In my last Japanese class, I asked my teacher, who is a native speaker, why the japanese word for "page" was taken from the English language ("pēji"), because apparently there were already books ("hon"), who had a Japanese name. My teacher could not answer me this. Is there a reason and, more important, how did the Japanese people called a sheet of paper being part of a book? Please feel free to replace with Kanji/Kana. I have some trouble with my IME, sorry for this.
おおがい(ketsu or yo) is used to indicate the pages in Kanji, which is quite rare to see nowadays.
Originally, 「葉」-leaf (yo) was said to be the unit of count for paper and in Edo period we borrowed the kanji 頁 so to mean the pages because its Chinese pronunciation (yo) is similar to ‘よう’.