Fertilization and Implantation Physio Flashcards
Steps of Fertilization
1) Sperm binds ZP3 of Zona Pellucida
2) Calcium triggers acrosomal reaction
3) Zona Pellucida dissolved, sperm penetrates
4) Zygote membranes fuse, sperm DNA inserted
5) Calcium triggers cortical reaction
6) Calcium triggers oocyte to complete Meiosis II
7) Male pronucleus formed
8) Male and Female pronuclei fuse
Acrosomal Reaction Description
Hydrolytic enzymes released by sperm to dissolve zona pellucida for penetration
Cortical Reaction Description
Zona pellucida hardens to prevent polyspermy
Female Gamete After Meiosis II
Ploidy and Created Structure
Oocyte is haploid (1n)
Second Polar body formed
Estrogen and Progesterone Effects on Uterus
Estrogen makes uterus secretions watery and causes contractions to move sperm to uterine tube
Progesterone makes uterus secretions thick and sticky
Capacitation Description
Sperm loses glycoproteins and carbohydrates to free up ZP3 receptors
Sperm loses cholesterol to soften head
Inhibitory factors washed away
Sperm increases calcium permeability to facilitate acrosomal reaction
hCG Functions and Secreting Cells
Secreted by syncytiotrophoblasts
Sustains the corpus luteum when LH drops
Increases trophoblast growth
Helps placental development
Implantation Steps
1) Hatching - facilitated by proteases from trophoblast
2) Apposition - initial contact, ICM faces endometrium
3) Adhesion - Trophoblast attaches via Ligand-Receptor interaction
4) Invasion - Syncytiotrophoblasts invade endometrium
Decidualization Description
Progesterone causes increased glycogen in endometrial cells in order to sustain developing embryo
Placentation Steps
1) Cytotrophoblasts create primary chorionic villi
2) EE Mesoderm mesenchymal cells invade to form secondary chorionic villi
3) Mesenchymal cells make vasculature turning it into tertiary chorionic villi
Syncytiotrophoblast
Structures, Functions and Secretions
Has cadherin and integrin binding proteins
Invades endometrium and breaks down ECM with metalloproteases and serine proteases
Secretes hCG, progesterone and TNF-alpha
Early Embryogenesis Stages with Days
1st cleavage by day 2
16 cell morula by day 3
Blastocyst by day 4-5
Implantation by day 6-7
