L3) Embryology 1 ✔

Question 1

define the pre-embryonic period of human development

Answer 1

first two weeks of development
processes involved include: cleavage, compaction and implantation begins

Question 2

how does fertilisation occur?

Answer 2

oocyte released from ovary
travels along fallopian tube
fertilised by sperm in ampulla

Question 3

what is a fertilised oocyte called?

Answer 3

zygote

Question 4

what is the ideal site for implantation of the zygote?

Answer 4

posterior uterine wall

Question 5

briefly describe what occurs in week 1 - cleavage

Answer 5

30 hrs after fertilisation
cleavage results in two blastomeres of equal size
zona pellucida sustained

Question 6

what is the zone pellucida?

Answer 6

protective glycoprotein shell

Question 7

briefly describe what occurs in week 1 - post cleavage

Answer 7

after zygote undergoes 4 cleavage divisions
embryo now defined as morula (16 cells)

Question 8

briefly describe what occurs in week 1 - compaction

Answer 8

morula cells shift to form the first cavity - blastocyst cavity
inner cell mass - embryoblast
outer cell mass - trophoblast
zona pellucida sustained
now defined as blastocyst

Question 9

what is the function of the zona pellucida being sustained?

Answer 9

remains constant in size
hence any successive division of zygote results in smaller cell size

Question 10

briefly describe what occurs in week 1 - hatching?

Answer 10

blastocyst hatches from zona pellucida
no longer constrained - can enlarge
now defined as a conceptus
can now interact with uterine wall

Question 11

briefly describe what occurs in week 1 - implantation begins?

Answer 11

conceptus now = 100 cells
8/100 = form embryo
92/100 = begin development of metal membranes

Question 12

broadly describe what occurs in week 2?

Answer 12

differentiation of outer cell mass and inner cell mass

Question 13

what does the outer cell mass give rise to in week 2?

Answer 13

syncytiotrophoblast
cytotrophoblast

Question 14

what does the inner cell mass give rise to in week 2?

Answer 14

epiblast
hypoblast
aka the bilaminar disc

Question 15

what is the potency of cells before compaction?

Answer 15

totipotent
capacity to become any cell type

Question 16

what is the potency of cells after compaction?

Answer 16

pluripotent
capacity to become one of many cell types

Question 17

briefly describe the development of a conceptus by the end of week 2

Answer 17

the conceptus has implanted
the embryo has two cavities (amniotic cavity and yolk sac)
and is suspended from the endometrium by a connecting stalk
within a supporting sac (chorionic cavity)

Question 18

broadly describe the process of implantation

Answer 18

invasive process
interstitial
establishes maternal blood flow within placenta
establishes the basic structural unit of matron-fetal exchange

Question 19

why is implantation interstitial?

Answer 19

uterine epithelium is breached
conceptus implants within the uterine stroma

Question 20

why is it important to establish a maternal blood flow within the placenta?

Answer 20

allow support of the embryo from maternal circulation

Question 21

what is the basic structural unit of matron-fetal exchange?

Answer 21

the chorionic villus

Question 22

what are some assisted reproductive techniques?

Answer 22

in vitro - oocytes fertilised in vitro (lab) and allowed to divide to 4 or 8 cell stage
morula then transferred to uterus
allows for PGD

Question 23

what is PGD?

Answer 23

Pre-implantation Genetic Diagnosis
removal of cell from morula
to test fro serious heritable conditions prior to transfer of embryo into mother

Question 24

what are some conditions linked to implantation defects?

Answer 24

placenta praevia
ectopic pregnancy

Question 25

what is placenta praaevia?

Answer 25

implantation in the lower uterine segment can cause haemorrhage in pregnancy placenta blocks the cervical canal requires C-section

Question 26

what is ectopic pregnancy?

Answer 26

implantation at site other than uterine body (mostly Fallopian tube) can be peritoneal or ovarian can quickly become life-threatening emergency

Question 27

briefly describe what occurs in week 2 - day 9?

Answer 27

at the embryonic pole - the rapid development of syncytiotrophoblast at the abembryonic pole - primitive yolk sac formed - this is in contact with the cytotrophoblast layer

Question 28

briefly describe what occurs in week 2 - day 11?

Answer 28

primitive yolk sac membrane pushed away from cytotrophoblast layer by acellular extraembryonic reticulum reticulum later converted to extraembryonic mesoderm by cell migration

Question 29

briefly describe what occurs in week 2 - day 12?

Answer 29

maternal sinusoids invaded by syncytiotrophoblast lacunae becomes continuous with sinusoids uteroplacental circulation begins uterine stroma prepares for support of the embryo

Question 30

what are maternal sinusoids?

Answer 30

uterine capillaries that develop after implantation allow the exchange of gas and nutrients with the mother

Question 31

briefly describe what occurs in week 2 - day 13?

Answer 31

formation of secondary (definitive) yolk sac pinches off the primitive yolk sac

Question 32

briefly describe what occurs week 2 - day 14?

Answer 32

spaces within extraembryonic mesoderm merge to form chorionic cavity the embryo and its cavities are suspended by a connecting stalk bleeding around now may be confused with menstrual bleeding

Question 33

what is the connecting stalk?

Answer 33

a column of mesoderm future umbilical cord

Question 34

what is the balstocoele?

Answer 34

first cavity formed as result of compaction

Question 35

what is the amniotic sac?

Answer 35

formed from spaces within epiblast

Question 36

what is the primitive yolk sac?

Answer 36

the exocoelomic cavity formed from hypoblast lining blastocoele

Question 37

what is the secondary yolk sac

Answer 37

the difinitive yolk sac formed within primitive YS

Question 38

what is the extraembryonic coelom?

Answer 38

the chorionic cavity/sac formed from spaces within extraembryonic reticulum and mesoderm

Question 39

epidemiology of early pregnancy loss

Answer 39

app. 50% of all zygotes lost in the first 2-3 weeks 15% diagnosed pregnancies will miscarry 1% women suffer from recurrent miscarriages

Question 40

why is a Caesarean section indicated in placenta praevia?

Answer 40

as the placenta blocks the cervical canal vaginal delivery can cause severe bleeding

Question 41

why is ectopic pregnancy a life-threatening emergency?

Answer 41

can cause your fallopian tube to burst open. without treatment, the ruptured tube can lead to life-threatening bleeding