Embryology

Question 1

The germinal stage refers to what time period after ovulation?

Answer 1

Through 2 weeks after ovulation. The germinal stage refers to the cell being fertilized inside the fallopian tubes, the cell forming into a zygote–> morula —> blastocyst (blastula) and some differentiation into layers such as the epiblast (baby tissue) and amnioblast (Forms walls of amniotic cavity). Ends right before the blastula becomes the gastrula.

Question 2

Zona pellucida

Answer 2

Glycoprotein protective outer covering of the egg that prevents multiple sperm fertilization.

Question 3

What occurs 30 hours after ovulation of fertilized successfully?

Answer 3

The cell will divide into 2 cells- a zygote.

Question 4

Around 7 days after ovulation, the cell mass is considered

Answer 4

A morula. Which is 16 cells inside the zona pellucida. The cells are highly condensed.

Question 5

Different areas within the morula

Answer 5

There is an outer cell mass and an inner cell mass. The outer cell mass brings in fluid to form a cyst and plays no role in the body of the baby. It is strictly there for support and to provide nutrients.

The inner cell mass + gap junctions will eventually form the baby.

Question 6

Once the inner cell mass of the morula moves to 1 side and the outer cell mass brings in enough fluid to create a cyst, the cell mass is now called

Answer 6

A blastocyst AKA blastula. The outer cells of the morula now form the outer wall of the blastocyst as zona pellucida degraded. The outer cells of the blastocyst are called trophoblast cells. There is a fluid filled cyst and the inner cell mass is clumped to one side. The inner cell mass is called the embryo blast.

Question 7

What are the cell groupings called within the blastocyst AKA blastula

Answer 7

Outer cells- trophoblasts.

Inner cells- embryo blast. Can be further divided into the epiblast and hypoblast Will eventually form the baby.

Question 8

What is the role of the trophoblast cells in the blastocyst AKA blastula

Answer 8

Form the outer wall, and use cellular projections to implant into the uterine wall. Support and nutrients provided. Forms part of the placenta eventually.

Question 9

Implantation commences at day

Answer 9

5-6. and embedded at day 12.

Question 10

Divisions of the embryo blast once the baby is embedded in the uterine wall

Answer 10

Epiblast- forms the baby. Golden tissue.
Hypoblast- Layers form a flat disc called the yolk sac.

Additionally, the trophoblast is the outer layer. The amnioblast forms the devloping amniotic cavity in the center of the epiblast

Question 11

Towards the end of week two, why do primitive yolk sac cells die off?

Answer 11

Nobody knows. However, they do know that hypoblast cells, surrounding the epiblast, migrate to replace the yolk sac cells.

Question 12

Why is the extra embryonic cavity (chorionic cavity) useful?

Answer 12

Useful if imaging to see if implantation has occurred. Diagnostic role for early on to detect pregnancy.

Question 13

Primitive streak can be first seen during

Answer 13

The germinal stage, week 2. The streak indicates the cranial side (where the head and neck will form) while the opposite indicates the caudal side. The cranial side is much larger than the caudal side.

Question 14

Embryonic period

Answer 14

Week 3. Blastula —> gastrula

Question 15

What period begins at week 3 after ovulation

Answer 15

Embryonic period. Blastula —> gastrula

Question 16

Gastrula

Answer 16

Forms from the blastula/blastocyst during week 3. At this point, the three germ layers are forming from the primitive streak, which is comprised of epiblastic cells from the blastula.

Question 17

Portions of the streak

Answer 17

Pit, node, and groove.

Question 18

Development of the three germ layers-

Answer 18

Ectoderm: Cells remain in the epiblast and form the ectoderm.

Mesoderm: cells travel down into pit and laterally towards the cranial end will form the mesoderm and notochord (which is a special structure in the mesoderm. This will develop into part of the spine)

Endoderm: Will travel down through the groove and replace hypoblast to form the endoderm.

Question 19

Is the primitive streak at the caudal end of cranial end

Answer 19

Caudal end is where the streak originates. The node is in the center and the cranial end is the longest.

Question 20

What cell layer formed the neural plate

Answer 20

The ectoderm thickens to form the neural plate which folds down into itself and creates the separated neural tube and layer of non-neural ectoderm.

Question 21

Neural crest cells

Answer 21

Play a large role in the formation of the neural tube. They are derived from the neural fold and develop into the flat bones of the skull, melanocytes, muscle, glands, and more.

Question 22

The neural tube eventually forms the

Answer 22

CNS (brain superiorly and spinal cord inferiorly)

Question 23

3 developmental layers of the neural tube (ectoderm)

Answer 23

The most interior: Ependymal layer/matrix cell layer/ventricular zone. Produces ependymal and choroid plexus. Play big role in CSF.

Middle: Intermediate zone/the Mantle layer. Produces grey matter (soma and dendrites)

Outside: Marginal layer/zone. Where the axons of the grey matter soma and dendrites are found. This is the white matter.

Question 24

Zipper effect of the ectoderm

Answer 24

After the neural tube has been formed by the ectoderm, it zips together first in the center and then towards the top and bottom.

Question 25

Development of the mesoderm

Answer 25

Axial- notochord
Paraxial- somites aka axial skeleton
lateral plate- visceral (covers surface of lungs) and parietal (Lines inside of chest wall)

Question 26

What has formed at the end of the mesoderm differentiation?

Answer 26

An amniotic cavity that is completely surrounding the embryo (inside is the ectoderm, which surrounds the mesoderm)

Question 27

What arises from the endoderm?

Answer 27

Lines the tubes of passage ways in the body.

Stomach, intestines, trachea, bronchi, GI tract…