What is the basic science behind length and girth gains

So As I’m reading the FAQ’s I was wondering what part of the penis is actually growing when gaining lengths? Are you just pulling the ligaments that attach your shaft to your pubic bone and stretching it out thus making your penis longer? Or is there more to it? Sorry I just signed up yesterday and trying to figure things out.

Also what is the basic science behind girth? And why does it get thicker when jelqing?

You gain length and girth by enlarging the tunica albuginea, which is a sheat of connective tissue which envelopes the corpora cavernosa. When tunica is enlarged, it gives room for more expansion of corpora cavernosa, which are filled with blood,