Lect 7: Embryogenesis

Question 1

Cleavage Divisions

Answer 1

reduce the size of the cells but increase the number of cells.

Question 2

During cleavage divisions the cells are known as

Answer 2

blastomeres

Question 3

after he 3rd cleavage, blastomeres maximize their contact with each other and form a compact ball of cells.

Answer 3

compaction (8-cell). It segregates inner cells from outer cells.

Question 4

Around 3 days after fertilization, the compacted embryo divides to form a 16-cell

Answer 4

morula (16-cell).

Question 5

ICM - Inner Cell Mass

Answer 5

these are the inner cells of the morula. - this ICM gives rise to the embryo proper

Question 6

The OCs give rise to the

Answer 6

trophoblast that later contributes to the placenta. Fluid then penetrates into the intercellular spaces of the ICM to form the blastocoel (fluid filled cavity). At this time the embryo is a BLASTOCYST

Question 7

Which cell type is the source of embryonic cells?

Answer 7

ICM - they are pluripotent (they can differentiate into any cell type in the body. They are the ones that latch onto the uterine wall, while the trophoblast will b the surrounding cells

Question 8

Trophoblast will gives rise to

Answer 8

extraembryonic cells - placenta etc

Question 9

Totipotent cells

Answer 9

can give rise to extraembryonic and all cell types in body

Question 10

Trophoblast cells penetrate between epithelial cells of the uterine via which molecule

Answer 10

L-selectins

Question 11

Next Step: Trophoblast differentiates into two layers -cytotrophoblast and synctiotrophoblast. Synctiotrophoblast expands into the uterus and lose the cellular morphology multinucleate .

Answer 11

Syctiotrophoblas begin to to invade the epithelium and expands into uterus.

Question 12

DAY 9. ICM splits into 2 layers 1hypoblast and epiblast.

Answer 12

Together they form a flat bilaminar disc.

The amniotic cavity forms within the epiblast.

The trophoblast invades maternal capillaries to establish uteroplacental citculation

Question 13

Summary thus far

Answer 13

Fertilization results in the formation of a diploid zygote and
activates cleavage division.
• Compaction forms a tight ball of cells that separate into inner
and outer layers. The inner cell mass (ICM) will give rise to the
embryo proper and the outer cells will form the trophoblast.
• Implantation occurs at the end of the first week, when
trophoblast cells invade the uterine wall epithelium.
• The trophoblast differentiates into cytotrophoblast and
syncytiotrophoblast that contribute to extraembryonic tissues.
• ICM differentiates into epiblast and hypoblast to form a bilaminar
disc.

Question 14

Gastrulation

Answer 14

wk 3: gastrulation establishes the three germ layers. it begins witht the primitive streak on the surface of the epiblast. The primitive streak becomes a narrow groove with a structutre called the primitive node surrounding primitive pit at the cephalic end

Question 15

Next in granulation

Answer 15

epiblasts mograte toward the primitive streak and then detach from the epiblast and move through the primitive streak to slip beneath it…inward movement is called invagination. Cells move inside the primitive streak toward the primitive node transforming a two-cell to ta three-cell.

Question 16

Next in gastrulation (2)

Answer 16

Once the cells hv invaginate, some displace the hypoblast to create the endoderm. Other invaginating cells lie between the epiblast and the new endoderm to form the mesoderm layer. Cells remaining in the epiblast form the ectoderm

Question 17

What is the primary driver?

Answer 17

the primitive node

Question 18

The Anterior Visceral Endoderm (AVE)

Answer 18

have genes for forming the head - the anterior side

Question 19

BMP -4 makes which side?

Answer 19

ventral side

Question 20

Summary again

Answer 20

During gastrulation extensive cell movements and
rearrangements of the bilaminar disc establish three germ layers
(ectoderm, mesoderm, endoderm).
• Epiblast cells invaginate through the primitive streak to form
endoderm and mesoderm.
• Epiblast cells give rise to all three germ layers, and therefore all
body tissues.
• Ectoderm, mesoderm and endoderm give rise to specific cell
types and body tissues.
• Body axes are established before or during gastrulation.

Question 21

Neuralation

Answer 21

the process by which the neural plate forms the neural tube

Question 22

Neurulation divides the ectoderm into three distinct domains

Answer 22

1. Surface epithelium (epidermis)
2. Neural crest
3. Neural tube - will form the brain and spine

Question 23

Failure of closure of the posterior neurophore results in

Answer 23

spina bifida

Question 24

Failure of closure of the anterior neurophore results in

Answer 24

anencephaly

Question 25

NTD prevented if mom takes folic acid

Answer 25

acid

Question 26

Neural crest cells give rise to mesoderm and ectoderm

Answer 26

The neural crest cells arising from the margins of the neural tube. These cells migrate to many different locations and differentiate into many cell types (heart, neural, skin, teeth, face etc) within the embryo.

Question 27

Neural Crest undergo an Epithelial-to-Mesenchymal transition

Answer 27

at the dorsal neural tube and then migrate to give rise to tissues. (Mesenchyme is loosely organized conn tissue of any origin)

Question 28

NC cells migrate to different tissues:

Answer 28

cranial, cardiac, Trunk and Enteric NC

Question 29

Cardiac NC enter the outflow tract of the heart

Answer 29

to generate the septum between the great arteries

Question 30

Summary 3.

Answer 30

During gastrulation extensive cell movements and rearrangements of the bilaminar disc establish three germ layers (ectoderm, mesoderm, endoderm). • Epiblast cells invaginate through the primitive streak to form endoderm and mesoderm. • Epiblast cells give rise to all three germ layers, and therefore all body tissues. • Ectoderm, mesoderm and endoderm give rise to specific cell types and body tissues. • Body axes are established before or during gastrulation

Question 31

Q1. The second week of embryogenesis can be regarded as the week of 2s. The formation of what structures supports this idea?

Answer 31

1. The trophoblast differentiates to form 1. cytotrophoblast and synctiotrophoblast 2. The ICM forms the hypolast and the epiblast

Question 32

Q2. What is gastrulation?

Answer 32

epiblast gives rise to endoderm, ectoderm and mesoderm

Question 33

Q.3 Where do ES come from?

Answer 33

inner cell mass

Question 34

Implantataion of the blastocyst occurs when?

Answer 34

one week post fertilization

Question 35

Cardiac neural crest cells migrate into the heart to contribute to?

Answer 35

the septum of the outflow tract that separates the aorta and pulmonary artery.