Basics Of embryology II

Question 1

When do we have a bilaminar embryo

Answer 1

14-15 days

Question 2

What is the 1st major event of the third week

Answer 2

Gastrulation

Question 3

Gastrulation

Answer 3

Commences with the formation of a longitudinal midline structure called the primitive streak in the epiblast near the caudal end of the bilaminar embryonic disc

Question 4

Primitive streak

Answer 4

Longitudinal midline structure formed during gastrulation

-in the epiblast near the caudal end of the bilaminar embryonic disc

Question 5

Cranial end of the primitive streak

Answer 5

Expanded as the primitive node

Question 6

Primitive node

Answer 6

Cranial end of the primitive streak is expanded as this. It contains a circular depression called the primitive pit.

Question 7

Primitive pit

Answer 7

Continuous caudally down the midline of the primitive streak with a trough like depression called the primitive groove

Question 8

What do the primitive pit and the primitive groove represent

Answer 8

Areas where cells are leaving the primitive streak and moving into the interior of the embryonic disc

Question 9

Where do the epiblast cells migrate during gastrulation

Answer 9

Can join hypoblasts and form the endoderm or can spread between and form the mesoderm

Question 10

Definitive endoderm

Answer 10

Some of these cells invade the hypoblast, displacing the original hypoblast cells and replacing them with this layer

Question 11

Infraembryonic mesoderm

Answer 11

Other cells migrate bilaterally from the primitive streak and then cranially or laterally between endoderm and epiblast and coalesce to form this

Question 12

What is the epiblast called after gastrulation

Answer 12

Ectoderm (blue)

Question 13

Just before the neural tube forms a mesoderm migration beings in an orderly fashion:

Answer 13

• prechordal plate: mouth
• cardiogenic mesoderm: heart
• extraembryonic mesoderm: amnion, yolk sac, allantois

*from cranial to caudal

Question 14

Mid gastrulation mesoderm migration from cranial to caudal in order

Answer 14

• notochord
• head mesoderm
• somites
• intermediate mesoderm
• lateral plate mesoderm

Question 15

Notochord formation

Answer 15

As the neural plate begins to induce change and the mesoderm migrations are occurring, the notochord cells are migrating. Notochord is another mesoderm derivative. All of this happens simultaneously and in concert

Question 16

What is the future vertebrae

Answer 16

Notochord

Question 17

What kind of origin does the notochord have?

Answer 17

Mesoderm origin

Question 18

What directs what will become the vertebral column?

Answer 18

Notochord

Question 19

Future head region in gastrulation

Answer 19

• The mesoderm forms bands of cells that remain unsegmented as the head mesoderm.
• mesoderm becomes more dispersed with development to loosely fill the developing head as the head mesenchyme
• the head mesoderm eventually gives rise to the striated muscles of the face, jaw, and throat

Question 20

What gives rise to the striated muscles of the face, jaw, and throat?

Answer 20

Head mesoderm

Question 21

Mesenchyme

Answer 21

Loosely organized, mainly mesodermal embryonic tissue that develops into connective and skeletal tissues including lymph and blood.

Question 22

What kind of origin does the blood and lymph have?

Answer 22

Mesoderm

Question 23

Somites

Answer 23

• Block like condensations of mesoderm

- first two develop at day 20 at the head trunk border

Question 24

Rate of progression of somites (not including the first to pairs)

Answer 24

Rate of about three or four a day, finishing on about day 30

Question 25

How many somites usually form?

Answer 25

42 to 44

Question 26

Which somites disappear

Answer 26

The caudalmost several somites because we don’t have tails.

Question 27

What is the FINAL count of somites

Answer 27

Approximately 37 pairs

Question 28

What does the lateral plate mesoderm split into?

Answer 28

Parietal and visceral layers

Question 29

Parietal layers of the lateral plate mesoderm

Answer 29

Together with the overlying ectoderm forms the lateral body wall folds

Question 30

Visceral layer of the lateral plate mesoderm

Answer 30

Forms the walls of the gut tube and the pleural and pericardial cavities

Question 31

Neurulation events

Answer 31

• neural plate formation
• neural plate shaping
• neural plate bending
• closure of the neural groove

Question 32

During gastrulation, a major _________ occurs in the embryo called ________

Answer 32

• inductive event

- neural induction

Question 33

Neural induction

Answer 33

The primitive node induces the overlying ectoderm to thicken as the neural plate

Question 34

What is the neural plate

Answer 34

The earliest rudiment of the CNS

Question 35

When does the primitive streak disappear

Answer 35

Day 25

Disappears as things start to spread cranially

Question 36

What is everything above somites?

Answer 36

Head structures

Question 37

What origin is the neural tube, crest, and plate?

Answer 37

Ectoderm (blue)

Question 38

How does the neural tube form

Answer 38

Starts in the middle and zips cranially and caudally

Question 39

Synchronized development

Answer 39

The development of the neural tube, mesoderm migrations, and notochord formation all happen simultaneously and in synchrony

Question 40

What does the endoderm become (yellow)

Answer 40

Gut tube