Fertilization Flashcards
Following deposition of semen
There is some retrograde loss of semen (backflow)
Series of steps after insemination
Transverse the cervix, travel through uterus and into oviduct, find the COC, penetrate cumulus of cells and bind ZP, undergo acrosome reaction, penetrate ZP, fuse with oocyte PM
High E2 during estrus increases blood flow to repro tract
More neutrophils in mucosal layers and lumen - phagocytosis of foreign material
At time of insemination
Spike in endometrial neutrophils that diminish over 48h
Persistent Post-Breeding Endometritis (PPBEM)
Overly inflamed endometrium following insemination that hinders or prevents embryogenesis
High E2 increases….
Mucus production and muscular tone of repro tract, both of which aid transport of sperm through uterus and oviducts
Passage through cervix is selective process
Helps select more viable, healthy/motile sperm
Folds of cervix
Barrier and a reservoir for spermatozoa
Sulfomucin
Produced by epithelium in apical portion of cervical crypts, has high viscosity and helps wash sperm out of repro tract
Sialomucin
Produces in basal portion of crypts, low viscosity and allows sperm to swim towards uterus
Prostaglandin
Produced by sperm induce contraction of myometrium in conjunction with E2
Rapid Transport Phase
Sperm reaches oviducts within a few mins of insemination but is not viable for fertilization
Sustained Transport Phase
Trickle of sperm from reservoirs, these sperm are more likely to successfully fertilizle oocyte b/c sperm must reside in female repro tract
Spermatogenesis
Head of sperm is covered with glycoproteins and sterols that distinguish it as a foreign cell from rest of body
Ejaculation
Proteins of seminal plasma coat head of sperm cells and prevent immune system destruction by male repro tract
Capacitation
Seminal plasma proteins stripped from sperm cell surface, exposing binding sites and increases membrane fluidity
-gradual process occurring along path of cervix to oviducts
Uterotubal Junction
Regulates passage of sperm into oviduct
Smooth muscle and Vascular beds
Compresses lumen of oviduct to avoid excessive number of sperm and polyspermy of oocytes
Lower Isthmus
Has tunnels in mucosa for sperm docking - storage and preservation of sperm
After release from resevoir
Sperm must still move from isthmus to ampulla
Hyperactivation
Required for penetration of viscoelastic substances and for penetration of ZP
Zona Pellucida
Membrane composed of structural and sperm protein receptor glycoporteins
2 components that bind ZP3
1: zona binding region - promotes physical attachment to ZP
2: acrosomal reaction promoting region: binding initiates acrosomal reaction
Acrosomal Reaction
PM over acrosome fuses with outer acrosomal membrane (OAM) - pores form and acrosomal enzymes are secreted - enzymes digest a hole in ZP
Cortical Reaction
During membrane fusion, exocytosis of cortical granules releases contents into PS
Zona Block
Contents of cortical granules change ZP so that more sperm cannot penetrate it
Vitelline Block
Contents reduce ability of oocyte RM to fuse with sperm
After membrane fusion
Nucleus of sperm decondenses into cytoplasm of oocyte by reduction of disulfide cross-links
Before Fertilization
Oocyte nucleus is diploid (arrested in metaphase 2) and capacitated sperm nucleus is haploid
After Fertilization
Maternal and paternal pronuclei (haploid nuclei of fertilized gametes) form
Oocyte
Influx of Ca2+ induces oocyte activation and completion of meiosis 2 and expulsion of 2nd polar body - formation of maternal pronucleus
Spermatozoon
Cytoplasmic environment of newly fertilized oocyte induces decondensation of chromosomes - formation of paternal pronucleus
Syngamy
Fusion of pronuclei to form a single diploid nucleus, last step before embryogenesis
