BL. session 3. embryology

Question 1

state the key events in early development

Answer 1

fertilisation and implantation
gastrulation
neurulation
segmentation
folding

Question 2

what happens in the pre embryonic period

Answer 2

1) cleavage> formation of morula (first mitotic division)
2) compaction > formation of blastocyst (formation of first cavity. fluid filled space) cells no longer totipotent, now pluripotent (become many cell types)

Question 3

what is the name given to the two cell masses in week 1

Answer 3

inner cell mass= embryoblast

outer cell mass= trophoblast (supporting cells/tissues. placenta and membranes)

Question 4

what is the two distinct layers that emerge from the outer cell mass

Answer 4

syncytiotrophoblast> transport of nutrients/waste across placenta

cytotrophoblast> forms stem cells for over transporting layer

Question 5

what does the inner cell mass become?

Answer 5

syncytiotrophoblast> transport of nutrients/waste across placenta

cytotrophoblast> forms stem cells for over transporting layer
---
bilaminar disk>
epiblast
hypoblast

Question 6

placenta praevia

Answer 6

• implantation in lower uterine segment
• can cause haemorrhage in pregnancy (highly vascular opening of cervix)
• requires C section delivery

Question 7

describe formation of trilaminar disk

Answer 7

1) cells of epiblast inc in number and pile towards the edges of primitive streak
2) push through the epithelial layer and squeeze through intracellular junctions
3) migrate across the embryonic disk

hypoblast completely removed/displaced

Question 8

what do ectoderm, mesoderm, endoderm derive from?

Answer 8

epiblast layer

Question 9

how is left right side asymmetry established?

Answer 9

primitive node.
cilated cells at the node waft leftward signals to the left
side specific signalling cascades

Question 10

summarise gastrulation

Answer 10

3rd week. (start of embryonic period)
primitive steak forms leading to migration and invagination
>trilaminar disk formation

Question 11

what is neurulation

Answer 11

notochord causes overlying ectoderm to thicken forming neurectoderm.
> neural plate forms neural tube as the disk curls inwards

Question 12

list 3 somite derivatives

Answer 12

dermatome (skin)
myotome (muscle)
sclerotome (bones)

Question 13

what is segmentation

Answer 13

organisation of mesoderm into somites give rise to repeating structures (ribs. intercostal muscles. spinal cord)

Question 14

what are the two folds that occur

Answer 14

cephalocaudal folding (head, tail)

lateral folding

(head fold, tail fold, then the two sides like an envelope.)

drawstring purse> ectoderm outside. endoderm inside.

Question 15

what does notochord go on to form

Answer 15

nucleus pulpous of intervertebral disks