Embryology 1,2/ Flashcards
when is the blastocyst formed?
day 5-6
which hormones help the endometrium grow?
progesterone and oestrogens
where does fertilisation happen most of the time?
distal end of fallopian tube
is the uterin tube capable of carrying out a pregnancy? what could happen?
no, could damage tube and this has complications
what cavity is on top?
amniotic
what cavity is on the bottom?
yolk sac
when does implantation happen?
2nd week
how many surfaces does the placenta have?
2 (maternal surface and fatal surface)
how do you know when the gastrulation process is complete?
3 layers are present
where does the notochord form?
mesoderm
how does the notochord act on the primitive line?
sends signals
what happens to the primitive line? what’s its new name?
thickens and becomes the neural plate
what happens to the neural plate?
sinks down and forms a tube (separates from the ectoderm)
what layer produces somites?
mesoderm
what does the mesoderm divide into?
3 plates on each side (lateral, intermediate, paraxial)
what happens to the para axial mesoderm?
it segments
how many pairs of somites do they segment in?
about 43
what happens to the lateral late mesoderm?
splits between the somatic and splanchnic side
NEW when is the pre-embryonic phase?
0-3 weeks
when is the embryonic phase ?
4-8 weeks
when is the foetal phase?
9-40 weeks
TRUE/FALSE spermatogenesis and oogenesis are made through mitosis
FALSE meiosis
what does spermatogenesis start with? end with?
starts with a spermatogonium (46 chromosomes), ends with 4 sperms (22+X or 22+Y)
what does oogenesis start with? end with?
starts with an oogonium (46 chromosome), ends with 3 polar bodies (which degenerate) and a 1 ovum (22+X)
what is the other name for sperm and ovum?
gametes
can a sperm penetrate the female gamete if it’s the only sperm around?
no, fertilisation requires that several sperms surround the ovum
what happens during fertilisation?
(pro)nucleus of sperm enters and fuses with the (pro)nucleus of ovum to give a diploid cell
what is the diploid cell formed during fertilisation called?
zygote
what happens during week 1 of pre-embryonic phase?
- zygote is formed; divides to form a blastocyst
- moves through uterine tube, to reach uterine cavity
how many chromosomes does the zygote cell have?
46 (diploid)
why is it genetically unique?
because it has 23 of mum’s & 23 of dad’s chromosomes
which parent does the mitochondria and organelles come from?
the mum
what structure is formed by the first cells of the division of the zygote?
morula (solid ball of cells)
what are examples of mitochondrial diseases?
Leber’s hereditary optic (neuropathy -> blindness)
in what ways are mitochondrial diseases transmitted?
inherited from mother
what happens as the morula increases in size?
getting nutrition to the central core of cells becomes difficult
how is this issue dealt with?
a cavity called the blastocystic cavity develops
what is the outer lining of cells called?
the trophoblast
what happens to the rest of the cells?
they accumulate at one end to form an inner cell mass
does the speed of the first divisions remain constant?
no (divisions accelerate at the beginning, 36h for first, 24h for 2nd, 12h for 3rd)
what happens in the ovary before fertilisation?
ovum is released from ovary
by what time is the blastula ready to implant?
5-6 days
where does the blastula implant?
in the uterine cavity
what does the dividing zygote/ morula/ blastocyst rely on to move from fallopian tube to uterine cavity?
healthy ciliated epithelium in the fallopian tube
what is an ectopic pregnancy?
when the implantation happens outside the uterine cavity
what happens during week 2 of pre-embryonic phase?
- implantation, placenta begins to develop
- cells form a bilaminar disc
- sacs, membranes and cord to nourish the human conceptus (baby) start to form
where does implantation usually occur?
uterine endometrial layer
when might implantation start in the early cases?
day 6 of 1st week
when does implantation usually start?
at 7 days
what happens during implantation?
blastocyst begins to burrow into the uterine wall (endometrium)
what cells does the chorion come from?
trophoblast cells
in how many layers does the trophoblast divide into?
2
what are chorionic villi?
finger like processes coming from the 2 layered chorion
what does the chorion do?
- implantation process (chorionic villi)
- forms part of the placenta in due course
- secretes human chorionic gonadotropin (HCG) (used to detect pregnancy)
what is the muscle layer surrounding the uterus called?
myometrium
what is the other name for endometrium?
decidua
what is the decidua basalis?
the base of the endometrium (with extra maternal blood vessels)
what secrets hCG?
human chorionic gonadotropin is secreted by chorion to help maintain the endometrium
till when do hCH levels of maternal blood and urine increase?
till around 12 weeks gestation
what happens to the inner cell mass?
form a 2-layered flat disc called the bilaminar disk
what 2 cavities begin to form after the bilaminar disk forms?
amniotic cavity (A) and yolk sac (Y)
what are the main function of the placenta?
- foetal nutrition
- transport of waste and gases
- immune (etc)
what two surfaces make up the placenta?
foetal part - smooth with foetal blood vessels and end of umbilical cord
maternal part - decidua basalis of endometrium, rough and has maternal blood vessels
by when does placenta mature?
