Early Embryonic Development

Question 1

What are cleavage divisions?

Answer 1

Mitotic cell divisions in early embryos

Question 2

What are cells of the cleavage divisions called?

Answer 2

Blastomeres

Question 3

What determines cleavage in most animals?

Answer 3

Amound and distribution of yolk

Question 4

Two types of cleavage patterns

Answer 4

Holoblastic

Meroblastic

Question 5

Explain Holoblastic

Answer 5

Furrow completely cuts through embryo

Question 6

In what type of embryos does holoblastic cleavage occur?

Answer 6

This occurs in embryos with moderate (amphibians) to little yolk (mammals) and can be unequal or equal

Question 7

What is meroblastic?

Answer 7

Incomplete cleavage divisions

Question 8

What type of embryos is meroblastic found?

Answer 8

Embryos with lots of yolk

• Fish
• Reptiles

Question 9

Are cleavage divisions synchronous or asynchronous in mammals?

Answer 9

Cleavage divisions are asynchronous in mammals

Question 10

In mammals when is pre-implantation development?

Answer 10

Period of embryonic development from fertilization to just prior to implantation

Question 11

What is the zona pellucida?

Answer 11

Glycoprotein containing extracellular matrix surrounding the oocyte and early embryo

Question 12

When does embryonic genome become activated?

Answer 12

During early cleavage stages

Question 13

What is morphogenetic event 1?

Answer 13

Compaction

Question 14

What occurs duing morphogenetic event I: Compaction?

Answer 14

Unique event that begins after 3rd cleavage

Cells huddle closely togeth and form compact ball at 8cell stage

Just prior to and durring compaction, blastomeres become polarized

Question 15

What occurs just prior to and during compaction to blastomers?

Answer 15

Blastomeres become polarized

Start to see presence of microvilli

Question 16

What is the 16-cell stage referred to as?

Answer 16

Morula

Question 17

What do the outside cells do during Morphogenetic Event I :Compaction?

Answer 17

Form tight permeability seal with tight junctions, desmosomes, and adherens junctions

Question 18

What do cells on the inside do durring Morphogentic Event I: Compaction?

Answer 18

Become connected by gap junctions

Question 19

What do the outside cells of the morulae destined to become?

Answer 19

Trophectoderm and the trophoblast

ie., extraembryonic lineage

Question 20

What do the inner cells of the morulae do durring Morphogenetic Event I: Compaction?

Answer 20

The inner cells will derive the embryo by first forming the inner cell mass (ICM

Question 21

What is Morphogenetic Event II also known as?

Answer 21

Cavitation

Question 22

What occurs durring Cavitation?

Answer 22

Fluid begins to accumulate in the compacted morulae forming small vessicles

The vessicles coalesce into a blastocoel and the embryo becomes a mammalian blastula known as a blastocyst

Question 23

What is a primary driver of Cavitation?

Answer 23

Enzyme NaK-ATPase

Question 24

What does NaK-ATPase do during cavitation?

Answer 24

Pumps 3 Na into cavity and 2K out

Creates an osmotic gradient to allow H2O to fill blastocoel

Question 25

What is Morphogenetic Event III also known as?

Answer 25

Blastocyst Expansion

Question 26

Primary driver of Morphogentic Event III: Blastocyst Expanison

Answer 26

NaK-ATPase

Question 27

Why is Morphogenetic Event III: Blastocyst Expansion essential?

Answer 27

Culminates in the first differentiative event

Question 28

What is the first differentiative event

Answer 28

Differentiation of

ICM

• Embryo proper

Trophectoderm

• Extraembryonic lineages

Question 29

What occurs with blastocyst expansion?

Answer 29

Hatching

Question 30

What does hatching prepare for?

Answer 30

Implantation

Question 31

At hatching what does the ICM differentiate into?

Answer 31

Hypoblast

Epiblastt

Question 32

What effect does blastocyst expansion have on the zona pellucida?

Answer 32

Weakens it

Question 33

What 3 forces govern hatching?

Answer 33

1. Growth and fluid accumulation within the blastocyst
2. Production of enzymes by the trophectoderm cells to break down the matrices comprising zona pellucida
3. Contraction of the blastocyst