Anatomy Theme 1 - Embryology Flashcards
how many sperm are there per ejaculate?
25 million
where does the sperm meet the ovum?
in the ampulla 12-24 hours after ovulation
how many sperm will reach the uterine tube and how many will get to where the oocyte is?
1000 sperm reach the uterine tube and 500 get to where the oocyte is
what is the layer of cells around the ovum called?
corona radiata
what happens when the DNA of the ovum and sperm join?
the second meiotic division
what do the acrosomal enzymes do?
make sure the zone pellucid is impermeable to any other sperm
what process occurs at day 2-3
cleavage - rapid mitotic divisions
how many cells are in the embryo at day 3
16 cells
when does the first mitotic division occur
30 hours post fertilisation
what is the solid sphere of cells called at day 2-3?
the morula (each cell is a blastomere)
how do cells in a morula communicate?
via gap junctions between them
at what day does the blastocyst develop from a morula?
day 4-5
what is the cavity within a blastocyst called?
blastocele
does the blastocyst have the zone pellucida?
no
what are the cells at the top and bottom of the blastocyst called?
top - inner cell pass and the bottom is the trophoblast
what part of the blastocyst is the whole embryo derived from?
the inner cell mass
at what day is the blastocyst in the uterine tube and preparing to implant?
4-5 days
what does the inner cell mass do when as is prepares for implantation and at what day does this occur?
starts to differentiate into two layers - the epiblast and hypoblast which occurs at day 6-7
which pole of the blastocyst is in contact with the uterine wall
the embryonic pole where the epiblast is
what does the hypoblast form?
extra embryonic membranes
where does the amniotic cavity form?
within the epiblast
at what point does the yolk sac develop and where does this happen?
day 6-8 starts to develop in the hypoblast
what is the function of the yolk sac and where is it found?
found in the blastocele cavity and supplies the embryo with nutrients before the placenta develops
what does the yolk sac form when the embryo folds?
part of the gut tube
what is secreted by the corpus luteum at week two and what is the function of this?
progesterone is secreted to maintain the endometrium and stop it shedding
what are the four stages of implantation?
shedding and hatching of the zone pellucida, rotation so the embryonic pole contacts the uterine wall, adhesion via molecular communication and invasion of cytotrophoblasts into the endometrium
what does invasion of cytotrophoblasts into the uterine wall trigger in week 2?
a decimal reaction - placenta begins to be made
what is a decidua?
a very early placenta
what does the syncytiotrophoblast originate from and what does it do?
forms from the trophoblast and burrows into the uterine wall
what does the syncytiotrophoblast secrete and what does this do?
secretes HCG and this maintains the endometrium
at the start of week three, how many layers does the embryo have?
two - bilaminar disk
what process begins at week three and where is it initiated?
gastrulation and is initiated at the primitive streak
which cells migrate towards the primitive streak in gastrulation?
epiblast cells
what is the first germ cell layer made of epiblast cells dropping down?
endoderm
what happens to the hypoblast after gastrulation?
it degenerates and the epiblast forms all three germ layers
in what two planes does folding occur from week 4 onwards?
longitudinal and lateral
what day does longitudinal folding happen and what does this cause?
starts at day 21 and brings the head and tail closer together
what day does lateral folding happen and what does this cause?
starts at day 18 and brings everything inwards and the amniotic cavity down
what does lateral folding lead to?
the future gut tube being inside the peritoneal cavity
