperm and oocyte and this occurs in the ampula  of the Fallopian tube. fertilization sperm usually binds to the surface of the zona pellucida before penetrating it. There is a strong correlation between the degree of zonal binding and fertilization rates. Zonal receptor and sperm receptor have been recently shown to exist and these complement each other before fertilization once the spern enters the previtline space, the inner membrene of the sperm fuse with the oolemma of the oocyte. The plasma membrane above the equatorial segment fuses first with the oolemma. upon fusion of the two membrane the oocyte undergo the activation phenomenon. This involves the following steps 

Resszumption of meiosis 

Exocitosis of cortical granules 

EARLY EMBRYONIC DEVELOPMENT 

After formation of the zygote, the early human preimplantation embnryo undergoes clevage through simple mitotic division while within the ampulaa of the isthmus of the fallopian tube up to the late morulla or early cavitation blastocyst stage. Thereafter it descends to the uterus is still surrounded by the zona poellucida. clevage take place reletively slowly in the human with the first division 

ANALYSIS OF EMBRYO MORPHOLOGY 

The pronuclear Embryo 

the early clevage 

the clevage stage embryo 

THE BLASTOCYSTS 

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