Capacitances in NAND2 depletion mode nmos logic

[reddvoid]

Why we are not writing Cgs Cdb in depletion mode nmos here
why no Csb in bottom nmos
Can somebody please explain how to write which components of Cload or provide some links from where i can understand it better

thank you,
this picture is from http://books.google.co.in/books?id=XUruXhP2s6gC&lpg=PP1&pg=PA285#v=onepage&q&f=false

 

[analogdesign]

There is so CsbB because the body is shorted to the source of the bottom transistor (in this circuit the substrate is connected to ground).