Lecture 4 Fertilization Flashcards
Describe capacitation
- required to undergo acrosomal reaction
- occurs in the uterine tube in isthmus
- binding of sperm to epithelium
- involves removal of cholesterol from sperm surface and removal of glycoproteins
- followed by sperm hyperactivity
What are the steps in fertilization?
- penetration of the corona radiata
- attachment to zona pellucida
- acrosomal rxn and penetration
- binding and fusion of sperm and egg
- prevent polyspermy
- metabolic activation of the egg
- decondensation of sperm nucleus
- completion of meiosis
- development and fusion of male and female
Describe the penetration of the corona radiata.
Fusion of the outer acrosomal membrane with the sperm plasma creates portals for acrosome release (with hyaluronidase)
fragmentation of the membrane with aid of swimming movements from the sperm to penetrate
What is the function of hyaluronidase?
helps to break down the hyaluronic acid component of the intercellular matrix between the corona radiata cells
Describe the steps of the acrosomal reaction
- ZP3 mediates the attachment of the sperm to the ZP and stimulates the acrosomal reaction via G proteins
- massive Ca2+ influx through the plasma membrane
- exchange of sodium and hydrogen ions (increases pH)
- sperm penetrates via acrosin
What is the function of acrosin?
digests a small hole through the ZP and assists in the penetration of the sperm
Describe the fast block of polyspermy
- rapid depolarization of the egg plasmalemma (-70 to +10mV in 2-3 seconds)
- temporarily prevents polyspermy and allow the egg to develop the slow block
Describe the slow block to polyspermy
-release of polysaccharides from the cortical granules under the plasmalemma of the egg
(hydration produces swelling that increases the width of the perivitelline space)
What are the two final steps of fertilization and briefly describe them?
- metabolic activation of the egg- via calcium release following the phospholipase C activation by the sperm
- Decondensation of the sperm nucleus- tightly packed sperm chromatin comes more loosely packed and male pronuclear is established
this leads to meiosis in oocyte and the organization for he mitotic spindle in the sperm centrosome
What is the function of the released calcium that occurs in the metabolic activation of the egg?
- blocks polyspermy
- stimulates increase in egg respiration and metabolism vis the NA-H exchange
- increase in pH and oxidate metabolism
Define pronucleus
nuclear material of the head of the sperm or the oocycyte after it has been penetrated
haploid
female pronucleus usually has a type of membrane surrounding genetic material
Define zygote
single celled stage in which the male and female pronuclei have fused together and share a membrane
Describe the two pregnancy dating systems
- fertilization age: date the age of the embryo from time to fertilization
- menstrual age: dates age of the embryo from the last menstrual period (2 weeks greater than fertilization)
