Fertilization, Implantation And Gametogenesis

Question 1

what are the functions of the zona pellucida?

Answer 1

1. prevents ectopic pregnancy (most common in the fallopian tubes, which would rupture and cause a hemorrhage, strong abdominal pain) / early implantation of the oocyte
2. similar to that of the Sertoli cells → immunoprotection since the oocyte is semi-allograft
3. supports the communication between oocytes and follicle cells during oogenesis
4. protects oocytes, eggs and embryos during development
5. regulates interactions between ovulated eggs and free-swimming sperm during and following fertilization
6. it triggers the sperm head to undergo the acrosomal reaction

Question 2

when does the hatching take place?

Answer 2

day 6-7

Question 3

when does the implantation of the blastocyst take place?

Answer 3

day 8-9
the blastocyst splits into epiblast and hypoblast

Question 4

what produces hCG?

Answer 4

the corpus luteum produces progesterone whereas the hCG is produced by the trophoblast.

Question 5

what the the function of hCG?

Answer 5

the Human Chorionic Gonadotropin is a hormone that helps thicken a person’s uterine lining to support a growing embryo and tells the body to stop menstruation

Question 6

how is the zona pellucida lost?

Answer 6

the vitelline membrane only affected the follicles - when cleavage happens, the throphoblast gets closer to the oocyte.
the microvilli of the trophoblast help disintegrate the zona pellucida and release enzyme ACROSIN

Question 7

where does implantation occur?

Answer 7

in the endometrium - the posterior uterine wall

Question 8

what are the two layers of the endometrium - and where should implantation ideally take place?

Answer 8

functional layer and basal layer
it takes place in the functional layer (things usually happen in the functional layer)

Question 9

in the apposition, which happens at day 8-9, we have two things occuring….

Answer 9

1. the blastocyst sheds its zona pellucida as it differentiates into an inner cell mass (embryo) and trophectoderm (placenta)
2. it approaches the endometrium with a particular orientation so that it can implant the uterine wall
   — stromal cells surrounding it differentiate into a specialized cell type called decidual cells, via decidualization

Question 10

what are the three decidual layers?

Answer 10

1. decidua basalis: under the site of implantation (basal → under
2. decidua capsularis: covering the ovum (capsularis → capsule ∴ covering)
3. decidua parietalis or vera: lining the rest of the uterine cavity (remember parietalis → parent ∴ on the side of the mom)

Question 11

important for the exam: which type of chorionic villi have blood vessels?

Answer 11

the tertiary ONLY

Question 12

what is the chorion made up of? and when does it start forming?

Answer 12

it starts on day 14. when the network of mesenchymal cells, derived from the embryonic disc spread underneath the inner surface of the cytotrophoblast of the implanted blastocyst and form the chorionic sac.
it consists of two layers: an outer formed by the trophoblast and na inner formed by the somatic mesoderm

Question 13

what does the trophoblast give rise to?

Answer 13

• an internal layer of cubical or prismatic cells ⇒ cytotrophoblast or layer of Langhans
• an external multinucleated layer ⇒ syncytiotrophoblast

Question 14

what does the theca interna become?

Answer 14

the corpus luteum

Question 15

which of the following does NOT occur during the acrosomal reaction?
a. influx of Na++
b. increased intracellular pH
c. fusion fo the sperm plasma membrane with the anterior region of the acrosome membrane
d. removal of cholesterol and glycoproteins
e. all of the above

Answer 15

d. removal of cholesterol

Question 16

what gives rise to the amniotic membrane, amniotic cavity and the yolk sac?

Answer 16

amniotic membrane ⇒ epiblast
amniotic cavity ⇒ epiblast
yolk sac ⇒ hypoblast

Question 17

the primitive ectoderm derives from…

Answer 17

the epiblast