Compact and Spongy Bone

Bones in the body contain both compact and spongy bone.

Compact Bone

Compact bone is made up of mature bone cells called osteocytes. The osteocytes are situated in small cavities called lacunae and surrounded by a mineralized extracellular matrix forming a structure called an osteon. The layers of calcified matrix, called lamellae, form a circular pattern similar to the growth rings of a tree. The buildup of calcium phosphate and collagen gives bones their strength. When these deposits are all in the same direction, the bone will be strong along one axis but will be susceptible to shattering when forces come in from other directions.

Spongy Bone

To deal with forces coming from different directions, the body has another type of bone called spongy bone. Spongy bone does not contain osteons but is instead made up of small circular "pipes" called trabeculae. These trabeculae are similar to compact bones in that they are also made up of an extracellular matrix that is formed in a circular deposition. However, the trabeculae are much thinner and run in different directions. This allows the bone to disperse forces coming from multiple directions, making it more resistant to shattering.


In summary, compact bone is very strong and able to withstand a lot of pressure along its axis, while spongy bone, although not as strong as compact bone, is able to withstand pressure from multiple directions. This allows the bones to support different parts of the body and withstand different types of forces.

Figure 1: A long bone made of compact and spongy bone.