Embryogenesis (7)

Question 1

When does embryogenesis occur?

Answer 1

Weeks 1-8 of human pregnancy

Question 2

Generally speaking, what occurs during embryogenesis?

Answer 2

Organ primordia is established

Question 3

Where is the oocyte fertilized?

Answer 3

In the ampullary region of the uterine tube

Question 4

What is the order of cleavage divisions?

Answer 4

Zygote
2 cell
4 cell
8 cell
Morula
Blasocyst

Question 5

When is the blastocyst formed?

Answer 5

By the end of the 1st week of pregnancy…it begins to implant into the uterine wall

Question 6

What does fertilization result in?

Answer 6

A diploid zygote

Question 7

What do cleavage divisions do to the size of the cells and the number of cells?

Answer 7

Decrease size

Increase number

Question 8

What happens after the third cleavage division?

Answer 8

Blastomeres maximize their contact with each other to form a compact ball of cells (compaction)

Question 9

What does compaction do to the cells?

Answer 9

Segregates inner cells from outer cells

Question 10

When is the morula formed?

Answer 10

About 3 days after fertilization?

Question 11

How many cells are present in the morula?

Answer 11

16 cells

Question 12

When does each of the following appear after fertilization:

2 cell
4 cell
16 cell
Late morula

Answer 12

2 cell: 30 hours

4 cell: 40 hours

16 cell: 3 days

Late morula: 4 days

Question 13

What are the components of the blastocyst?

Answer 13

Inner cell mass (ICM) and Outer cells and Blastocoel

Question 14

What does the ICM give rise to?

Answer 14

Tissues in the embryo proper

Question 15

What doe the outer cells of the blastocyst give rise to?

Answer 15

The trophoblast that later contributes to the placent

Question 16

How is the blastocoel formed?

Answer 16

Fluid penetrates the ICM

Question 17

What type of cells are ICM cells?

Answer 17

Pluripotent stem cells

Question 18

What do trophoblast cells attach to and how?

Answer 18

Attach to the uterine wall epithelium. They penetrate between the epithelial cells of the uterine mucosa (endometrium)

Question 19

What are L-selectins?

Answer 19

Carbohydrate binding proteins on the trophoblast cells. They interact with carbohydrate receptors on the uterine epithelium and mediate attachment

Question 20

What happens in trophoblast differentiation?

Answer 20

2 layers are formed.

Cytotrophoblast: inner layer of mononucleated cells

Synchtiotrophoblast: Outer multinucleated layer that lacks distinct cell bondaries

Question 21

Which layer of the trophoblast continues to expand into the uterine wall?

Answer 21

Syncytiotrophoblast

Question 22

What does the ICM differentiate into? When does this occur?

Answer 22

Hypoblast and epiblast. Together these form a flat bilaminar disc.

Occurs at day 9.

Question 23

What forms within the epiblast?

Answer 23

Amniotic cavity

Question 24

Where do embryonic tissues arise from?

Answer 24

Epiblast layer if ICM

Question 25

What does gastrulation achieve?

Answer 25

3 germ layers

Question 26

What are the goals of gastrulation?

Answer 26

1- Bring inside the embryo areas destined to form endodermal organs 2- Surround the embryo with cells capable of forming ectoderm 3- Place mesodermal cells in proper positions inbetween

Question 27

When does gastrulation occur? And what does it begin with?

Answer 27

Week 3 Begins with formation of the primitive streak.

Question 28

What is invagination?

Answer 28

The epiblast cells migrate into the primitive streak after detaching from the epiblast. They move through the streak and slip beneath it

Question 29

What does invagination give rise to?

Answer 29

Endoderm and mesoderm. Some cells displace the hypoblast and create endoderm Some cells lie between epiblast and new endoderm and create mesoderm.

Question 30

After invagination occurs...what do cells remaining in the epiblast form?

Answer 30

The ectoderm

Question 31

What does the ectoderm lead to?

Answer 31

Outer surface, CNS, Neural crest

Question 32

What does the mesoderm lead to?

Answer 32

Muscle, skeletal system, circulatory system

Question 33

What does the endoderm lead to?

Answer 33

Digestive tube, pharyxn, respiratory tube, other internal organs

Question 34

What is neurulation?

Answer 34

Process of neural tube formation

Question 35

What are the steps of neurulation?

Answer 35

``` 1- Formation 2- Folding 3- Elevation of neural crest 4- Convergence 5- Closure ```

Question 36

What does neurulation divide the neural ectoderm into?

Answer 36

3 distinct domains: Neural tube Neural crest Surface ectoderm

Question 37

What do the retina and CNS develop from?

Answer 37

Neural tube

Question 38

What do the PNS, teeth, melanocytes and facial cartilage develop from?

Answer 38

Neural crest

Question 39

How many site of neural tube closure is there and how does closure proceed?

Answer 39

3 sites of closure and fusion occurs bidirectionally

Question 40

What is failure of posterior neural tube closure?

Answer 40

Spina bifida

Question 41

What is failure of anterior neural tube closure?

Answer 41

Anacephaly

Question 42

What is complete failure of neural tube closure?

Answer 42

Craniorachischisis

Question 43

Where does theneural crest cell transition from epithelium to mesenchymal occur?

Answer 43

At the dorsal neural tube (and then after they give rise to tissues)

Question 44

What are the regions of neural crest cells?

Answer 44

Cranial (cephalic) neural crest Cardiac neural crest Trunk neural crest Enteric (vagal and sacral) neural crest

Question 45

True or False: Neural crest cells follow distinct migration patterns.

Answer 45

True