Week 3 onwards and embryonic folding

Question 1

What are the derivatives of the ectoderm?

Answer 1

1) Nervous system
2) Sensory epithelium of ear, nose, and eye
3) Epidermis (including hair & nail)
4) Subcutaneous glands
5) Mammary glands
6) Pituitary gland
7) Teeth enamel

Question 2

What is neurulation, and describe its process?

Answer 2

It is the formation of the neural tube (forms the Brain and spinal cord)

• Firstly the notochord induces the thickening of the overlying ectoderm forming a neural plate, The lateral edges of the neural plate form neural folds its raised areas is called the neural crest, and the depressed mid-region is called the neural groove (which will later form the neural tube giving rise to the brain and spinal cord)

Question 3

What are the derivatives of the neural crest cells?

Answer 3

• After the complete closure of the neural tube, neural crest cells migrate from the lateral edges

Neural crest cells give rise to:
1) Dorsal root ganglia
2) Sympathetic chain ganglia
3) Adrenal medulla
4) Preaortic ganglia
5) Enteric ganglia
6) etc

Question 4

On which day does the cranial neuropore close?

Answer 4

• Fusion starts from the middle then it is like a double-sided zipper

Day 25

Question 5

On which day does the caudal neuropore close?

Answer 5

• Fusion starts from the middle then it is like a double-sided zipper

Day 28

Question 6

What are the types of neural tube defects (NTDs)?

Answer 6

1) Cranial neural tube defect leads to Anencephaly (it is lethal and the pregnancy is terminated)

2) Caudal neural tube closer failure (Leads to Spina Bifida (the child will have neurological functional loss), it is caused due to Folic acid deficiency

Question 7

What are the derivatives of the mesoderm?

Answer 7

1) Paraxial mesoderm gives rise to:
- Head
-Somites, including (Sclerotome “Cartilage”, Myotome “Skeletal muscles”, Dermatome “Dermis”, Endothelial cells, and Syndotome “Tendons”)

2) Intermediate mesoderm give rise to:
- Kidney
- Gonads

3) Lateral plate mesoderm gives rise to:
- Splanchnic (circulatory system)
- Somatic (body cavity, pelvis, limb bones)
- Extraembryonic

Question 8

Describe the lateral folding

Answer 8

1) The lateral plate mesoderm is connected to the extraembryonic mesoderm

2) The lateral plate has two layers (parietal and visceral

3) The layers of the lateral plate are further apart (forms the endoderm)

4) The parietal layer of the lateral plate mesoderm and overlying ectoderm approaches each other in the midline

5) By the end of 4th week, the Lateral body wall folds and fused in the midline

Question 9

What are the ventral body wall defects?

Answer 9

1) Ectopic cordis
2) Gastroschisis

Question 10

Describe ectopic carditis

Answer 10

1) The lateral body wall fails to close in the midline “thoracic region”
2) The heart lies outside the body cavity
3) Death shortly after birth due to infection, hypoxemia, cardiac failure

Question 11

Describe gastroschisis

Answer 11

1) The body wall fails to close in the abdominal region
2) Intestinal loops herniate in the amniotic cavity
3) Survival rate is 83-97%

Question 12

Allantois will later form which organ?

Answer 12

Bladder

Question 13

Describe the cephalocaudal folding

Answer 13

The cephalocauldal folding does not fuse.
During folding the oropharyngeal membrane will go down and the brain will go up
Also due to folding, the heart will go down to be under the brain
Some part of the yolk sac cavity will go into the embryo, the rest will be separated out due to the fusion of the mesoderms