Embryology 1 Flashcards
Primordial Germ Cells (PGC)
precursors to the developement of gametes in males and females
Epiblast
where primordial germ cells arise from
Where do PGCs migrate in the fourth week of development?
yolk sac
T or F yolk sac serves as nutritional support in development?
false
What happens to PGCs during the 4th and 6th weeks of developement?
migration of PGCs from yolk sac to populate gonads
Where do gonads develope weeks 4-6?
urogenital ridge on posterior abd. wall
What happens to PGCs on their way to gonads?
rapid MITOSIS
When do PGCs begin gametogenesis?
when they enter testis/ovary and begin meiosis
If primordial germ cells fail to migrate to urogenital crest what will happen?
No gonad will develop at that site
what two major events occcur in meiosis 1 but not in meiosis 2?
crossover and synapsis
What is the foundation for most genetic variability from person to person?
crossover
Crossover
segmental exchange of DNA from part of one chromosome to another
What happens to male primordial cells when they populate the future testis?
they go dormant until puberty
When does male spermatogensis begin?
puberty
What happens to male PGCs at puberty?
they diffentiate into type A and B spermatogonia
What do type A spermatogonia do?
remain in seminiferous tubules for life and go through mitotic divisions to keep a constant supply of type B. (funct. as stem cells)
What do type B spermatogonia do?
undergo meiosis 1 and 2 to from haploid spermatozoa (birth to death)
Primary spermatocyte
cells in meiosis I
secondary spermatocyte
cells in meiosis II
In males is there interphase between meiosis I and II?
NO
what does a secondary spermatocyte split to form?
spermatids
What happens when PGC’s in females migrate to the urogenital region from the yolk sac?
immediate differentiation to primary oocyte
When does Oogenesis and meiosis one begin in females?
5th month of development
What happens in females at puberty to oocytes?
exit the arrest of prophase of meiosis 1
How many gametes are produced from one spermatogonia?
4
How many gametes from one oogonia
1 and 2 polar bodies
Where does fertilization generally take place?
ampulla (distal in of fallopian)
capacitation reaction
takes 7-8 hours, rearrangement of proteins in acrosome to allow it to drill a hole through the zona pellucida
acrosome reaction
initiates on sperm contact with zona pellucida, pore in head opens up and releases proteolytic enzymes to bore through zona pellucida (much faster than capacitation)
What part of sperm actually enters the oocyte?
head- mitochondria left behind
cortical/zonal reaction
makes oocyte impermeable to other sperm
Male pronucleus
induces oocyte to unarrest
zygote
single cell resulting from fertilization
Graffin follicle
develops ~day14
oocyte becomes unarrested and quickly forms secondary oocyte (before arresting again)
Event after zygote formation is…
cleavage
When does cleavage take place?
days 1-4 initiated by fusion of male and female pronuclei
What happens during cleavage
cell divisions (1,4,8,16, 32)
What prevents the mass of cells from growing during cleavage?
zona pellucida encapsulates cells and prevents growth
When does morula form?
Day 5 (16-32 cell) when zona pellucida breaks down
when the morula undergoes reorganization it becomes the…
blastocyst
3 parts of the blastocyst
embryoblast (embryo), trophoblast (placenta), Blastocyst cavity
Where does implantation normally take place?
inner wall of the uterine cavity
What does the trophoblast layer do to aid in implanation?
differentiates into two cells lines cytotrophoblasts and syncyiotrophoblasts
What is the cytotrophoblast?
layer that remains in the postion of the trophoblast after trophoblast differentiation
What is the syncyiotrophoblast?
portion of trophoblast that differntiates into projections that release enzymes that erode uterine lining (allow adherance of embryo)
where is morula found?
in ampulla
how is morula moved?
moved to uterine cavity using cilia, fluid movement, and muscular contraction
What marks the beginning of week 2?
completion of implantation and uteroplacental blood flow
w2
What happens to the embryoblast at the beginning of week 2?
it has reorganized into a bilaminar disc
w2
What composes the bilaminar disc?
epiblast cells (dorsal surface), hypoblast cells (ventral surface) w2
Which tissue is more important between epiblast and hypoblast?
all tissues making up humans derived from epiblast
w2
What is the role of the hypoblast?
lays extraembryonic mesoderm (plays role in placenta and umbilical cord developement)
w2
how long does the hypoblast persist?