18-20 weeks
how much does the placenta weigh as opposed to the foetus?
1/6
how do you get fraternal/ dizygotic twins?
2 ova releases, 2 sperms -> 2 separate zygotes, 2 different genetic makeups, 2 placentae
how do you get identical/ monozygotic?
1 ovum, 1 sperm, 1 zygote initially -> divides into 2 and each cell develops into a different embryo, same genetic makeup share one placenta; (might/ might not share amnionic and chorionic sac)
what happens during week 3?
- formation of germ layers (gastrulation)
- formation of neural tube (neurulation)
- development of somites
- early development of cardiovascular system
where is the primitive streak formed?
formed in the midline of the epiblast by the dipping in of cells (invagination)
what happens to the embryo once the primitive streak forms?
the AXIS of the embryo is formed (it has a front and a back)
what is gastrulation?
formation of 3 germ layers
how is the 3rd germ layer formed?
epiblast cells migrate into space between epiblast and hypoblast layers, cells then displace hypoblast, forming 3 germ layers
what are the 3 germ layers called?
ectoderm, mesoderm and endoderm
what is the other name for the 3 germ layers?
trilaminar disc
how have the cells changed at this point?
they are specialised from this point on
summary of the different changes in week 3:
inner cell mass of blastocyst -> bilaminar disc, primitive streak -> cells from primitive streak invaginate -> displace hypoblast -> endoderm, mesoderm, ectoderm
how does the notochord form?
ectoderm invaginates (primitive streak), the cells then sink down to form a solid tube in the mesoderm
what is neurulation?
formation of the neural tube
how does the neural tube form?
notochord induces ectodermal cells in the midline to form a neural tube, which is actually just a thickening of the ectoderm forming a neural plate, which then invaginates in between the ectoderm and the mesoderm
where do somites develop?
mesoderm
what induces the mesoderm to thicken?
neutral tube
what does the mesoderm separate into?
paraxial mesoderm, intermediate mesoderm and lateral plate mesoderm
what happens to the lateral plate mesoderm?
splits to form a somatic and splanchnic mesoderm
what is the space formed in between the somatic and splanchnic mesoderm called?
intra-embryonic coelom
which part of the mesoderm gives the somites?
paraxial mesoderm
which part of the mesoderm gives the urogenital system?
intermediate plate mesoderm
which part of the mesoderm die body cavity and covering?
lateral plate mesoderm
what happens in the embryonic/ organogenetic period? (4-8 weeks)
- folding into a tube (lateral folds) which started in 3rd week completes
- neural tube - forebrain, midbrain, hindbrain and spinal cord development
- heart starts to beat on day 24
- gut formation from endoderm
- urogenital system formation from intermediate mesoderm
- body cavities from lateral plate mesoderm
- 43 pairs of somites form in the paraxial mesoderm and differentiate further
- limb buds form
- neck development - pharyngeal arches
how does the lateral folding of embryo happen?
endoderm becomes round, splanchnic and somatic mesoderm go around endoderm, ectoderm covers them all up
which is more peripheral? somatic or splanchnic mesoderm?
somatic
how do the somites further develop?
each somite divides into 3: dermatome, myotome, sclerotome
what will happen to the dermatome?
becomes the dermis of the skin
what will happen to the myotome?
becomes the muscles
what will happen to the sclerotome?
becomes the bones including vertebrae
what is teratology?
study of when things go wrong during development
what are teratogens?
environmental factors that cause abnormal development
what virus causes congenital rubella syndrome? under which conditions?
german measles when pregnant
what chemical compound provokes malformed limbs when administered to the pregnant mother?
thalidomide
how frequently is the cause of abnormal development environmental factors?
10% of cases
what are the causes of environmental-caused abnormal development?
- drugs (prescription/others)
- alcohol/ tobacco
- infections agents: ToRCH (toxoplasma, rubella, cytomegalovirus, herpes) can transfer through placenta and affect developing embryo
- radiations
how frequently is the cause of abnormal development genetic factors?
10% of cases
what are the causes of genetically-caused abnormal development?
- too many/ too few chromosomes (Turner, Down’s)
- structural changes (deletion of genes, segments of chromosomes)
- causes: increased maternal age, damage from environmental factors such as radiation (ex: Xrays)
when (during the pregnancy) is the sensibility to teratogens the greatest?
weeks 1-2: low
weeks 3-8: highest
weeks 9-38: decreasing
when (during the pregnancy) is the risk of death due to teratogens the greatest?
weeks 1-2: high risk
what does the risk posed by a teratogen depend on?
- exposure during critical periods of development
- dosage of drug/ chemical/ factor
- genetic constitution of embryo i.e. some more susceptible than others at equivalent doses etc
how do you diagnose malformations prenatally?
blood (AFP), ultrasound scan - 12 week anomaly scan, invasive tests: chorionic villus sampling and amniocentesis
how do you diagnose malformations postnatally?
hip stability, testes (proper descent), fingers and toes, hearing
