Fertilisation Flashcards
what do sperm cells acquire in epididymis?
glycoprotein and sterol coat
what do proteases in the uterine/cervical fluid do?
removes the sterol coat and glycoprotein, this causes the cell membrane to become more permeable to calcium ions
what do calcium ions activate in sperm cells?
activate strong tail lashing and make the acrosome reaction possible later (indirectly, via cAMP)
what happens when sperm meet the zona pellucida?
undergo an acrosome reaction
what occurs during an acrosome reaction?
acrosome membrane and plasma membrane fuse at many points
acrosomal contents spill out and can digest the zona pellucida
what happens after the acrosome reaction?
acrosome reacted sperm burrow towards the oocyte, one sperm reaches the oocyte membrane and fuses with the membrane
what does fusion cause?
a wave of calcium entry, which keeps repeating ever 10 mins or so
what is the effect of calcium waves?
cortical granules are released, these alter the zona pellucida and make it impenetrable by sperm
change in polarisation which blocks membrane fusion
meiosis of the oocyte resumes
what occurs after fusion?
chromosomes decondense and form the female and male pronuclei
what are the reasons for assisted fertilisation?
blocked or absent oviducts
blocked vasa deferentia/eferentia
low male fertility
impotence
female age
what are the causes for blocked or absent oviducts?
pelvic inflammatory disease
chlamydia or gonorrhoea
congenital absence
endometriosis of earlier elective tubule ligation
stages of assisted fertilisation?
superovulation
oocyte harvesting
sperm harvesting
capacitation of sperm
mixing of sperm and oocytes
observation of early development
embryo transfer
how are oocytes harvested?
follicular aspiration
can be done laparoscopically or transvaginally
can be from either would be pregnant woman or a donor
when is the best time to do follicular aspiration?
before follicle is released, the granulosa cells are cleaned away with a fine needle
how is sperm harvested?
usually masturbation
can be done by aspiration from epididymis or even testis for ICSI
what is capacitation?
artificial mimicking of the female environment
how are sperm and oocytes mixed?
placed in a test tube together
intra-cytoplasmic sperm injection (direct injection of sperm into oocyte if sperm does not function properly)
what occurs during observation?
often genetic testing of 1 cell
what does the new embryo have to do?
gorw much bigger (adults are 1 million times larger than a fertilised egg
create internal differences
organise the axes and complex anatomy of the body
what is cleavage?
mitosis with no growth
when is development most likely to fail?
activation of embryonic transfer
what begins at the 4 cell stage?
mRNA synthesis from embryo’s own DNA begins
maternal mRNA is destroyed at an increasing rate
what is the morula?
ball of cells - cells on the inside have contact all round, cells on the outside have a free surface
how does the morula begin to differentiate?
cells on the outside specialise into a simple epithelium and eventually form the placenta (trophoblast)
inner cells mass does not specialise (blastocyst)
what does the blastocyst do?
hatches through the zona pellucida
when does implantation occur?
2nd week after fertilisation, prior to this the embryo is unattached and travels down the fallopian tube
what is implantation?
when the trophoblast of the hatched blastocyst invades the uterine epithelium
what odes the trophoblast develop into?
placenta
