Question

I got a question from a textbook <> that does not have an answer at the back of the book (only odd numbered questions do have an answer and this question is even):

Explain why bones cannot undergo interstitial growth as cartilage does.

i can only think of two reasons:

1)In bones, calcification causes the chondrocytes to die, so cartilage cannot form in the bone, leading to no interstitial growth in the bone.

2)Cartilages are usually only found at the tip of the bones, so its growth can cause the bone to lengthen, which is interstitial growth.

I got a nagging feeling that there is got to be more. Did i miss any other reason? (Also are my reasons correct?)

Answer 1

Bones cannot undergo interstitial growth because their calcified matrix prevents chondrocytes from living and proliferating within it, unlike the avascular cartilage which grows at the bone ends and uses diffusion for nutrient transport. Once ossified, bones can only grow through appositional growth, not interstitially.

Step-by-step explanation:

The question asks why bones cannot undergo interstitial growth as cartilage does. Your reasons are along the correct lines. Interstitial growth is when tissues grow from within, typical of cartilage proliferation. In bones, this process is not possible due to several factors:

1. The calcification of the cartilage matrix during endochondral ossification prevents nutrient diffusion, causing chondrocytes to die and stopping further interstitial growth in that area.
2. Cartilage growth occurs at the ends of bones, within the epiphyseal plates, which contributes to bone elongation via endochondral ossification rather than interstitial growth within the bone tissue itself.
3. Unlike cartilage, which is avascular and relies on diffusion, bone tissue requires a direct blood supply which supports a different pattern of growth known as appositional growth. Appositional growth allows for the addition of new layers on the outside of the bone, rather than growth from within.

Hence, although cartilage at the epiphyseal plate can contribute to the length of the bone through interstitial growth, bone tissue itself cannot grow interstitially once it has replaced cartilage and fully ossified.