Complex sentence: Atrophy of mucosa, turbinal bones and seromucinous glands tends to occur, due to obliterative endarteritis causing decreased blood supply, hence the supplying area atrophies.
Split into simpler sentences: Atrophy of mucosa, turbinal bones, seromucinous glands tend to occur. This is due to obliterative endarteritis causing decreased blood supply hence the supplying area atrophies.