Fertilization and Implantation and Week 1 post-fertilization Flashcards
What is fertilization?
fusion of 1 male gamete with 1 female gamete
What are the 7 requirements for in vivo fertilization?
- Successful coitus including release of semen into vagina
- Adequate numbers of competent spermatozoa
- Ability of spermatozoa to overcome obstacles in female genital tract
- Ovum must encounter competent spermatozoon within 24hrs of release
- Ovum must be free from structural and chromosomal abnormalities.
- Female genital tract must be free from infections and appropriately primed by sex hormones.
- Spermatozoa undergo 2 processes in the female genital tract to prepare them for fertilization
What are the 2 processes spermatozoa go through to prepare them for fertilization?
- Capacitation
2. Acrosomal reaction
When does fertilization occur?
Occurs when there is a binding and fusion of the oocyte and sperm cell membranes.
What does fertilization first result in?
Release of paternal chromosomes from sperm head into oocyte to form male pronucleus
The 6 immediate events of fertilization are
- Completion of 2nd meiotic division of oocyte, formation of female pronucleus and expulsion of secondary polar body.
- Formation of zygote by fusion of male and female pronuclei
- Determination of genetic sex of zygote
- Restoration of diploid number of chromosomes (46)
- Introduction of genetic variation
- Initiation of cleavage of zygote
What results in genetic variation in a zygote?
- Crossing over
2. Independent assortment of chromosomes
What is cleavage?
the successive mitotic divisions of zygote
When does cleavage commence?
Commences 24hrs post-fertilization
What are the daughter cells in cleavage called?
blastomeres
What encloses blastomeres?
zona pelucida of precursor ovum
Where does cleavage occur?
Within the oviducts
What happens between divisions and to nuclear to cytoplasmic ratio?
no growths between divisions
nuclear to cytoplasmic ration decreases about 1000 fold (G1 is almost absent)
What happens to the cell cycles during cleavage?
they are unusual lacking or having very short G1 and G2 phases
Cleavage continues throughout
first week
What is a morula?
ball of blastomeres from 16-cell stage
During week 1 post-fertilization?
morula is transported from the oviduct towards the cavity of the uterus
What happens if the zona pellucida splits during cleavage?
monozygotic twinning will occur
When do blastomeres differentiate into 2 cell groups?
5-7 days post-fertilization
What are trophoblasts?
one of the group of cells from blastomeres that form a single peripheral layer around a cavity filled with fluid.
What happens to the remaining cells after trophoblast formation?
they aggregate inside the ball of cells and are known inner cell mass or embryoblasts
What is a blastocyst?
the resulting structure from the grouping of blastomeres
What’s the 1st stage of obvious cell division?
blastocyst formation
What do embryoblasts give rise to?
embryo or foetus
What do trophoblasts give rise to?
placenta, chorion and umbilical cord(major components of foetal membranes)
