Publishing your own textbook: how does it affect copyright/quotation rights?

Dear community,

As part of my training, I compiled over 700 pages from a textbook and teaching materials that I considered important.

I came up with the idea of ​​publishing this as a kind of nonfiction/textbook/exam prep book. However, I'm wondering whether that's possible and what copyright issues I have to consider.

For example, the structure and layout of certain topics are somewhat reminiscent of the original textbook. It has simply been shortened, reworded, and supplemented.

Since this is a textbook/technical book, there are many phrases that I cannot paraphrase.

Example: Medicine
Structure of the heart (there is hardly any other formulation?)
The diagnostic options would be the same in my textbook and the one I've used extensively. I could just change the order.
Nevertheless, much would be identical.

I would be very happy if someone could help me with this.
Thanks so much!!