What does atrophy refer to?

Atrophy refers to the wasting away or decrease in size of an organ or tissue, which is precisely what option B describes. This process can occur due to various reasons, such as disuse, aging, malnutrition, or decreased blood supply. When a muscle or tissue is not used or stimulated adequately, it can shrink in size and lose functionality, leading to atrophy.

In contrast, the other choices describe processes that are opposite to atrophy. An increase in organ size is an example of hypertrophy, where cells increase in size or number. The formation of new blood cells relates to hematopoiesis, a necessary physiological process in maintaining healthy blood levels. Lastly, the build-up of fat in tissues refers to adiposity, which can occur in the context of obesity or metabolic disorders, rather than a reduction in tissue size. Understanding these distinctions is essential in the study of physiology and pathophysiology.