What is the Difference Between Atrophy and Hypertrophy

The main difference between atrophy and hypertrophy is that atrophy is the reduction of the functionality of an organ with the decreasing number of cells or the volume, whereas hypertrophy is the increase in the volume of cells. Furthermore, in muscles, atrophy occurs when they are not used at all while hypertrophy occurs due to excess work. 

Atrophy and hypertrophy are two conditions of development. Generally, they have both physiological and pathological importance. 

Key Areas Covered 

1. What is Atrophy
      – Definition, Features, Importance
2. What is Hypertrophy
     – Definition, Features, Importance
3. What are the Similarities Between Atrophy and Hypertrophy
     – Outline of Common Features
4. What is the Difference Between Atrophy and Hypertrophy
     – Comparison of Key Differences

Key Terms 

Atrophy, Hypertrophy, Hyperplasia, Muscles, Sarcopenia

What is Atrophy 

Atrophy is the complete or partial wasting of a part of the body. Generally, the causes of atrophy include the poor supply of nutrients or hormones, poor circulation, loss of nerve supply, lack of exercise, an excessive amount of apoptosis, etc. In order to maintain body parts under normal functioning conditions, there should be trophic effects of the hormonal and nerve inputs. Therefore, diminished conditions of these supplies cause atrophy. Meanwhile, atrophy causes a reduction in cell size, which in turn reduces the size of the organ or tissue.

Figure 1: Mouse with Spinal Muscular Atrophy (right)

Furthermore, muscle atrophy is the decrease in muscle strength due to the decrease in muscle mass. Usually, it occurs due to cancer, heart failure, renal failure, burns, starvation, sedentary lifestyle, bed rest, etc. On the other hand, sarcopenia is the atrophy occur due to ageing. The main cause of it is the decline of satellite cells to regenerate skeletal muscle cells. 

What is Hypertrophy 

Hypertrophy is the condition of increasing the volume of an organ or tissue due to excess work. Generally, this is by increasing the volume of the cells but, not by increasing the number of cells in the organ or tissue. The latter condition is known as hyperplasia. 

Figure 2: Muscle Hypertrophy Achieved through a Combination of Strength Training, Diet, and Nutritional Supplementation

Furthermore, based on the type of work, hypertrophy occurs either by increasing the sarcoplasmic volume or the amount of contractile proteins in muscles. Meanwhile, other biological factors, such as the amount of nutrients, also affect hypertrophy in muscles. Moreover, in males, muscle hypertrophy occurs at a high rate after puberty. Significantly, the adequate supply of growth hormones such as testosterone and amino acids are essential for muscular hypertrophy. 

Similarities Between Atrophy and Hypertrophy 

• Atrophy and hypertrophy are two medical conditions related to the development of tissues and organs. 
• They occur due to different degrees of usage. 
• They cause changes in the size of tissues and organs. 
• Both have physiological and pathological importance. 

Difference Between Atrophy and Hypertrophy 

Definition 

Atrophy refers to the decrease in size of a body part, cell, organ or other tissue while hypertrophy refers to the enlargement of an organ or tissue from the increase in the size of its cells.  

Cause 

Moreover, atrophy occurs when organs or tissues are not used at all while hypertrophy occurs due to the excess work. 

Results in 

While atrophy results in the decrease in size of the organ, the hypertrophy results in the increase in the size of the organ. 

Physiological Importance 

Senile atrophy, the atrophy in the thymus after puberty, and atrophy in ovaries and breast during menopause are the physiological conditions of atrophy while the muscles of bodybuilders and uterus in pregnant mothers are the physiological conditions of hypertrophy. 

Pathological Importance 

Chronic malnutrition and other chronic diseases cause atrophy, while hypertrophy can be either adaptive or compensatory. 

Conclusion 

Atrophy is the condition of decreasing the size of an organ or tissue when they are not used for a long time. Further, malnutrition, chronic diseases, and ageing are the causes of atrophy. On the other hand, hypertrophy is the condition of increasing the size of an organ or tissue due to excess work. Generally, this is by increasing cell volume. As an example, muscle hypertrophy occurs in bodybuilders. Therefore, the main difference between atrophy and hypertrophy is the type of change in organs and tissues and causes.  

References:

1. Aragon, Pepe. “Muscular Atrophy and Hypertrophy | Wellness HE 130.” ER Services, Available Here.

Image Courtesy:

1. “Mouse with spinal muscular atrophy” By US National Institute of Health – US National Institute of Health (Public Domain)  via Commons Wikimedia  
2. “Hairy chest – Foto Giovanni Dall’Orto, 25 luglio 2010a” By G.dallorto – Own work (Attribution) via Commons Wikimedia