Lecture 2 (gametogensis -> gastrulation/end of wk 3) Flashcards
Why is a zygote protected from exposure in the 1st two weeks of development?
implantation doesn’t occur until roughly 2 weeks after fertilization (not connected to mother yet)
What timeframe is the fetus most sensitive to exposures?
weeks 3-8
Where/as what do germ cells originate?
outside of the gonads
primordial germ cells
Where are germ cells formed? Where do they travel?
in the epiblast in 2nd wk
travel to the wall o the yolk sac
When do the germ cells arrive at the gonads?
by the 5th week of pregnancy
primordial germ cells migrate to where after gastrulation?
they migrate to the somatic region of the kidney and then differentiate thank to their somatic cell partners
during what period do oogonia increase in number? what process is this?
then what happens?
2nd and 5th month of pregnancy - mitosis
atresia until menopasuce
When do spermatogonia undergo mitotic arrest? When do they resume division?
perinatally
at puberty
How long does it take for sperm to mature?
64-74 days
What cells hold all spermatogonia?
sertoli cells
Which type of spermatogonia undergo meiosis?
Type B
Once Type B spermatogonia undergo meiosis I you have ->
secondary spermatocytes
Secondary spermatocytes undergo ________ to form ->
meiosis II
4 haploid spermatids
spermatids mature and become ->
spermatozoans
How long does spermatogenesis take? What is the beginning and end?
64 days
spermatogonia -> spermatozoa
Primary oocytes are frozen in ->
Meiosis I
How many follicles mature every month in females? When does this begin? How many reach full maturation?
15-20
after puberty
only one
When does the oocyte cease Meiosis II? does it begin again?
3 hours before ovulation
and yes, if fertilized
What is leftover once the ovum is released from the Graffian follicle?
the corpus luteum
What does the corpus luteum do?
produces hormones like progesterone to prepare the uterus for implantation
What does the corpus luteum become if fertilization doesn’t occur?
the corpus albicans
What forms the acrosome of the sperm?
golgi bodies accumulate
What organelle(s) are left in the mature sperm?
mitochondria
What damages mitochondria in sperm? How far out can these exposures impact pregnancy?
oxidative stressors
30-60 days
What hormone is required for the production of testosterone?
LH
Where does fertiization typically occur?
ampullary region of the uterus
What happens to the sperms prior to fertilization?
capacitation -> sheds glycoproteins
What happens once the sperm binds to the zona pellucida?
acrosome rxn -> sperm can now make it’s way to egg’s cell membrane
What happens after the sperm breaks down the zona pellucida?
- it binds to cell membrane
- cell membrane hardens so no other sperm can bind
- membranes fuse together and sperm nucleus enters
- pronuclei fuse together
- form the diploid zygote
What occurs during 0-3wks?
early development
cleavage
gastrulation
What takes place from 4-8wks?
period of embryonic organogenesis
What is considered 9-38wks?
fetal period
How long after fertilization does the 1st cell division occur?
30-36 hours
Meiosis is completed ___________ after the ovum is released.
12-24 hours
By day 3 you have the:
morula stage
By day 4 you have the:
blastocyst
btwn thew morula and early blastocyst the embryo undergoes:
compaction
the blastocyst becomes two cell layers, known as _________. when does this happen?
inner cell mass
trophoblasts (outside)
days 4.5-5
What pole does the ICM form on of the embryo?
animal pole
What occupies that opposite pole of the ICM?
fluid-filled space that -> endodermal layer and yolk sac
Where do ectopic pregnancies occur?
abdominal cavity ampullary region of the tube (80%) tubal implantation interstitial implantation implantation in region of the internal os
How do ectopic pregnancies occur?
- due to invasive nature of trophoblasts
- due to abnormal transport or recognition of blastocysts
What are some adverse outcomes of ART?
embryo effects spontaneous abortions multiple births adverse perinatal outcomes birth defects DD childhood malignancies longer-term outcomes?
the inner cell mass is also known as the:
embryoblast
What two things are interacting as the 1st week ends?
syncytiotrophblasts and the endometrium
What days make up wk 2?
Days 6-15
What’s the other name for the 2nd week of development?
The week of 2s
During the 2nd wk of development, the trophoblast gives rise to ->
cytotrophoblasts
syncytiotrophoblasts
During the 2nd wk of development, the embryoblast gives rise to ->
hypoblast
epiblast
During the 2nd wk of development, the extraembryonic mesoderm ->
splits into the somatic (parietal) and splanchic (visceral) layers
During the 2nd wk of development, what cavities form?
yolk sac
amniotic cavity
By what day is the embryo implanted into the endometrium?
Day 7.5
What is happening in the syncytiotrophoblasts on day 9?
Maternal blood vessels?
lacunae are forming
blood vessels are enlarging
What is occurring in the syncytiotrophoblasts by day 12?
maternal sinusoids are fusing with lacunae
What begins forming by Day 13?
primary villi surrounded by trophoblastic lacunae filled with maternal blood
When do the primitive streak and node begin forming?
Day 15
In what direction does the primitive streak grow?
caudal to cranial
What happens as the primitive streak forms?
cells invaginate and migrate through the primitive streak
What happens to the first wave of cells that migrate thru the primitive streak?
When does this begin?
they replace the hypoblast cells -> eventually differentiate into endodermal cells
Day 16
What happens to the cells that migrate through the primitive streak after the 1st wave? When? What do they form?
they fill the resulting space between the yolk sac and epiblast layer -> eventually differentiate into mesoderm cells
Day 17
extend cranially from primitive node to form notochordal process
the mesoderm that is lateral to the midline in gastrulation becomes ->
paraxial, intermediate, and lateral plate mesoderm
By day 18, lateral plate mesoderm has split into what two layers ->
somatic and splanchic mesoderm
By day 19, what membranes and plate have formed?
oropharyngeal and cloacal
neural plate
What has happened by day 20 with the notochordal process?
notochordal process fuses with endoderm to form notochordal plate
What happens to the notochordal plate at wk 3->4 (Day 22)?
notochord plate separates from endoderm to form the solid notochord
What cells form the lining of the yolk sac (not from germ layer)?
hypoblast cells
