Coitus, fertilisation and implantation Flashcards
what is the EPOR model of sexual response
excitement- sexual arousal, tumesence and erection, engorgement,
plateau- intensification of arousal
orgasm- involuntary muscular contractions with intense pleasure
resolution- rearousal may be impossible
what is the length of the luteal phase
14 days
follicular phase is more variable
what is the time window for fertilisation
3 days before ovulation up to 1 day after
what percentage of pregnancies miscarry
10-15%
what proportion of couples are subfertile?
5%
what proportion of intercourse results in a blastocyst
20%
what proportion of blastocysts fail to implant
15%
what percentage of clincally detected pregnancies fail
15-20%
what proportion of conceptions survive until birth
20%
how long is the embryonic period
8 weeks
how long is the foetal period
8-40 weeks
what is the function of cumulus cells
aid transport from the surface of the ovary
cling to the ciliated surface of the fimbriae
why is sperm mortality high
acidic vagina
length and energy requirement of trip
describe capacitation
change from wavelike beats to whip like action to propel sperm
sperm plasma membrane is altered
destabilisation to enhance fusion with oocyte
increase in Ca permeability, removal of membrane proteins
depletion of cholesterol
where does ferlisation normally occur
ampulla
what does the sperm bind to
zona pellucida
what does a rise in Ca inside the sperm cell trigger
exocytosis of the acrosome which contains hydrolytic enzymes
what glycoproteins are involved in the acrosome reaction
ZP3 and ZP2
describe the acrosome reaction
fusion of the acrosome plasma membranes
releases contents of the acrosome, causes entry of more calcium
sperm digest the zona pellucida
describe fertilisation
- The sperm cell weaves past follicular cells and binds to the zona
pellucida. - A rise in [Ca2+]i
inside the sperm cell triggers the exocytosis of the
acrosome (acrosomal reac/on) which contains hydroly/c
enzymes. - Hydroly/c enzymes contained in the acrosomal cap are released.
These enzymes locally dissolceolve the zona pellucida. The whiplike
ac/on of the tail pushes the sperm head towards the oocyte
membrane. - With the head of the sperm now on lying sideways, microvilli on
the oocyte surround the sperm head. The two membranes fuse.
The contents of the sprem-cell enter the oocyte; the sperm-cell
membrane remains behind.
A rise in [Ca2+]i
inside the oocyte triggers the cor/cal reac/on, in
which there is exocytosis of granules that previously lay
immediately beneath the plasma membrane. The enzymes
released lead to changes in the zona-pellucida proteins, causing
the zona-pellucida to harden, preven/ng the entry of other
sperm cells. - The rise in [Ca2+]i
inside the oocyte induces the comple/on of the
oocyte’s second meio/c division and the forma/on of the second
polar body, which usually lies next to the first polar body. - The sperm head enlarges to become the male pronucleus.
- The male and female pronuclei fuse.
a. Sperm contributes its nuclear material and centrioles
b. All other organelles are present in the oocyte cytoplasm
c. Mitochondrial DNA inherited exclusively via maternal route
how long does it take for the blastocyst to reach the uterine cavity
5 days
when does hCG get secreted
from 9 days onwards
what are totipotent cells
can form all the cell types in a body, plus
the extraembryonic, or placental, cells. Embryonic cells
within the first couple of cell divisions a^er fer/liza/on
are the only cells that are to/potent.
what are pluripotent cells
can give rise to all of the cell types that
make up the body; embryonic stem cells are considered
pluripotent.
what are multipotent cells
can develop into more than one cell
type, but are more limited than pluripotent cells; adult
stem cells and cord blood stem cells are considered
mul/potent.
what does the trophoblast form
the placenta
inner cytotrophoblast and outer syncytiotrophoblast which invade the endometrium
what is the cortical reaction
a rise in Ca inside the oocyte triggers exocytosis of granules that lay immediately beneath the plasma membrane
this leads to changes to the zona which hardens to prevent entry of sperm
what triggers the completion of the oocytes second meiotic division
rise in Ca
what forms the male pronucleus
the head of the sperm enlarging
what surrounds the sperm head when it lies sideways against the oocyte
microvilli
this causes the two membranes to fuse
when does implantation happen
day 7
