Fertilization

Question 1

When does fertilization occur?

Answer 1

Approx day 15-16

Question 2

Where does fertilization occur?

Answer 2

Ampulla of oviduct

Question 3

2 mechanisms of the female RT propelling sperm

Answer 3

1. Causes cervix to produce watery mucus to help sperm enter uterus.
2. Activates myometrial contractions to propel sperm.

Question 4

What is capacitation and where does it occur?

Answer 4

Helps seem be capable of fertilizing egg.

Happens in oviduct.

Question 5

What layers must sperm penetrate to get to the egg?

Answer 5

Corona radiata
ZP
PM of egg

Question 6

What is the sperm-ZP3?

Answer 6

The sperm head attaching to the glycoproteins coat of ZP

Question 7

How does the acrosome reaction occur?

Answer 7

Intracellular Ca2+ increases and causes the fusion of acrosomal membrane w/ sperm’s PM leading to exocytosis of acrosomal contents.

Question 8

What is the cortical reaction? Caused by?

Answer 8

Caused by increased IC Ca2+ in oocyte. Leads to release of granules w/ enzyme that cause ZP to harden —> blocks polyspermy.

Question 9

What happens after the cortical recitation?

Answer 9

The 2nd meiosis division (due to high Ca2+) and formation of 2nd polar body.

Question 10

What marks the end of fertilization and start of embryonic development?

Answer 10

M and FM DNA replicates as 2 pronuclei join.

When they join, the membranes breakdown, chromosomes align at metaphase plate and first cleavage occurs.

Question 11

1st wk occurs where?

Answer 11

Lumina of oviduct and uterus

Question 12

16 cell morula by day:
Blastocyst:
Implantation:

Answer 12

16 cell morula by day: day 3
Blastocyst: days 4-5
Implantation: days 6-7 post ovulation

Question 13

How are the outer cell bound?

Answer 13

By desmosomes and gap junctions = compaction

Question 14

How is the blastocyst cavity formed?

Answer 14

Active transport of Na+ from trophos and osmosis

Question 15

ICM is:

Answer 15

Pluripotent

Question 16

Trophoectoderm becomes:

What is it?

Answer 16

Placenta and extra-embryonic tissues.

The outer layer of blastocyst.

Question 17

What are pinopods?
When do they appear?
What +, what -?
What is their function?

Answer 17

Projections of endometrial cells that appear between days 19 - 21 for a couple days only.
+ by progesterone, - by estrogen
In early stages of implantation, they endocytose fluids in the uterus.

Question 18

What does the blastocyst secrete to facilitate implantation?

Answer 18

Immunosuppressive agents to avoid rejection.

HCG which inhibits menstruation by keeping the CL.

Question 19

What is hCG?

Answer 19

Related to LH.
Sustains CL.
Promotes trophoblast growth and placental development.

Question 20

What are cytotrophoblasts?

Answer 20

Rapidly dividing cells that provide a feeder layer.

Question 21

Syncytiotrophoblasts do what?

Answer 21

Activates adhesion of embryo to uterine epilethia.
Causes “interstitial implantation”.
Secrete hCG at onset on implantation.
Makes tons of progesterone.
As pregnancy ensues, they have phagocytic functions, transfer wastes, nutrients, etc.

Question 22

What is hatching? What causes it?

Answer 22

Degeneration of the ZP about 6-7 days post ovulation.

Lyric factors like plasmin.

Question 23

3 stages of implantation

Answer 23

Apposition
Adhesion
Invasion

Question 24

Apposition

Answer 24

Earliest contact between ICM/trophoblasts/endometrial epithelium.
Occurs at crypts in endometrium.

Question 25

What is MUC1?

Answer 25

Transmembrane proteins on endometrium that may be involved in apposition phase.

Question 26

Adhesion

Answer 26

Microvilli of trophoblasts attach to uterine wall. Likely ligand-receptor interactions (integrins). Adhesion causes a dislodging of decidual cells —> further invasion

Question 27

Invasion (simple)

Answer 27

Trophoblasts contact cytotrophoblasts and syncytiotrophoblasts once blastocyst attaches.

Question 28

What do extensions of syntioitrophoblasts do during Invasion?

Answer 28

Dissociate endometrial epithelial cell by secreting TNF-a which damages the cell-to-cell adhesions.

Question 29

What do trophoblasts secrete during invasion?

Answer 29

Auto rinse factors and protease that further promote invasion.

Question 30

Metalloproteases and serine protease function

Answer 30

Degrade the ECM

Question 31

What does the blastocyst implant in within the endometrium? What is it embedded in?

Answer 31

Implants in zone compacta and is embedded in deciduas.

Question 32

Decidualization

Answer 32

Occurs in response to progesterone (which converts stromal cells). Decidua forms junctions that do not allow movement of the implanting embryo.

Question 33

In what order does the invading syntiotrophoblasts invade the endometrial Vasculature? What does it allow for?

Answer 33

Veins first them arteries. Direct communication between between lacunae and mom’s BVs.

Question 34

Formation of primary, secondary and tertiary chorionic villi?

Answer 34

Proliferation of cytotrophoblasts —> primary chorionic villi. Mesenchymal cells from mesoderm invade the primary CV —> secondary CV. Eventually the mesenchymal cells form fetal BVs de novo form tertiary CV.