Human Embryology 3

Question 1

when does gastrulation occur? What does it consist of?

Answer 1

third week of development

1) Epiblast movements
2) Primitive streak Formation
3) Segregation of the three germ layers
4) Node Development & Function

Question 2

what is gastrulation

Answer 2

• coordinated process of cell & tissue migration
• blastula cells are rearranged
• transforms epiblast into 3-layered embryo
• establishment of 3 primary germ layers

Question 3

what are the 3 primary germ layers?

Answer 3

• ectoderm, mesoderm and endoderm

- building blocks of the body

Question 4

Ectoderm consist of

Answer 4

• the epidermis, central & peripheral nervous systems, eyes and internal ears, neural crest cells, and many connective tissues of the head.

Question 5

Mesoderm consist of

Answer 5

Muscle, Bone, Kidneys, Blood

-skeletal muscles, blood cells, lining of blood vessels, all visceral smooth muscular coats

Question 6

Endodem consist of

Answer 6

Gut, Thyroid, Lungs, Pancreas

• -epithelial linings of respiratory and alimentary (digestive) tracts
• glands opening into the GI tract
• glandular cells of associated organs (liver & pancreas)

Question 7

Where is the ectoderm, mesoderm, and endoderm tissue in the early gastrula

Answer 7

• above the midline (opposite side of streak)= ecdoderm

- below midline (on side of streak): mesoderm and endoderm

Question 8

Gastrulation initation

Answer 8

• hypoblasts and epiblasts move in circular fashion (polynation movements), allows accumulation in bottom of embryo
• converging circular motions of epiblast converge at posterior end, leads to primitive streak formation

Question 9

Gastrulation: Primitive streak Initiation?

Answer 9

• cells converge to form valley/depression (primitive streak)
• streak grows (cordial to cranial); when hit max length develop Hensen’s node at cranial end of streak

Question 10

Hensen’s node?

Answer 10

• only forms when streak reaches full length
• is circular depression at end cranial streak
• at most anterior end endowed w/ “organizing” capabilities

Question 11

Gastrulation, EMT & Mesenchymal migration?

Answer 11

-epiblast cells move inward into streak, down the streak, then laterally to dispense between the hypoblast and previous epiblast layer
(invagination)

Question 12

What happens to hypoblast cells as epiblasts invaginate into the primitive streak?

Answer 12

-they are displaced; and start to become the endoderm germ layer

Question 13

what does the ectoderm get made out of?

Answer 13

-ectoderm= the previous layer of epiblasts before invagination happened

Question 14

How make the mesoderm layer?

Answer 14

-the epiblasts cells that invaginated into the primitive streak and remained between the now ectoderm and endoderm layers differentiate to become mesoderm

Question 15

When do epiblasts stop migrating, inward, down, and laterally into the primitive streak?

Answer 15

-once ectoderm, mesoderm, and endoderm layers are formed

Question 16

What does the primitive streak represent?

Answer 16

-the first indication of asymmetric Embryonic development
-BUT is clear that asymmetry (axis specification) was
established prior to primitive streak formation

Question 17

primitive streak formation molecular steps?

Answer 17

• Established in epiblast stages, defines the position of Primitive streak
  1) VG1 + Wnt8C induce Nodal in nearby epiblast
  2) Nodal inhibited by Cerberus(made by underlying hypoblast )
  3) before primitive streak formation, the hypoblast are displaced by non-Cerberus-expressing endoblast
  4) Nodal now signals to act Nodal + FGF induce ingression of cells from epiblast to form primitive streak

Question 18

How is Hensen’s node an organizer? How prove it?

Answer 18

-transplanted the node from frog (A) into frog (B) embryo, put in opposite end (cordial, posterior)
-now frog B embryo has TWO nodes, made 2 weird embryos
-

Question 19

Conclusion of the node transplant exp

Answer 19

• Tissue (node) they transplanted organized HOST cells around it, changed their function from making belly…to making neural tube, endorser etc for new embryo
• if original tissue cells were left unintterupted, would have made belly, but instead the node from diff tissue organized host cells, made new axis, new embryo
• ended up with 2 weird embryos from 2 different tissue samples
• NODE CAN FORM FULL SECONDARY AXIS

Question 20

Inducer vs organizer molecules

Answer 20

Organizer: Cells/Tissue able to force the change of fate of other cells

Inducer:
act on organizer signals, are the molecules responsible for Organizer effect

Question 21

What is the notochord? How made? Where positioned & functions?

Answer 21

1) Defining structure from chordate embryos
2) axial mesoderm, derived from the node, laid down as the node regresses
3) Medially positioned signaling center that helps form adjacent tissues (i.e. Neural Tube)

Question 22

Role of notochord (x5)

Answer 22

1) structural support to the embryo
2) “Cartilage related” serves as axial skeleton of embryo until vertebrae forms
3) Defines the primordial longitudinal axis of the embryo
4) Contributes to nucleus pulposus of the intervertebral disc of vertebral column
5) helps form adjacent tissues (i.e. Neural Tube)

Question 23

notochord present in adults?

Answer 23

• Nope

- Is transient, not present in adults

Question 24

mesendoderm movement?

Answer 24

-Mesendoderm ingression starts with PS growth

-

Question 25

mesendoderm?

Answer 25

• both mesoderm & endoederm cells

- the cells that go through primitive streak & invaginate to from the two germ layers

Question 26

What happens to mesendoderm when primitive streak (PS) reaches max length?

Answer 26

maximum length (most anterior position):

1) mesendoderm starts to regress
2) Newly formed Node generate mesoderm cells that move anteriorly (toward cranial end) to generate notochordal process under the ectoderm

Question 27

Notochord develop into?

Answer 27

• has organizational role in nervous system development
• becomes part of the vertebral column
• invovled with proper axis development of embryo

Question 28

Mesoderm Derivatives?

Answer 28

1) Notochord- Axial Mesoderm
2) Somites - paraxial mesoderm
3) Intermediate mesoderm
4) Lateral mesoderm - somatic & splanchnic
5) Intraembryonic coelom

Question 29

Contributions of mesoderm derivatives?

Answer 29

1) Head: Portions of cranium & head connective tissue
2) paraxial mesoderm: Muscles of Head, Dermis of Skin, Connective Tissue
3) intermediate mesoderm:Urogenital System (Gonads, Ducts, Glands)
4) lateral mesoderm: Connective Tissue, heart, steel
5) axial mesoderm: Embryonic cartilagenous structural support, and nucleus of intervertebral disc