Embryology

Question 1

In an embryo, which part gives rise to finally lead to the neural plate?

Answer 1

Blastocyst (inner cell mass) gives rise to the epiblast and hypoblast layer. During gastrulation, the epiblast layer gives rise to the 3 germ layers (ectoderm. mesoderm and endoderm). The ectoderm gives rise to the neural plate.
Cells in the epiblast migrate to the primitive streak and form the mesoderm and endoderm.

Question 2

What are neural crest cells?

Answer 2

Cells which migrate from the neural tube.

Question 3

Explain what a blastocyst is and what forms there

What is the trophectoderm?

Answer 3

A blastocyst is when cells divide to form a ball of cells. They are encased in a membrane and the cells begin to produce different proteins.

This lines the blastocyst and forms extra-embryonic structures.

Question 4

What does the inner cell mass do? What is it a source of?

Answer 4

It generates the embryo.

Source of pluripotent embryonic stem cells.

Question 5

Which embryonic cells make contact with he uterus ready to penetrate it?

Answer 5

Trophoblast cells.

• Cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta.

Question 6

What does the inner cell mass subdivide to?

What then happens to the inner cell mass?

Answer 6

Epiblast and hypoblast

It flatterns and begins to make separate tissues (the epiblast and hypoblast).

Question 7

What is the primitive streak the first sign of? What is it the site of?

Answer 7

Cell differentiation

Gastrulation

Question 8

Does the epiblast or the hypoblast sit above?

Answer 8

The epiblast

Question 9

What happens in gastrulation and what does it give rise to?

Answer 9

Cells in the epiblast move towards the primitive streak (periphery to midline). These migrating cells form mesoderm and endoderm. Cells that remain at the surface form ectoderm.

Question 10

The cells coming out the primitive streak first form —-?
Coming out second form —-?
Last?

Answer 10

Endoderm.

Mesoderm

Ectoderm (cells which remain at the surface).

Question 11

What cell types are each of the germ layers?

Answer 11

Ectoderm - columnar
Mesoderm - irregular shape
Endoderm - cuboidal

Question 12

What does each germ layer give rise to in the body?

Answer 12

Ectoderm: skin, nervous system
Mesoderm: Vertebral column, skeleton, skeletal muscle, circulatory system, blood, kidney
Endoderm: Gastrointestinal tract

Question 13

Explain the establishment of the body axes

Answer 13

The medial-lateral (dorso-ventral) axis is established during gastrulation.
Axial: notochord (running down the body) and prechordal (the prechordal plate is a “uniquely thickened portion” of the endoderm that is in contact with ectoderm immediately rostral to the cephalic tip of the notochord).

Paraxial: somites in the trunk (skeleton, muscles, dermis)

Lateral plate: viscera, inner lining of body wall, dermis (in skin)

Question 14

What does the position of cells along the primitive streak determine?
What does timing affect?

Answer 14

Their final position in the medial-lateral axis.

The head-tail axis. Leaving first end in head and last in tail.

Question 15

If cells move along the primitive streak, where do they end up?

Answer 15

Lateral in the mesoderm

Question 16

Where do cells at the tip of the streak move into?

How about cells slightly more along the streak?

Answer 16

The notochord.

Somites (more ventral than notochord)

Question 17

Cells that leave the primitive streak first are —- and cells that leave later are —-.

Answer 17

Rostral (front end of body, especially in mouth or nose).

Caudal (near the tail or posterior part of the body).

Question 18

What is the neural plate the origin of?

What germ layer does this come from and how?

Answer 18

Origin of the nervous system.

Ectodermal layer, cells elongate and narrow. The plate then splits into separate parts.

Cells in the centre become longer than those at the periphery. Neural plates fold and fuse together. The plates meet in the midline and takes place at the height of the mid-brain. The neural tube then closes.

Question 19

What is neurulation?

What does the ventral side form?
Dorsal side?

Answer 19

The transformation of the neural plate into the tube and the closing of the tube.

Ventral side - makes motor neurons
Dorsal side - makes sensory neurons

Question 20

What folds up to form the flat germ layers?

What does this mean about the ectoderm?

Answer 20

The lateral side of the embryos fold up.

This means the ectoderm is around the whole of the outside of the embryo.

Question 21

Give details on neural crest cells

Answer 21

They are migratory cells from the dorsal neural tube. Once the neural tube is closed, they leave and migrate to make parts of the body.

Question 22

What cells do neural crest cells give rise to in the head?

Answer 22

Melanocytes
Cranial ganglia
Craniofacial skeleton
Odontogenic mesenchyme (ectomesenchyme).