Embryo: Fertilization & Preimplantation

Question 0

What is the usual site of fertilization?

Answer 0

Ampulla of uterine tube

Question 1

What are the requirements for fertilization?

Answer 1

1. Viable gametes
2. Gametes must meet
3. Ability of sperm to fertilize

Question 2

What is capacitation of the sperm?

Answer 2

An increase in the fragility of the membranes of sperm cells when exposed to the female reproductive tract

• capacitation is required so that the acrosomal enzymes can be released to facilitate fertilization:
  1. In the female tract under influence of female secretions
  2. Removal of glyocoprotein coat overlying acrosome

Question 3

What is an acrosome reaction?

Answer 3

The fusion of the outer acrosomal membrane with the plasma membrane. The contents of the sperm acrosome then leaks out and participates in sperm penetration of the zona pellucida and modifies the plasma membrane of the sperm such that it can fuse with the oocyte plasma membrane

1. After contacting the zona pellucida
2. Release of acrosomal enzymes (proteases) needed to penetrate

Question 4

What are the 3 steps to prevent polyspermy?

Answer 4

1. Depolarization of the cell membrane
2. Cortical reaction
3. Zona reaction

Question 5

What is the cortical reaction?

Answer 5

Release of granules (lysosomal enzymes) from oocyte caused by penetration.
- This changes the characteristic of the zona pellucida

Question 6

What does the zona reaction do?

Answer 6

Changes in zona pellucida caused by enzymes released in cortical reaction
- inactivated receptors for sperm

Question 7

What happens after fusion of the sperm and oocyte membranes?

Answer 7

1. Oocyte membranes become impenetrable to sperm by depolarization of the membrane
2. Oocyte completes meiosis 2 and secondary polar body forms
3. Male and female pronuclei replicate DNA
4. Fusion of pronuclei forms zygote (usually within 24 hours of ovulation)

Question 8

What happens with the fusion of pronuclei when it forms a zygote?

Answer 8

1. Restores diploid # of chromosomes
2. Determines genetic gender (XX= female; XY=male)
3. Becomes the first cell of the new individual
4. Initiates cleavage

Question 9

What is the name of the first cell of the new individual?

Answer 9

Conceptus/ embryo

Question 10

What is a blastomere?

Answer 10

An early embryonic cell arising during the cleavage stage of an early embryo

Question 11

What is cleavage?

Answer 11

Like taking a block of wood and cutting it into smaller blocks

Question 12

What is a Morula?

Answer 12

When there are 12-32 blastomeres; after about 3 days

- zona pellucida still intact

Question 13

What is compaction?

Answer 13

1. Inner cell mass - forms embryo (embryoblast)

2. Outer cell mass - forms trophoblast

Question 14

What is an embryoblast?

Answer 14

A group of cells at one end of the blastocyst that develops into the embryo

Question 15

What is a trophoblast?

Answer 15

The outer ring of cells of a blastocyst

- takes part in the formation of the placenta

Question 16

What is a blastocyst?

Answer 16

After the Morula enters the uterus. Has inner and outer cell mass

1. 4 days after fertilization
2. Fluid-filled cavity (blastocele) surrounded by single layer trophoblast with inner cell mass at one pole
3. Zona pellucida disintegrates
4. Implantation begins (approx day 6)
5. Increases in size