1 week
w2
What happens to cytotrophoblast cells in week 2?
grow and push into syncytiotrophoblast until they lose membranes and become part of the mass
w2
What second fluid filled space besides blastocyst arises in week 2?
amnion
w2
Where does amnion arise?
in epiblast layer as a cleft
w2
What are the epiblast cells that form the roof of the amnion?
amnioblasts
w2
Polyhydramnios
amniotic fluid levels that are too high
oligohydramnios
amniotic fluid levels are too low
what is the primary yolk sac?
its what the blastocyst is referred to once Heuser’s (exocoelomic) membrane forms
w2
What happens after after exocoelomic membrane?
extraembyonic mesoderm forms
w2
How is chorionic space formed?
extraembyonic layer forms vacuoles that fuse
w2
How is the definitive yolk sac different than the primary yolk sac?
definitive yolk sac is directly against the hypoblast, while cells off hypoblast push the primary yolk sac away
w2
What is the purpose of the definitive yolk sac?
houses primordial germ cells early in development and hematopoiesis
w2
What gives rise to the umbilical cord?
the connecting stalk - arises dorsal to amnion where chorionic cavity doesn’t separate the layers
w2
The chorion is made of what 3 layers?
(int –> ext) extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast (THESE GIVE RISE TO FETUS)
w2
T or F it is important to have rudimentary circulation in developing embryo by end of week 2?
T
w2
What are lacunar networks?
Lakes of blood formed by syncytiotrophoblasts penetrating multiple vessels
w2
What does the prechordal plate give rise to?
marks future mouth
w2
What major 4 events occur in week 2 of development?
trophoblast divides into 2 layers (cytotrophoblast and syncytiotrophoblast)
embryoblast forms 2 layers (epiblast and hypoblast)
extraembryonic mesoderm splits to 2 layers (somatic and splanchnic)
two fluid filled spaces for (amnion and yolk sac)
Syncytiotrophoblasts secrete which important hormone for maintaining pregnancy?
hCG-secretion begins in week 2
w2
What important events occur during the first 3 and a half days of the third week?
- Formation of the primitive streak and node
2. Migration of epiblast cells through the primitive streak and subsequent development of 3 germ layers
What begins in the second half of the third week of pregnancy?
organogenesis (continues through 8th week)
What is the first step in gastrulation?
formation of primitive streak and primitive node
w3
What covers the definitive yolk sac?
extraembryonic mesoderm
w3
What axis is the primitive streak formed along?
cranial-caudal axis
w3
What forms the future mouth?
prechordal plate - marks cranial end
w3
What marks the caudal end during gastrulation?
cloacal membrane - future anus
marks caudal end
w3
Where does the primative streak form?
in the caudal end during gastrulation
w3
What is the elevated disc formed by thickening of epiblast cells?
Primitive groove (streak)
w3
What happens after primitive groove formation?
epiblast cells migrate from all directions and fall into the streak (groove)
w3
Define gastrulation?
migration of epiblast cells to the primitive streak
w3
T or F: the primitive streak extends to the cranial end
False
w3
What is located at the end of the primitive streak?
Primitive node
w3
What is the center point of the primitive node called?
primitive pit
w3
What happens to the first wave of epiblast cells to move through the primitive streak?
- They move ventrally to become adjacent to hypoblast cells
- They move hypoblast cells out
- These cells make up the endoderm
w3
What happens to the second wave epiblast cells that move through the primitive streak?
- they move between 1st layer of epiblast cells and hypoblast
- they form the mesoderm
w3
What happens to the third wave of epiblast cells that in gastrulation?
- They do not move through primitive streak
- they form the ectoderm
w3
What is the trilaminar disc?
3 layered disc formed by gastrulation of epiblast cells to form endoderm, mesoderm, and ectoderm
w3
What is sarcococcygeal teratoma?
Tumor made of tissue from all three germ layers (hair, bone, and nerve)
T or F sarcococcygeal teratomas usually become malignant.
True
What is the cause of sarcococcygeal teratoma?
failure of primative streak to fully regress after gastrulation
T or F: sarcococcygeal teratoma is most common in males
False
What is a mature male gamete called?
Spermatozoa
What are three parts of a spermatozoa?
Head Piece (contains acrosome), Middle piece (mitochondria), Tail (microtubules)
What is the zona pelluida?
Very dense PROTEIN coat surrounding the secondary oocyte
What is the corona radiata?
A network of follicular cells outside of the corona radiata
What are the zona pellucida and corona radiata derived from?
the graffian follicle
