Lecture 18: Fertilization

Question 1

after insemination the spermatozoa must:

Answer 1

1. transverse the cervix
2. go through the uterus to the oviducts (aided by uterus and oviducts contractions)
3. undergo capacitation
4. find the COC
5. penetrate through cumulus cells and bind to the zona pellucida
6. undergo the acrosome pellucida reaction
7. penetrate the zona pellucida
8. fuse with the oocyte plasma membrane
9. eneter the oocyte cytoplasm and release the nucleus for decondensation and formation of male pronucleus in the newly formed zygote

Question 2

insemination occurs during estrus when…

Answer 2

the female reproductive tract is under influence of high concentrations of estradiol

• increased blood flow to the entire reproductive tract
• migration of neutrophils into the mucosa layers and lumen
• phagocytosis of foreign material
• spermatozoal losses
• prevention of infections

Question 3

sulfomucin

Answer 3

produced by epithelium in the apical portion of the cervical crypts
has high viscosity
wash sperm out of the reproductive tract

Question 4

Sialomucin

Answer 4

produced by epithelium in the basal portion of the cervical crypts
lower viscosity
allow sperm to swim towards the uterus - privileged pathways

Question 5

transport of spermin the oviducts

Answer 5

aided by:

1. mucus produced by the reproductive tract - allow sperm to swim
2. elevated tone and motility of the muscular of the female tract
   - promoted by high estradiol from the ovarian follicle(s) and prostaglandin production by sperm

Question 6

Rapid Transport phase

Answer 6

sperm reaches the oviducts within a few minutes of insemination
not viable for fertilization - it is unknown whether it serves any purpose

Question 7

Sustained transport phase

Answer 7

trickled-like transport from reservoirs (cervix and uterotubule junction)
important to fertility- more likely to fertilize the oocyte successfully

Question 8

zona pellucida - glycoprotein membrane

Answer 8

3 types (4 in some species ) of glycoprotein:

• ZP1 and ZP2= structural proteins
• ZP3: serve as a receptor for sperm proteins

Question 9

plasma membrane proteins of spermatozoa heads

Answer 9

specific proteins organized in zonas that bind specifically to receptors (ZP3)
zona binding region - promotes physical attachment
acrosomal reaction promoting region- induced initiation of the acrosomal reaction

during the acrosomal reaction, the plasma membrane overlying the acrosome begins to fuse with the outer acrosome membrane, leading to vesiculation of membranes and the formation of pores through which acrosomal enzymes can pass

Question 10

acrosomal enzymes

Answer 10

allow the spermatozoon to digest a small hole in the zona pellucida through which it can pass to enter the perivitelline space

Question 11

Sperm-Ooctye Fusion

Answer 11

an equatorial segment of the spermatozoon in the perivitelline space fuses with the plasma membrane of the oocyte

content of cortical granules are released into the perivitelline space and cause biochemical changes in the zona pellucida and plasma membrane

Question 12

zona block and vitelline block

Answer 12

prevent polyspermy fertilization which causes embryonic death

the nucleus of sperm decondensed into the cytoplasm of the oocyte

Question 13

Formation of the Maternal and Parenteral Pronucleui

Answer 13

right before fertilization:
- nucleus of the mature oocyte (2n)- arrested in metaphase II

• nucleus of the capacitated sperm (1n)- inert - highly packed with disulphide crosslinks

right after fertilization

• influx of Ca2+ induces activation of the oocyte and:
  
  • resumption and completion of meiosis II and extrusion of the 2nd polar body
  • formation of maternal pronucleus

particular cytoplasm environment of the newly fertilized oocyte induces

• decondensation of sperm chromosomes
• formation of the paternal nucleus