Difference Between Interstitial and Appositional Growth

Growth is a vital process in all living organisms. It is the process by which organisms develop, matures, and maintain their tissues and organs. There are two types of growth mechanisms in plants and animals: interstitial growth and appositional growth.

Interstitial growth occurs by the addition of new cells within the existing tissue, while appositional growth involves the addition of new cells to the surface of the tissue. These growth mechanisms have different characteristics and occur in different types of tissues. In the following sections, we will discuss both growth mechanisms separately, highlighting their differences and similarities.

What is Interstitial Growth?

Interstitial growth is the process of growth that occurs through the addition of new cells within the existing tissue. It is commonly observed in tissues that have the capacity to divide, such as bone and cartilage tissues. During interstitial growth, the existing cells of the tissue undergo mitosis and divide into two daughter cells, resulting in an increase in the number of cells.

In bone tissue, interstitial growth occurs at the epiphyseal plates, which are found at the ends of long bones in children and adolescents. The cartilage cells in the epiphyseal plates divide and differentiate into bone cells, resulting in an increase in bone length. In cartilage tissue, interstitial growth occurs throughout life and is essential for maintaining the cartilage structure.

What is Appositional Growth?

Appositional growth is the process of growth that involves the addition of new cells to the surface of the tissue. It is commonly observed in tissues that do not have the capacity to divide, such as the outer layer of bone tissue and the skin. During appositional growth, the stem cells present in the tissue differentiate into specialized cells that add to the surface of the tissue.

In bone tissue, appositional growth occurs at the outer surface of the bone. The stem cells present in the periosteum differentiate into osteoblasts, which produce new bone tissue, resulting in an increase in bone thickness. In the skin, appositional growth occurs at the basal layer, where the stem cells differentiate into keratinocytes, resulting in the formation of a new layer of skin.

Differences Between Interstitial Growth and Appositional Growth in Table Format

Basis of Comparison	Interstitial Growth	Appositional Growth
Definition	The growth occurs through the addition of new cells within the existing tissue.	The growth involves the addition of new cells to the surface of the tissue.
Tissues Involved	Occurs in tissues that have the capacity to divide, such as cartilage and bone tissue.	Occurs in tissues that do not have the capacity to divide, such as the outer layer of bone tissue and the skin.
Mechanism	Involves cell division (mitosis) of the existing cells in the tissue.	Involves the differentiation of stem cells present in the tissue.
Increase in Size	Results in an increase in tissue size by the addition of new cells.	Results in an increase in tissue size by the addition of new tissue layers.
Occurrence	Occurs throughout life and is essential for tissue maintenance.	Occurs during growth and is essential for tissue development.

Conclusion

Growth is a continuous process in all living organisms. Interstitial growth and appositional growth are two essential mechanisms that contribute to tissue development, maintenance, and repair. Interstitial growth occurs by the addition of new cells within the existing tissue, while appositional growth involves the addition of new cells to the surface of the tissue. These growth mechanisms have distinct characteristics and occur in different types of tissues. While interstitial growth occurs in tissues that have the capacity to divide, such as bone and cartilage tissues, appositional growth occurs in tissues that do not have the capacity to divide, such as the outer layer of bone tissue and the skin. Understanding the differences between these growth mechanisms is crucial for understanding tissue development, repair, and maintenance.