IMMS and Embryology

Question 1

Show the early stages of embryonic development. (days 1-3)

Answer 1

Question 2

Show days 4-6 of embryo development

Answer 2

Endometrial epithelium - wall of uterus (I think)

Synctiotrophoblasts - epithelial cells determine which substances cross placenta.

Question 3

show days 5-13 of embro development

Answer 3

Bilaminar disk gives rise to ectdoderm, endoderm and eventually the mesoderm.
Yolk sac - provides nutrition and gas exchange before the placenta.
Amnion eventually fills with fluid to form the embryonic sac.

Question 4

Summarise the first 23 days of embyo development.

Answer 4

Question 5

How is the umbilical cord formed?

Answer 5

Connecting stalk becomes umbilical cord.

Question 6

What happens in week 3 of embryo development?

Answer 6

Gastrulation - formation of the trilaminar disk from the bilaminar disk.

Folding occurs across the caudal midline of the bilaminar disk to form the primitive streak.
The gastrula forms as it becomes a 3D structure.

The cells as the base of the primitive streak detach and migrate to lie between the ectoderm and endoderm. These cells develop into the mesoderm. (trilaminar disk for 3 germ layers)

At the caudal end, the primitive streak lies.
The oropharyngeal membrane is at the cranial end.

Question 7

What does the ectoderm develop into?

Answer 7

Question 8

What does the endoderm develop into?

Answer 8

Question 9

What does the mesoderm develop into?

Answer 9

Question 10

Describe the formation of the notochord?

Answer 10

The notochord has a central role in further midline devlopment.

Question 11

What happens in week 4?

Answer 11

neurulation and embryo folding.
in neurulation: The neural plate (thickened portion of ectoderem along midline) which folds to form a hollow tube. This eventually develops into the nervous system, spinal chord, etc.

Question 12

What happens in spina bifida?

Answer 12

There is a gap in the spine.
Where fusion in neurulation does not occur properly.

Question 13

Show the differentiation of the mesoderm

Answer 13

Occurs simultaneously to neurulation.

The paraxial mesoderm differentiates into paired cuboidal bodies (somites).
Intercellular cavities in the lateral plate are formed from the lateral mesoderm.

The lateral mesoderm splits into two layers:
* somatic layer (outer) covers inside of chest and abdominal walls.
* Splanchnic (visceral) layer - second layer which covers organs in thorax and abdomen.

Question 14

What are somites?

Answer 14

Precursor cells which give rise to important structures (skeletal muscle, tendons, vertebrae etc).
Develops cranocaudally (from cranial end)

Gives rise to:
* axial skeleton (sclerotome)
* Associated musculature (myotome)
*Adjacent dermis of skin (dermatome)

Question 15

What happens in embryo folding?

Answer 15

Lateral folding and caudal folding

Lateral folding: starts with trilaminar disk.
A portion of the yolk sac (which is lined with endoderm) is incorporated into the embryo to form the primitive gut
The remaining part of the yolk sac and allantois remain outside the embryo, connected through the umbilicus.

Caudal folding: division along the saggital slice )along the length of embryo).

Question 16

Lateral folding

Answer 16

Question 17

How are the body cavities formed?

Answer 17

Question 18

Caudal folding pt 1

Answer 18

Question 19

Caudal folding pt2

Answer 19

Question 20

How are blood vessels formed in an embryo?

Answer 20

1. Blood islands begin to form from the mesoderm, which are cores of haemoblasts surrounded by endothelial cells.
2. The cells vascularize the yolk sac, chorionic villus and stalk.
3. They migrate into the disk of the embryo, in vasculogenesis, so a single tube down the middle (all from the mesoderm).
4. Angiogenesis - Endothelial cells grow out from the central tube to form to form new blood vessels.
5. Other mesodermal cells are recruited to form the media and the adventitia.

Question 21

What drives embryonic vessel development?

Answer 21

Angiogenic growth factors.

Repulsive and attractive signals cause the blood vessels grow in the right way.

Question 22

Show aortic arch development

Answer 22

1. 29 days - same as fish. Symmertical aortic arches. 2 aorta come from the heart, meet one dorsal aorta.
2. ends as asymmetric stuff.

Question 23

1st and 2nd aortic arch development
Note card needs 2nd look when revising (CBA now)

Answer 23

They migrate into the head (1st axillary artery) (2nd is artery to stapedius).

3rd - becomes carotid arteries.

4th - on RHS, loses aortic connection. Becomes part of arteries that go down the right upper limb. Right subclavian artery, grow from right dorsal aorta and right 7th intersegmental artery.
On LHS, it grows into the left 7th cervical intersegmental artery, which in turn develops into the left subclavian artery.

6th arch - left arch becomes ductus arteriosus. connection between pulmonary artery and aorta. Blood doesnt pass through lungs.
Right arch forms part of artery that goes through the lungs.

Question 24

Show the stages of cardiac formation in the embryo

Answer 24

1. formation of the primitive heart tube. (Week 3)
2. cardiac looping
3. cardiac septation

Question 25

Descirbe the formation of the primitive heart tube.

Answer 25

1. the heart is formed from cells that form a horseshoe shaped region called the cardiogenic region.
2. They divide into two endocaridal tubes
3. During lateral folding, they fuse to form a single heart tube.
4. Formed is the bulbus cordis (where RV and outflow tracts will form), primitive ventricle in the middle, a single atrium at the bottom. At the horns at the bottom, the sinus venosus is formed. Will form superior vena cava and parts of the RA.

Question 26

Describe cardiac looping

Answer 26

The bulbus cordis moves inferiorly, anteriorly and to the embryos right.
the primitive ventricle moves to the embryos left
The primitive atrium and sinus venosus move superiorly and posteriorly
The sinus venosus is now posterior to the primitive atrium

Question 27

how does the heart know which way is left

Answer 27

All vertebrate hearts have a leftward ventricle.
During development, the node secretes nodal, which circulates left due to cilia.

A cascade of transcription factors transduce cardiac looping.

Question 28

Describe cardiac septation

Answer 28

At this stage, there is one atrium and one ventricle. This process is driven by endocardial cushions, which septate the two sides of the heart.

1. The atrium and ventricle are connected by an opening called the atrioventricular canal.
2. Masses of tissue called endocardial cushions grow down from the top and up from the bottom, by the side of the atrioventricular canal to partition it into two openings.