Embryology

Question 1

Where and when do primordial germ cells arise?

Where do they migrate to?

Answer 1

PGCs arise in the wall of the wall of the embryonic yolk sac in week 4 and migrate to the primitive gonad

Question 2

Once in the primitive gonad, what happens to PGCs?

Answer 2

PGCs replicate by mitosis and then enter meiosis, pausing at prophase I until hormonal signals of the reproductive cycle

Question 3

FSH stimulates what?

Answer 3

Once the female reaches reproductive age, follicle stimulating hormone (FSH) stimulates primordial follicles to grow into vesicular or graafian follicles

Question 4

LH stimulates what?

Answer 4

Luteneizing Hormone stimulates ovulation and resumption of meiosis until re-arrest at metaphase II.
The Corpus luteum (eventual placenta) develops from the ruptured follicle (degenerates if fertilization does not occur).
Granulosa and theca interna cells secrete progesterone and estrogen.

Question 5

How do sperm become capacitated? What happens when sperm meets egg?

Answer 5

Sperm are capacitated by uterine fluid and undergo the acrosome reaction. The capacitated sperm penetrate the corona radiata of the oocyte and zona pellucida and create the barrier to polyspermy.
Sperm and egg pronuclei mitotic spindles fuse and the first mitotic division is completed (diploidy is restored).

Question 6

After fertilization, a ball of cells forms, what is this ball called? What does it become?

Answer 6

The morula forms 4 days of fertilization. The morula becomes a blastocyst by day 6 and the syncytiotrophoblast cells bind to the uterine wall where they will eventually connect to maternal blood vessels.

Question 7

The epiblast, hyopblast, and amniotic cavity form by __ days.

Answer 7

The epiblast, hyopblast, and amniotic cavity form by 7.5 days.

Question 8

The inner cell mass of the blastocyst forms what?

Answer 8

The inner cell mass of the blastocyst forms an embryionic disc of epiblast and hypoblast between the amniotic cavity and the yolk sac.

Question 9

The Extraembryonic mesoderm eventually becomes what? what does this eventually do?

Answer 9

The Extraembryonic mesoderm eventually becomes the chorionic cavity which expands around the suspended embryo and its yolk sac.

Question 10

What are some differences between mitosis and meiosis?

Answer 10

Mitosis has 1 division and gives rise to 2 identical daughter cells. Meiosis has two divisions, crossing over occurs when daughter cells pair on the metaphase plate, 4 genetically unique haploid cells are produced.

Question 11

After the blastocyst has implanted at day 6, what maintains the corpus luteum?

Answer 11

Human chorionic gonadotropin (hCG)

Question 12

What is special about the mitosis of the fertilized egg?

Answer 12

The cells divide without going through Gap phases (G1 and G2), they undergo S and then divide.

Question 13

Implantation vs no implantation?

Answer 13

No implantation- corpus luteum degenerates and the uterine lining sheds.
Implantation- hCG is produced by the blastocyst. hCG acts on the corpus luteum for 3 months until the CL becomes the placenta. The uterine lining grows and development begins to occur.

Question 14

Syncytiotrophoblast cells develop lacunae which eventually do what?

Answer 14

Syncytiotrophoblast cells form lacunae which eventually become filled with maternal blood.

Question 15

Cytotrophoblast cells eventually do what?

Answer 15

Cytotrophoblast cells eventually cover the entire outside of the embryo and yolk sac (chorionic cavity).

Question 16

Definitive germ layers are formed by _____. The _____ contributes to the yolk sac and the extra-embryonic mesoderm.

Answer 16

Definitive germ layers are formed by epiblast. The hypoblast contributes to the yolk sac and the extra-embryonic mesoderm.

Question 17

The _____ triggers gastrulation

Answer 17

The primitive streak triggers gastrulation. Epiblast cells migrate up into the primitive streak and through the primitive node.

Question 18

After the epiblast cells move through the primitive node and primitive streak (which signals differentiation), which cells become the three definitive germ layers in the 3rd week of development?

Answer 18

Embryonic mesoderm spreads out between the epiblast and hypoblast. Invaginating cells that invade the hypoblast become the true embryonic endoderm. The epiblast cells that remain on the upper surface after gastrulation will become the ectoderm.

Question 19

Oropharyngeal and cloacal plates mark what?

Answer 19

Oropharyngeal and cloacal plates mark the anterior and posterior openings of the gut tube.

Question 20

What is the role of the primitive node?

Answer 20

It produces factors that cause cells to differentiate into endoderm, ectoderm, and mesoderm. Their later function is determined by this and their position in the embryo.
It is also responsible for asymmetry along the longitudinal body axis.

Question 21

What is the position of the notochord, paraxial, intermediate, and lateral plate mesoderm?

Answer 21

The notochord lies at the center and is surrounded (from medial to lateral) by paraxial, intermediate, and lateral plate mesoderm.

Question 22

What is EMT?

Answer 22

Epithelial-mesenchymal transition. This occurs at gastrulation and is required for cells to leave the epiblast and migrate between epiblast and hypoblast. Cells go through reverse EMT as they form the endoderm.

Question 23

The neural tube begins to fold in at day 19, what cells develop along its cranial to caudal axis?

Answer 23

Somites develop along the cranial to caudal axis

Question 24

Somites form in the ______ mesoderm along the neural tube and give rise to dermatome, myotome, and sclerotome. What do these 3 cell types form?

Answer 24

Somites form in paraxial mesoderm along the neural tube and give rise to dermatome (dermis), myotome (muscle), and sclerotome (axial skeleton)

Question 25

By week 4 the embryo has a _____-like structure and the ________ closes.
The _______ arches form, the ______ bulge forms and the _______ begins to extend.

Answer 25

By week 4 the embryo has a tadpole-like structure and the neuropore closes.
The pharyngeal arches form, the heart bulge forms and the umbilicus begins to extend.

Question 26

By the end of the 3rd week, tertiary stem villi have pushed through the lacunae and now begin to line the entire external surface of the placenta with _________.

Answer 26

cytotrophoblast

Question 27

By the end of the 4th week, the embryo has a beating heart and circulation between itself and the _______.

Answer 27

placenta

Question 28

_________ allows blood to pass the syncytiotrophoblast, cytotrophoblast, and endothelial cells that line the vessels.

Answer 28

Transcytosis

Question 29

The amniotic cavity obliterates the _____ and ______ cavities by the end of the 3rd month.

Answer 29

The amniotic cavity obliterates the chorionic and uterine cavities by the end of the 3rd month.