All the following are examples of atrophy except

A. skeletal muscle, following transection of its motor neuron.
B. skeletal muscles, following long-term immobilization of the broken extremity in a cast
C.ovary following hypophysectomy
D. endometrium following long-term administration of estrogen

The answer is D.
All answers except for D are examples of atrophy. Atrophy of skeletal muscles can result from a loss of innervation due to spinal cord or peripheral nerve trauma. Inactivity, as is often seen following the long-term immobilization of an extremity in a cast, has the same effect. Hypophysectomy is accompanied by atrophy of the thyroid, adrenal cortex, and ovary, which are all organs that depend on stimulation by pituitary trophic hormones. The brain atrophies with advancing age. Estrogen exerts trophic effects on the endometrium, causing hyperplasia rather than atrophy.Endometrial atrophy occurs following ovariectomy or after the menopause, when the ovaries no longer produce estrogen.