fertilisation and embryogenesis Flashcards
what are the requirements for conception
functioning gametes
patent reproductive pathway
how long can the gametes survive if fertilisation doesn’t occur
sperm - 5 days
egg - 1 day
describe the process of a sperm entering an egg
sperm has hydrolytic enzymes that act on the zona pellucida and vetelline layer of the egg
once it has entered a chemical reaction occurs which causes the plasma membrane to thicken so no more sperm can enter
what happens if more thsn one sperm fertilises an egg
this is abnormal and abnormally fertilised eggs are not viable
can cause a molar pregnancy
what is the pronuclei
when the sperm has entered the egg and there are two nuclei in the egg
when does the first cell division occur
day 2
what day does the morula form
day 4
when does the blastocyst form
by day 5
what is the structure of a blastocyst
outer trophoblast layer
inner cell mass/endoderm
what is adhesion
trophoblast adheres to endometrium
what is hatching
trophoectoderm cells produce protease to dissolve zona pellucida (protective layer)
what is apposition
trophoblast cells adhere to epithelial layer of endometrium
when does hCG get produced
when apposition occurs
what is invasion
trophoblast proliferates and differentiates
crosses epithelium BM and invades endometrial stroma
forms placenta
remodels uterine spiral arteries
what are the four steps of implantation
hatching
apposition
adhesion
invasion
what is required for invasion to take place
the endometrium needs to have under gone decidualisation
transformation of endometrium into a vascular receptive tissue for blastocyst invasion
what regulates the steps of implantation
hormones cytokines growth factors regulators free oxygen radicals
what hormone mediates decidualisation
progesterone
what changes to the endometrium occur in decidualisation
stromal cells differentiate from elongated fibroblast like cells to rounded epithelial decidual cells
angiogenesis
increase in macrophages, lymphocytes, leukocytes
what is the process of placentation
invading trophoblast forms primary villi
secondary villi infiltrate the embryonic mesoderm
tertiary villi have developed capillaries
the cytotrophoblast remodels spinal arteries to increase blood flow to embryo
what is a mature placenta formed from
chorionic villi
intervillous space
placental septae
cotyledons
what are the functions of the placenta
immunological barrier gas exchange nutrient exchange waste excretion endocrine functions secretion of hCG to maintain pregnancy
what is embryogenesis
first 8 weeks of development
when is the bilaminar disk formed and when does it differentiate into the trilaminar disk
formed week 2-3
differentiates into trilaminar disk week 3-4
what is the structure of the bilaminar disk
made up of epiblast and hypoblast
two cavities form either side of it
where are the amniotic and yolk sac cavities in relation to the hypoblast and epiblast
amniotic cavity is between the epiblast and endometrium
yolk sac cavity is below the hypoblast
what forms the bilaminar disk
pluripotent cells of the inner cell mass of the blastocyst
what happens to the epiblast layer of the bilaminar disk
undergoes gastrulation to form the three germ layers
what is the process of gastrulation
primitive streak appears at caudal end of epiblast
epiblast cells displace hypoblast cells forming the endoderm
epiblast cells migrate through primitive streak and form mesoderm
remaining epiblast becomes endoderm
what are the three layers in the trilaminar disk
ectoderm
mesoderm
endoderm
what does the ectoderm form
epidermis central and peripheral nervous system hair nails neuroendocrine organs enamel of teeth
what does the mesoderm form
dermis MSK structures CVS kidneys ureters trigone of bladder gonads adrenal cortex visceral and parietal linings
what are the mesoderm subunits
paraxial
intermediate
lateral plate
what part of the mesoderm forms kidney, ureter and gonads
intermediate mesoderm
what is a dizygotic pregnancy
two or more eggs fertilising and implanting
note: different eggs
what is a monozygotic pregnancy
one embryo splitting
produces identical twins
less common
what does dichorionic diamniotic mean
twins with separate placentas and amniotic sacs
what does monochorionic diamniotic mean
twins that share a placenta but have separate amniotic sacs
most common
what does monochorionic monoamniotic mean
twins that share a placenta and an amniotic sac
what are conjoined twins
twins that share a placenta, amniotic sac and have joined up organs
how does egg splitting in monozygotic twins impact on placental/amniotic sac sharing
later splitting = less separated
if egg splits early twins will have separate placenta and amniotic sac
if egg implants in womb then splits there will be a shared placenta and separate amniotic sacs
if the egg implants then splits later on there will be a shared placenta and sac
