93. molecular and genetic basis of embryo development

Question 1

what is the embryonic period and what is fetal period

Answer 1

embryonic: fertilization to 8th week
fetal: 9th week to birth

Question 2

When is it called a zygote

Answer 2

once sperm cell has fertilized with the ovum (single diploid cell)

multiple mitotic divisions with no significant growth leads to multicellular embryo

Question 3

what is the protective envelope the egg surrounded with

Answer 3

zona pellucida (glycoproteins)e

Question 4

What is cleavage

Answer 4

cell division of zygote to produce more cells without much growth

Question 5

What is a morula

Answer 5

after many cleavage divisions, at least 16 cells is called morula

Question 6

the process of cleavage leads to many cells being derived which are called what

Answer 6

blastomeres

Question 7

2 different types of cleavage

Answer 7

holoblastic (total): occurs when little yolk is in egg eg humans as they have placenta/milk for nourishment

meroblastic (partial): eggs with more yolk eg birds

Question 8

What is the peripheral layer of cells in amniotes that do not form the dense inner mass

Answer 8

trophoblasts

Question 9

What does the blastocyst look like

Answer 9

inner cell mass of 128 cells
cavity called blastocoel
trophoblasts on periphery
zona pellucida begins to disintegrate

Question 10

before gastrulation, the trophoblasts differentiate into what 2 types

Answer 10

outer layer: synctiotrophoblast
inner layer:cytotrophoblast/ layers of langhans

Question 11

what is the function of the synctiotrophoblasts

Answer 11

surrounds the chorionic villi
prevents mother blood mixing with the fetal blood in placenta

Question 12

What does gastrulation gives rise to

Answer 12

the germ layers
ectoderm- nervous system and skin
mesoderm- muscles
endoderm- lining of vessels eg GIT

Question 13

Where is the notochord located within germ layers and what does it do

Answer 13

induces neuralation
within mesoderm

Question 14

neuralation

Answer 14

folding up of ectoderm forming neural folds

between the folds is the neural groove which deepens as the neural folds elevate more

the folds join and fuse together forming the neural tube

neural crest cells are formed from the cells of the ectoderm- the cells differentiate and forms the PNS, glial cells baso lots of the nervous system

Question 15

one group of cells or tissues
causes another set of cells or tissues to change
their fate. what is this process called

Answer 15

induction- for organ formation

Question 16

what is the interation within induction

Answer 16

one cell type or tissue is the inducer that produces a signal

the responder responds to that signal

Question 17

which is a common induction interaction

Answer 17

epithelial mesenchymal interactions

Question 18

cell to cell signaling is important for induction. which are the 2 ways of communication

Answer 18

paracrine interactions- protein made by one cell diffuses short distance to other cells (GDFs)
juxtacrine interations- does not involve diffusable proteins

Question 19

What is involved in signalling transduction pathways

Answer 19

paracrine: ligand (signalling molecule) and receptor
when ligand binds to receptor, induces
conformational change. results in activity of kinase
which phosphorylates other proteins.
eventually activates transcription factor

juxtacrine: 1.Notch pathway 2.ligands interact with receptors
on neighboring cells 3.direct transmission by gap
junctions

Question 20

What are the paracrine signalling factors called

Answer 20

GDFs there are 4 groups

Question 21

What are the 4 groups of GDFs

Answer 21

Fibroblast growth factor (FGF)- 25
WNT-15
hedgehog proteins (SHH)
transforming growth factor-b (TGF-b)