Atrophy is a decrease in decrease in size, number, and function.
If enough cells in an organ atrophy the entire organ will decrease in size. Thymus atrophy during early human development is an example of physiologic atrophy. Skeletal muscle atrophy is a common pathologic adaptation to skeletal muscle disuse. Tissue and organs especially susceptible to atrophy include skeletal muscle, cardiac muscle, secondary sex organs, and the brain.
Types of atrophy
- Physiologic atrophy: Occurs due to a normal stressor. For example, decrease in the size of the uterus after pregnancy.
- Pathologic atrophy: Occurs due to an abnormal stressor. In general, atrophy is due to the loss of stimulus to the organ. Specific types of loss of stimulus include loss of blood supply or innervation, loss of endocrine stimulus, disuse, mechanical compression, decreased workload, or aging.
Atrophy occurs in a once normally developed organ. If the organ was never a normal size (i.e., because it did not develop normally), the condition is called hypoplasia.
1b. Hypoplasia: failure to grow to normal size; usually applied to a tissue or organ and indicates that there are fewer or smaller cells.
1c. Aplasia: failure to grow; usually meaning a complete absence of a cell type, organ or tissue (agenesis).