Fertilisation And Contraception Flashcards
Spermatozoa
Spermatozoal membrane (over head)-> receptors form chemo attractants, ADAM3, sperm adhesion molecules, hyaluranidase enzyme
Acrosome (inside head) contains acrosin enzyme
Mitochondria in mid piece power tail
Pre ovulatory changes in oocyte
LH surge-> progesterone surge-> first meiotic division-> secondary oocyte and first polar body
Secondary oocyte-> enters second meiotic division-> stops when chromosomes divided on second metaphase spindle
Movement of sperm from vagina to oviduct
2-7 hours Have to undergo Capacitisation Full capacity reached by isthmus Over 99% don't make it to cervix Regulated by cervix mucous consistancy Successful sperm survive for many hours in cervical crypts Transported in oviduct by own activity Linger in isthmus and become immotic Only regain motility at ovulation
Capacitation, movement capability
Changes to movement capability
Hyperactivated movement pattern-> regular wave like becomes wide whiplash
Attracted by chemorecptants from oocyte
Selective pressure created by cilia beating against sperm
Capacititation, spermatozoal surface
Stripping of glycoproteins in epidymus
Exposure to O2-> hydrogenperoxide production-> capacitation agent
-> decrease stability of plasma membranes
-> increased permeability to calcium, enhances motility and increases cAMP-> phosphorylation necessary for acrosome reaction-> increased protein kinase which phosphorylation tyrosine kinase
F actin prevents premature acrosome reaction
Fusion events, penetration of corna radiata
Secretion of hyaluranidase
Digestion of extra cellular matrix
Active movement to reach zona pellucida
Structure of zona pellucida
Three sulphates:
ZP1-> minor component, forms cross links
ZP3-> dominant binding role but only when in conjunction with ZP2
ZP2-> species specific so prevents cross fertilisation
Penetration of zona pellucida
ZP3R (on sperm head) binds to ZP3
Ca influx-> depolymerisation of F actin-> expansion of acrosome
Increase cAMP, increase pH
Acrosome fuses with with overlying membrane-> exteriorisation of inner membrane of acrosome and contents-> release of acrosin
Exposure of ZP2R-> binds to ZP2-> pulls sperm to oocyte plasma membrane
Gamete fusion
Oocyte microvilli envelope sperm head and the sperm binds to the oocyte
Requires adhesion molecules
Sperm-> desintegrins, fertili, izumol,
Egg-> integrity, alpha 6 beta1, Cd9
Post fusion, establish diploid genetic constitution
Centres one developes around sperm tail
Two centrosomes by nuclei
Nuclear envelopes interdigiate, chromosomes have duplicated
Replication of centrosomes
Nuclear envelope breakdown
Chromosomes from egg and spindle align along a single metaphase spindle
Division to produce two diploid cells
Prevention of polyspermy
Electrical activity in egg: Ca wave from internal stores every 2-3 mins Corticol reaction: Release of corticol Cleavage of ZP2 and 3 Cross linking of tyrosine residues Impenetrable zona pellucida
Avoidance of gynogenetic triploidy
Ca required, breakdown stable spindle in egg so it resumes meiosis, second half set of chromosomes release in second polar body
Sperm doesn’t bind over second metaphase spindle to avoid it fusing to second polar body
Cytoplasmic inheritance
Spermatazoon-> centriole
Oocyte-> cell membrane, cytoplasm, cell organelles, mitochondria
Parthenogenesis
Activation of oocyte in absence of spermatozoon, can occur but eventually fails as lacks centriole and parental imprinting
Parental imprinting
Chromatin wrapped around chromosomes leaves imprint that is remembered and effects the expression of encoded genes-> epigenetic change to genome
Genes effects differ in oogenic and spermatogenic lineage
