Origin of tissue layers

[desertreefer]

Dr. Ron,

I was planning to ask this question in group discussion last night, but apparently we had some kind of network problem and everyone disappeared from the chat room. I gave up after fifteen minutes of trying to reconnect. Anyway....

Referring to the picture in the R&B text of the process of gastrulation.....The blastula is a sphere of cells surrounding the blastecoel, through evagination a cavity is created in the sphere. (Right so far?) Why is the tissue that ends up on the inside of the cavity called the endoderm and the tissue outside the cavity the ectoderm when it was all the same tissue to begin with? Do the cells on the inside of the cavity go through some significant changes that differentiate them from the cells that stay on the outside?

 

[rshimek]

<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote

Originally posted by desertreefer:

Hi,

(Right so far?)

Yup.

Why is the tissue that ends up on the inside of the cavity called the endoderm and the tissue outside the cavity the ectoderm when it was all the same tissue to begin with?

The cells on the inside change or differentiate, and have different functions from those on the outside.

Do the cells on the inside of the cavity go through some significant changes that differentiate them from the cells that stay on the outside?

Absolutely.

This change is is referred to as differenttiation. The endodermal cells have a fundamentally different function from the ectodermal ones.

And, as we shall see, the mesodermal ones (which differentiate a bit later in development in most animals.