Step 1: Understanding the Concept.
Cells and tissues adapt to stress or changing conditions in a small set of recognised ways: they can shrink (atrophy), grow larger (hypertrophy), increase in number (hyperplasia), or change into a different cell type (metaplasia). Osteoporosis needs to be matched to one of these patterns.
Step 2: Key Approach.
Look at what actually happens to the bone tissue: is it getting bigger, smaller, more numerous, or changing type?
Step 3: Detailed Explanation.
In osteoporosis, bone breakdown by osteoclasts outpaces bone building by osteoblasts, so the total mass and density of bone tissue drops over months and years.
This is a pure loss of tissue mass with no change in the type of tissue present and no increase in cell number, which rules out metaplasia and hyperplasia.
It is also not hypertrophy, since hypertrophy describes cells getting bigger, and the bone cells themselves are not enlarging.
A gradual wasting of tissue caused by reduced formation and continued breakdown is the textbook picture of atrophy.
Step 4: Final Answer.
The progressive loss of bone in osteoporosis is an example of atrophy.