The compact and spongy bones are two different types of bone tissue that constitute our bones. While the compact ones refer to the hard, outer layers of the bones, the inner layers are formed by the spongy bones, which are also dubbed cancellous bones. Compact bones carry a proper osteon pattern, whereas spongy bones are free of osteons, i.e. they contain a lamellar pattern of trabeculae. These trabeculae are located in between red bone marrow.
As discussed above, compact bone indicates the outer layer or shaft of bones. Compact bones are also called cortical bones, which contain osteons or Haversian systems. The compact bone gets its white, smooth structure owing to the connective tissues that cover around ¾ part of the bone from inside. The shafts found in long bones are also compact bones. These bones are tough and hard with negligible gaps inside them.
Contrary to compact bone, spongy bone or cancellous bone forms the interior part of the bone. In fact, these bones cover a large area inside the bone. Though, these bones are a little softer as compared to compact bones, these are not literally spongy as their name may indicate. The tissues in spongy bone are less densely arranged, thereby giving the bone its name. The blood is produced in this very bone, which is responsible for protecting the internal body parts. Minerals are stored here. Also, the manufacturing of red and white blood cells takes place in the spongy bone.
Though both comprise the two major types of osseous tissue, the key difference between compact and spongy bone occurs in their structure and in terms of the functions they perform. Compact bone is hard and forms the outer layer of any bone. On the other hand, spongy bone is softer, and forms the inner layer of bones while covering a large surface area.
The main function of compact bone is to support the whole body, whereas spongy bones support the body structure. The latter helps save materials, and provide movement to the key body organs. Compact bones are heavy and tough as they store calcium in them, contributing to over 80% of total human skeleton weight. Spongy bones are lighter in weight; the lesser amount of calcium supply to these bones makes them weak and vulnerable to breaking easily.
|Compact Bone||Spongy Bone|
|Made up of osteons||Made up of trabeculae|
|Calcium is present in high quantity in them||Very small amount of calcium is present in them|
|Almost 80% or above weight of human skeleton is contributed by compact bones||The rest 20% weight of the skeleton is contributed by spongy bones|
|These bones are cylindrical in shape||These are cuboidal in shape|
|These contain yellow marrow||These mostly contain red bone marrow|
|Compact bones form major part of human body’s long bones. For e.g. arms, legs, etc.||Spongy bones form major part of our short bones. For e.g. ankles or wrists|
Please take some time to watch this video that explains this difference in quite a lot of detail.