lec 8

Question 1

what is the outer layer of blastocyst called?

Answer 1

trophoblast - turns to placenta

Question 2

what is the inner part of blastocyst called?

Answer 2

inner cell mass - actual embryo

Question 3

what happens after inner cell mass is formed?

Answer 3

it separates from the trophoblast by the release of fluid (amniotic sac)

Question 4

what is the fate of the inner cell mass?

Answer 4

epiblast and hypoblast

Question 5

what does the epiblast form?

Answer 5

primitive streak which ultimately gives rise to the germ layers

Question 6

what does the hypoblast become?

Answer 6

umbilical cord

Question 7

what is the order of formation of the germ layers?

Answer 7

endoderm, mesoderm and ectoderm

Question 8

What do the 3 germ layers form?

Answer 8

ecto-outer surfaces and nervous system

meso - organs

endo - inner layers such as epithelial linings of the gut and resp tract

Question 9

Why is pattern baldness important in the study of germ layers?

Answer 9

baldness due to immune cells can cause frontal baldness but the back is spared, this is due to the difference in lineage of the cells.

The back is mesoderm and front is ecto

Question 10

Define Stem Cell

Answer 10

A cell that has the ability to differentiate into multiple other cell types and have the capacity for self renewal.

Question 11

Gives the plasticity of zygote, inner cell mass and germ layers

Answer 11

Totipotent, pluripotent and multipotent respectively.
Zygote is totipotent because it can differentiate into every type of cell
Inner cell mass cannot differentiate into placenta.

Question 12

How can embryonic stem cells be useful for regen?

Answer 12

ESCs have the promise to provide unlimited supply of transplantable cells

ESC provides an in vitro model of development and disease.

Question 13

Why are human ESC controversial?

Answer 13

they are effectively human lives and creation for research purposes is possible and has been done.

Question 14

What is the ontological status of ESCs?

Answer 14

ESCs refers to the inner cell mass, which cannot form into a baby without the trophoblast cells which provide the implantation and nourishment.

So is it truly wrong? and can be possibly save them by enveloping in trophoblasts in the future?

Question 15

Explanation of the expansion of Intestinal cells

Answer 15

Stem cells are at the bottom of the crypt (crypt base columnar stem cells) The niche is the paneth cells
CBC gives rise to stem cells, paneth niche cells and DLL1+ cells
They migrate up the crypt into the top of the crypt.
Turnover is roughly 5 days. So need a lot of cell division. They divide once a day.
At the top after their life time they apoptose.

Question 16

How do we know how it divides?

Answer 16

We can see if it is invariant or population asymmetry by labelling the cells in the gut, this is done by using a confetti mouse.
Invariant would produce - a combination of different stem cells equally, shown by the mixture of colours associated with the cells
Population would produce - a domination of one stem cell lineage over time. So if we have 5 CBCs in the crypt and one is producing stem cells and the others producing TA s the TA producing stem cells will eventually be pushed out of the crypt.