Basic Embryology of the Head and Neck 2

Question 1

what is grastulation?

Answer 1

the process which transforms the bilaminar embryonic disc to a trilaminar embryonic disc

• transformation from 1D layer of epithelial cells and reorganises into multilayered structure called the gastrula

Question 2

what is the process of gastrulation?

Answer 2

1. starts in week 3 from the formation of the PRIMITIVE STREAK - made up of a primitive pit, primitive node and primitive groove
2. epiblast cells move towards primitive streak
3. cells detach from epiblast and insert into hypoblast to replace hypoblast cells
4. 3 germ layers form from this

Question 3

what are the different germ layers?

Answer 3

ectoderm
mesoderm
endoderm

Question 4

how are the germ layers formed?

Answer 4

gastrulation

endoderm
- epiblast cells differentiate into endoderm cells, replace the hypoblast cells

mesoderm
- when theres enough endoderm cells
- epiblast cells differentiate into mesoderm cells

ectoderm
- remaining epiblast cells become ectoderm

Question 5

what are the 2 main consequences of abnormal gastrulation?

Answer 5

• sirenomelia
• sacrococcygneal teratoma

Question 6

what is sirenomelia?

Answer 6

aka mermaid syndrome
- when there is insufficient mesoderm in the caudal region
- usually get legs not separated properly

Question 7

what is sacrococcygneal teratoma?

Answer 7

• when remains of primitive streak remain and give rise to a tumour
• the most common tumour in female newborns

Question 8

what is the notochord?

Answer 8

structure specifying the midline of the embryo

Question 9

how is the notochord formed?

Answer 9

• when the primitive streak regresses, the primitive node forms the notochordal process
• fuses w/ endoderm = notochordal plate
• separates from endoderm = solid notochord

Question 10

what is neurulation?

Answer 10

the first event developing the CNS

Question 11

what is the role of the notochord in inducting neurulation and formation of the verterbrae?

Answer 11

neurulation
- signals from notochord induce ectoderm to thicken and form neural plate

vertebrae
- notochord organises the formation of somites
- somites differentiate into: 1. sclerotome, myotome and dermatome

Question 12

give a consequence of abnormal formation of the vertebrae

Answer 12

spina bifida

Question 13

describe spina bifida and the 3 severities

Answer 13

• the scelerotomes (bony parts) of the notochord forming the vertebrae are abnormal

spina bifida aculta - least severe
- fatty tissue is separating the spine from the outside body
- skin becomes obviously dimpled

meningocele
- the meninges are protruding out to the outside skin
- pocket of cerebral spinal fluid

myelomeningocele - most severe
- sclerotomes haven’t formed
- dermatomes don’t form skin over the surface of the baby